Investments - Impaired Loans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 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	5.5		5.5		5.6
Subtotal	5.5		5.5		5.6
Less: Allowances for losses on impaired loans	0		0		0
Impaired loans, net	5.5		5.5		5.6
Unpaid principal balance of impaired loans	7.0		7.0		7.1
Impaired loans, average investment during the period	5.5	5.8	5.6	5.8
Interest income recognized on impaired loans, on an accrual basis	0.1	0.1	0.2	0.2
Interest income recognized on impaired loans, on a cash basis	0.1	0.1	0.2	0.2
Interest income recognized on restructured loans, on an accrual basis	$ 0	$ 0	$ 0	$ 0