Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Loss carryforwards	$ 823	$ 1,526
Deferred rents	0	784
Lease liability	3,403
Reserves and accruals	659	668
Federal and state tax credits	331	340
Other	903	620
Deferred tax assets, gross	6,119	3,938
Valuation allowance	(129)	(210)	$ (273)
Deferred tax assets, net	5,990	3,728
Deferred tax liabilities
Spectrum licenses	5,902	5,494
Property and equipment	2,506	2,434
Lease right-of-use assets	2,881
Other intangible assets	19	40
Other	289	232
Total deferred tax liabilities	11,597	8,200
Net deferred tax liabilities	$ 5,607	$ 4,472