Sales of Certain Receivables - Sales of Receivables and Continuing Involvement (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Qualitative and Quantitative Information, Transferor's Continuing Involvement [Line Items]
Other current assets	$ 2,305	$ 1,676		$ 1,598
Other long-term assets	1,891	1,623		1,552
Accounts payable and accrued liabilities	6,746	7,741		7,676
Other current liabilities	1,673	787		815
Other long-term liabilities	954	967		$ 903
Of which:
Losses from sales of receivables	130	157	$ 299
Factoring and EIP Securitization Arrangement | Variable Interest Entity, Primary Beneficiary
Of which:
Maximum exposure to loss, Factoring VIE	1,100
Factoring and EIP Securitization Arrangement | Variable Interest Entity, Primary Beneficiary
Qualitative and Quantitative Information, Transferor's Continuing Involvement [Line Items]
Derecognized net service receivables and EIP receivables	2,584	2,577
Other current assets	694	660
Deferred purchase price assets	781	746
Other long-term assets	89	88
Accounts payable and accrued liabilities	25	59
Other current liabilities	342	149
Other long-term liabilities	18	22
Net cash proceeds since inception	1,944	1,879
Of which:
Change in net cash proceeds during the year-to-date period	65	(179)
Net cash proceeds funded by reinvested collections	1,879	2,058
Losses from sales of receivables	130	157	$ 299
Factoring and EIP Securitization Arrangement | Other current assets - of which, deferred purchase price | Variable Interest Entity, Primary Beneficiary
Qualitative and Quantitative Information, Transferor's Continuing Involvement [Line Items]
Deferred purchase price assets	692	658
Factoring and EIP Securitization Arrangement | Other long-term assets - of which, deferred purchase price | Variable Interest Entity, Primary Beneficiary
Qualitative and Quantitative Information, Transferor's Continuing Involvement [Line Items]
Deferred purchase price assets	$ 89	$ 88