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Debt - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended
Apr. 17, 2019
Apr. 30, 2019
Mar. 31, 2019
Mar. 31, 2018
Jan. 31, 2019
Dec. 31, 2018
Jun. 06, 2017
Jan. 31, 2017
Debt Instrument [Line Items]                
Aggregate principal amount of notes outstanding     $ 1,336,000,000          
Loss on debt extinguishment     (3,000,000) $ 10,000,000        
Proceeds from borrowings under Term Loan     $ 100,000,000 0        
1.125% Convertible Notes                
Debt Instrument [Line Items]                
Percentage of contractual interest rate on Notes     1.125%          
Senior Notes | 4.875% Notes                
Debt Instrument [Line Items]                
Aggregate principal amount of notes outstanding     $ 330,000,000          
Face amount             $ 330,000,000  
Percentage of contractual interest rate on Notes     4.875%       4.875%  
Senior Notes | 5.375% Notes                
Debt Instrument [Line Items]                
Aggregate principal amount of notes outstanding     $ 700,000,000          
Face amount     $ 700,000,000          
Percentage of contractual interest rate on Notes     5.375%          
Line of Credit | Term Loan                
Debt Instrument [Line Items]                
Aggregate principal amount of notes outstanding     $ 100,000,000          
Current borrowing capacity     500,000,000          
Line of Credit | Credit Facility                
Debt Instrument [Line Items]                
Maximum borrowing capacity         $ 600,000,000     $ 500,000,000
Minimum principal amount of advancements         $ 50,000,000      
Current borrowing capacity     498,000,000          
Line of Credit | Letter of Credit                
Debt Instrument [Line Items]                
Amount outstanding under Letter of Credit     2,000,000          
Convertible Notes | 1.125% Convertible Notes                
Debt Instrument [Line Items]                
Aggregate principal amount of notes outstanding     $ 206,000,000          
Percentage of contractual interest rate on Notes     1.125%     1.125%    
Repayments of principal     $ 46,000,000          
Repayment of aggregate carrying amount     44,000,000          
Repayments of debt     115,000,000          
Loss on debt extinguishment     $ 3,000,000          
Conversion ratio     0.0245277          
Conversion price per share of common stock (in dollars per share)     $ 40.77          
Effective interest percentage     6.00%          
Remaining amortization period (less than)     1 year          
If-converted value     $ 456,000,000 $ 581,000,000        
Subsequent Event | Line of Credit | Credit Facility                
Debt Instrument [Line Items]                
Proceeds from borrowings under Term Loan $ 120,000,000              
Subsequent Event | Convertible Notes | 1.125% Convertible Notes                
Debt Instrument [Line Items]                
Repayments of principal   $ 128,000,000            
Repayment of aggregate carrying amount   123,000,000            
Repayments of debt   $ 332,000,000            
Minimum | Line of Credit | Credit Facility                
Debt Instrument [Line Items]                
Amortization payment percentage     1.25%          
Maximum | Line of Credit | Credit Facility                
Debt Instrument [Line Items]                
Amortization payment percentage     2.50%