Investments - Impaired Loans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investments, Debt and Equity Securities [Abstract]
Impaired loans with allowances for losses	$ 0	$ 0
Impaired loans without valuation allowances	5.6	5.8
Subtotal	5.6	5.8
Less: Allowances for losses on impaired loans	0	0
Impaired loans, net	5.6	5.8
Unpaid principal balance of impaired loans	7.1	7.3
Impaired loans, average investment during the period	5.7	7.7
Interest income recognized on impaired loans, on an accrual basis	0.4	0.6	0.9
Interest income recognized on impaired loans, on a cash basis	$ 0.4	$ 0.6	$ 1.0