Accumulated Other Comprehensive Income (Loss) (Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment Security Gains (Losses), net (Note)	$ (2.4)	$ (0.4)	$ (2.1)	$ (0.3)
Other Operating Income	141.2	137.4	179.3	176.0
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	0.0	0.4	(0.3)	0.3
Net Unrealized Gains (Losses) on Securities Available for Sale | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment Security Gains (Losses), net (Note)	0.0		(0.3)
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	0.0	1.3	0.6	2.3
Net Unrealized Gains (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Operating Income	0.0		0.6
Amortization of Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment for (Gains) Losses Included in Net Income	6.5		12.9
Amortization of Prior Service Cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.1)		(0.1)
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	$ 6.4	$ 9.7	$ 12.8	$ 19.2