Investments - Impaired Loans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Impaired loans with allowances for losses	$ 0		$ 0
Impaired loans without valuation allowances	42.8		42.9
Subtotal	42.8		42.9
Less: Allowances for losses on impaired loans	0		0
Impaired loans, net	42.8		42.9
Unpaid principal balance of impaired loans	44.3		44.4
Impaired loans, average investment during the period (amortized cost)	42.8	5.7
Interest income recognized on impaired loans, on an accrual basis	0.6	0.1
Interest income recognized on impaired loans, on a cash basis	0.4	0.1
Interest income recognized on restructured loans, on an accrual basis	$ 0.5	$ 0