Accumulated Other Comprehensive Income (Loss) (Details of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
After Tax
Other Comprehensive Income	$ (66.1)	$ 18.0
Unrealized Gains (Losses) on Securities Available for Sale
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	(75.4)	30.9
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	20.4	(11.7)
After Tax
Other comprehensive income (loss), before reclassification, after tax	(55.0)	19.2
Net Unrealized Gains (Losses) on Debt Securities Available for Sale
Before Tax
Reclassification adjustment, before tax	0.0	0.2
Net Change	(75.4)	31.1
Tax Effect
Reclassification adjustment, tax	0.0	(0.1)
Net Change	20.4	(11.8)
After Tax
Reclassification adjustment, after tax	0.0	0.1
Other Comprehensive Income	(55.0)	19.3
Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	11.6	8.7
Reclassification adjustment, before tax	(16.6)	(5.1)
Net Change	(5.0)	3.6
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(2.8)	(10.8)
Reclassification adjustment, tax	4.1	1.9
Net Change	1.3	(8.9)
After Tax
Other comprehensive income (loss), before reclassification, after tax	8.8	(2.1)
Reclassification adjustment, after tax	(12.5)	(3.2)
Other Comprehensive Income	(3.7)	(5.3)
Net Foreign Currency Adjustments
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	44.6	22.4
Net Change	(28.5)	(8.1)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(2.8)	(1.5)
Net Change	15.4	10.1
After Tax
Other comprehensive income (loss), before reclassification, after tax	41.8	20.9
Other Comprehensive Income	(13.1)	2.0
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	1.2	0.0
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(0.3)	0.0
After Tax
Other comprehensive income (loss), before reclassification, after tax	0.9	0.0
Net Investment Hedge Gains (Losses)
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	(74.3)	(30.5)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	18.5	11.6
After Tax
Other comprehensive income (loss), before reclassification, after tax	(55.8)	(18.9)
Net Pension and Other Postretirement Benefit Adjustments
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	10.1	(2.3)
Reclassification adjustment, before tax	9.1	6.4
Net Change	19.2	4.1
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(2.5)	0.0
Reclassification adjustment, tax	(11.0)	(2.1)
Net Change	(13.5)	(2.1)
After Tax
Other comprehensive income (loss), before reclassification, after tax	7.6	(2.3)
Reclassification adjustment, after tax	(1.9)	4.3
Other Comprehensive Income	$ 5.7	$ 2.0