Income Taxes - Components (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal									$ 795	$ 191	$ 3
State and local									109	27	35
Foreign									21	11	2
Total current									925	229	40
Deferred									303	(140)	190
Total income tax expense (benefit)	$ 907	$ 61	$ 108	$ 152	$ (11)	$ 26	$ (5)	$ 79	$ 1,228	$ 89	$ 230