Debt - Note Redemption (Details)	6 Months Ended
Jun. 30, 2021 USD ($)
Debt Instrument [Line Items]
Principal Amount	$ 660,000,000
Write off of Premiums, Discounts and Issuance Costs	0
Call Penalties	0
6.500% Senior Notes due 2026 \| Senior Notes
Debt Instrument [Line Items]
Principal Amount	2,000,000,000.0
Write off of Premiums, Discounts and Issuance Costs	36,000,000
Call Penalties	$ 65,000,000
Redemption Price (as a percent)	103.25%
Interest rate, stated percentage	6.50%
6.000% Senior Notes due 2023 \| Senior Notes
Debt Instrument [Line Items]
Principal Amount	$ 1,300,000,000
Write off of Premiums, Discounts and Issuance Costs	10,000,000
Call Penalties	$ 0
Redemption Price (as a percent)	100.00%
Interest rate, stated percentage	6.00%
6.000% Senior Notes due 2024 \| Senior Notes
Debt Instrument [Line Items]
Principal Amount	$ 1,000,000,000
Write off of Premiums, Discounts and Issuance Costs	9,000,000
Call Penalties	$ 0
Redemption Price (as a percent)	100.00%
Interest rate, stated percentage	6.00%
5.125% Senior Notes due 2025 \| Senior Notes
Debt Instrument [Line Items]
Principal Amount	$ 500,000,000
Write off of Premiums, Discounts and Issuance Costs	3,000,000
Call Penalties	$ 6,000,000
Redemption Price (as a percent)	101.281%
Interest rate, stated percentage	5.125%
Total Senior Notes to third parties redeemed
Debt Instrument [Line Items]
Principal Amount	$ 4,800,000,000
Write off of Premiums, Discounts and Issuance Costs	58,000,000
Call Penalties	71,000,000
3.360% Secured Series 2016-1 A-1 Notes due 2021 \| Senior Notes
Debt Instrument [Line Items]
Principal Amount	438,000,000
Write off of Premiums, Discounts and Issuance Costs	0
Call Penalties	$ 0
Interest rate, stated percentage	3.36%
4.738% Secured Series 2018-1 A-1 Notes due 2025 \| Senior Notes
Debt Instrument [Line Items]
Principal Amount	$ 131,000,000
Write off of Premiums, Discounts and Issuance Costs	0
Call Penalties	$ 0
Interest rate, stated percentage	4.738%
Other debt
Debt Instrument [Line Items]
Principal Amount	$ 91,000,000
Write off of Premiums, Discounts and Issuance Costs	0
Call Penalties	$ 0

Reimbursement of Call Penalties

No definition available.

Name:	tmus_ReimbursementOfCallPenalties
Namespace Prefix:	tmus_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Write off of Premiums, Discounts and Issuance Costs

+ References

No definition available.

+ Details

Name:	tmus_WriteoffofPremiumsDiscountsandIssuanceCosts
Namespace Prefix:	tmus_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentRepurchasedFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=tmus_A6500SeniorNotesDue2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmus_A6000SeniorNotesDue2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmus_A6000SeniorNotesDue2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmus_A5125SeniorNotesDue2025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmus_TotalOfSecuredBridgeLoanFacilityAndSeniorNotesToThirdPartiesRedeemedMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmus_SeniorSecuredSeries20161A1NotesDue20213360Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmus_SeniorSecuredSeries20181A1NotesDue20254738Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmus_DebtOtherMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: