Carrying Amount and Fair Value of Financial Instruments (Detail) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Assets
Fixed Maturity Securities	$ 40,768.4	$ 40,035.6
Mortgage Loans	1,576.3	1,516.8
Policy Loans	2,948.8	2,996.1
Other Long-term Investments
Derivatives	85.0	99.1
Equity Securities	13.2	10.4
Miscellaneous Long-term Investments	573.9	529.3
Policyholders' Funds
Short-term Debt	140.4	225.1
Long-term Debt	2,589.1	2,631.3
Other Liabilities
Derivatives	290.6	295.9
Embedded Derivative in Modified Coinsurance Arrangement	87.0	96.3
Unfunded Commitments to Investment Partnerships	177.8
Carrying Amount
Assets
Fixed Maturity Securities	40,768.4	40,035.6
Mortgage Loans	1,576.3	1,516.8
Policy Loans	2,948.8	2,996.1
Other Long-term Investments
Derivatives	85.0	99.1
Equity Securities	13.2	10.4
Miscellaneous Long-term Investments	475.7	419.8
Policyholders' Funds
Deferred Annuity Products	643.5	656.3
Supplementary Contracts without Life Contingencies	497.9	508.5
Short-term Debt	140.4	225.1
Long-term Debt	2,589.1	2,631.3
Other Liabilities
Derivatives	203.6	199.6
Embedded Derivative in Modified Coinsurance Arrangement	87.0	96.3
Unfunded Commitments to Investment Partnerships	177.8	169.9
Fair Value
Assets
Fixed Maturity Securities	40,768.4	40,035.6
Mortgage Loans	1,699.9	1,685.4
Policy Loans	2,997.8	3,044.4
Other Long-term Investments
Derivatives	85.0	99.1
Equity Securities	13.2	10.4
Miscellaneous Long-term Investments	475.7	419.8
Policyholders' Funds
Deferred Annuity Products	643.5	656.3
Supplementary Contracts without Life Contingencies	497.9	508.5
Short-term Debt	140.4	226.8
Long-term Debt	2,572.0	2,483.8
Other Liabilities
Derivatives	203.6	199.6
Embedded Derivative in Modified Coinsurance Arrangement	87.0	96.3
Unfunded Commitments to Investment Partnerships	$ 177.8	$ 169.9

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