Accumulated Other Comprehensive Income (Loss) - Changes in AOCI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Derivatives			$ 39.9	$ 29.9
DAC/VOBA and sales inducements adjustment on available-for-sale securities			(73.0)	(20.8)
Premium deficiency reserve adjustment			(31.2)	(5.2)
Changes in unrealized gains/losses on securities, before tax			201.5	4.4
Deferred income tax asset/liability			(58.5)	6.4
Change in unrealized gains/losses on securities, after tax			143.0	10.8
Change in OTTI, before tax	2.0	97.7	3.6	103.0
Deferred income tax asset/liability			(1.3)	(36.1)
Change in OTTI, after tax			2.3	66.9
Pension and other post-employment benefit liability, before tax	(0.5)	(0.1)	(1.1)	(0.1)
Deferred income tax asset/liability			0.4	0
Pension and other post-employment benefit liability, after tax			(0.7)	(0.1)
Other comprehensive income (loss), after tax	184.9	90.3	144.6	77.6
Fixed maturities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Fixed maturities, net of OTTI	1,787.6	1,035.2	1,787.6	1,035.2
Unrealized capital gains (losses)			265.4	(1.6)
Equity securities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Unrealized capital gains (losses)			$ 0.4	$ 2.1