Investing Activities - Unrealized Investment Gains/Losses (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011
Investments, Debt and Equity Securities [Abstract]
Debt securities	$ (3.1)	$ 51.0	$ (129.3)	$ 112.5
Equity securities	0	0	0	0
Other investments	(0.2)	0	(0.1)	0
Net unrealized investment gains (losses)	(3.3)	51.0	(129.4)	112.5
Applicable to DAC	(1.6)	(5.8)	(45.5)	25.6
Applicable to other actuarial offsets	(11.6)	54.8	(68.4)	68.2
Applicable to deferred income tax expense (benefit)	(0.3)	7.1	(9.7)	17.1
Offsets to net unrealized investment gains (losses)	(13.5)	56.1	(123.6)	110.9
Net unrealized investment gains (losses) included in OCI	$ 10.2	$ (5.1)	$ (5.8)	$ 1.6