Schedule I Summary of Investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 38,289.6	[1]	$ 37,751.5
Fixed Maturity Securities	42,344.4		44,973.0
Mortgage Loans	1,815.1	[1]	1,712.7
Policy Loans	3,276.0	[1]	3,133.8
Short-term Investments	913.4	[1]
Investment Owned, at Cost	44,836.1	[1]
Investments	48,914.9		51,904.8
Other Long-term Investments
Available-for-sale Equity Securities, Amortized Cost Basis	11.3	[1]
Equity Securities	16.4		14.6
Other Investments and Securities, at Cost	530.7	[1]
United States Government and Government Agencies and Authorities
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,028.6	[1]	1,020.9
Fixed Maturity Securities	1,196.1		1,348.8
States, Municipalities, and Political Subdivisions
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,706.0	[1]	1,498.4
Fixed Maturity Securities	1,783.2		1,806.8
Foreign Government Debt Securities
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,226.4	[1]	1,280.4
Fixed Maturity Securities	1,373.2		1,507.0
Public Utility, Bonds [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	9,328.9	[1]	9,294.3
Fixed Maturity Securities	10,403.0		11,144.2
Mortgage/Asset-backed Securities
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,858.7	[1]	1,927.9
Fixed Maturity Securities	2,039.3		2,216.5
All Other Corporate Bonds
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	23,108.0	[1]	22,696.6
Fixed Maturity Securities	25,511.9		26,910.4
Redeemable Preferred Stocks
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	33.0	[1]	33.0
Fixed Maturity Securities	37.7		39.3
Measurement at Cost [Member]
Other Long-term Investments
Derivative Assets	0	[1]
Carrying Amount
Schedule of Investments [Line Items]
Fixed Maturity Securities	42,344.4
Mortgage Loans	1,815.1		1,712.7
Policy Loans	3,276.0		3,133.8
Short-term Investments	913.4
Other Long-term Investments
Derivative Assets	10.8	[2]	81.6
Equity Securities	16.4		14.6
Other Long-term Investments	538.8	[3]
Carrying Amount | United States Government and Government Agencies and Authorities
Schedule of Investments [Line Items]
Fixed Maturity Securities	1,196.1
Carrying Amount | States, Municipalities, and Political Subdivisions
Schedule of Investments [Line Items]
Fixed Maturity Securities	1,783.2
Carrying Amount | Foreign Government Debt Securities
Schedule of Investments [Line Items]
Fixed Maturity Securities	1,373.2
Carrying Amount | Public Utility, Bonds [Member]
Schedule of Investments [Line Items]
Fixed Maturity Securities	10,403.0
Carrying Amount | Mortgage/Asset-backed Securities
Schedule of Investments [Line Items]
Fixed Maturity Securities	2,039.3
Carrying Amount | All Other Corporate Bonds
Schedule of Investments [Line Items]
Fixed Maturity Securities	25,511.9
Carrying Amount | Redeemable Preferred Stocks
Schedule of Investments [Line Items]
Fixed Maturity Securities	$ 37.7

[1] (1)The amortized cost for fixed maturity securities and mortgage loans represents original cost reduced by repayments, write-downs from other-than-temporary declines in fair value, amortization of premiums, and/or accretion of discounts.

[2] (2)Derivatives are carried at fair value.

[3] (3)The difference between amortized cost and carrying value primarily results from changes in the partnership owner's equity since acquisition.