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Employee Benefit Plans Amounts Charged to Income for employees Incentive Compensation Plans (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Incentive Compensation Cash Award      
Incentive Compensation Plans Expense [Line Items]      
Pretax $ 461.3 $ 386.8 $ 337.7
After Tax 299.8 251.4 219.5
Employee Stock [Member]      
Incentive Compensation Plans Expense [Line Items]      
Pretax 92.9 80.9 64.5
After Tax 60.4 52.6 41.9
Employee Stock Option      
Incentive Compensation Plans Expense [Line Items]      
Pretax 2.5 4.3 1.7
After Tax $ 1.6 $ 2.8 $ 1.1