Location of Gains and Losses on Derivative Financial Instruments Designated as Cash Flow Hedging Instruments (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ 12.3	$ 13.8	$ 28.1	$ 24.1
Interest Rate Swaps \| Net Investment Income
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	13.6	13.0	26.8	25.5
Interest Rate Swaps \| Net Realized Investments Gain (Loss)
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0.0	0.3	3.2	0.3
Interest Rate Swaps \| Interest Expense
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(0.4)	(0.4)	(0.9)	(0.9)
Foreign Exchange Contracts
Derivative Instruments, Gain (Loss)
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(0.2)	(15.9)	(24.5)	26.4
Foreign Exchange Contracts \| Net Investment Income
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(0.4)	(0.5)	(0.5)	(1.0)
Foreign Exchange Contracts \| Net Realized Investments Gain (Loss)
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (0.5)	$ 1.4	$ (0.5)	$ 0.2

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- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624177-113959

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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