Investments - Impaired Loans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Impaired loans with allowances for losses	$ 0				$ 0				$ 0
Impaired loans without valuation allowances	37.2				37.2				42.9
Subtotal	37.2				37.2				42.9
Less: Allowances for losses on impaired loans	0				0				0
Impaired loans, net	37.2				37.2				42.9
Unpaid principal balance of impaired loans	38.7				38.7				44.4
Impaired loans, average investment during the period (amortized cost)	40.0	[1]	5.5	[1]	40.0	[1]	5.6	[1]
Interest income recognized on impaired loans, on an accrual basis	0.6	[1]	0.1	[1]	1.2	[1]	0.2	[1]
Interest income recognized on impaired loans, on a cash basis	0.6	[1]	0.1	[1]	1.0	[1]	0.2	[1]
Interest income recognized on restructured loans, on an accrual basis	$ 0.5	[1]	$ 0	[1]	$ 1.0	[1]	$ 0	[1]

[1] Includes amounts for Troubled debt restructured loans.