Income Tax Expense (Components of Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal	$ 7	$ 24	$ 0
State	(30)	4	2
Total current income tax expense (benefit)	(23)	28	2
Federal	2	(14)	(302)
State	4	20	(6)
Total deferred tax expense (benefit)	6	6	(308)
Net income tax expense (benefit)	$ (17)	$ 34	$ (306)