Commitments and Contingent Liabilities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Loss Contingencies [Line Items]
Collateral in fixed maturities pledged under derivatives contracts	$ 649.1	$ 1,012.8
Funding agreement, including accrued interest | FHLB
Loss Contingencies [Line Items]
Non-putable funding agreements, including accrued interest, issued to FHLB	1,579.6	1,579.6
Fixed maturities
Loss Contingencies [Line Items]
Collateral in fixed maturities pledged under derivatives contracts	582.9	779.8
Collateral assets for FHLB funding agreements	1,854.6	1,897.9
Cash collateral, included in Payables
Loss Contingencies [Line Items]
Cash collateral held related to derivative contracts	847.1	821.2
Investment purchase commitment
Loss Contingencies [Line Items]
Commitments to purchase investments	$ 251.1	$ 255.3