Investing Activities - Unrealized Investment Gains/Losses (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Investments, Debt and Equity Securities [Abstract]
Debt securities	$ 62.4	$ (124.3)	$ 124.6	$ (126.2)
Other investments	0.1	0.1	0.2	0.1
Net unrealized investment gains (losses)	62.5	(124.2)	124.8	(126.1)
Applicable to DAC	14.5	(39.7)	31.2	(44.0)
Applicable to other actuarial offsets	9.3	(72.4)	43.8	(56.7)
Applicable to deferred income tax expense (benefit)	6.4	(12.1)	20.4	(9.4)
Offsets to net unrealized investment gains (losses)	30.2	(124.2)	95.4	(110.1)
Net unrealized investment gains (losses) included in OCI	$ 32.3	$ 0	$ 29.4	$ (16.0)