Fair Value Measurements - Level 3 Inputs Reconciliation (Details) - USD ($)	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Total Losses:
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 210,200,000	$ 218,900,000	$ 230,000,000.0	$ 251,400,000
Included in Condensed Consolidated Statement of Operations	(100,000)	(5,700,000)
Included in Other Comprehensive Income (Loss)	1,700,000	(3,000,000.0)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	19,400,000	13,700,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(41,200,000)	(42,800,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	400,000	5,300,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0
Corporate Debt Securities [Member]
Total Losses:
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	196,100,000	205,600,000	216,000,000.0	236,800,000
Included in Condensed Consolidated Statement of Operations	400,000	(5,700,000)
Included in Other Comprehensive Income (Loss)	1,500,000	(1,700,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	19,400,000	13,700,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(41,200,000)	(42,800,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	5,300,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0
Redeemable Preferred Stocks
Total Losses:
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	6,800,000	5,600,000	6,800,000	6,100,000
Included in Condensed Consolidated Statement of Operations	0	0
Included in Other Comprehensive Income (Loss)	0	(500,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0
Other Mortgage- and Asset-backed
Total Losses:
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	5,300,000	6,200,000	5,100,000	7,000,000.0
Included in Condensed Consolidated Statement of Operations	0	0
Included in Other Comprehensive Income (Loss)	200,000	(800,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0
Equity Securities
Total Losses:
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	2,000,000.0	1,500,000	$ 2,100,000	$ 1,500,000
Included in Condensed Consolidated Statement of Operations	(500,000)	0
Included in Other Comprehensive Income (Loss)	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	400,000	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	$ 0	$ 0

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Publisher FASB
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-SubTopic 10
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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Section 50
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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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