Accounting Developments (Details) $ / shares in Units, $ in Millions		3 Months Ended					6 Months Ended
		Jun. 30, 2023 USD ($) $ / shares	Jun. 30, 2022 USD ($) $ / shares		Jun. 30, 2022 USD ($) $ / shares		Jun. 30, 2023 USD ($) $ / shares	Jun. 30, 2022 USD ($) $ / shares		Jun. 30, 2022 USD ($) $ / shares		Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)		Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jan. 01, 2021 USD ($)		Dec. 31, 2020 USD ($)
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ (3,457.6)	$ (3,809.5)		$ (3,809.5)		$ (3,457.6)	$ (3,809.5)		$ (3,809.5)		$ (3,162.3)	$ (3,448.3)		$ (4,438.5)	$ (5,164.6)	$ 4,166.0
Deferred Acquisition Costs		2,647.2	2,493.3		2,493.3		2,647.2	2,493.3		2,493.3			2,560.0				2,357.7
Reinsurance Recoverable		9,383.1	10,110.9		10,110.9		9,383.1	10,110.9		10,110.9			9,608.0
Deferred Income Tax		582.9	686.7		686.7		582.9	686.7		686.7			586.0
Other Assets		1,656.4	1,684.0	[1]	1,684.0	[1]	1,656.4	1,684.0	[1]	1,684.0	[1]		1,666.6
Total Assets		61,904.4	63,510.1		63,510.1		61,904.4	63,510.1		63,510.1			61,148.5
Policy and Contract Benefits			0.0	[2]	0.0	[2]		0.0	[2]	0.0	[2]		0.0	[3]
Reserves for Future Policy and Contract Benefits			0.0	[2]	0.0	[2]		0.0	[2]	0.0	[2]		0.0	[3]
Future Policy Benefits		38,945.3	41,407.7	[2]	41,407.7	[2]	38,945.3	41,407.7	[2]	41,407.7	[2]		38,577.1	[3]
Policyholders' Account Balances		5,692.4	5,758.7	[2]	5,758.7	[2]	5,692.4	5,758.7	[2]	5,758.7	[2]		5,740.2	[3]
Unearned Premiums		494.7	449.9		449.9		494.7	449.9		449.9			365.5
Deferred Income Tax		23.9	36.7		36.7		23.9	36.7		36.7			25.2
Liabilities		52,658.5	55,722.3		55,722.3		52,658.5	55,722.3		55,722.3			52,413.5
Accumulated Other Comprehensive Loss		(3,457.6)	(3,809.5)		(3,809.5)		(3,457.6)	(3,809.5)		(3,809.5)			(3,448.3)		(4,438.5)	(5,164.6)
Retained Earnings		13,758.1	12,473.7		12,473.7		13,758.1	12,473.7		12,473.7			13,141.3		12,166.9	11,989.4
Stockholders' Equity Attributable to Parent		9,245.9	7,787.8		7,787.8		9,245.9	7,787.8		7,787.8			8,735.0
Premium Income		2,509.1	2,416.0				4,968.4	4,817.4
Policy Benefits		1,837.9	1,865.7				3,720.0	3,848.7
Policy Benefits - Remeasurement Gain		(84.3)	(65.6)				(230.0)	(134.4)
Amortization of Deferred Acquisition Costs		113.7	106.5				229.6	210.1
Other Expenses		273.6	250.0				546.8	490.5
Income Tax - Deferred		(23.1)	(71.7)				4.3	(99.7)
Net Income		$ 392.9	$ 367.3				$ 751.2	$ 607.7
Basic Earnings Per Share | $ / shares		$ 1.99	$ 1.83				$ 3.80	$ 3.01
Diluted Earnings Per Share | $ / shares		$ 1.98	$ 1.81				$ 3.78	$ 2.99
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance			$ 0.0					$ 0.0
Change in Foreign Currency Translation Adjustment		$ 38.3	(61.4)				$ 63.0	(93.4)
Comprehensive Income (Loss)		97.6	996.3				741.9	1,962.8
Other Comprehensive Income (Loss)		(295.3)	629.0				(9.3)	1,355.1
Change in Receivables							285.6	481.1
Change in Deferred Acquisition Costs							84.6	69.6
Change in Insurance Liabilities							(194.2)	(10.9)
Change in Income Taxes							10.6	23.0
Amortization of the Cost of Reinsurance							22.0	26.7
Operating Segments
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		38,704.9	41,191.3		41,191.3		38,704.9	41,191.3		41,191.3							55,585.4
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		7,922.9	8,621.9		8,621.9		7,922.9	8,621.9		8,621.9							10,496.0	[4]
Liability for Future Policy Benefit, after Reinsurance		30,782.0	32,569.4		32,569.4		30,782.0	32,569.4		32,569.4							45,089.4
Deferred Acquisition Costs		2,647.2	2,493.3		2,493.3		2,647.2	2,493.3		2,493.3			2,560.0			2,427.4
Future Policy Benefits		38,945.3	41,407.7		41,407.7		38,945.3	41,407.7		41,407.7
