Investments - Impaired Loans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Impaired loans with allowances for losses	$ 0		$ 0		$ 0
Impaired loans without valuation allowances	42.9		42.9		5.6
Subtotal	42.9		42.9		5.6
Less: Allowances for losses on impaired loans	0		0		0
Impaired loans, net	42.9		42.9		5.6
Unpaid principal balance of impaired loans	44.4		44.4		7.1
Impaired loans, average investment during the period (amortized cost)	24.2	5.7	24.3	5.8
Interest income recognized on impaired loans, on an accrual basis	0.5	0.1	0.7	0.3
Interest income recognized on impaired loans, on a cash basis	0.5	0.1	0.7	0.3
Interest income recognized on restructured loans, on an accrual basis	$ 0.4	$ 0	$ 0.4	$ 0