Income Taxes (Schedule Of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Current income tax expense (benefit):
United States federal, current income tax expense (benefit)	$ 10	$ 5		$ (243)
Various states, current income tax expense (benefit)		(11)		(8)
Canada and various provinces, current income tax expense (benefit)	102	106		14
Total current tax expense (benefit)	112	100		(237)
Deferred income tax expense (benefit):
United States federal, deferred income tax expense (benefit)	(192)	(3)		(5,487)
Various states, deferred income tax expense (benefit)	(5)			(332)
Canada and various provinces, deferred income tax expense (benefit)	(97)	44		(157)
Total deferred tax expense (benefit)	(294)	41	[1]	(5,976)	[1]
Total income tax expense (benefit)	$ (182)	$ 141	[1]	$ (6,213)	[1]

[1] Prior year amounts have been recast due to change in accounting principle. See Note 2 in “Item 8. Financial Statements and Supplementary Data” of this report.