Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Expense (Benefit):
Federal	$ 2,411	$ 3,190	$ 3,210
State	277	480	570
Foreign	389	194	221
Current income tax expense (benefit)	3,077	3,864	4,001
Deferred Expense (Benefit):
Federal	(10,659)	1,192	890
State	10	154	66
Foreign	(6)	98	2
Deferred income tax expense (benefit)	(10,655)	1,444	958
Income tax expense (benefit)	(7,578)	5,308	4,959
NBCUniversal Media LLC [Member]
Current Expense (Benefit):
Foreign	201	38	81
Deferred Expense (Benefit):
Foreign	(7)	96	2
Deferred income tax expense (benefit)	2	89	(11)
Withholding tax expense	187	158	139
U.S. domestic tax expense	11	13	5
Income tax expense (benefit)	$ 392	$ 305	$ 227