Policyholders' Account Balances		5,692.4	5,758.7		5,758.7		5,692.4	5,758.7		5,758.7
Premium Income		2,509.1	2,416.0				4,968.4	4,817.4
Amortization of Deferred Acquisition Costs							229.6	210.1
Unum US
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		9,496.1	10,339.9		10,339.9		9,496.1	10,339.9		10,339.9							12,861.4
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		242.9	270.8		270.8		242.9	270.8		270.8							357.7	[4]
Liability for Future Policy Benefit, after Reinsurance		9,253.2	10,069.1		10,069.1		9,253.2	10,069.1		10,069.1							12,503.7
Deferred Acquisition Costs		1,212.0	1,170.5		1,170.5		1,212.0	1,170.5		1,170.5			1,185.1			1,152.9	1,181.0
Future Policy Benefits	[5]	9,496.1	10,339.9		10,339.9		9,496.1	10,339.9		10,339.9
Amortization of Deferred Acquisition Costs							129.2	115.6
Unum US | Group Disability
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		5,364.3	5,998.1		5,998.1		5,364.3	5,998.1		5,998.1							7,295.7
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		33.7	37.4		37.4		33.7	37.4		37.4							58.3
Liability for Future Policy Benefit, after Reinsurance		5,330.6	5,960.7		5,960.7		5,330.6	5,960.7		5,960.7							7,237.4
Deferred Acquisition Costs		65.5	62.3		62.3		65.5	62.3		62.3			61.0			60.9
Amortization of Deferred Acquisition Costs							25.9	23.8
Unum US | Group Life and AD&D
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		924.2	973.8		973.8		924.2	973.8		973.8							1,127.3
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		6.5	5.6		5.6		6.5	5.6		5.6							3.0
Liability for Future Policy Benefit, after Reinsurance		917.7	968.2		968.2		917.7	968.2		968.2							1,124.3
Deferred Acquisition Costs		49.9	52.3		52.3		49.9	52.3		52.3			49.3			53.9
Amortization of Deferred Acquisition Costs							19.3	19.5
Unum US | Individual Disability
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		2,031.1	2,131.4		2,131.4		2,031.1	2,131.4		2,131.4							2,767.7
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		190.7	201.8		201.8		190.7	201.8		201.8							260.6
Liability for Future Policy Benefit, after Reinsurance		1,840.4	1,929.6		1,929.6		1,840.4	1,929.6		1,929.6							2,507.1
Deferred Acquisition Costs		479.8	450.5		450.5		479.8	450.5		450.5			464.4			441.8
Amortization of Deferred Acquisition Costs							26.7	24.3
Unum US | Voluntary Benefits
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		1,176.5	1,236.6		1,236.6		1,176.5	1,236.6		1,236.6							1,659.2
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		12.0	26.0		26.0		12.0	26.0		26.0							35.7
Liability for Future Policy Benefit, after Reinsurance		1,164.5	1,210.6		1,210.6		1,164.5	1,210.6		1,210.6							1,623.5
Deferred Acquisition Costs		606.4	597.2		597.2		606.4	597.2		597.2			601.0			588.6
Policyholders' Account Balances		677.2	677.3		677.3		677.2	677.3		677.3
Amortization of Deferred Acquisition Costs							52.2	43.6
Unum US | Dental and Vision
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other																	11.5
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance																	0.1
Liability for Future Policy Benefit, after Reinsurance																	11.4
Deferred Acquisition Costs		10.4	8.2		8.2		10.4	8.2		8.2			9.4			7.7
Amortization of Deferred Acquisition Costs							5.1	4.4
Unum US | Operating Segments
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Total Assets		15,813.2					15,813.2						16,356.3
Premium Income		1,641.4	1,571.0				3,251.0	3,114.0
Unum US | Operating Segments | Voluntary Benefits
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Premium Income		213.4	214.4				427.9	433.0
Unum US | Operating Segments | Dental and Vision
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Premium Income		68.1	68.9				137.4	139.5
Unum International
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		2,114.1	2,214.9		2,214.9		2,114.1	2,214.9		2,214.9							3,203.4
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		73.4	82.0		82.0		73.4	82.0		82.0							132.5	[4]
Liability for Future Policy Benefit, after Reinsurance		2,040.7	2,132.9		2,132.9		2,040.7	2,132.9		2,132.9							3,070.9
Deferred Acquisition Costs		42.9	34.3		34.3		42.9	34.3		34.3			37.0			36.4	32.0
Future Policy Benefits		2,114.1	2,214.9		2,214.9		2,114.1	2,214.9		2,214.9
Amortization of Deferred Acquisition Costs							3.7	4.8
Unum International | Operating Segments
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Total Assets		3,315.2					3,315.2						3,129.4
Premium Income		207.9	179.4				396.5	367.2
Colonial Life
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		1,951.4	2,018.9		2,018.9		1,951.4	2,018.9		2,018.9							2,528.6
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		1.0	1.5		1.5		1.0	1.5		1.5							4.4	[4]
Liability for Future Policy Benefit, after Reinsurance		1,950.4	2,017.4		2,017.4		1,950.4	2,017.4		2,017.4							2,524.2
Deferred Acquisition Costs		1,392.3	1,288.5		1,288.5		1,392.3	1,288.5		1,288.5			1,337.9			1,238.1	1,144.7
Future Policy Benefits		1,951.4	2,018.9		2,018.9		1,951.4	2,018.9		2,018.9
Policyholders' Account Balances		867.0	868.3		868.3		867.0	868.3		868.3
Amortization of Deferred Acquisition Costs							96.7	89.7
Colonial Life | Operating Segments
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Total Assets		4,674.9					4,674.9						4,575.0
Premium Income		430.6	427.6				860.1	858.3
Closed Block
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		25,143.3	26,617.6		26,617.6		25,143.3	26,617.6		26,617.6							36,992.0
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		7,605.5	8,267.5		8,267.5		7,605.5	8,267.5		8,267.5							10,001.4	[4]
Liability for Future Policy Benefit, after Reinsurance		17,537.8	18,350.1		18,350.1		17,537.8	18,350.1		18,350.1							26,990.6
Future Policy Benefits	[5]	25,143.3	26,617.6		26,617.6		25,143.3	26,617.6		26,617.6
Closed Block | Long-term Care
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		15,450.3	16,049.1		16,049.1		15,450.3	16,049.1		16,049.1							22,740.9
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		5.4	5.7		5.7		5.4	5.7		5.7							44.4
Liability for Future Policy Benefit, after Reinsurance		15,444.9	16,043.4		16,043.4		15,444.9	16,043.4		16,043.4							22,696.5
Closed Block | Other Insurance Product Line
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other		9,693.0	10,568.5		10,568.5		9,693.0	10,568.5		10,568.5							14,251.1
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance		7,600.1	8,261.8		8,261.8		7,600.1	8,261.8		8,261.8							9,957.0
Liability for Future Policy Benefit, after Reinsurance		2,092.9	2,306.7		2,306.7		2,092.9	2,306.7		2,306.7							4,294.1
Policyholders' Account Balances		4,148.2	4,213.1		4,213.1		4,148.2	4,213.1		4,213.1
Closed Block | Operating Segments
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Total Assets		34,309.8					34,309.8						33,776.6
Premium Income		229.2	238.0				460.8	477.9
Closed Block | Operating Segments | Long-term Care
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Premium Income		174.0	173.7				349.1	348.5
Closed Block | Operating Segments | Other Insurance Product Line
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Premium Income		55.2	64.3				111.7	129.4
Retained Earnings
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest																	11,249.0
Stockholders' Equity Attributable to Parent		13,758.1	12,473.7		12,473.7		13,758.1	12,473.7		12,473.7		13,430.4	13,141.3		12,166.9	11,989.4
