Investing Activities - Net Realized Investment Gains/Losses (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Total other-than-temporary debt impairments	$ 0		$ (0.3)
Portion of gains (losses) recognized in OCI	0		(0.7)
Net debt impairments recognized in earnings	0		(1.0)
Debt security impairments:
U.S. government and agency	0		0
State and political subdivision	0		0
Foreign government	0		0
Corporate	0		0
CMBS	0		(0.1)
RMBS	0		(0.7)
CDO/CLO	0		(0.2)
Other asset-backed	0		0
Net debt security impairments	0		(1.0)
Limited partnerships and other investment impairments	0		0
Net OTTI losses recognized in earnings	0		(1.0)
Debt security transaction gains	2.1		5.2
Debt security transaction losses	(0.7)		(0.1)
Limited partnerships and other investment transaction gains	0		0
Limited partnerships and other investment transaction losses	0		0
Net transaction gains (losses)	1.4		5.1
Derivative instruments	(23.6)		(20.9)
Embedded derivatives	(11.7)	[1]	(0.6)	[1]
Net realized investment gains (losses), excluding impairment losses	(33.9)		(16.4)
Net realized investment gains (losses), including impairment losses	$ (33.9)		$ (17.4)

[1] Includes the change in fair value of embedded derivatives associated with fixed index annuity indexed crediting feature and variable annuity riders. See Note 7 to these interim unaudited financial statements for additional disclosures.