Prior Period Consolidated Financial Statements - Consolidated Statement of Operations and Comprehensive Income (Loss) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Revenues
Net premiums and contract charges earned	$ 259.1	$ 257.4	$ 255.4	$ 255.8	$ 210.6	$ 225.2	$ 225.6	$ 227.4	$ 1,057.1	$ 1,027.7		$ 888.8
Net investment income									444.8	400.9	[1]	422.5	[1]
Net investment losses									(24.0)	(56.5)	[1]	(11.0)	[1]
Other income									14.0	9.5	[1]	29.0	[1]
Total revenues	346.4	342.6	345.9	346.7	331.2	329.4	346.9	321.7	1,491.9	1,381.6	[1]	1,329.3	[1]
Benefits, losses and expenses
Benefits, claims and settlement expenses									769.1	747.0	[1]	590.7	[1]
Interest credited									205.7	173.4	[1]	160.0	[1]
Operating expenses									318.1	315.5	[1]	251.0	[1]
DAC amortization expense									101.2	88.2	[1]	90.6	[1]
Intangible asset amortization expense									14.8	16.8	[1]	13.0	[1]
Interest expense									29.7	19.4	[1]	13.9	[1]
Other expense - goodwill and intangible asset impairments									0.0	4.8	[1],[2]	0.0	[1],[2]
Total benefits, losses and expenses									1,438.6	1,365.1	[1]	1,119.2	[1]
Income before income taxes									53.3	16.5	[1]	210.1	[1]
Income tax expense									8.3	(3.3)	[1]	39.7	[1]
Net income	$ (16.7)	$ 20.4	$ (4.2)	$ 20.3	$ 46.9	$ 20.2	$ 54.2	$ 49.1	$ 45.0	$ 19.8	[1],[2]	$ 170.4	[1],[2]
Net income per share
Basic (in usd per share)	$ (0.40)	$ 0.49	$ (0.10)	$ 0.48	$ 1.12	$ 0.48	$ 1.29	$ 1.17	$ 1.09	$ 0.48	[1]	$ 4.06	[1]
Net income - diluted (in usd per share)	$ (0.40)	$ 0.49	$ (0.10)	$ 0.48	$ 1.11	$ 0.48	$ 1.29	$ 1.16	$ 1.09	$ 0.47	[1]	$ 4.04	[1]
Weighted average number of shares and equivalent shares
Basic (in shares)	41.4	41.4	41.8	41.9	42.0	42.0	42.0	41.9	41.3	41.6	[1]	42.0	[1]
Diluted (in shares)	41.4	41.6	41.8	42.1	42.2	42.2	42.2	42.1	41.4	41.8	[1]	42.2	[1]
Other comprehensive loss, net of tax:
Effect of adopting ASU 2018-12									$ 0.0	$ 0.0	[1]	$ (426.6)	[1]
Change in net unrealized investment losses on fixed maturity securities									121.3	(796.7)	[1]	(90.3)	[1]
Change in net reserve remeasurements attributable to discount rates									(37.1)	445.9	[1]	110.8	[1]
Change in net funded status of benefit plans									1.2	1.4	[1]	1.0	[1]
Other comprehensive income (loss)									85.4	(349.4)	[1]	(405.1)	[1]
Total comprehensive income (loss)									$ 130.4	(329.6)	[1]	(234.7)	[1]
Previously Reported
Revenues
Net premiums and contract charges earned										1,029.0		889.6
Net investment income										400.9		422.5
Net investment losses										(56.5)		(11.0)
Other income										9.5		29.0
Total revenues										1,382.9		1,330.1
Benefits, losses and expenses
Benefits, claims and settlement expenses										761.6		617.7
Interest credited										177.6		164.4
Operating expenses										315.9		251.5
DAC amortization expense										98.7		94.7
Intangible asset amortization expense										16.8		13.0
Interest expense										19.4		13.9
Other expense - goodwill and intangible asset impairments										4.8		0.0
Total benefits, losses and expenses										1,394.8		1,155.2
Income before income taxes										(11.9)		174.9
Income tax expense										(9.3)		32.1
Net income										$ (2.6)		$ 142.8
Net income per share
Basic (in usd per share)										$ (0.06)		$ 3.40
Net income - diluted (in usd per share)										$ (0.06)		$ 3.39
Weighted average number of shares and equivalent shares
Basic (in shares)										41.6		42.0
Diluted (in shares)										41.8		42.2
Other comprehensive loss, net of tax:
Effect of adopting ASU 2018-12												$ 0.0
Change in net unrealized investment losses on fixed maturity securities										$ (647.6)		(75.6)
Change in net reserve remeasurements attributable to discount rates										0.0		0.0
Change in net funded status of benefit plans										1.4		1.0
Other comprehensive income (loss)										(646.2)		(74.6)
Total comprehensive income (loss)										(648.8)		68.2
Effect of the Adoption of ASU 2018-12
Revenues
Net premiums and contract charges earned										(1.3)		(0.8)
Net investment income										0.0		0.0
Net investment losses										0.0		0.0
Other income										0.0		0.0
Total revenues										(1.3)		(0.8)
Benefits, losses and expenses
Benefits, claims and settlement expenses										(14.6)		(27.0)
Interest credited										(4.2)		(4.4)
Operating expenses										(0.4)		(0.5)
DAC amortization expense										(10.5)		(4.1)
Intangible asset amortization expense										0.0		0.0
Interest expense										0.0		0.0
Other expense - goodwill and intangible asset impairments										0.0		0.0
Total benefits, losses and expenses										(29.7)		(36.0)
Income before income taxes										28.4		35.2
Income tax expense										6.0		7.6
Net income										$ 22.4		$ 27.6
Net income per share
Basic (in usd per share)										$ 0.54		$ 0.66
Net income - diluted (in usd per share)										$ 0.53		$ 0.65
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:
Effect of adopting ASU 2018-12												$ (426.6)
Change in net unrealized investment losses on fixed maturity securities										$ (149.1)		(14.7)
Change in net reserve remeasurements attributable to discount rates										445.9		110.8
Change in net funded status of benefit plans										0.0		0.0
Other comprehensive income (loss)										296.8		(330.5)
Total comprehensive income (loss)										$ 319.2		$ (302.9)

[1] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements

[2] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements