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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
BEFORE TAX
Net Change	$ 427.2	$ 245.9	$ 765.5	$ 395.2
TAX EFFECT
Net Change	(101.8)	(60.4)	(200.4)	(101.3)
AFTER TAX
Net Change	325.4	185.5	565.1	293.9
Unrealized Gains (Losses) on Debt Securities Available for Sale
BEFORE TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	424.6	217.6	691.4	332.9
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.1)	0.1	(0.1)	0.3
Net Change	424.5	217.7	691.3	333.2
TAX EFFECT
Unrealized Gains (Losses) on Debt Securities Available for Sale	(106.4)	(55.3)	(173.5)	(85.2)
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0	0.0	0.0	0.0
Net Change	(106.4)	(55.3)	(173.5)	(85.2)
AFTER TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	318.2	162.3	517.9	247.7
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.1)	0.1	(0.1)	0.3
Net Change	318.1	162.4	517.8	248.0
Unrealized Gains (Losses) on Cash Flow Hedges
BEFORE TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(2.5)	(3.8)	(6.5)	(17.4)
Net Change	(4.3)	6.4	5.4	0.6
TAX EFFECT
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.6	0.9	1.6	4.3
Net Change	1.0	(1.6)	(1.4)	(0.1)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(1.9)	(2.9)	(4.9)	(13.1)
Net Change	(3.3)	4.8	4.0	0.5
Foreign Currency Adjustments
BEFORE TAX
Net Change	(4.2)	16.2	48.1	39.1
TAX EFFECT
Net Change	6.2	(2.1)	(20.4)	(10.2)
AFTER TAX
Net Change	2.0	14.1	27.7	28.9
Foreign Currency Translation Adjustments
BEFORE TAX
Net Change	50.7	9.0	(39.1)	2.6
TAX EFFECT
Net Change	(7.5)	(0.3)	2.1	1.2
AFTER TAX
Net Change	43.2	8.7	(37.0)	3.8
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
BEFORE TAX
Net Change	0.1	(0.7)	(0.5)	0.0
TAX EFFECT
Net Change	0.0	0.2	0.1	0.0
AFTER TAX
Net Change	0.1	(0.5)	(0.4)	0.0
Net Investment Hedge Gains (Losses)
BEFORE TAX
Net Change	(55.0)	7.9	87.7	36.5
TAX EFFECT
Net Change	13.7	(2.0)	(22.6)	(11.4)
AFTER TAX
Net Change	(41.3)	5.9	65.1	25.1
Pension and Other Postretirement Benefit Adjustments
BEFORE TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	0.5	0.0	(0.8)	11.3
Net Change	11.2	5.6	20.7	22.3
TAX EFFECT
Unrealized Gains (Losses) on Debt Securities Available for Sale	0.0	0.0	0.1	(3.1)
Net Change	(2.6)	(1.4)	(5.1)	(5.8)
AFTER TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	0.5	0.0	(0.7)	8.2
Net Change	8.6	4.2	15.6	16.5
Amortization of Net Actuarial Loss
BEFORE TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	10.7	5.6	21.6	11.1
TAX EFFECT
Reclassification Adjustment for (Gains) Losses Included in Net Income	(2.6)	(1.4)	(5.2)	(2.7)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	8.1	4.2	16.4	8.4
Amortization of Prior Service Cost
BEFORE TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income			(0.1)	(0.1)
TAX EFFECT
Reclassification Adjustment for (Gains) Losses Included in Net Income			0.0	0.0
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income			(0.1)	(0.1)
Foreign Exchange Contracts \| Unrealized Gains (Losses) on Cash Flow Hedges
BEFORE TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	(1.8)	9.4	11.5	16.6
TAX EFFECT
Unrealized Gains (Losses) on Debt Securities Available for Sale	0.4	(2.3)	(2.9)	(4.0)
AFTER TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	(1.4)	7.1	8.6	12.6
Interest Rate Contracts \| Unrealized Gains (Losses) on Cash Flow Hedges
BEFORE TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	0.0	0.8	0.4	1.4
TAX EFFECT
Unrealized Gains (Losses) on Debt Securities Available for Sale	0.0	(0.2)	(0.1)	(0.4)
AFTER TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	$ 0.0	$ 0.6	$ 0.3	$ 1.0

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