Income Taxes Schedule of Deferred tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred income tax assets:
Employee benefits	$ 170	$ 161
Price risk management	112	88
Deferred income taxes	42	48
Deferred Tax Assets, tax credits, net of valuation allowance	46	13
Deferred Tax Assets, Tax Deferred Expense, Other	0	1
Total deferred income tax assets	370	311
Deferred income tax liabilities:
Depreciation and amortization	781	693
Regulatory assets	220	210
Deferred Tax Liabilities, Other	1	0
Deferred Tax Liabilities, Gross, Noncurrent	1,002	903
Total deferred income tax liabilities	(632)	(592)
Classification of net deferred income taxes:
Current deferred income tax asset	0	(33)
Noncurrent deferred income tax liability	$ (632)	$ (625)