Income Taxes (Reconciliation of Provision for Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Expected provision at federal statutory rate	$ 101	$ 113	$ 333
Decrease resulting from:
State income taxes, net of federal income tax effect	11	13	16
Rate impacts due to tax reform	0	0	370
Changes to valuation allowance due to tax reform	0	0	(370)
AMT tax reform impact – valuation allowance release	0	0	(68)
Changes in uncertain tax positions	0	0	(5)
Change in valuation allowance	(522)	(121)	(364)
Removal of sequestration fee on AMT receivables	0	(5)	0
Other	(1)	1	(5)
Provision (benefit) for income taxes	$ (411)	$ 1	$ (93)