Income Taxes Schedule of Deferred tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred income tax assets:
Price risk management	$ 77	$ 145
Employee benefits	162	135
Deferred Tax Assets, tax credits, net of valuation allowance	55	56
Deferred income taxes	20	22
Tax loss carryforwards	0	1
Total deferred income tax assets	314	359
Deferred income tax liabilities:
Depreciation and amortization	623	572
Regulatory assets	224	274
Other	4	9
Total deferred income tax liabilities	851	855
Deferred income tax liability, net	(537)	(496)
Classification of net deferred income taxes:
Current deferred income tax asset	51	33
Noncurrent deferred income tax liability	$ (588)	$ (529)