Sales of Certain Receivables - Sales of EIP Receivables (Details) - USD ($)	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2015
Variable Interest Entity [Line Items]
Other current assets	$ 2,305,000,000	$ 1,598,000,000	$ 1,676,000,000
Other assets	1,891,000,000	$ 1,552,000,000	1,623,000,000
EIP Securitization Arrangement
Variable Interest Entity [Line Items]
Revolving receivables facility, maximum borrowing capacity	1,300,000,000		1,300,000,000	$ 1,300,000,000
Other current assets	344,000,000		321,000,000
Other assets	89,000,000		88,000,000
Other long-term liabilities	$ 18,000,000		$ 22,000,000