Significant Transactions - Ark (Details) - USD ($) $ in Millions		3 Months Ended
	Oct. 01, 2020	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Sep. 30, 2021	Jan. 01, 2021	Dec. 31, 2020
Other Significant Noncash Transactions [Line Items]
Change in fair value of contingent consideration		$ 0.1
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		$ 38.1		$ 39.1
Ark
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)		72.00%
Goodwill and other intangible assets		$ 292.5		292.5
Contingent consideration		30.1		28.0
Change in fair value of contingent consideration		2.1
Ark | In-force Business Acquired
Other Significant Noncash Transactions [Line Items]
Amortization		$ 4.7	$ 28.8
Ark | Ark
Other Significant Noncash Transactions [Line Items]
Fully diluted ownership interest (as a percent)		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%
Fully diluted ownership interest (as a percent)		63.00%		63.00%
Percent of outstanding shares after performance obligations are satisfied		12.50%
Ark | Group Ark Insurance Limited | Unsecured Subordinated Debt
Other Significant Noncash Transactions [Line Items]
Notes issued					$ 163.3