Equipment Installment Plans - Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Allowance for credit losses
Allowance for credit losses, beginning of year	$ 78
Allowance for credit losses, end of year	72	$ 78
Equipment Installment Plan Receivable
Allowance for credit losses
Allowance for credit losses, beginning of year	78	84
Bad debts expense	38	50
Write-offs, net of recoveries	(44)	(56)
Allowance for credit losses, end of year	$ 72	$ 78