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		$ 0.0	$ 0.0	$ 1,050.9	$ 7,625.4	$ (319.7)	$ (704.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Options and Awards				(64.3)			140.2
Stock Options and Awards — Amortization				42.6
Stock Options and Awards — Tax Benefit				15.4
Net Income	$ 499.9				499.9
Dividends Declared — Common Stock					(163.8)
Dividends Declared — Preferred Stock					(11.7)
Net Unrealized Gains (Losses) on Securities Available for Sale	31.7					31.7
Net Unrealized Gains (Losses) on Cash Flow Hedges	2.1					2.1
Foreign Currency Translation Adjustments	(0.1)					(0.1)
Pension and Other Postretirement Benefit Adjustments	12.3					12.3
Stock Purchased							(203.9)
Ending balance at Jun. 30, 2015	8,749.3	388.5	408.6	1,044.6	7,949.8	(273.7)	(768.5)
Beginning balance at Dec. 31, 2015	8,705.9	0.0	0.0	1,072.2	8,242.8	(372.7)	(1,033.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Options and Awards				(75.4)			102.2
Stock Options and Awards — Amortization				46.6
Stock Options and Awards — Tax Benefit				(3.2)
Net Income	502.5				502.5
Dividends Declared — Common Stock					(167.3)
Dividends Declared — Preferred Stock					(11.7)
Net Unrealized Gains (Losses) on Securities Available for Sale	108.2					108.2
Net Unrealized Gains (Losses) on Cash Flow Hedges	6.6					6.6
Foreign Currency Translation Adjustments	10.2					10.2
Pension and Other Postretirement Benefit Adjustments	8.1					8.1
Stock Purchased	(281.1)						(281.1)
Ending balance at Jun. 30, 2016	$ 8,951.5	$ 388.5	$ 408.6	$ 1,040.2	$ 8,566.3	$ (239.6)	$ (1,212.5)