Investments - Mortgage Loans Purchased and Sold (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Commercial mortgage loans
Mortgage loan disclosures
Mortgage loans, purchased	$ 141.2	$ 1.4	$ 265.8	$ 71.7
Mortgage loans, sold		0.1	356.6	109.3
Amount of financing receivable held for sale sold	0.0		300.6
Residential mortgage loans
Mortgage loan disclosures
Mortgage loans, purchased	716.7	376.7	1,601.5	1,027.6
Mortgage loans, sold	$ 12.1	$ 11.1	$ 22.6	$ 20.9

Amount of financing receivable held for sale in prior year sold during the current period.

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+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
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-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Amount of increase in financing receivable from purchase. Excludes net investment in lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
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-URI https://asc.fasb.org/1943274/2147481962/310-10-50-11B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
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Amount of decrease in financing receivable from sale and reclassification to held-for-sale. Excludes net investment in lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
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-Topic 326
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-URI https://asc.fasb.org/1943274/2147479319/326-20-50-11

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