Accumulated Other Comprehensive Income - Components of AOCI (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Derivatives	$ 174.8		$ 150.1
DAC/VOBA and sales inducements adjustment on available-for-sale securities	(580.2)		(398.2)
Premium deficiency reserve adjustment	(127.7)		(94.4)
Unrealized capital gains (losses), before tax	1,128.4		648.4
Deferred income tax asset (liability)	(265.9)		(163.6)
Unrealized capital gains (losses), after tax	862.5		484.8
Pension and other post-employment benefits liability, net of tax	9.1		10.2
AOCI	871.6	495.4	495.0
Fixed maturities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Fixed maturities, net of OTTI	1,645.9		974.4
Equity securities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Equity securities, available-for-sale	$ 15.6		$ 16.5