Net Income		392.9	367.3				751.2	607.7
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest																	(6,310.2)
Stockholders' Equity Attributable to Parent		(3,457.6)	(3,809.5)		(3,809.5)		(3,457.6)	(3,809.5)		(3,809.5)		$ (3,162.3)	(3,448.3)		(4,438.5)	(5,164.6)
Other Comprehensive Income (Loss)		$ (295.3)	629.0				$ (9.3)
Previously Reported
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest																			$ 10,871.0
Deferred Acquisition Costs			2,247.6		2,247.6			2,247.6		2,247.6			2,252.3						2,272.6
Reinsurance Recoverable			10,377.7		10,377.7			10,377.7		10,377.7			10,218.6
Deferred Income Tax			149.9		149.9			149.9		149.9			449.8
Other Assets			1,810.7	[1]	1,810.7	[1]		1,810.7	[1]	1,810.7	[1]		1,786.3
Total Assets			63,121.1		63,121.1			63,121.1		63,121.1			61,434.9
Policy and Contract Benefits			1,815.9	[2]	1,815.9	[2]		1,815.9	[2]	1,815.9	[2]		1,839.8	[3]
Reserves for Future Policy and Contract Benefits			43,088.0	[2]	43,088.0	[2]		43,088.0	[2]	43,088.0	[2]		42,330.2	[3]
Future Policy Benefits			0.0	[2]	0.0	[2]		0.0	[2]	0.0	[2]		0.0	[3]
Policyholders' Account Balances			0.0	[2]	0.0	[2]		0.0	[2]	0.0	[2]		0.0	[3]
Unearned Premiums			437.0		437.0			437.0		437.0			352.7
Deferred Income Tax			5.8		5.8			5.8		5.8			9.2
Liabilities			53,416.0		53,416.0			53,416.0		53,416.0			52,237.4
Accumulated Other Comprehensive Loss			(1,772.2)		(1,772.2)			(1,772.2)		(1,772.2)			(2,756.6)		(580.1)	354.1
Retained Earnings			12,353.7		12,353.7			12,353.7		12,353.7			12,912.1		12,043.8	11,853.2
Stockholders' Equity Attributable to Parent			9,705.1		$ 9,705.1			9,705.1		$ 9,705.1			9,197.5
Premium Income			2,417.3					4,820.6
Policy Benefits	[6]		1,758.1					3,602.0
Policy Benefits - Remeasurement Gain			0.0					0.0
Amortization of Deferred Acquisition Costs			142.6					298.7
Other Expenses			253.3					497.1
Income Tax - Deferred			(70.9)					(95.6)
Net Income			370.4					623.9
Basic Earnings Per Share | $ / shares					$ 1.84					$ 3.09
Diluted Earnings Per Share | $ / shares					$ 1.83					$ 3.07
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance			1,550.1					3,547.8
Change in the Effect of Discount Rate Assumptions on the Liability for Future Policy Benefits, Net of Reinsurance			0.0					0.0
Change in Foreign Currency Translation Adjustment			(61.1)					(93.0)
Comprehensive Income (Loss)			(821.7)					(1,502.4)
Other Comprehensive Income (Loss)			(1,192.1)					(2,126.3)
Change in Receivables								469.3
Change in Deferred Acquisition Costs								19.0
Change in Insurance Liabilities								(112.4)
Change in Income Taxes								24.9
Amortization of the Cost of Reinsurance								33.3
Previously Reported | Operating Segments
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other	[7]																		45,704.4
Previously Reported | Unum US
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other	[7]																		12,184.6
Deferred Acquisition Costs																			1,168.7
Previously Reported | Unum US | Group Disability
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other																			7,409.0
Previously Reported | Unum US | Group Life and AD&D
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other																			1,123.9
Previously Reported | Unum US | Individual Disability
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other																			2,485.3
Previously Reported | Unum US | Voluntary Benefits
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other																			1,154.9
Previously Reported | Unum US | Dental and Vision
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other																			11.5
