Accumulated Other Comprehensive Income (Loss) (Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (372.7)	$ (319.7)
Net Change	88.8	53.3
Ending balance	(283.9)	(266.4)
Net Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(31.0)	27.6
Net Change	74.7	54.1
Ending balance	43.7	81.7
Net Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(3.0)	(4.7)
Net Change	6.1	(1.1)
Ending balance	3.1	(5.8)
Net Foreign Currency Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(17.6)	(1.7)
Net Change	3.9	(5.9)
Ending balance	(13.7)	(7.6)
Net Pension and Other Postretirement Benefit Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(321.1)	(340.9)
Net Change	4.1	6.2
Ending balance	$ (317.0)	$ (334.7)