Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2014		$ 388.5	$ 408.6	$ 1,050.9	$ 7,625.4	$ (319.7)	$ (704.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Options and Awards				(60.1)			92.3
Stock Options and Awards — Amortization				23.4
Stock Options and Awards — Tax Benefit				10.7
Net Income	$ 230.7				230.7
Dividends Declared — Common Stock					(78.5)
Dividends Declared — Preferred Stock					(5.9)
Net Unrealized Gains (Losses) on Securities Available for Sale	54.1					54.1
Net Unrealized Gains (Losses) on Cash Flow Hedges	(1.1)					(1.1)
Foreign Currency Translation Adjustments	(5.9)					(5.9)
Pension and Other Postretirement Benefit Adjustments	6.2					6.2
Stock Purchased							(107.2)
Ending balance at Mar. 31, 2015	8,607.6		408.6	1,024.9	7,771.7	(266.4)	(719.7)
Beginning balance at Dec. 31, 2015	8,705.9	$ 388.5	408.6	1,072.2	8,242.8	(372.7)	(1,033.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Options and Awards				(71.2)			76.6
Stock Options and Awards — Amortization				26.4
Stock Options and Awards — Tax Benefit				(5.3)
Net Income	241.8				241.8
Dividends Declared — Common Stock					(83.9)
Dividends Declared — Preferred Stock					(5.9)
Net Unrealized Gains (Losses) on Securities Available for Sale	74.7					74.7
Net Unrealized Gains (Losses) on Cash Flow Hedges	6.1					6.1
Foreign Currency Translation Adjustments	3.9					3.9
Pension and Other Postretirement Benefit Adjustments	4.1					4.1
Stock Purchased	(140.3)						(140.3)
Ending balance at Mar. 31, 2016	$ 8,832.8		$ 408.6	$ 1,022.1	$ 8,394.8	$ (283.9)	$ (1,097.3)