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Debt - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended
Nov. 08, 2017
May 31, 2011
Jun. 30, 2018
Amended Credit Agreement      
Debt Instrument [Line Items]      
Maximum borrowing capacity under revolving credit facility   $ 1,200,000,000  
Maturity date of term loan Facility   May 13, 2021  
Expiration period under the new Facility   5 years  
Available credit under the Facility     $ 1,000,000,000
Amount outstanding under letters of credit     80,000,000
Average borrowings under the Facility     $ 0
Term Loan Facility      
Debt Instrument [Line Items]      
Maturity date of term loan Facility Nov. 08, 2022    
Senior secured term loan $ 750,000,000