Accumulated Other Comprehensive Income (Loss) - Changes in AOCI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Derivatives			$ 47.3	$ 155.6
DAC/VOBA and sales inducements adjustment on available-for-sale securities			(231.0)	(199.8)
Premium deficiency reserve adjustment			(52.2)	(32.9)
Changes in unrealized gains/losses on securities, before tax			455.4	305.2
Deferred income tax asset/liability			(154.5)	(53.0)
Change in unrealized gains/losses on securities, after tax			300.9	252.2
Change in OTTI, before tax	7.0	(84.7)	10.6	18.3
Deferred income tax asset/liability			(3.7)	(6.4)
Change in OTTI, after tax			6.9	11.9
Pension and other post-employment benefit liability, before tax	(0.6)	0	(1.7)	(0.1)
Deferred income tax asset/liability			0.6	0.4
Pension and other post-employment benefit liability, after tax			(1.1)	0.3
Other comprehensive income (loss), after tax	162.1	186.8	306.7	264.4
Fixed maturities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Fixed maturities, net of OTTI	2,221.3	1,340.5	2,221.3	1,340.5
Unrealized capital gains (losses)			692.1	388.4
Equity securities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Unrealized capital gains (losses)			$ (0.8)	$ (6.1)