Accounting Developments - ASU Impact (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Acquisition Costs	$ 1,711.2		$ 1,711.2		$ 1,677.1
Deferred Income Tax	256.2		256.2		44.7
Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired	728.1		728.1		614.8
Foreign Currency Translation Adjustment	(108.0)		(108.0)		(117.6)
Deferral of Acquisition Costs	(119.2)	(112.4)	(236.6)	(224.6)
Amortization of Deferred Acquisition Costs	99.2	94.6	198.6	189.6
Income Tax - Deferred	76.4	15.9	135.2	54.4
Net Income	216.4	227.6	430.3	451.2
Basic	$ 0.76	$ 0.74	$ 1.50	$ 1.46
Assuming Dilution	$ 0.76	$ 0.74	$ 1.50	$ 1.45
Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other	(420.3)	(341.1)	(253.5)	(227.9)
Change in Foreign Currency Translation Adjustment	(18.6)	1.3	9.6	27.8
Change in Deferred Acquisition Costs			(38.0)	(35.0)
Change in Income Taxes			134.7	41.3
Retained Earnings (Accumulated Deficit)	6,979.7		6,979.7		6,611.0
Previous Accounting Guidance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Acquisition Costs		2,557.6		2,557.6	2,300.9
Deferred Income Tax		507.6		507.6	261.2
Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired		471.7		471.7	605.8
Foreign Currency Translation Adjustment		(82.8)		(82.8)	(121.5)
Deferral of Acquisition Costs		(158.2)		(316.5)
Amortization of Deferred Acquisition Costs		136.9		275.2
Income Tax - Deferred		17.2		56.7
Net Income		229.8		455.2
Basic		$ 0.75		$ 1.47
Assuming Dilution		$ 0.75		$ 1.46
Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other		(341.9)		(228.7)
Change in Foreign Currency Translation Adjustment		1.3		28.1
Change in Deferred Acquisition Costs				(41.3)
Change in Income Taxes				43.6
Retained Earnings (Accumulated Deficit)		7,313.7		7,313.7	7,031.2
Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Acquisition Costs		1,847.1		1,847.1	1,677.1
Deferred Income Tax		260.1		260.1	44.7
Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired		478.2		478.2	614.8
Foreign Currency Translation Adjustment		(79.3)		(79.3)	(117.6)
Deferral of Acquisition Costs		(112.4)		(224.6)
Amortization of Deferred Acquisition Costs		94.6		189.6
Income Tax - Deferred		15.9		54.4
Net Income		227.6		451.2
Basic		$ 0.74		$ 1.46
Assuming Dilution		$ 0.74		$ 1.45
Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other		(341.1)		(227.9)
Change in Foreign Currency Translation Adjustment		1.3		27.8
Change in Deferred Acquisition Costs				(35.0)
Change in Income Taxes				41.3
Retained Earnings (Accumulated Deficit)		6,840.7		6,840.7	6,611.0
Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Acquisition Costs		(710.5)		(710.5)	(623.8)
Deferred Income Tax		(247.5)		(247.5)	(216.5)
Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired		6.5		6.5	9.0
Foreign Currency Translation Adjustment		3.5		3.5	3.9
Deferral of Acquisition Costs		45.8		91.9
Amortization of Deferred Acquisition Costs		(42.3)		(85.6)
Income Tax - Deferred		(1.3)		(2.3)
Net Income		(2.2)		(4.0)
Basic		$ (0.01)		$ (0.01)
Assuming Dilution		$ (0.01)		$ (0.01)
Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other		0.8		0.8
Change in Foreign Currency Translation Adjustment		0		(0.3)
Change in Deferred Acquisition Costs				6.3
Change in Income Taxes				(2.3)
Retained Earnings (Accumulated Deficit)		$ (473.0)		$ (473.0)	$ (420.2)