Insurance Liabilities - Liability for Unpaid Claims (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Change in unpaid claims
Balance at beginning of period, unpaid claims	$ 2,659.4	$ 2,534.9
Balance at beginning of period, reinsurance recoverables for unpaid claims	442.1	436.9
Net balance at beginning of period, unpaid claims	2,217.3	2,098.0
Incurred:
Incurred: Current year	403.5	362.2
Incurred: Prior years	16.6	28.3
Total incurred	420.1	390.5
Payments:
Payments: Current year	196.0	187.9
Payments: Prior years	191.8	175.1
Total payments	387.8	363.0
Net balance at end of period, unpaid claims	2,249.6	2,125.5
Balance at end of period, reinsurance recoverables for unpaid claims	454.2	433.9
Balance at end of period, unpaid claims	2,703.8	2,559.4
Amount not included in the rollforward above:
Claim adjustment expense liabilities	$ 60.6	$ 58.5