Accumulated Other Comprehensive Income (Loss) (Details of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
PRE-TAX
Net Change	$ 312.5	$ 259.0
TAX
Net Change	(92.2)	(56.0)
AFTER TAX
Net Change	220.3	203.0
Unrealized Gains (Losses) on Available for Sale Debt Securities
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	73.2	229.3
Net Change	287.0	244.3
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(19.4)	(60.3)
Net Change	(73.6)	(64.1)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	53.8	169.0
Net Change	213.4	180.2
Interest Income on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	24.4	21.9
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(6.2)	(5.5)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	18.2	16.4
Net Losses on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	189.4	(6.9)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(48.0)	1.7
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	141.4	(5.2)
Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(5.5)	(0.6)
Net Change	(1.0)	(0.1)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	1.4	0.1
Net Change	0.3	0.0
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(4.1)	(0.5)
Net Change	(0.7)	(0.1)
Foreign Currency Adjustments
PRE-TAX
Net Change	22.2	14.3
TAX
Net Change	(17.6)	8.4
AFTER TAX
Net Change	4.6	22.7
Foreign Currency Translation Adjustments
PRE-TAX
Net Change	(58.5)	46.8
TAX
Net Change	2.9	0.2
AFTER TAX
Net Change	(55.6)	47.0
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
PRE-TAX
Net Change	(0.6)	0.0
TAX
Net Change	0.1	0.0
AFTER TAX
Net Change	(0.5)	0.0
Net Investment Hedge Gains (Losses)
PRE-TAX
Net Change	81.3	(32.5)
TAX
Net Change	(20.6)	8.2
AFTER TAX
Net Change	60.7	(24.3)
Pension and Other Postretirement Benefit Adjustments
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	1.1	(1.1)
Net Change	4.3	0.5
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(0.5)	0.1
Net Change	(1.3)	(0.3)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	0.6	(1.0)
Net Change	3.0	0.2
Amortization of Net Actuarial Loss
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	3.2	1.6
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.8)	(0.4)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	2.4	1.2
Foreign Exchange Contracts \| Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	4.5	0.5
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(1.1)	(0.1)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	$ 3.4	$ 0.4

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