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External Debt and Financing Arrangements - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]          
Revolving credit facility, extended expiration date     2021-06    
Current portion of long-term debt     $ 0 $ 0  
Prepaid debt issuance cost, write off $ 1,300,000        
Uncommitted bank lines of credit, which provide for unsecured borrowings for working capital     23,500,000 23,500,000  
Uncommitted bank lines of credit, which provide for unsecured borrowings for working capital amount outstanding     $ 0 $ 0  
Weighted-average interest rates on borrowings     0.00% 1.50% 1.00%
LIBOR [Member] | Minimum [Member]          
Debt Instrument [Line Items]          
Interest rate over LIBOR     0.90%    
LIBOR [Member] | Maximum [Member]          
Debt Instrument [Line Items]          
Interest rate over LIBOR     1.50%    
Revolving Credit Facility [Member]          
Debt Instrument [Line Items]          
Term loan, outstanding borrowings     $ 615,000,000 $ 540,000,000  
Current portion of long-term debt     0 0  
Line of Credit Facility, Maximum Borrowing Capacity     1,250,000,000 1,250,000,000  
Senior Unsecured Notes [Member]          
Debt Instrument [Line Items]          
Senior unsecured notes, price   $ 900,000,000      
Senior notes, outstanding amount     892,600,000 $ 891,100,000  
Senior Unsecured Notes [Member] | Notes Due 2020 [Member]          
Debt Instrument [Line Items]          
Senior unsecured notes, price   $ 400,000,000      
Senior unsecured notes, maturity period   5 years      
Senior unsecured notes, maturity year   2020      
Senior unsecured notes, coupon rate   3.00%      
Senior Unsecured Notes [Member] | Notes Due 2025 [Member]          
Debt Instrument [Line Items]          
Senior unsecured notes, price   $ 500,000,000      
Senior unsecured notes, maturity period   10 years      
Senior unsecured notes, maturity year   2025      
Senior unsecured notes, coupon rate   4.00%      
Amended and Restated Credit Agreement [Member] | Revolving Credit Facility [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Maximum Borrowing Capacity $ 1,250,000,000        
Senior Notes          
Debt Instrument [Line Items]          
Long-term debt payments in 2018     0    
Long-term debt payments in 2019     0    
Long-term debt payments in 2020     400,000,000    
Long-term debt payments in 2021     0    
Long-term debt payments in 2022     $ 0