Accumulated Other Comprehensive Income - Components of AOCI (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Derivatives	$ 158.0		$ 201.5
DAC/VOBA adjustment on available-for-sale securities	(1,514.7)		(2,397.6)
Sales inducements adjustment on available-for-sale securities	(74.8)		(119.0)
Other	(28.0)		(28.8)
Unrealized capital gains (losses), before tax	3,332.0		4,759.1
Deferred income tax asset (liability)	(802.7)		(1,363.4)
Unrealized capital gains (losses), after tax	2,529.3		3,395.7
Pension and other post-employment benefits liability, net of tax	48.2		57.1
AOCI	2,577.5	1,849.1	3,452.8
Fixed maturities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Fixed maturities, net of OTTI	4,759.7		7,067.2
Equity securities
Components Of Accumulated Other Comprehensive Income Loss [Line Items]
Equity securities, available-for-sale	$ 31.8		$ 35.8