Income Taxes - Schedule of Components of Income Tax Provision (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current expense:
Federal	$ 629	$ 539	$ 959
State	151	80	97
Total current expense	780	619	1,056
Deferred expense:
Federal	26	253	(14)
State	(3)	39	16
Total deferred expense	23	292	2
Provision for income taxes	$ 803	$ 911	$ 1,058