Accumulated Other Comprehensive Income (Loss) (Details 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) [Line Items]
Other Comprehensive Income (Loss)	$ 88.8	$ 53.3
Net Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	120.2	86.7
Tax Effect	(45.5)	(32.6)
Other Comprehensive Income (Loss)	74.7	54.1
Net Unrealized Gains (Losses) on Securities Available for Sale | Noncredit-Related Unrealized Losses on Securities OTTI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	0.0	0.0
Tax Effect	0.0	0.0
Other Comprehensive Income (Loss)	0.0	0.0
Net Unrealized Gains (Losses) on Securities Available for Sale | Other Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	120.5	86.8
Tax Effect	(45.6)	(32.7)
Other Comprehensive Income (Loss)	74.9	54.1
Net Unrealized Gains (Losses) on Securities Available for Sale | Reclassification Adjustment for (Gains) Losses Included in Net Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(0.3)	(0.1)
Tax Effect	0.1	0.1
Other Comprehensive Income (Loss)	(0.2)	0.0
Net Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	10.0	(3.7)
Tax Effect	(3.9)	2.6
Other Comprehensive Income (Loss)	6.1	(1.1)
Net Unrealized Gains (Losses) on Cash Flow Hedges | Reclassification Adjustment for (Gains) Losses Included in Net Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	0.6	1.0
Tax Effect	(0.2)	(0.4)
Other Comprehensive Income (Loss)	0.4	0.6
Net Unrealized Gains (Losses) on Cash Flow Hedges | Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	9.4	(4.7)
Tax Effect	(3.7)	3.0
Other Comprehensive Income (Loss)	5.7	(1.7)
Net Foreign Currency Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(5.0)	25.5
Tax Effect	8.9	(31.4)
Other Comprehensive Income (Loss)	3.9	(5.9)
Net Foreign Currency Adjustments | Reclassification Adjustment for (Gains) Losses Included in Net Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	0.0	0.0
Tax Effect	0.0	0.0
Other Comprehensive Income (Loss)	0.0	0.0
Net Foreign Currency Adjustments | Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	17.3	(90.1)
Tax Effect	(0.3)	12.2
Other Comprehensive Income (Loss)	17.0	(77.9)
Net Foreign Currency Adjustments | Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	4.2	(1.0)
Tax Effect	(1.0)	0.3
Other Comprehensive Income (Loss)	3.2	(0.7)
Net Foreign Currency Adjustments | Net Investment Hedge Gains (Losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(26.5)	116.6
Tax Effect	10.2	(43.9)
Other Comprehensive Income (Loss)	(16.3)	72.7
Net Pension and Other Postretirement Benefit Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	6.4	9.5
Tax Effect	(2.3)	(3.3)
Other Comprehensive Income (Loss)	4.1	6.2
Net Pension and Other Postretirement Benefit Adjustments | Reclassification Adjustment for (Gains) Losses Included in Net Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	6.4	9.5
Tax Effect	(2.3)	(3.3)
Other Comprehensive Income (Loss)	4.1	6.2
Net Pension and Other Postretirement Benefit Adjustments | Net Actuarial Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	0.0	0.0
Tax Effect	0.0	0.0
Other Comprehensive Income (Loss)	$ 0.0	$ 0.0