Derviative Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Hybrid instruments disclosures
Amortized cost	$ 109.8	$ 110.9
Carrying value	101.4	99.7
Weighted average expected life	3 years 8 months 12 days	3 years 10 months 24 days
Corporate debt securities
Hybrid instruments disclosures
Amortized cost	44.3	43.4
Carrying value	39.6	36.2
Weighted average expected life	2 years 4 months 24 days	2 years 10 months 24 days
Corporate debt securities | BBB
Hybrid instruments disclosures
Amortized cost	15.5
Carrying value	15.5
Weighted average expected life	4 years 6 months
Corporate debt securities | BB
Hybrid instruments disclosures
Amortized cost		14.7
Carrying value		14.7
Weighted average expected life		5 years
Corporate debt securities | B
Hybrid instruments disclosures
Amortized cost	25.0
Carrying value	23.3
Weighted average expected life	1 year
Corporate debt securities | CCC
Hybrid instruments disclosures
Amortized cost		25.0
Carrying value		20.8
Weighted average expected life		1 year 6 months
Corporate debt securities | CC
Hybrid instruments disclosures
Amortized cost	3.8	3.7
Carrying value	0.8	0.7
Weighted average expected life	3 years 7 months 6 days	4 years
Structured finance
Hybrid instruments disclosures
Amortized cost	65.5	67.5
Carrying value	61.8	63.5
Weighted average expected life	4 years 6 months	4 years 6 months
Structured finance | AA
Hybrid instruments disclosures
Amortized cost	6.3	9.3
Carrying value	6.3	9.3
Weighted average expected life	6 years 9 months 18 days	6 years 4 months 24 days
Structured finance | BBB
Hybrid instruments disclosures
Amortized cost	24.8	27.4
Carrying value	22.5	24.5
Weighted average expected life	4 years 3 months 18 days	4 years 6 months
Structured finance | BB
Hybrid instruments disclosures
Amortized cost	18.2	15.0
Carrying value	16.4	13.9
Weighted average expected life	2 years 7 months 6 days	2 years 6 months
Structured finance | B
Hybrid instruments disclosures
Amortized cost	8.4	11.2
Carrying value	8.4	11.2
Weighted average expected life	5 years 2 months 12 days	5 years 4 months 24 days
Structured finance | CCC
Hybrid instruments disclosures
Amortized cost	7.4	3.5
Carrying value	7.8	3.6
Weighted average expected life	6 years 10 months 24 days	4 years 9 months 18 days
Structured finance | CC
Hybrid instruments disclosures
Amortized cost	0.4	0.7
Carrying value	0.4	0.7
Weighted average expected life	7 years 6 months	5 years 3 months 18 days
Structured finance | C
Hybrid instruments disclosures
Amortized cost		0.2
Carrying value		0.1
Weighted average expected life	2 years	8 years 2 months 12 days
Structured finance | Near default
Hybrid instruments disclosures
Amortized cost		0.2
Carrying value		$ 0.2
Weighted average expected life		4 years 8 months 12 days