Insurance Liabilities - Liability for Unpaid Claims (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Change in unpaid claims
Balance at beginning of period, unpaid claims	$ 2,365.5	$ 2,252.7
Balance at beginning of period, reinsurance recoverables for unpaid claims	403.8	404.3
Net balance at beginning of period, unpaid claims	1,961.7	1,848.4
Incurred:
Incurred: Current year	609.5	653.6
Incurred: Prior years	34.7	29.0
Total incurred	644.2	682.6
Payments:
Payments: Current year	333.7	387.8
Payments: Prior years	257.6	238.1
Total payments	591.3	625.9
Net balance at end of period, unpaid claims	2,014.6	1,905.1
Balance at end of period, reinsurance recoverables for unpaid claims	418.0	403.7
Balance at end of period, unpaid claims	2,432.6	2,308.8
Amount not included in the rollforward above:
Claim adjustment expense liabilities	$ 56.9	$ 55.1