CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 129.2	$ 42.0	$ 190.0	$ 131.4
Other comprehensive income, before tax:
Unrealized gains on investments	428.4	619.5	759.2	1,991.0
Adjustment to present value of future profits and deferred acquisition costs	(59.9)	(58.3)	(54.6)	(175.0)
Amount related to premium deficiencies assuming the net unrealized gains had been realized	(1.0)	(124.0)	(196.0)	(200.5)
Reclassification adjustments:
For net realized investment (gains) losses included in net income	(8.5)	2.6	41.2	(0.3)
For amortization of the present value of future profits and deferred acquisition costs related to net realized investment (gains) losses included in net income	0.1	0.2	(3.0)	0.6
Other comprehensive income before tax	359.1	440.0	546.8	1,615.8
Income tax expense related to items of accumulated other comprehensive income	(77.7)	(95.3)	(117.7)	(350.6)
Other comprehensive income, net of tax	281.4	344.7	429.1	1,265.2
Comprehensive income	$ 410.6	$ 386.7	$ 619.1	$ 1,396.6