Significant Transactions - Ark (Details) - USD ($) $ in Millions			3 Months Ended			6 Months Ended
	Jan. 01, 2021	Oct. 01, 2020	Jun. 30, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020
Ark
Other Significant Noncash Transactions [Line Items]
Cash pre-funded/placed in escrow for Ark Transaction										$ 366.3
Other Operations
Other Significant Noncash Transactions [Line Items]
Cash pre-funded/placed in escrow for Ark Transaction										646.3
Goodwill and other intangible assets			$ 96.8			$ 96.8		$ 39.1
Ark
Other Significant Noncash Transactions [Line Items]
Goodwill and other intangible assets			292.5			292.5		292.5
Contingent consideration			30.2			30.2		28.0
Change in fair value of contingent consideration liabilities			0.1			2.2
Ark | In-force Business Acquired
Other Significant Noncash Transactions [Line Items]
Amortization			$ 1.4	$ 15.1		$ 6.1	$ 43.9
Ark | Ark
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)			72.00%			72.00%
Fully diluted ownership interest (as a percent)			63.00%			63.00%
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
Equity capital, pre money valuation amount		$ 300.0
Additional equity purchase from shareholders		40.9
Investment, potential additional contribution of equity capital		$ 200.0
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
Investment, potential additional contribution of equity capital terminated								$ 200.0
Ark | Ark
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)			72.00%			72.00%		72.00%
Fully diluted ownership interest (as a percent)			63.00%			63.00%		63.00%
Percent of outstanding shares after performance obligations are satisfied			12.50%			12.50%
Ark | Group Ark Insurance Limited | Unsecured Subordinated Debt
Other Significant Noncash Transactions [Line Items]
Notes issued									$ 163.3