Accumulated Other Comprehensive Income (Loss) (Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 9,770.4
Net Change	18.0	$ 88.8
Ending balance	9,977.7	8,832.8
Net Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(32.4)	(31.0)
Net Change	19.3	74.7
Ending balance	(13.1)	43.7
Net Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	6.1	(3.0)
Net Change	(5.3)	6.1
Ending balance	0.8	3.1
Net Foreign Currency Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(18.5)	(17.6)
Net Change	2.0	3.9
Ending balance	(16.5)	(13.7)
Net Pension and Other Postretirement Benefit Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(325.2)	(321.1)
Net Change	2.0	4.1
Ending balance	(323.2)	(317.0)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(370.0)	(372.7)
Net Change	18.0	88.8
Ending balance	$ (352.0)	$ (283.9)