Prior Period Consolidated Financial Statements - Consolidated Statement of Operations and Comprehensive Income (Loss)(Unaudited) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenues
Net premiums and contract charges earned	$ 260.7	$ 255.4	$ 516.6	$ 511.2
Net investment income	108.5	105.2	208.9	203.1
Net investment losses	(17.4)	(15.5)	(21.3)	(31.0)
Other income	4.6	0.8	6.1	9.3
Total revenues	356.4	345.9	710.3	692.6
Benefits, losses and expenses
Benefits, claims and settlement expenses	205.2	203.4	388.4	378.6
Interest credited	50.7	41.4	99.4	81.1
Operating expenses	80.1	77.1	159.9	153.8
DAC amortization expense	25.4	21.5	49.1	43.5
Intangible asset amortization expense	3.7	4.2	7.4	8.4
Interest expense	6.9	4.3	13.6	8.2
Total benefits, losses and expenses	372.0	351.9	717.8	673.6
Income (loss) before income taxes	(15.6)	(6.0)	(7.5)	19.0
Income tax expense (benefit)	(2.8)	(1.8)	(1.3)	2.9
Net income (loss)	$ (12.8)	$ (4.2)	$ (6.2)	$ 16.1
Net income (loss) per share
Basic (in usd per share)	$ (0.31)	$ (0.10)	$ (0.15)	$ 0.38
Diluted (in usd per share)	$ (0.31)	$ (0.10)	$ (0.15)	$ 0.38
Weighted average number of shares and equivalent shares
Basic (in shares)	41.3	41.8	41.3	41.8
Diluted (in shares)	41.4	41.8	41.4	42.0
Other comprehensive loss, net of tax:
Change in net unrealized investment losses on fixed maturity securities	$ (37.3)	$ (294.8)	$ 55.9	$ (628.9)
Change in net reserve remeasurements attributable to discount rates	25.1	168.5	(16.1)	350.0
Change in net funded status of benefit plans	0.0	0.0	0.0	0.0
Other comprehensive loss	(12.2)	(126.3)	39.8	(278.9)
Comprehensive income (loss)	$ (25.0)	(130.5)	$ 33.6	(262.8)
Previously Reported
Revenues
Net premiums and contract charges earned		255.8		511.7
Net investment income		105.2		203.1
Net investment losses		(15.5)		(31.0)
Other income		0.8		9.3
Total revenues		346.3		693.1
Benefits, losses and expenses
Benefits, claims and settlement expenses		207.6		384.6
Interest credited		42.4		83.2
Operating expenses		77.3		154.1
DAC amortization expense		27.0		53.4
Intangible asset amortization expense		4.2		8.4
Interest expense		4.3		8.2
Total benefits, losses and expenses		362.8		691.9
Income (loss) before income taxes		(16.5)		1.2
Income tax expense (benefit)		(4.0)		(0.8)
Net income (loss)		$ (12.5)		$ 2.0
Net income (loss) per share
Basic (in usd per share)		$ (0.30)		$ 0.05
Diluted (in usd per share)		$ (0.30)		$ 0.05
Weighted average number of shares and equivalent shares
Basic (in shares)		41.8		41.8
Diluted (in shares)		41.8		42.0
Other comprehensive loss, net of tax:
Change in net unrealized investment losses on fixed maturity securities		$ (240.4)		$ (511.1)
Change in net reserve remeasurements attributable to discount rates		0.0		0.0
Change in net funded status of benefit plans		0.0		0.0
Other comprehensive loss		(240.4)		(511.1)
Comprehensive income (loss)		(252.9)		(509.1)
Effect of the Adoption of ASU 2018-12
Revenues
Net premiums and contract charges earned		(0.4)		(0.5)
Net investment income		0.0		0.0
Net investment losses		0.0		0.0
Other income		0.0		0.0
Total revenues		(0.4)		(0.5)
Benefits, losses and expenses
Benefits, claims and settlement expenses		(4.2)		(6.0)
Interest credited		(1.0)		(2.1)
Operating expenses		(0.2)		(0.3)
DAC amortization expense		(5.5)		(9.9)
Intangible asset amortization expense		0.0		0.0
Interest expense		0.0		0.0
Total benefits, losses and expenses		(10.9)		(18.3)
Income (loss) before income taxes		10.5		17.8
Income tax expense (benefit)		2.2		3.7
Net income (loss)		$ 8.3		$ 14.1
Net income (loss) per share
Basic (in usd per share)		$ 0.20		$ 0.33
Diluted (in usd per share)		$ 0.20		$ 0.33
Weighted average number of shares and equivalent shares
Basic (in shares)		0.0		0.0
Diluted (in shares)		0.0		0.0
Other comprehensive loss, net of tax:
Change in net unrealized investment losses on fixed maturity securities		$ (54.4)		$ (117.8)
Change in net reserve remeasurements attributable to discount rates		168.5		350.0
Change in net funded status of benefit plans		0.0		0.0
Other comprehensive loss		114.1		232.2
Comprehensive income (loss)		$ 122.4		$ 246.3