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Debt And Related Expenses (Narrative) (Details) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended
Jul. 31, 2018
Mar. 31, 2018
Jun. 30, 2018
Dec. 31, 2017
Debt Instrument [Line Items]        
Redemption of senior notes     $ 807,000,000  
Loss on early retirement of debt     (312,000,000)  
Loss on early retirement of debt, cash retirement costs     $ 304,000,000  
Senior Notes [Member]        
Debt Instrument [Line Items]        
Redemption of senior notes   $ 807,000,000    
Loss on early retirement of debt   (312,000,000)    
Loss on early retirement of debt, cash retirement costs   304,000,000    
Loss on early retirement of debt, noncash charges   8,000,000    
7.875% due September 30, 2031 [Member]        
Debt Instrument [Line Items]        
Debt interest rate, stated percentage     7.875% 7.875%
Debt, maturity date     Sep. 30, 2031  
7.875% due September 30, 2031 [Member] | Senior Notes [Member]        
Debt Instrument [Line Items]        
Redemption of senior notes   $ 384,000,000    
Debt interest rate, stated percentage   7.875%    
Debt, maturity date   Sep. 30, 2031    
7.95% due April 15, 2032 [Member]        
Debt Instrument [Line Items]        
Debt interest rate, stated percentage     7.95% 7.95%
Debt, maturity date     Apr. 15, 2032  
7.95% due April 15, 2032 [Member] | Senior Notes [Member]        
Debt Instrument [Line Items]        
Redemption of senior notes   $ 423,000,000    
Debt interest rate, stated percentage   7.95%    
Debt, maturity date   Apr. 15, 2032    
8.25% Due July 1, 2018 [Member]        
Debt Instrument [Line Items]        
Debt interest rate, stated percentage     8.25% 8.25%
Debt, maturity date     Jul. 01, 2018  
8.25% Due July 1, 2018 [Member] | Senior Notes [Member] | Subsequent Event [Member]        
Debt Instrument [Line Items]        
Redemption of senior notes $ 20,000,000      
Debt interest rate, stated percentage 8.25%      
Senior Credit Facility [Member]        
Debt Instrument [Line Items]        
Credit Facility, borrowing capacity     $ 3,000,000,000  
Outstanding credit facility borrowings     $ 0  
Debt-to-capitalization ratio     0.261  
Outstanding letters of credit     $ 51,000,000  
Maximum [Member] | Senior Credit Facility [Member]        
Debt Instrument [Line Items]        
Debt-to-capitalization ratio     0.65