Accumulated Other Comprehensive Income (Loss) (Reclassification Adjustment Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment Security Gains (Losses), net	$ (0.4)	$ 0.2	$ (1.1)	$ (1.9)
Other Operating Income	40.0	33.1	122.7	212.4
Net Unrealized Gains (Losses) on Securities Available for Sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.4	(0.2)	1.0	(0.5)
Net Unrealized Gains (Losses) on Securities Available for Sale | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment Security Gains (Losses), net	0.4		1.0
Net Unrealized Gains (Losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment for (Gains) Losses Included in Net Income	(6.1)	4.6	(16.4)	5.2
Net Unrealized Gains (Losses) on Cash Flow Hedges | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Operating Income	(6.1)		(16.4)
Amortization of Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment for (Gains) Losses Included in Net Income	7.4		20.8
Amortization of Prior Service Cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0		(0.2)
Net Pension and Other Postretirement Benefit Adjustments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment for (Gains) Losses Included in Net Income	$ 7.4	$ 6.3	$ 20.6	$ 19.1