Derivative Financial Instruments (Details 5) (Fair Value Hedges, USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Effect of derivatives in fair value hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in net income on derivatives	$ (138.2)	$ (48.5)	$ (140.6)	$ (232.6)
Amount of gain (loss) recognized in net income on related hedged item	134.1	44.6	137.9	231.2
Gain (loss) on periodic settlements on interest rate and foreign exchange contracts in fair value hedge of fixed maturities, available-for-sale reported in net investment income	(40.2)	(39.9)	(120.3)	(122.3)
Gain (loss) on periodic settlements on interest rate and foreign exchange contracts in fair value hedge of investment-type insurance contracts reported in benefits, claims and settlement expenses	11.0	18.4	33.6	61.1
Interest rate contracts | Fixed maturities, available-for-sale
Effect of derivatives in fair value hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in net income on derivatives	(114.8)	(76.7)	(126.1)	(230.0)
Amount of gain (loss) recognized in net income on related hedged item	109.2	76.5	121.1	226.4
Interest rate contracts | Investment-type insurance contracts
Effect of derivatives in fair value hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in net income on derivatives	(0.1)	(10.4)	(2.3)	(8.7)
Amount of gain (loss) recognized in net income on related hedged item		8.9	2.4	10.5
Foreign exchange contracts | Fixed maturities, available-for-sale
Effect of derivatives in fair value hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in net income on derivatives	3.0	(5.7)	(0.3)	5.2
Amount of gain (loss) recognized in net income on related hedged item	(3.3)	5.8	0.3	(3.8)
Foreign exchange contracts | Investment-type insurance contracts
Effect of derivatives in fair value hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in net income on derivatives	(26.3)	44.3	(11.9)	0.9
Amount of gain (loss) recognized in net income on related hedged item	$ 28.2	$ (46.6)	$ 14.1	$ (1.9)