AOCI Attributable To Parent, After Tax [Abstract]

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AOCI Attributable To Parent, Before Tax [Abstract]

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AOCI Attributable To Parent, Tax [Abstract]

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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-Name Accounting Standards Codification
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Amount of tax expense (benefit) allocated to other comprehensive income (loss) before reclassification adjustment from accumulated other comprehensive income (loss).

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Amount before tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.

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Amount before tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).

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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, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
PRE-TAX
Net Change	$ 76.0		$ (63.2)		$ 388.5	$ 195.8
TAX
Net Change	(23.4)		23.5		(115.6)	(32.5)
AFTER TAX
Net Change	52.6	$ 220.3	(39.7)	$ 203.0	272.9	163.3
Unrealized Gains (Losses) on Available for Sale Debt Securities
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	40.0		(88.7)		113.2	140.6
Net Change	67.1		(58.3)		354.1	186.0
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(17.1)		23.9		(36.5)	(36.4)
Net Change	(23.7)		16.3		(97.3)	(47.8)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	22.9		(64.8)		76.7	104.2
Net Change	43.4		(42.0)		256.8	138.2
Interest Income on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	27.2		30.4		51.6	52.3
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(6.7)		(7.6)		(12.9)	(13.1)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	20.5		22.8		38.7	39.2
Net Losses on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.1)		0.0		189.3	(6.9)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.1		0.0		(47.9)	1.7
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0		0.0		141.4	(5.2)
Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(1.0)		(2.2)		(6.5)	(2.8)
Net Change	(0.1)		(0.8)		(1.1)	(0.9)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.2		0.6		1.6	0.7
Net Change	0.0		0.2		0.3	0.2
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.8)		(1.6)		(4.9)	(2.1)
Net Change	(0.1)		(0.6)		(0.8)	(0.7)
Foreign Currency Adjustments
PRE-TAX
Net Change	5.9		(5.5)		28.1	8.8
TAX
Net Change	1.1		7.4		(16.5)	15.8
AFTER TAX
Net Change	7.0		1.9		11.6	24.6
Foreign Currency Translation Adjustments
PRE-TAX
Net Change	(11.9)		26.7		(70.4)	73.5
TAX
Net Change	(1.7)		(0.7)		1.2	(0.5)
AFTER TAX
Net Change	(13.6)		26.0		(69.2)	73.0
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
PRE-TAX
Net Change	(0.2)		(1.6)		(0.8)	(1.6)
TAX
Net Change	0.1		0.4		0.2	0.4
AFTER TAX
Net Change	(0.1)		(1.2)		(0.6)	(1.2)
Net Investment Hedge Gains (Losses)
PRE-TAX
Net Change	18.0		(30.6)		99.3	(63.1)
TAX
Net Change	2.7		7.7		(17.9)	15.9
AFTER TAX
Net Change	20.7		(22.9)		81.4	(47.2)
Pension and Other Postretirement Benefit Adjustments
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(0.1)		(0.2)		1.0	(1.3)
Net Change	3.1		1.4		7.4	1.9
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	0.0		0.0		(0.5)	0.1
Net Change	(0.8)		(0.4)		(2.1)	(0.7)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(0.1)		(0.2)		0.5	(1.2)
Net Change	2.3		1.0		5.3	1.2
Amortization of Net Actuarial Loss
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	3.2		1.6		6.4	3.2
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.8)		(0.4)		(1.6)	(0.8)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	2.4		1.2		4.8	2.4
Foreign Exchange Contracts \| Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	0.9		1.4		5.4	1.9
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(0.2)		(0.4)		(1.3)	(0.5)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	$ 0.7		$ 1.0		$ 4.1	$ 1.4