Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current Expense (Benefit):
Federal	$ 2,026	$ 2,411	$ 3,190
State	639	277	480
Foreign	425	389	194
Current income tax expense (benefit)	3,090	3,077	3,864
Deferred Expense (Benefit):
Federal	546	(10,651)	1,183
State	(167)	11	153
Foreign	(89)	(6)	98
Deferred income tax expense (benefit)	290	(10,646)	1,434
Income tax expense (benefit)	3,380	(7,569)	5,298
NBCUniversal Media LLC [Member]
Current Expense (Benefit):
Foreign	230	201	38
Deferred Expense (Benefit):
Foreign	(31)	(7)	96
Deferred income tax expense (benefit)	(39)	2	89
Withholding tax expense	163	187	158
U.S. domestic tax expense	(11)	11	13
Income tax expense (benefit)	$ 351	$ 392	$ 305