Accumulated Other Comprehensive Income (Loss) (Details of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
After Tax
Other Comprehensive Income	$ 108.4	$ (66.1)
Net Unrealized Gains (Losses) on Debt Securities Available for Sale
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	115.3	(75.4)
Reclassification adjustment, before tax	0.2	0.0
Net Change	115.5	(75.4)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(29.9)	20.4
Reclassification adjustment, tax	0.0	0.0
Net Change	(29.9)	20.4
After Tax
Other comprehensive income (loss), before reclassification, after tax	85.4	(55.0)
Reclassification adjustment, after tax	0.2	0.0
Other Comprehensive Income	85.6	(55.0)
Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Reclassification adjustment, before tax	(13.6)	(16.6)
Net Change	(5.8)	(5.0)
Tax Effect
Reclassification adjustment, tax	3.4	4.1
Net Change	1.5	1.3
After Tax
Reclassification adjustment, after tax	(10.2)	(12.5)
Other Comprehensive Income	(4.3)	(3.7)
Net Foreign Currency Adjustments
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	(6.5)	44.6
Net Change	22.8	(28.5)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	1.6	(2.8)
Net Change	(8.0)	15.4
After Tax
Other comprehensive income (loss), before reclassification, after tax	(4.9)	41.8
Other Comprehensive Income	14.8	(13.1)
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	0.7	1.2
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(0.2)	(0.3)
After Tax
Other comprehensive income (loss), before reclassification, after tax	0.5	0.9
Net Investment Hedge Gains (Losses)
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	28.6	(74.3)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(9.4)	18.5
After Tax
Other comprehensive income (loss), before reclassification, after tax	19.2	(55.8)
Net Pension and Other Postretirement Benefit Adjustments
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	11.3	10.1
Reclassification adjustment, before tax	5.4	9.1
Net Change	16.7	19.2
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(3.1)	(2.5)
Reclassification adjustment, tax	(1.3)	(11.0)
Net Change	(4.4)	(13.5)
After Tax
Other comprehensive income (loss), before reclassification, after tax	8.2	7.6
Reclassification adjustment, after tax	4.1	(1.9)
Other Comprehensive Income	12.3	5.7
Foreign Exchange Contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	7.2	13.0
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(1.7)	(3.2)
After Tax
Other comprehensive income (loss), before reclassification, after tax	5.5	9.8
Interest Rate Contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	0.6	(1.4)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(0.2)	0.4
After Tax
Other comprehensive income (loss), before reclassification, after tax	$ 0.4	$ (1.0)