Derivative Financial Instruments - Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Cash Flow Hedges
Maximum length of time hedging exposure to variability in future cash flows for forecasted transactions	2 years 10 months 24 days
Net gains (losses) reported in AOCI related to active cash flow hedges of forecasted transactions	$ (3.5)
Amount of gain (loss) recognized in AOCI on derivatives in cash flow hedging relationships	23.0	$ 2.5
Net gains (losses) expected to be reclassified from accumulated OCI into net income in the next 12 months	24.7
Interest rate contracts \| Fixed maturities, available-for-sale
Cash Flow Hedges
Amount of gain (loss) recognized in AOCI on derivatives in cash flow hedging relationships	(3.5)	15.9
Interest rate contracts \| Investment contracts
Cash Flow Hedges
Amount of gain (loss) recognized in AOCI on derivatives in cash flow hedging relationships	(2.9)	(3.3)
Foreign exchange contracts \| Fixed maturities, available-for-sale
Cash Flow Hedges
Amount of gain (loss) recognized in AOCI on derivatives in cash flow hedging relationships	$ 29.4	$ (10.1)

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://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-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 length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-SubTopic 30
-Topic 815
-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/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
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-Name Accounting Standards Codification
-Section 50
-Paragraph 4C
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-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480627/815-20-45-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
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-Section 45
-Paragraph 10A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-10A

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- References

No definition available.

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