Investments - Impaired Loans (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) loan	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) loan
Investments, Debt and Equity Securities [Abstract]
Impaired loans without valuation allowances	$ 4.8		$ 10.7
Less: Allowances for losses on impaired loans	0.0		0.0
Impaired loans, net	4.8		10.7
Unpaid principal balance of impaired loans	6.3		$ 12.2
Impaired loans, average investment during the period (amortized cost)	7.8	$ 26.6
Interest income recognized on impaired loans, on an accrual basis	0.1	0.4
Interest income recognized on impaired loans, on a cash basis	0.1	0.5
Interest income recognized on restructured loans, on an accrual basis	$ 0.0	$ 0.3
Number of loans in arrears 30 days or less | loan	0		2
Amortized cost of loans in arrears 30 days or less	$ 0.0		$ 1.0