Derivative Financial Instruments (Details 6) (Cash Flow Hedges, USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Maximum length of time hedging exposure to variability in future cash flows for forecasted transactions			7 years 8 months 12 days
Gross unrealized gains (losses) reported in accumulated OCI related to active hedges of forecasted transactions	$ 130.7		$ 130.7
Amount of gain (loss) recognized in accumulated OCI on derivatives (effective portion)	(22.4)	188.0	29.7	108.6
Amount of gain (loss) reclassified from accumulated OCI on derivatives (effective portion)	0.5	0.7	(10.2)	(14.5)
Gain (loss) on periodic settlements on interest rate and foreign exchange contracts in cash flow hedge of fixed maturities, available-for-sale reported in net investment income	2.0	1.9	5.9	7.3
Gain (loss) on periodic settlements on interest rate and foreign exchange contracts in cash flow hedge of investment-type insurance contracts reported in benefits, claims and settlement expenses	(3.4)	(3.3)	(9.8)	(9.6)
Net gains (losses) expected to be reclassified from accumulated OCI into net income in the next 12 months			(1.2)
Gross unrealized gains (losses) reclassified from OCI into net income due to forecasted transaction probable of not occurring	0	0	0	0
Interest rate contracts | Fixed maturities, available-for-sale
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in accumulated OCI on derivatives (effective portion)	3.6	95.2	29.5	97.8
Interest rate contracts | Fixed maturities, available-for-sale | Net investment income
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) reclassified from accumulated OCI on derivatives (effective portion)	2.3	1.8	6.4	5.4
Interest rate contracts | Investment-type insurance contracts
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in accumulated OCI on derivatives (effective portion)	0.6	(3.7)	1.2	(1.4)
Interest rate contracts | Investment-type insurance contracts | Benefits, claims and settlement expenses
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) reclassified from accumulated OCI on derivatives (effective portion)		(0.1)		(0.6)
Interest rate contracts | Hedged debt | Operating expense
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) reclassified from accumulated OCI on derivatives (effective portion)	(1.5)	(1.3)	(4.4)	(3.9)
Foreign exchange contracts | Net realized capital gains (losses)
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Gain (loss) resulting from the ineffective portion in cash flow hedging relationships	0.1	0.1	0.4	0.3
Foreign exchange contracts | Fixed maturities, available-for-sale
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in accumulated OCI on derivatives (effective portion)	(25.2)	87.5	3.2	20.1
Foreign exchange contracts | Fixed maturities, available-for-sale | Net realized capital gains (losses)
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) reclassified from accumulated OCI on derivatives (effective portion)	(0.3)	0.3	(12.2)	(13.7)
Foreign exchange contracts | Investment-type insurance contracts
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) recognized in accumulated OCI on derivatives (effective portion)	(1.4)	9.0	(4.2)	(7.9)
Foreign exchange contracts | Investment-type insurance contracts | Benefits, claims and settlement expenses
Effect of derivatives in cash flow hedging relationships and the related hedged items on the consolidated statements of operations
Amount of gain (loss) reclassified from accumulated OCI on derivatives (effective portion)				$ (1.7)