Accumulated Other Comprehensive Income (Loss) (Details of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
After Tax
Other Comprehensive Income	$ 185.5	$ (2.4)	$ 293.9	$ (68.5)
Net Unrealized Gains (Losses) on Debt Securities Available for Sale
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	217.6	(26.4)	332.9	(101.8)
Reclassification adjustment, before tax	0.1	0.0	0.3	0.0
Net Change	217.7	(26.4)	333.2	(101.8)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(55.3)	6.5	(85.2)	26.9
Reclassification adjustment, tax	0.0	0.0	0.0	0.0
Net Change	(55.3)	6.5	(85.2)	26.9
After Tax
Other comprehensive income (loss), before reclassification, after tax	162.3	(19.9)	247.7	(74.9)
Reclassification adjustment, after tax	0.1	0.0	0.3	0.0
Other Comprehensive Income	162.4	(19.9)	248.0	(74.9)
Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Reclassification adjustment, before tax	(3.8)	(17.0)	(17.4)	(33.6)
Net Change	6.4	(4.7)	0.6	(9.7)
Tax Effect
Reclassification adjustment, tax	0.9	4.3	4.3	8.4
Net Change	(1.6)	1.2	(0.1)	2.5
After Tax
Reclassification adjustment, after tax	(2.9)	(12.7)	(13.1)	(25.2)
Other Comprehensive Income	4.8	(3.5)	0.5	(7.2)
Net Foreign Currency Adjustments
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	9.0	(105.5)	2.6	(60.9)
Net Change	16.2	50.3	39.1	21.8
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(0.3)	2.3	1.2	(0.5)
Net Change	(2.1)	(36.7)	(10.2)	(21.3)
After Tax
Other comprehensive income (loss), before reclassification, after tax	8.7	(103.2)	3.8	(61.4)
Other Comprehensive Income	14.1	13.6	28.9	0.5
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	(0.7)	(1.9)	0.0	(0.7)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	0.2	0.6	0.0	0.3
After Tax
Other comprehensive income (loss), before reclassification, after tax	(0.5)	(1.3)	0.0	(0.4)
Net Investment Hedge Gains (Losses)
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	7.9	157.7	36.5	83.4
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(2.0)	(39.6)	(11.4)	(21.1)
After Tax
Other comprehensive income (loss), before reclassification, after tax	5.9	118.1	25.1	62.3
Net Pension and Other Postretirement Benefit Adjustments
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	0.0	0.0	11.3	10.1
Reclassification adjustment, before tax	5.6	9.5	11.0	18.6
Net Change	5.6	9.5	22.3	28.7
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	0.0	0.0	(3.1)	(2.5)
Reclassification adjustment, tax	(1.4)	(2.1)	(2.7)	(13.1)
Net Change	(1.4)	(2.1)	(5.8)	(15.6)
After Tax
Other comprehensive income (loss), before reclassification, after tax	0.0	0.0	8.2	7.6
Reclassification adjustment, after tax	4.2	7.4	8.3	5.5
Other Comprehensive Income	4.2	7.4	16.5	13.1
Foreign Exchange Contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	9.4	12.2	16.6	25.2
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(2.3)	(3.1)	(4.0)	(6.2)
After Tax
Other comprehensive income (loss), before reclassification, after tax	7.1	9.1	12.6	19.0
Interest Rate Contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	0.8	0.1	1.4	(1.3)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(0.2)	0.0	(0.4)	0.3
After Tax
Other comprehensive income (loss), before reclassification, after tax	$ 0.6	$ 0.1	$ 1.0	$ (1.0)