Income Taxes Schedule of Deferred tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred income tax assets:
Price risk management	$ 145	$ 72
Employee benefits	135	98
Deferred Tax Assets, tax credits, net of valuation allowance	56	40
Deferred income taxes	22	37
Tax loss carryforwards	1	17
Total deferred income tax assets	359	264
Deferred income tax liabilities:
Depreciation and amortization	572	534
Regulatory assets	274	175
Other	9	4
Total deferred income tax liabilities	855	713
Deferred income tax liability, net	(496)	(449)
Classification of net deferred income taxes:
Current deferred income tax asset	33	0
Current deferred income tax liability	0	(4)
Noncurrent deferred income tax liability	$ (529)	$ (445)