Income Taxes Schedule of Deferred tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred income tax assets:
Employee benefits	$ 181	$ 170
Price risk management	59	112
Deferred income taxes	29	42
Deferred Tax Assets, tax credits, net of valuation allowance	56	46
Deferred Tax Assets, Tax Deferred Expense, Other	5	0
Total deferred income tax assets	330	370
Deferred income tax liabilities:
Depreciation and amortization	829	781
Regulatory assets	170	220
Deferred Tax Liabilities, Other	0	1
Deferred Tax Liabilities, Gross, Noncurrent	999	1,002
Total deferred income tax liabilities	$ (669)	$ (632)