Debt (Credit Facilities) (Narrative) (Details) - USD ($) |
1 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2019 |
Dec. 31, 2018 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Line Of Credit Facility [Line Items] | |||||
| Repayment of long-term debt | $ 27,592,000,000 | $ 52,643,000,000 | $ 12,339,000,000 | ||
| Revolving Credit Facility [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - maximum borrowing capacity | $ 15,000,000,000 | 15,000,000,000 | |||
| Credit agreement - advances outstanding | 0 | $ 0 | |||
| Line of Credit Facility, Covenant Terms | Each of the Agreements contains covenants that are customary for an issuer with an investment grade senior debt credit rating, as well as a net debt-to-EBITDA (earnings before interest, taxes, depreciation and amortization, and other modifications described in each agreement) financial ratio covenant requiring AT&T to maintain, as of the last day of each fiscal quarter, a ratio of not more than 3.5-to-1. The events of default are customary for agreements of this type and such events would result in the acceleration of, or would permit the lenders to accelerate, as applicable, required payments and would increase each agreement’s relevant Applicable Margin by 2.00% per annum. | ||||
| Amended and Restated Credit Agreement [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - initiation date | Dec. 01, 2018 | ||||
| Credit agreement - maturity date | Dec. 11, 2021 | ||||
| Credit agreement - Term of Loan | 5 years | ||||
| Line of Credit Facility, Covenant Terms | Each of the Agreements contains covenants that are customary for an issuer with an investment grade senior debt credit rating, as well as a net debt-to-EBITDA (earnings before interest, taxes, depreciation and amortization, and other modifications described in each agreement) financial ratio covenant requiring AT&T to maintain, as of the last day of each fiscal quarter, a ratio of not more than 3.5-to-1. The events of default are customary for agreements of this type and such events would result in the acceleration of, or would permit the lenders to accelerate, as applicable, required payments and would increase each agreement’s relevant Applicable Margin by 2.00% per annum. | ||||
| Amended and Restated Credit Agreement [Member] | Additional Margin Upon Default [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - basis spread of variable rate | 2.00% | ||||
| Five Year Credit Agreement [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - maximum borrowing capacity | $ 7,500,000,000 | $ 7,500,000,000 | |||
| Credit agreement - initiation date | Dec. 31, 2018 | ||||
| Credit agreement - maturity date | Dec. 11, 2023 | ||||
| Credit agreement - Term of Loan | 5 years | ||||
| Line of Credit Facility, Covenant Terms | Each of the Agreements contains covenants that are customary for an issuer with an investment grade senior debt credit rating, as well as a net debt-to-EBITDA (earnings before interest, taxes, depreciation and amortization, and other modifications described in each agreement) financial ratio covenant requiring AT&T to maintain, as of the last day of each fiscal quarter, a ratio of not more than 3.5-to-1. The events of default are customary for agreements of this type and such events would result in the acceleration of, or would permit the lenders to accelerate, as applicable, required payments and would increase each agreement’s relevant Applicable Margin by 2.00% per annum. | ||||
| Five Year Credit Agreement [Member] | Additional Margin Upon Default [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - basis spread of variable rate | 2.00% | ||||
| September 2019 Term Loan [Member] | Bank of America, N.A. [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - maximum borrowing capacity | $ 1,300,000,000 | ||||
| Credit agreement - initiation date | Sep. 30, 2019 | ||||
| Credit agreement - maximum amount outstanding during period | $ 1,300,000,000 | ||||
| Credit agreement - advances outstanding | $ 1,300,000,000 | ||||
| Line of Credit Facility, Covenant Terms | Each of the Agreements contains covenants that are customary for an issuer with an investment grade senior debt credit rating, as well as a net debt-to-EBITDA (earnings before interest, taxes, depreciation and amortization, and other modifications described in each agreement) financial ratio covenant requiring AT&T to maintain, as of the last day of each fiscal quarter, a ratio of not more than 3.5-to-1. The events of default are customary for agreements of this type and such events would result in the acceleration of, or would permit the lenders to accelerate, as applicable, required payments and would increase each agreement's relevant Applicable Margin by 2.00% per annum. | ||||
