Share-Based Compensation Plans (Compensation Expense for Share-Based Arrangements and Tax Impacts) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 33.2	$ 28.6	$ 89.7	$ 84.6
Tax Benefits Recognized	8.2	10.7	22.2	31.9
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	18.1	15.6	64.8	56.8
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	0.7	1.0	1.5	7.3
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 14.4	$ 12.0	$ 23.4	$ 20.5