Additional Financial Information - Accounts Payable and Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Supplemental Financial Statement Elements [Abstract]
Accounts payable	$ 4,322		$ 5,487
Payroll and related benefits	802		709
Property and other taxes, including payroll	682		642
Interest	227		227
Commissions	251		243
Network decommissioning	0		65
Toll and interconnect	156		157
Advertising	127		76
Other	179		135
Accounts payable and accrued liabilities	6,746	$ 7,676	7,741
Accounts Payable and Accrued Liabilities
Accounts Payable and Accrued Liabilities [Line Items]
Outstanding checks	$ 463		$ 630