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Defined Benefit Plans - Additional Information (Detail)
3 Months Ended 12 Months Ended
Mar. 31, 2016
USD ($)
Dec. 31, 2018
USD ($)
age
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Recognition of actuarial gains (losses)   $ (3,800,000) $ 500,000 $ (1,900,000)
Accumulated other comprehensive income, net periodic benefit cost     0  
Defined Contribution Plan, cash contributions   29,500,000 29,100,000 22,700,000
Accounting Standards Update 2017-07 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Reclassifications from operating income to other income     9,600,000 $ 14,100,000
Fair Value Measured at Net Asset Value Per Share [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investments measured using net asset value per share   $ 576,000,000 633,300,000  
Real estate [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Assets redemption notice period   45 days    
Investment Assets [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Assets redemption notice period   95 days    
Pension Benefits [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Recognition of actuarial gains (losses)   $ 63,100,000 (40,600,000)  
Defined benefit plans, increase (decrease) in liability     $ (5,000,000)  
Defined benefit plans, blended long-term rate of return on plan assets   6.00% 6.40% 6.60%
Pension Benefits [Member] | Minimum [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined benefit plans, retirement benefits payment commencement age | age   55    
Pension Benefits [Member] | Maximum [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined benefit plans, retirement benefits payment commencement age | age   65    
Postretirement Benefits [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Reduction in accrued retiree benefit plans $ (10,700,000)      
Recognition of actuarial gains (losses) $ (900,000) $ 200,000 $ 1,400,000  
Equity Securities | Minimum [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined benefit asset allocation, maximum   0.00%    
Equity Securities | Maximum [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined benefit asset allocation, maximum   75.00%    
Fixed income | Minimum [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined benefit asset allocation, maximum   25.00%    
Fixed income | Maximum [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined benefit asset allocation, maximum   100.00%    
Cash and cash equivalents        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined benefit asset allocation, maximum   25.00%    
Other Investment        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined benefit asset allocation, maximum   20.00%