Income Taxes (Reconciliation Of Provision For Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Abstract]
Expected provision (benefit) at federal statutory rate	$ (935)	$ (2,296)	$ 507
Increase (decrease) resulting from:
State income taxes, net of federal income tax effect	(79)	(194)	58
Nondeductible expenses			3
State rate redetermination			(48)
Change in uncertain tax positions	(19)	(7)
Change in valuation allowance	1,002	495	5
Other	2	(3)
Provision (Benefit) for Income Taxes	$ (29)	$ (2,005)	$ 525