Income Taxes (Components of Deferred Tax Balances) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred tax liabilities:
Differences between book and tax basis of property	$ 312	$ 226
Derivative activity	34	12
Right of use lease assets	37	0
Other	2	2
Total deferred tax liabilities	385	240
Deferred tax assets
Accrued compensation	33	33
Accrued pension costs	9	10
Asset retirement obligations	13	15
Net operating loss carryforward	769	777
Future lease payments	37	0
Other	18	14
Total deferred tax assets	879	849
Valuation allowance	(87)	(609)
Net deferred tax asset	$ 407	$ 0