v3.19.1
Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Valuation Allowance [Line Items]      
Income Tax Expense (Benefit), Intraperiod Tax Allocation $ 1 $ 6 $ 0
NOL and credit carryforwards 1,595 1,810  
Taxes related to risk management activities and derivatives 7 20  
Reorganization items and impairments 166 146  
Deferred Tax Assets, Other 101 28  
Deferred tax assets before valuation allowance 1,869 2,004  
Valuation allowance (1,000) (1,168)  
Valuation Allowance, Deferred Tax Asset, Change in Amount 168 413 $ 56
Total deferred tax assets 869 836  
Deferred tax liabilities: property, plant and equipment (890) (805)  
Deferred Tax Liabilities, Gross (890) (805)  
Deferred Tax Liabilities, Net (21)    
Net deferred tax asset (liability)   31  
Deferred Tax Liabilities, Gross, Noncurrent (22) (28)  
Deferred income tax asset, non-current 1 $ 59  
Change in Valuation due to Merger [Member]      
Valuation Allowance [Line Items]      
Valuation Allowance, Deferred Tax Asset, Change in Amount $ (58)