Accounting Developments - ASU Impact (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Acquisition Costs	$ 1,728.3		$ 1,728.3		$ 1,677.1
Deferred Income Tax	347.2		347.2		44.7
Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired	892.2		892.2		614.8
Foreign Currency Translation Adjustment	(78.6)		(78.6)		(117.6)
Deferral of Acquisition Costs	(111.0)	(110.1)	(347.6)	(334.7)
Amortization of Deferred Acquisition Costs	87.0	84.3	285.6	273.9
Income Tax - Deferred	4.7	32.3	139.9	86.7
Net Income	230.2	202.0	660.5	653.2
Basic	$ 0.83	$ 0.68	$ 2.33	$ 2.14
Assuming Dilution	$ 0.83	$ 0.68	$ 2.32	$ 2.13
Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other	(430.1)	(703.3)	(683.6)	(931.2)
Change in Foreign Currency Translation Adjustment	29.4	(33.8)	39.0	(6.0)
Change in Deferred Acquisition Costs			(62.0)	(60.8)
Change in Income Taxes			151.9	37.9
Retained Earnings (Accumulated Deficit)	7,173.4		7,173.4		6,611.0
Previous Accounting Guidance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Acquisition Costs		2,572.4		2,572.4	2,300.9
Deferred Income Tax		795.3		795.3	261.2
Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired		885.6		885.6	605.8
Foreign Currency Translation Adjustment		(116.9)		(116.9)	(121.5)
Deferral of Acquisition Costs		(155.6)		(472.1)
Amortization of Deferred Acquisition Costs		125.2		400.4
Income Tax - Deferred		33.3		90.0
Net Income		205.6		660.8
Basic		$ 0.69		$ 2.16
Assuming Dilution		$ 0.69		$ 2.15
Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other		(705.3)		(934.0)
Change in Foreign Currency Translation Adjustment		(34.1)		(6.0)
Change in Deferred Acquisition Costs				(71.7)
Change in Income Taxes				41.2
Retained Earnings (Accumulated Deficit)		7,487.3		7,487.3	7,031.2
Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Acquisition Costs		1,860.6		1,860.6	1,677.1
Deferred Income Tax		547.8		547.8	44.7
Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired		894.0		894.0	614.8
Foreign Currency Translation Adjustment		(113.0)		(113.0)	(117.6)
Deferral of Acquisition Costs		(110.1)		(334.7)
Amortization of Deferred Acquisition Costs		84.3		273.9
Income Tax - Deferred		32.3		86.7
Net Income		202.0		653.2
Basic		$ 0.68		$ 2.14
Assuming Dilution		$ 0.68		$ 2.13
Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other		(703.3)		(931.2)
Change in Foreign Currency Translation Adjustment		(33.8)		(6.0)
Change in Deferred Acquisition Costs				(60.8)
Change in Income Taxes				37.9
Retained Earnings (Accumulated Deficit)		7,010.7		7,010.7	6,611.0
Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Acquisition Costs		(711.8)		(711.8)	(623.8)
Deferred Income Tax		(247.5)		(247.5)	(216.5)
Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired		8.4		8.4	9.0
Foreign Currency Translation Adjustment		3.9		3.9	3.9
Deferral of Acquisition Costs		45.5		137.4
Amortization of Deferred Acquisition Costs		(40.9)		(126.5)
Income Tax - Deferred		(1.0)		(3.3)
Net Income		(3.6)		(7.6)
Basic		$ (0.01)		$ (0.02)
Assuming Dilution		$ (0.01)		$ (0.02)
Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other		2.0		2.8
Change in Foreign Currency Translation Adjustment		0.3		0
Change in Deferred Acquisition Costs				10.9
Change in Income Taxes				(3.3)
Retained Earnings (Accumulated Deficit)		$ (476.6)		$ (476.6)	$ (420.2)