Statutory Requirements and Dividend Restrictions - Statutory Requirements (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Bermuda
Effects of Reinsurance [Line Items]
Required statutory capital and surplus	$ 1,095.0	$ 910.0
Actual statutory capital and surplus	2,220.0	1,830.0
United Kingdom
Effects of Reinsurance [Line Items]
Required statutory capital and surplus	535.0	540.0
Actual statutory capital and surplus	1,055.0	950.0
Republic of Ireland
Effects of Reinsurance [Line Items]
Required statutory capital and surplus	95.0	100.0
Actual statutory capital and surplus	$ 165.0	$ 175.0

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 505
-Name Accounting Standards Codification
-Section 55
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478420/944-505-55-2

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 505
-Name Accounting Standards Codification
-Section 55
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478420/944-505-55-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477908/944-505-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant