Derivative Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Derivative Financial Instruments
Future potential payments in the event of default of an investment in fixed maturity securities that contain embedded credit derivatives	$ 0
Hybrid instruments disclosures
Amortized cost	77.5	111.4
Carrying value	76.1	109.2
Weighted average expected life	4 years	3 years 9 months 18 days
Corporate debt securities
Hybrid instruments disclosures
Amortized cost	22.5	45.5
Carrying value	22.5	45.4
Weighted average expected life	3 years 3 months 18 days	2 years 1 month 6 days
Corporate debt securities | BBB
Hybrid instruments disclosures
Amortized cost	22.5	20.5
Carrying value	22.5	20.5
Weighted average expected life	3 years 3 months 18 days	4 years
Corporate debt securities | B
Hybrid instruments disclosures
Amortized cost		25.0
Carrying value		24.9
Weighted average expected life		6 months
Structured finance
Hybrid instruments disclosures
Amortized cost	55.0	65.9
Carrying value	53.6	63.8
Weighted average expected life	4 years 4 months 24 days	4 years 10 months 24 days
Structured finance | A
Hybrid instruments disclosures
Amortized cost	21.6
Carrying value	20.2
Weighted average expected life	4 years 1 month 6 days
Structured finance | AA
Hybrid instruments disclosures
Amortized cost		4.6
Carrying value		4.6
Weighted average expected life		17 years
Structured finance | BB
Hybrid instruments disclosures
Amortized cost	5.6	39.6
Carrying value	5.6	37.5
Weighted average expected life	3 years 3 months 18 days	2 years 10 months 24 days
Structured finance | B
Hybrid instruments disclosures
Amortized cost	4.2	4.0
Carrying value	4.2	4.0
Weighted average expected life	3 years 2 months 12 days	4 years 4 months 24 days
Structured finance | CCC
Hybrid instruments disclosures
Amortized cost	23.6	17.7
Carrying value	$ 23.6	$ 17.7
Weighted average expected life	5 years	6 years 4 months 24 days