Carrying Amount and Fair Value of Financial Instruments (Detail) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Assets
Fixed Maturity Securities	$ 42,434.7	$ 40,035.6
Mortgage Loans	1,606.9	1,516.8
Policy Loans	3,075.1	2,996.1
Other Long-term Investments
Derivatives	143.2	99.1
Equity Securities	10.4	10.4
Miscellaneous Long-term Investments	611.1	529.3
Policyholders' Funds
Short-term Debt	342.4	225.1
Long-term Debt	2,586.5	2,631.3
Other Liabilities
Derivatives	275.4	295.9
Unfunded Commitments to Investment Partnerships	158.6
Carrying Amount
Assets
Available-for-sale Securities, Fair Value Disclosure	42,434.7	40,035.6
Mortgage Loans	1,606.9	1,516.8
Policy Loans	3,075.1	2,996.1
Other Long-term Investments
Derivatives	143.2	99.1
Equity Securities	10.4	10.4
Miscellaneous Long-term Investments	457.5	419.8
Policyholders' Funds
Deferred Annuity Products	642.5	656.3
Supplementary Contracts without Life Contingencies	491.8	508.5
Short-term Debt	342.4	225.1
Long-term Debt	2,586.5	2,631.3
Other Liabilities
Derivatives	154.7	199.6
Embedded Derivative in Modified Coinsurance Arrangement	120.7	96.3
Unfunded Commitments to Investment Partnerships	158.6	169.9
Fair Value
Assets
Available-for-sale Securities, Fair Value Disclosure	42,434.7	40,035.6
Mortgage Loans	1,789.9	1,685.4
Policy Loans	3,146.0	3,044.4
Other Long-term Investments
Derivatives	143.2	99.1
Equity Securities	10.4	10.4
Miscellaneous Long-term Investments	457.5	419.8
Policyholders' Funds
Deferred Annuity Products	642.5	656.3
Supplementary Contracts without Life Contingencies	491.8	508.5
Short-term Debt	342.4	226.8
Long-term Debt	2,589.9	2,483.8
Other Liabilities
Derivatives	154.7	199.6
Embedded Derivative in Modified Coinsurance Arrangement	120.7	96.3
Unfunded Commitments to Investment Partnerships	$ 158.6	$ 169.9

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