Previously Reported | Unum International
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other	[7]																		2,969.8
Deferred Acquisition Costs																			32.0
Previously Reported | Colonial Life
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other	[7]																		1,977.2
Deferred Acquisition Costs																			1,071.9
Previously Reported | Closed Block
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other	[7]																		28,572.8
Previously Reported | Closed Block | Long-term Care
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other																			16,283.4
Previously Reported | Closed Block | Other Insurance Product Line
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Liability for Future Policy Benefit, before Reinsurance, after Other																			12,289.4
Previously Reported | Retained Earnings
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest																			11,269.6
Previously Reported | Accumulated Other Comprehensive Income (Loss)
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest																			$ 374.2
Revision of Prior Period, Accounting Standards Update, Adjustment | Accounting Standards Update 2018-12
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest																	(6,705.0)
Deferred Acquisition Costs			245.7		$ 245.7			245.7		$ 245.7			307.7
Removal of Shadow Adjustments, DAC																	85.1
Reinsurance Recoverable			(266.8)		(266.8)			(266.8)		(266.8)			(610.6)
Deferred Income Tax			536.8		536.8			536.8		536.8			136.2
Other Assets			(126.7)	[1]	(126.7)	[1]		(126.7)	[1]	(126.7)	[1]		(119.7)
Total Assets			389.0		389.0			389.0		389.0			(286.4)
Policy and Contract Benefits			(1,815.9)	[2]	(1,815.9)	[2]		(1,815.9)	[2]	(1,815.9)	[2]		(1,839.8)	[3]
Reserves for Future Policy and Contract Benefits			(43,088.0)	[2]	(43,088.0)	[2]		(43,088.0)	[2]	(43,088.0)	[2]		(42,330.2)	[3]
Future Policy Benefits			41,407.7	[2]	41,407.7	[2]		41,407.7	[2]	41,407.7	[2]		38,577.1	[3]
Policyholders' Account Balances			5,758.7	[2]	5,758.7	[2]		5,758.7	[2]	5,758.7	[2]		5,740.2	[3]
Unearned Premiums			12.9		12.9			12.9		12.9			12.8
Deferred Income Tax			30.9		30.9			30.9		30.9			16.0
Liabilities			2,306.3		2,306.3			2,306.3		2,306.3			176.1
Accumulated Other Comprehensive Loss			(2,037.3)		(2,037.3)			(2,037.3)		(2,037.3)			(691.7)		(3,858.4)	(5,518.7)
Retained Earnings			120.0		120.0			120.0		120.0			229.2		$ 123.1	$ 136.2
Stockholders' Equity Attributable to Parent			(1,917.3)		$ (1,917.3)			(1,917.3)		$ (1,917.3)			$ (462.5)
Premium Income			(1.3)					(3.2)
Policy Benefits	[6]		107.6					246.7
Policy Benefits - Remeasurement Gain			(65.6)					(134.4)
Amortization of Deferred Acquisition Costs			(36.1)					(88.6)
Other Expenses			(3.3)					(6.6)
Income Tax - Deferred			(0.8)					(4.1)
Net Income			(3.1)					(16.2)
Basic Earnings Per Share | $ / shares					$ (0.01)					$ (0.08)
Diluted Earnings Per Share | $ / shares					$ (0.02)					$ (0.08)
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance			(1,550.1)					(3,547.8)
Change in the Effect of Discount Rate Assumptions on the Liability for Future Policy Benefits, Net of Reinsurance			3,371.4					7,029.5
Change in Foreign Currency Translation Adjustment			(0.3)					(0.4)
Comprehensive Income (Loss)			1,818.0					3,465.2
Other Comprehensive Income (Loss)			$ 1,821.1					3,481.4
Change in Receivables								11.8
Change in Deferred Acquisition Costs								(88.6)
Change in Insurance Liabilities								101.5
Change in Income Taxes								(1.9)
Amortization of the Cost of Reinsurance								$ (6.6)
Revision of Prior Period, Accounting Standards Update, Adjustment | Operating Segments | Accounting Standards Update 2018-12
