Accumulated Other Comprehensive Income (Loss) - Components of AOCI (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Derivatives	$ 148.8		$ 221.0
DAC/VOBA and sales inducements adjustment on available-for-sale securities	(363.1)		(834.6)
Premium deficiency reserve adjustment	(89.7)		(117.0)
Unrealized capital gains (losses), before tax	597.5		1,503.0
Deferred income tax asset (liability)	(118.6)		(460.4)
Unrealized capital gains (losses), after tax	478.9		1,042.6
Pension and other post-employment benefits liability, net of tax	10.2		11.6
AOCI	489.1	1,023.0	1,054.2
Fixed maturities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Fixed maturities, net of OTTI	885.4		2,221.3
Equity securities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Equity securities, available-for-sale	$ 16.1		$ 12.3