Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt (Debt) (Details)

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Long-Term Debt (Debt) (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Sep. 13, 2018
Mar. 18, 2014
Debt Instrument [Line Items]        
Debt Issuance Costs $ (25) $ (25)    
Total debt and finance lease obligations 5,219 5,120    
Less current portion (420) (421)    
Long-term portion of debt and finance lease obligations 4,799 4,699    
3.125% Senior Secured Notes due 2019, net of original issue discount        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 399 399    
Debt Instrument, Interest Rate, Stated Percentage 3.125%     3.125%
5.125% Senior Secured Notes due 2022        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 500 500    
Debt Instrument, Interest Rate, Stated Percentage 5.125%      
4.375% Senior Secured Notes due 2023, net of original issue discount        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 750 750    
Debt Instrument, Interest Rate, Stated Percentage 4.375%      
4.85% Senior Secured Notes due 2024, net of original issue discount        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 600 600    
Debt Instrument, Interest Rate, Stated Percentage 4.85%      
4.45% Senior Secured Notes due 2025, net of original issue discount        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 599 599    
Debt Instrument, Interest Rate, Stated Percentage 4.45%      
5.45% Senior Secured Notes due 2034, net of original issue discount        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 399 399    
Debt Instrument, Interest Rate, Stated Percentage 5.45%      
5.95% Senior Secured Notes due 2043, net of original issue discount        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 300 300    
Debt Instrument, Interest Rate, Stated Percentage 5.95%      
6.375% Senior Secured Notes [Member]        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 225 225 $ 0  
Debt Instrument, Interest Rate, Stated Percentage     6.375%  
Senior secured credit facility        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations 1,290 1,185    
Finance lease obligations        
Debt Instrument [Line Items]        
Debt and Capital Lease Obligations $ 182 $ 188