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Income Taxes - Reconciliation of Income Taxes at Federal Statutory Income Tax Rate (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Reconciliation Of Income Taxes [Line Items]      
Income tax expense computed at federal statutory income tax rate $ 112.8 $ 222.2 $ 203.7
Other income taxes, net of federal tax benefit 13.7 13.4 12.6
Foreign taxes at a different rate than U.S. federal statutory income tax rate 3.5 (8.3) (7.6)
Tax benefit on income attributable to domestic production activities 0.0 (10.9) (13.0)
Net adjustments for uncertain tax positions 4.1 11.6 13.2
Share-based compensation (ASU 2016-09) (2.1) (23.9) (27.8)
Tax Act impact 5.5 (25.7)  
Deferred tax impact of state tax rate changes 3.5 (2.0) (1.1)
Valuation allowance increase (decrease) 3.0 (5.2) (2.1)
Miscellaneous other, net 3.0 (11.7) (8.2)
Income tax expense as reported $ 147.0 $ 159.5 $ 169.7
Effective income tax rate 27.40% 25.10% 29.20%