Accumulated Other Comprehensive Income (Loss) - Components of AOCI (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Equity [Abstract]
Fixed maturities, net of OTTI	$ 967.0		$ 1,645.9
Equity securities, available-for-sale	14.7		15.6
Derivatives	201.0		174.8
DAC/VOBA and sales inducements adjustment on available-for-sale securities	(372.0)		(580.2)
Premium deficiency reserve adjustment	(94.8)		(127.7)
Unrealized capital gains (losses), before tax	715.9		1,128.4
Deferred income tax asset (liability)	(126.9)		(265.9)
Unrealized capital gains (losses), after tax	589.0		862.5
Pension and other post-employment benefits liability, net of tax	7.7		9.1
AOCI	$ 596.7	$ 841.5	$ 871.6