Derivative Financial Instruments (Details 5) - Fair Value Hedges - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
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	$ (4.6)	$ 19.1	$ 18.8	$ 31.4
Amount of gain (loss) recognized in net income on related hedged item	4.3	(19.0)	(18.6)	(32.5)
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	(17.6)	(22.2)	(56.9)	(71.5)
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	0.9	1.0	2.8	3.4
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	(7.0)	18.5	11.1	27.2
Amount of gain (loss) recognized in net income on related hedged item	6.7	(18.3)	(11.0)	(28.4)
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	2.4	(2.4)	3.9	0.2
Amount of gain (loss) recognized in net income on related hedged item	$ (2.4)	2.4	(3.8)	(0.1)
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	3.8	3.8
Amount of gain (loss) recognized in net income on related hedged item		$ (3.1)	$ (3.8)	(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				0.2
Amount of gain (loss) recognized in net income on related hedged item				$ (0.2)