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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)

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