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Long-term Debt - Summary of Long-term Debt (Details) - Senior Notes - USD ($)
Jun. 30, 2016
Dec. 31, 2015
5.50% Senior Notes    
Debt Instrument [Line Items]    
Principal Amount at Par $ 700,000,000  
Fair Value $ 729,800,000 $ 717,500,000
Interest rate 5.50%  
5.875% Senior Notes    
Debt Instrument [Line Items]    
Principal Amount at Par $ 800,000,000  
Fair Value $ 839,000,000 820,000,000
Interest rate 5.875%  
5.750% Senior Notes    
Debt Instrument [Line Items]    
Principal Amount at Par $ 400,000,000  
Fair Value $ 417,000,000 411,000,000
Interest rate 5.75%  
5.375% Senior Notes    
Debt Instrument [Line Items]    
Principal Amount at Par $ 500,000,000  
Fair Value $ 531,000,000 $ 525,000,000
Interest rate 5.375%