Share-Based Compensation Plans - Total Compensation Expense for Share-Based Payment Arrangements to Employees (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	$ 128.0	$ 86.8	$ 76.4
Tax Benefits Recognized	48.7	32.8	28.8
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	87.3	60.2	51.5
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	9.0	9.0	10.0
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	$ 31.7	$ 17.6	$ 14.9