Insurance Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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	312.8	301.0
Incurred: Prior years	(0.1)	11.3
Total incurred	312.7	312.3
Payments:
Payments: Current year	146.9	140.4
Payments: Prior years	145.8	143.9
Total payments	292.7	284.3
Net balance at end of period, unpaid claims	1,774.7	1,689.0
Balance at end of period, reinsurance recoverables for unpaid claims	378.5	345.9
Balance at end of period, unpaid claims	2,153.2	2,034.9
Amount not included in the rollforward above:
Claim adjustment expense liabilities	$ 51.5	$ 50.0