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Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Apr. 09, 2020	Apr. 06, 2020	Oct. 31, 2018
Derivative [Line Items]
Net collateral transfers to certain derivative counterparties	$ (580)	$ (1,212)	$ 0	$ (632)	$ 0
Accumulated other comprehensive loss	868	1,658		1,658
Amount amortized from AOCI into Interest expense		39		39
Amount expected to be amortized from AOCI into interest expense over next 12 months				182
Guarantee liabilities	62	51		51
Total EIP Receivables, net of unamortized imputed discounts	4,582	5,084		5,084
Equipment installment plan receivables, net of allowance for credit losses and imputed discount
Derivative [Line Items]
Total EIP Receivables, net of unamortized imputed discounts		$ 2,800		$ 2,800
3.500% Senior Secured Notes due 2025 \| Senior Notes
Derivative [Line Items]
Interest rate, stated percentage						3.50%
4.500% Senior Secured Notes due 2050 \| Senior Notes
Derivative [Line Items]
Interest rate, stated percentage						4.50%
Interest Rate Contract
Derivative [Line Items]
Derivative liabilities							$ 2,300
Cash-collateralized							$ 1,200
Interest Rate Contract \| Cash Flow Hedging
Derivative [Line Items]
Aggregate notional amount								$ 9,600
Fair value of derivative instrument	$ 1,200