Insurance Liabilities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Change in unpaid claims
Balance at beginning of period, unpaid claims	$ 2,001.3	$ 1,872.2
Balance at beginning of period, reinsurance recoverables for unpaid claims	340.3	314.1
Net balance at beginning of period, unpaid claims	1,661.0	1,558.1
Incurred:
Incurred: Current year	867.2	816.4
Incurred: Prior years	42.2	30.7
Total incurred	909.4	847.1
Payments:
Payments: Current year	527.8	500.5
Payments: Prior years	318.3	266.5
Total payments	846.1	767.0
Net balance at end of period, unpaid claims	1,724.3	1,638.2
Balance at end of period, reinsurance recoverables for unpaid claims	369.9	334.8
Balance at end of period, unpaid claims	2,094.2	1,973.0
Amount not included in the rollforward above:
Claim adjustment expense liabilities	$ 50.5	$ 49.2