Income Taxes (Components Of Deferred Tax Balances) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities:
Differences between book and tax basis of property	$ 81	$ 216
Other	1	2
Total deferred tax liabilities	82	218
Deferred tax assets
Accrued compensation	38	19
Alternative minimum tax credit carryforward	100	125
Accrued pension costs	19	19
Asset retirement obligations	53	77
Net operating loss carryforward	1,177	445
Derivative activity	142
Other	29	26
Total deferred tax assets	1,558	711
Valuation allowance	(1,476)	(493)
Net deferred tax liability