CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 100.8	$ 18.6	$ 246.5	$ 124.0
Other comprehensive income, before tax:
Unrealized gains for the period	120.9	228.3	794.5	1,329.2
Adjustment to present value of future profits and deferred acquisition costs	(1.8)	(11.3)	(25.3)	(119.6)
Amount related to premium deficiencies assuming the net unrealized gains (losses) had been realized	(31.0)	(82.8)	(243.0)	(493.4)
Reclassification adjustments:
For net realized investment (gains) losses included in net income	(27.7)	(14.6)	(44.0)	(24.2)
For amortization of the present value of future profits and deferred acquisition costs related to net realized investment gains (losses) included in net income	0.7	0.2	1.0	0.9
Unrealized gains on investments	61.1	119.8	483.2	692.9
Change related to deferred compensation plan	0.0	0.0	0.0	8.6
Other comprehensive income before tax	61.1	119.8	483.2	701.5
Income tax expense related to items of accumulated other comprehensive income	(22.0)	(42.1)	(172.0)	(248.8)
Other comprehensive income, net of tax	39.1	77.7	311.2	452.7
Comprehensive income	$ 139.9	$ 96.3	$ 557.7	$ 576.7