Insurance Liabilities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Change in unpaid claims
Balance at beginning of period, unpaid claims	$ 2,130.5	$ 2,001.3
Balance at beginning of period, reinsurance recoverables for unpaid claims	375.8	340.3
Net balance at beginning of period, unpaid claims	1,754.7	1,661.0
Incurred:
Incurred: Current year	617.3	591.6
Incurred: Prior years	17.9	23.9
Total incurred	635.2	615.5
Payments:
Payments: Current year	358.3	343.4
Payments: Prior years	231.8	225.9
Total payments	590.1	569.3
Net balance at end of period, unpaid claims	1,799.8	1,707.2
Balance at end of period, reinsurance recoverables for unpaid claims	388.2	356.1
Balance at end of period, unpaid claims	2,188.0	2,063.3
Amount not included in the rollforward above:
Claim adjustment expense liabilities	$ 51.9	$ 50.3