Income Taxes (Income Tax Components) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax:
Federal	$ 468	$ 245	$ 509
State and local	58	44	36
Foreign	52	23	41
Total current income tax	578	312	586
Deferred income tax:
Federal	169	(36)	(124)
State and local	(5)	3	(4)
Foreign	(8)	(1)	(3)
Total deferred income tax	156	(34)	(131)
Total income tax provision	734	$ 278	$ 455
Expense related to the enactment of the Tax Act	286
Remeasurement of deferred tax assets and liabilities to Tax Act's statutory 21%	221
Expense for the foreign provisions of the Tax Act	57
Remeasurement of tax contingencies related to the Tax Act	$ 8