Derivative Financial Instruments - Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Cash Flow Hedges
Maximum length of time hedging exposure to variability in future cash flows for forecasted transactions			4 months 24 days
Net losses reported in AOCI related to active cash flow hedges of forecasted transactions	$ 60.9		$ 60.9
Amount of gain (loss) recognized in AOCI on derivatives in cash flow hedging relationships	(105.3)	$ 85.3	(63.3)	$ (102.8)
Net gains (losses) expected to be reclassified from accumulated OCI into net income in the next 12 months			26.8
Interest rate contracts - hedged on fixed maturities, available-for-sale
Cash Flow Hedges
Amount of gain (loss) recognized in AOCI on derivatives in cash flow hedging relationships	(46.5)	10.5	(60.9)	21.0
Foreign exchange contracts - hedged on fixed maturities, available-for-sale
Cash Flow Hedges
Amount of gain (loss) recognized in AOCI on derivatives in cash flow hedging relationships	$ (58.8)	$ 74.8	$ (2.4)	$ (123.8)

Amount of accumulated gain (loss) on derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

No definition available.

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480870/815-30-50-1

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- Definition

Maximum period of hedging exposure to variability in future cash flow for forecasted transaction of cash flow hedge, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Excludes forecasted transaction for payment of variable interest on existing financial instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480870/815-30-50-1

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- Definition

Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 182
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-182

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-URI https://asc.fasb.org/1943274/2147480627/815-20-45-3

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- References

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