Commitments and Contingent Liabilities (Narrative) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Commitments And Contingent Liabilities [Line Items]
Undrawn outstanding letters of credit in favor of third parties	$ 16.4	$ 16.0
Undrawn outstanding letters of credit between subsidiaries	465.0	518.4
Syndicated revolving credit facility capacity	750.0
Syndicated revolving credit facility undrawn outstanding	213.6
Other Long Term Credit Facility Capacity 200 Million Dollar	200.0
Other Long Term Credit Facility Undrawn Outstanding 200 Million Dollar	200.0
Other Long Term Credit Facility Capacity 120 Million Dollar	120.0
Other Long Term Credit Facility Undrawn Outstanding 120 Million Dollar	0
Limited Partnerships Member
Commitments And Contingent Liabilities [Line Items]
Unfunded commitments to fund partnership investments, mortgage loans and private corporate bond investments	181.0	147.2
Commercial Mortgage Loans Member
Commitments And Contingent Liabilities [Line Items]
Unfunded commitments to fund partnership investments, mortgage loans and private corporate bond investments	3.0	6.7
Private Placement Investments Member
Commitments And Contingent Liabilities [Line Items]
Unfunded commitments to fund partnership investments, mortgage loans and private corporate bond investments	14.8	7.5
Insurance Treaty Guarantee Member
Commitments And Contingent Liabilities [Line Items]
Guarantee Obligations Current Carrying Value	710.6	600.8
Insurance Treaty Guarantee Net Of Assets Held In Trust Member
Commitments And Contingent Liabilities [Line Items]
Guarantee Obligations Current Carrying Value	466.5	352.0
Guarantee Of Borrowed Securities [Member]
Commitments And Contingent Liabilities [Line Items]
Guarantee Obligations Current Carrying Value	150.7
Guarantee Of Subsidiary Collateral Financing [Member]
Commitments And Contingent Liabilities [Line Items]
Guarantee Obligations Current Carrying Value	$ 300.0