Income Taxes Schedule of Deferred tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax assets:
Employee benefits	$ 134	$ 128
Price risk management	36	56
Deferred income taxes	26	14
Deferred Tax Assets, tax credits, net of valuation allowance	52	50
Deferred Tax Assets, Tax Deferred Expense, Other	9	4
Total deferred income tax assets	257	252
Deferred income tax liabilities:
Depreciation and amortization	511	496
Regulatory assets	115	132
Deferred Tax Liabilities, Gross, Noncurrent	626	628
Total deferred income tax liabilities	$ 369	$ 376