Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 1,199.0	$ 1,032.5	$ 973.8
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized (Losses) Gains on Securities Available for Sale	(42.4)	(1.4)	(58.6)
Net Unrealized Gains (Losses) on Cash Flow Hedges	(1.6)	9.1	1.7
Foreign Currency Translation Adjustments	16.7	(0.9)	(15.9)
Pension and Other Postretirement Benefit Adjustments	(17.0)	(4.1)	19.8
Other Comprehensive Income (Loss)	(44.3)	2.7	(53.0)
Comprehensive Income	$ 1,154.7	$ 1,035.2	$ 920.8