Income Taxes Income Taxes - Deferred Tax Assets and Liabilities Table (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Deferred Tax Liabilities, Deferred Expense, Other Capitalized Costs	$ (129)	$ (223)
Deferred Tax Liabilities, Other	(20)	(62)
Deferred Tax Liabilities, Gross	149	285
Deferred Tax Assets, Property, Plant and Equipment	1	593
Deferred Tax Assets, Operating Loss Carryforwards	2,248	2,587
Deferred Tax Assets, Carrying Value of Debt	161	539
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Asset Retirement Obligations	42	98
Deferred Tax Assets, Investments	161	275
Deferred Tax Assets, Derivative Instruments	17	161
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	125	319
Deferred Tax Assets, Other	71	118
Deferred Tax Assets, Gross	2,826	4,690
Deferred Tax Assets, Valuation Allowance	(2,674)	(4,389)
Deferred Tax Assets, Net of Valuation Allowance	152	301
Deferred Tax Assets, Net	$ 3	$ 16