Significant Transactions - Ark (Details) - USD ($) $ in Millions			3 Months Ended	12 Months Ended
	Jan. 01, 2021	Oct. 01, 2020	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020
Other Operations
Other Significant Noncash Transactions [Line Items]
Cash pre-funded/placed in escrow for Ark Transaction							$ 646.3
Goodwill and other intangible assets				$ 91.3	$ 39.1
Ark
Other Significant Noncash Transactions [Line Items]
Cash pre-funded/placed in escrow for Ark Transaction							366.3
Goodwill and other intangible assets				292.5	292.5
Contingent consideration				45.3	28.0
Purchase price adjustment				17.3	5.5
Ark | In-force Business Acquired
Other Significant Noncash Transactions [Line Items]
Amortization				$ 7.5	$ 64.2
Ark | Lloyd
Other Significant Noncash Transactions [Line Items]
Cash pre-funded/placed in escrow for Ark Transaction							$ 280.0
Ark
Other Significant Noncash Transactions [Line Items]
Merger agreement, equity capital contributed	$ 605.4	$ 605.4
Equity capital, pre money valuation amount		300.0
Additional equity purchase from shareholders		40.9
Investment, potential additional contribution of equity capital	$ 200.0	$ 200.0
Ownership interest after all transactions (as a percent)	72.00%
Ownership interest on fully-diluted basis (as a percent)	63.00%
Percent of shares outstanding	12.50%			12.50%
Assets acquired	$ 2,500.0
Goodwill and other intangible assets	292.5
Liabilities acquired	1,700.0
Contingent consideration	22.5
Noncontrolling interest acquired	$ 220.2
Transaction costs			$ 25.3
Ark | Group Ark Insurance Limited | Unsecured Subordinated Debt
Other Significant Noncash Transactions [Line Items]
Notes issued						$ 163.3