Accumulated Other Comprehensive Income - Components of AOCI (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Derivatives	$ 150.1		$ 213.6
DAC/VOBA and sales inducements adjustment on available-for-sale securities	(398.2)		(676.6)
Premium deficiency reserve adjustment	(94.4)		(96.0)
Unrealized capital gains (losses), before tax	648.4		1,242.1
Deferred income tax asset (liability)	(163.6)		(362.0)
Unrealized capital gains (losses), after tax	484.8		880.1
Pension and other post-employment benefits liability, net of tax	10.2		12.0
AOCI	495.0	1,023.0	892.1
Fixed maturities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Fixed maturities, net of OTTI	974.4		1,787.6
Equity securities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Equity securities, available-for-sale	$ 16.5		$ 13.5