Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current tax expense (benefit):
Federal	$ 126	$ 123	$ (128)
State	1	(2)	0
Total current tax expense (benefit)	127	121	(128)
Deferred tax expense (benefit):
Federal	(335)	(84)	812
State	3	0	3
Total deferred tax expense (benefit)	(332)	(84)	815
Total income tax expense (benefit)	$ (205)	$ 37	$ 687