Derviative Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 Y	Dec. 31, 2010 Y
Hybrid instruments disclosures
Amortized cost	$ 110.9	$ 160.9
Carrying value	99.7	134.2
Weighted average expected life (in years)	3.9	5.0
Corporate debt securities
Hybrid instruments disclosures
Amortized cost	43.4	80.2
Carrying value	36.2	65.9
Weighted average expected life (in years)	2.9	3.4
Corporate debt securities | BB
Hybrid instruments disclosures
Amortized cost	14.7	18.1
Carrying value	14.7	18.1
Weighted average expected life (in years)	5.0	6.0
Corporate debt securities | CCC
Hybrid instruments disclosures
Amortized cost	25.0	50.0
Carrying value	20.8	46.2
Weighted average expected life (in years)	1.5	2.1
Corporate debt securities | CC
Hybrid instruments disclosures
Amortized cost	3.7	12.1
Carrying value	0.7	1.6
Weighted average expected life (in years)	4.0	4.9
Structured finance
Hybrid instruments disclosures
Amortized cost	67.5	80.7
Carrying value	63.5	68.3
Weighted average expected life (in years)	4.5	6.6
Structured finance | AA
Hybrid instruments disclosures
Amortized cost	9.3	5.2
Carrying value	9.3	5.2
Weighted average expected life (in years)	6.4	5.8
Structured finance | BBB
Hybrid instruments disclosures
Amortized cost	27.4	26.8
Carrying value	24.5	23.1
Weighted average expected life (in years)	4.5	5.5
Structured finance | BB
Hybrid instruments disclosures
Amortized cost	15.0	15.5
Carrying value	13.9	15.0
Weighted average expected life (in years)	2.5	3.7
Structured finance | B
Hybrid instruments disclosures
Amortized cost	11.2	10.5
Carrying value	11.2	10.5
Weighted average expected life (in years)	5.4	6.4
Structured finance | CCC
Hybrid instruments disclosures
Amortized cost	3.5	9.2
Carrying value	3.6	8.7
Weighted average expected life (in years)	4.8	5.9
Structured finance | CC
Hybrid instruments disclosures
Amortized cost	0.7
Carrying value	0.7
Weighted average expected life (in years)	5.3
Structured finance | C
Hybrid instruments disclosures
Amortized cost	0.2	13.5
Carrying value	0.1	5.8
Weighted average expected life (in years)	8.2	12.8
Structured finance | Near default
Hybrid instruments disclosures
Amortized cost	0.2
Carrying value	$ 0.2
Weighted average expected life (in years)	4.7