Accumulated Other Comprehensive Income (Loss) (Details of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
PRE-TAX
Net Change	$ 259.0	$ (1,153.2)
TAX
Net Change	(56.0)	281.8
AFTER TAX
Net Change	203.0	(871.4)
Unrealized Gains (Losses) on Available for Sale Debt Securities
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	229.3	(1,171.5)
Net Change	244.3	(1,169.2)
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(60.3)	301.4
Net Change	(64.1)	300.8
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	169.0	(870.1)
Net Change	180.2	(868.4)
Interest Income on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	21.9	2.3
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(5.5)	(0.6)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	16.4	1.7
Net Losses on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(6.9)	0.0
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	1.7	0.0
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(5.2)	0.0
Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.6)	1.7
Net Change	(0.1)	(1.9)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.1	(0.4)
Net Change	0.0	0.5
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.5)	1.3
Net Change	(0.1)	(1.4)
Foreign Currency Adjustments
PRE-TAX
Net Change	14.3	9.1
TAX
Net Change	8.4	(17.0)
AFTER TAX
Net Change	22.7	(7.9)
Foreign Currency Translation Adjustments
PRE-TAX
Net Change	46.8	(50.3)
TAX
Net Change	0.2	(1.8)
AFTER TAX
Net Change	47.0	(52.1)
Net Investment Hedge Gains (Losses)
PRE-TAX
Net Change	(32.5)	59.4
TAX
Net Change	8.2	(15.2)
AFTER TAX
Net Change	(24.3)	44.2
Pension and Other Postretirement Benefit Adjustments
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(1.1)	0.8
Net Change	0.5	8.8
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	0.1	(0.6)
Net Change	(0.3)	(2.5)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(1.0)	0.2
Net Change	0.2	6.3
Amortization of Net Actuarial Loss
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	1.6	7.6
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.4)	(1.9)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	1.2	5.7
Amortization of Prior Service Cost (Credit)
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0	(0.3)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0	0.1
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0	(0.2)
Settlement Loss
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0	0.7
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0	(0.1)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.0	0.6
Foreign Exchange Contracts \| Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	0.5	(3.6)
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(0.1)	0.9
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	$ 0.4	$ (2.7)

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