Accumulated Other Comprehensive Income (Loss) Components (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Derivatives	$ (0.8)		$ (4.5)
DAC/VOBA and sales inducements adjustment on available-for-sale securities	(1,325.8)		(902.5)
Other investments	(35.4)		(35.5)
Unrealized capital gains (losses), before tax	643.6		221.4
Deferred income tax asset (liability)	(206.7)		43.2
Unrealized capital gains (losses), after tax	436.9		264.6
Pension liability, net of tax	1.1		1.1
AOCI	438.0	245.1	265.7
Fixed maturities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Fixed maturities, net of OTTI	2,002.3		1,165.3
Equity securities, available-for-sale
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Equity securities, available-for-sale	$ 3.3		$ (1.4)