| Repayment of long-term debt | $ 0 | ||||
| September 2019 Term Loan [Member] | Bank of America, N.A. [Member] | Additional Margin Upon Default [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - basis spread of variable rate | 2.00% | ||||
| 1.25 year BAML Tranche A Facility Term Loan [Member] | Bank of America, N.A. [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - maximum borrowing capacity | 400,000,000 | ||||
| Credit agreement - initiation date | Sep. 01, 2019 | ||||
| Credit agreement - maturity date | Dec. 01, 2020 | ||||
| Credit agreement - Term of Loan | 1 year 3 months | ||||
| Credit agreement - maximum amount outstanding during period | $ 400,000,000 | ||||
| Credit agreement - advances outstanding | 400,000,000 | ||||
| Line of Credit Facility, Covenant Terms | Each of the Agreements contains covenants that are customary for an issuer with an investment grade senior debt credit rating, as well as a net debt-to-EBITDA (earnings before interest, taxes, depreciation and amortization, and other modifications described in each agreement) financial ratio covenant requiring AT&T to maintain, as of the last day of each fiscal quarter, a ratio of not more than 3.5-to-1. The events of default are customary for agreements of this type and such events would result in the acceleration of, or would permit the lenders to accelerate, as applicable, required payments and would increase each agreement's relevant Applicable Margin by 2.00% per annum. | ||||
| Repayment of long-term debt | $ 0 | ||||
| 1.25 year BAML Tranche A Facility Term Loan [Member] | Bank of America, N.A. [Member] | Additional Margin Upon Default [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - basis spread of variable rate | 2.00% | ||||
| 2.25 year BAML Tranche B Facility Term Loan [Member] | Bank of America, N.A. [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - maximum borrowing capacity | 400,000,000 | ||||
| Credit agreement - initiation date | Sep. 01, 2019 | ||||
| Credit agreement - maturity date | Dec. 01, 2021 | ||||
| Credit agreement - Term of Loan | 2 years 3 months | ||||
| Credit agreement - maximum amount outstanding during period | $ 400,000,000 | ||||
| Credit agreement - advances outstanding | 400,000,000 | ||||
| Line of Credit Facility, Covenant Terms | Each of the Agreements contains covenants that are customary for an issuer with an investment grade senior debt credit rating, as well as a net debt-to-EBITDA (earnings before interest, taxes, depreciation and amortization, and other modifications described in each agreement) financial ratio covenant requiring AT&T to maintain, as of the last day of each fiscal quarter, a ratio of not more than 3.5-to-1. The events of default are customary for agreements of this type and such events would result in the acceleration of, or would permit the lenders to accelerate, as applicable, required payments and would increase each agreement's relevant Applicable Margin by 2.00% per annum. | ||||
| Repayment of long-term debt | $ 0 | ||||
| 2.25 year BAML Tranche B Facility Term Loan [Member] | Bank of America, N.A. [Member] | Additional Margin Upon Default [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - basis spread of variable rate | 2.00% | ||||
| 3.25 year BAML Tranche C Facility Term Loan [Member] | Bank of America, N.A. [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - maximum borrowing capacity | 500,000,000 | ||||
| Credit agreement - initiation date | Sep. 01, 2019 | ||||
| Credit agreement - maturity date | Dec. 01, 2022 | ||||
| Credit agreement - Term of Loan | 3 years 3 months | ||||
| Credit agreement - maximum amount outstanding during period | $ 500,000,000 | ||||
| Credit agreement - advances outstanding | $ 500,000,000 | ||||
| Line of Credit Facility, Covenant Terms | Each of the Agreements contains covenants that are customary for an issuer with an investment grade senior debt credit rating, as well as a net debt-to-EBITDA (earnings before interest, taxes, depreciation and amortization, and other modifications described in each agreement) financial ratio covenant requiring AT&T to maintain, as of the last day of each fiscal quarter, a ratio of not more than 3.5-to-1. The events of default are customary for agreements of this type and such events would result in the acceleration of, or would permit the lenders to accelerate, as applicable, required payments and would increase each agreement's relevant Applicable Margin by 2.00% per annum. | ||||
| Repayment of long-term debt | $ 0 | ||||
| 3.25 year BAML Tranche C Facility Term Loan [Member] | Bank of America, N.A. [Member] | Additional Margin Upon Default [Member] | |||||
| Line Of Credit Facility [Line Items] | |||||
| Credit agreement - basis spread of variable rate | 2.00% | ||||