Investing Activities - Unrealized Investment Gains/Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Other investments	$ (0.2)	$ 0.0	$ (0.3)	$ 0.0
Net unrealized investment gains (losses)	(141.0)	62.6	(81.8)	124.7
Applicable to DAC	(42.1)	14.5	(24.8)	30.0
Applicable to other actuarial offsets	(65.6)	11.5	(25.4)	45.1
Applicable to deferred income tax expense (benefit)	(14.3)	6.9	(11.3)	21.3
Offsets to net unrealized investment gains (losses)	(122.0)	32.9	(61.5)	96.4
Net unrealized gains (losses) included in OCI	(19.0)	29.7	(20.3)	28.3
Debt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, gross unrealized gain (loss)	(140.3)	62.6	(81.8)	124.7
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, gross unrealized gain (loss)	$ (0.5)	$ 0.0	$ 0.3	$ 0.0