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Variable Interest Entity and Noncontrolling Interests - Variable interest entity (Details) - Watford Holdings Ltd - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 16, 2021	Mar. 31, 2014	Mar. 31, 2014	Dec. 31, 2020
Variable Interest Entity [Line Items]
Business acquisition, share price (per share)				$ 35.00
Kelso And Company
Variable Interest Entity [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners				30.00%
Warburg Pincus
Variable Interest Entity [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners				30.00%
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Initial capitalization amount			$ 1,100.0
Proceeds from from common shares issued, net		$ 895.6
Proceeds on issuance of preference shares		219.2
Initial investment contribution amount		$ 100.0
Ownership percentage				13.00%
Number of shares acquired		2,500,000	2,500,000
Variable Interest Entity, Primary Beneficiary | Subsequent Event
Variable Interest Entity [Line Items]
Ownership percentage	10.30%
Variable Interest Entity, Primary Beneficiary | Watford Merger Transaction
Variable Interest Entity [Line Items]
Percentage ownership after merger transaction				40.00%
Variable Interest Entity, Primary Beneficiary | Common shares
Variable Interest Entity [Line Items]
Initial capitalization amount			$ 907.3
Variable Interest Entity, Primary Beneficiary | Preference equity
Variable Interest Entity [Line Items]
Initial capitalization amount			$ 226.6

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