Investments - Impaired Loans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Impaired loans without valuation allowances	$ 4.5		$ 4.6
Less: Allowances for losses on impaired loans	0.0		0.0
Impaired loans, net	4.5		4.6
Unpaid principal balance of impaired loans	6.0		$ 6.1
Impaired loans, average investment during the period (amortized cost)	4.5	$ 7.8
Interest income recognized on impaired loans, on an accrual basis	0.1	0.1
Interest income recognized on impaired loans, on a cash basis	0.1	0.1
Interest income recognized on restructured loans, on an accrual basis	$ 0.0	$ 0.0