Share-Based Compensation Plans (Compensation Expense for Share-Based Arrangements and Tax Impacts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 19.5	$ 21.6	$ 109.2	$ 106.2
Tax Benefits Recognized	4.9	8.5	27.1	40.4
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	15.5	15.8	80.3	72.6
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	0.5	0.9	2.0	8.2
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 3.5	$ 4.9	$ 26.9	$ 25.4