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	$ 9	$ 3	$ (6)
Total current tax expense (benefit)	9	3	(6)
Deferred tax expense (benefit):
Federal	23	58	(95)
Total deferred tax expense (benefit)	23	58	(95)
Income tax expense (benefit)	$ 32	$ 61	$ (101)