Investing Activities - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2014 counterparty	Sep. 30, 2014 security counterparty	Dec. 31, 2013
Concentration Risk [Line Items]
Unrealized losses on below-investment-grade debt securities depressed of amortized cost, percentage	20.00%	20.00%
Unrealized losses on below-investment-grade debt securities depressed of amortized cost, amount	$ 0.6	$ 0.6
Unrealized losses on below-investment-grade debt securities depressed of amortized cost for more than 12 month, amount	0.6	0.6
Unrealized losses on below-investment-grade debt securities depressed of amortized cost for more than 12 month, percentage	20.00%	20.00%
Number of debt securities		159
Carrying value of investments in non-consolidated VIEs	14.3	14.3	15.6
Fixed maturities below-investment-grade assets	195.2	195.2	137.7
Derivative assets, net of liabilities	74.8	74.8
Number of counterparties	11	11
Debt securities, fair value	74.9	74.9
Maximum amount of loss due to credit risk	149.7
Stockholders' Equity, Total
Concentration Risk [Line Items]
Concentration risk (percent)	10.00%
Private Equity Investment
Concentration Risk [Line Items]
Equity method investments	8.8	8.8	7.9
Direct Equity Investment
Concentration Risk [Line Items]
Equity method investments	$ 2.1	$ 2.1	$ 2.6