Income Taxes Schedule of Deferred tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets:
Employee benefits	$ 128	$ 181
Price risk management	56	59
Deferred income taxes	14	29
Deferred Tax Assets, tax credits, net of valuation allowance	50	56
Deferred Tax Assets, Tax Deferred Expense, Other	4	5
Total deferred income tax assets	252	330
Deferred income tax liabilities:
Depreciation and amortization	496	829
Regulatory assets	132	170
Deferred Tax Liabilities, Other	0	0
Deferred Tax Liabilities, Gross, Noncurrent	628	999
Total deferred income tax liabilities	$ (376)	$ (669)