CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 59.9	$ 46.8	$ 105.4	$ 99.6
Other comprehensive income, before tax:
Unrealized gains (losses) for the period	669.8	(1,016.1)	1,100.9	(747.1)
Adjustment to present value of future profits and deferred acquisition costs	(63.1)	99.4	(108.3)	90.2
Amount related to premium deficiencies assuming the net unrealized gains (losses) had been realized	(242.6)	402.4	(410.6)	310.3
Reclassification adjustments:
For net realized investment (gains) losses included in net income	(4.7)	1.4	(9.6)	1.8
For amortization of the present value of future profits and deferred acquisition costs related to net realized investment gains (losses) included in net income	0.6	0.3	0.7	0.1
Unrealized gains (losses) on investments	360.0	(512.6)	573.1	(344.7)
Change related to deferred compensation plan	8.0	1.2	8.6	2.5
Other comprehensive income (loss) before tax	368.0	(511.4)	581.7	(342.2)
Income tax (expense) benefit related to items of accumulated other comprehensive income	(130.7)	182.2	(206.7)	121.9
Other comprehensive income (loss), net of tax	237.3	(329.2)	375.0	(220.3)
Comprehensive income (loss)	$ 297.2	$ (282.4)	$ 480.4	$ (120.7)