Quarterly report pursuant to Section 13 or 15(d)

Debt - (Schedule of Debt) (Details)

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Debt - (Schedule of Debt) (Details) - USD ($)
Mar. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Fair value of interest rate swap agreements $ (120,000,000) $ (71,000,000)
Total senior notes 4,486,000,000 4,535,000,000
Mortgage notes payable 60,000,000 61,000,000
Capital leases and other 17,000,000 18,000,000
Debt issuance costs (62,000,000) (65,000,000)
Total debt 5,176,000,000 4,699,000,000
Less current portion (4,000,000) (4,000,000)
Long-term debt 5,172,000,000 4,695,000,000
Revolving credit agreement    
Debt Instrument [Line Items]    
Revolving credit agreement 675,000,000 150,000,000
Senior Notes | $1,400 million 5.625% Senior notes, due February 15, 2021    
Debt Instrument [Line Items]    
Debt, face amount $ 1,400,000,000  
Interest rate, stated 5.625%  
Senior notes $ 1,400,000,000 1,400,000,000
Senior Notes | $1,000 million 4.75% Senior notes, due May 15, 2022    
Debt Instrument [Line Items]    
Debt, face amount $ 1,000,000,000  
Interest rate, stated 4.75%  
Senior notes $ 1,006,000,000 1,006,000,000
Senior Notes | $1,000 million 6.125% Senior notes, due February 15, 2024    
Debt Instrument [Line Items]    
Debt, face amount $ 1,000,000,000  
Interest rate, stated 6.125%  
Senior notes $ 1,000,000,000 1,000,000,000
Senior Notes | $1,200 million 4.75% Senior notes, due January 15, 2025    
Debt Instrument [Line Items]    
Debt, face amount $ 1,200,000,000  
Interest rate, stated 4.75%  
Senior notes $ 1,200,000,000 $ 1,200,000,000