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External Debt and Financing Arrangements - Components of External Long-Term Debt (Parenthetical) (Detail) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Jun. 30, 2015
Senior Unsecured Notes [Member]      
Debt Instrument [Line Items]      
Debt instrument face amount     $ 900,000,000
Senior Unsecured Notes [Member] | Notes Due June Twenty Twenty [Member]      
Debt Instrument [Line Items]      
Debt instrument face amount $ 400,000,000    
Debt instrument, maturity date 2020-06    
Senior Unsecured Notes [Member] | Notes Due June Twenty Twenty Five [Member]      
Debt Instrument [Line Items]      
Debt instrument face amount $ 500,000,000    
Debt instrument, maturity date 2025-06    
Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Revolving credit facility, maximum borrowing capacity $ 975,000,000 $ 975,000,000  
Revolving credit facility, expiration date 2018-07 2018-07  
Term Loan Facilities [Member]      
Debt Instrument [Line Items]      
Debt instrument face amount $ 525,000,000 $ 525,000,000  
Debt instrument, maturity date 2018-07 2018-07