Derivative Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 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	75.4	111.4
Carrying value	73.8	109.2
Weighted average expected life	5 years	3 years 9 months 18 days
Corporate debt securities
Hybrid instruments disclosures
Amortized cost	21.5	45.5
Carrying value	21.5	45.4
Weighted average expected life	3 years 6 months	2 years 1 month 6 days
Corporate debt securities | BBB
Hybrid instruments disclosures
Amortized cost	21.5	20.5
Carrying value	21.5	20.5
Weighted average expected life	3 years 6 months	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	53.9	65.9
Carrying value	52.3	63.8
Weighted average expected life	5 years 7 months 6 days	4 years 10 months 24 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	20.6	39.6
Carrying value	19.0	37.5
Weighted average expected life	3 years 2 months 12 days	2 years 10 months 24 days
Structured finance | B
Hybrid instruments disclosures
Amortized cost	4.1	4.0
Carrying value	4.1	4.0
Weighted average expected life	3 years 7 months 6 days	4 years 4 months 24 days
Structured finance | CCC
Hybrid instruments disclosures
Amortized cost	22.9	17.7
Carrying value	22.9	17.7
Weighted average expected life	5 years 1 month 6 days	6 years 4 months 24 days
Structured finance | A
Hybrid instruments disclosures
Amortized cost	6.3
Carrying value	$ 6.3
Weighted average expected life	16 years 10 months 24 days