Carrying Amount and Fair Value of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Mortgage Loans	$ 1,735.3	$ 1,712.7
Policy Loans	3,113.1	3,133.8
Other Long Term Investments
Derivatives	36.4	81.6
Equity Securities	14.3	14.6
Policyholders' Funds
Long-term Debt	2,644.0	2,755.4
Other Liabilities
Derivatives	202.7	254.4
Unfunded commitment to fund Investment Partnerships	56.8
Carrying Amount
Assets
Fixed Maturity Securities	42,594.2	44,973.0
Mortgage Loans	1,735.3	1,712.7
Policy Loans	3,113.1	3,133.8
Other Long Term Investments
Derivatives	36.4	81.6
Equity Securities	14.3	14.6
Miscellaneous Long-Term Investments	460.1	455.1
Policyholders' Funds
Deferred Annuity Products	634.1	640.1
Supplementary Contracts without Life Contingencies	555.9	535.5
Long-term Debt	2,644.0	2,755.4
Other Liabilities
Derivatives	137.6	170.5
Embedded Derivative in Modified Coinsurance Arrangement	65.1	83.9
Unfunded commitment to fund Investment Partnerships	56.8	83.7
Fair Value
Assets
Fixed Maturity Securities	42,594.2	44,973.0
Mortgage Loans	1,906.8	1,937.1
Policy Loans	3,183.4	3,215.3
Other Long Term Investments
Derivatives	36.4	81.6
Equity Securities	14.3	14.6
Miscellaneous Long-Term Investments	460.1	455.1
Policyholders' Funds
Deferred Annuity Products	634.1	640.1
Supplementary Contracts without Life Contingencies	555.9	535.5
Long-term Debt	2,865.4	2,968.8
Other Liabilities
Derivatives	137.6	170.5
Embedded Derivative in Modified Coinsurance Arrangement	65.1	83.9
Unfunded commitment to fund Investment Partnerships	$ 56.8	$ 83.7

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