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB	[8]																(6,225.6)
Adjustments for Loss Contracts	[9]																34.9
Effect of Change in Discount Rate Assumptions																	16,084.6
Other increase (decrease)	[10]																(12.9)
Revision of Prior Period, Accounting Standards Update, Adjustment | Unum US | Accounting Standards Update 2018-12
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB	[8]																(1,569.7)
Adjustments for Loss Contracts	[9]																0.0
Effect of Change in Discount Rate Assumptions																	2,251.8
Other increase (decrease)	[10]																(5.3)
Removal of Shadow Adjustments, DAC	[11]																12.3
Revision of Prior Period, Accounting Standards Update, Adjustment | Unum US | Accounting Standards Update 2018-12 | Group Disability
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB																	(1,025.2)
Effect of Change in Discount Rate Assumptions																	911.9
Other increase (decrease)																	0.0
Revision of Prior Period, Accounting Standards Update, Adjustment | Unum US | Accounting Standards Update 2018-12 | Group Life and AD&D
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB																	(88.5)
Effect of Change in Discount Rate Assumptions																	91.9
Other increase (decrease)																	0.0
Revision of Prior Period, Accounting Standards Update, Adjustment | Unum US | Accounting Standards Update 2018-12 | Individual Disability
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB																	(446.1)
Effect of Change in Discount Rate Assumptions																	728.5
Other increase (decrease)																	0.0
Revision of Prior Period, Accounting Standards Update, Adjustment | Unum US | Accounting Standards Update 2018-12 | Voluntary Benefits
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB																	(9.9)
Effect of Change in Discount Rate Assumptions																	519.5
Other increase (decrease)																	(5.3)
Revision of Prior Period, Accounting Standards Update, Adjustment | Unum US | Accounting Standards Update 2018-12 | Dental and Vision
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB																	0.0
Effect of Change in Discount Rate Assumptions																	0.0
Other increase (decrease)																	0.0
Revision of Prior Period, Accounting Standards Update, Adjustment | Unum International | Accounting Standards Update 2018-12
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB	[8]																(545.8)
Adjustments for Loss Contracts	[9]																0.0
Effect of Change in Discount Rate Assumptions																	779.4
Other increase (decrease)	[10]																0.0
Removal of Shadow Adjustments, DAC																	0.0
Revision of Prior Period, Accounting Standards Update, Adjustment | Colonial Life | Accounting Standards Update 2018-12
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB	[8]																(44.5)
Adjustments for Loss Contracts	[9]																34.9
Effect of Change in Discount Rate Assumptions																	568.6
Other increase (decrease)	[10]																(7.6)
Removal of Shadow Adjustments, DAC																	72.8
Revision of Prior Period, Accounting Standards Update, Adjustment | Closed Block | Accounting Standards Update 2018-12
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB	[8]																(4,065.6)
Adjustments for Loss Contracts	[9]																0.0
Effect of Change in Discount Rate Assumptions																	12,484.8
Other increase (decrease)	[10]																0.0
Revision of Prior Period, Accounting Standards Update, Adjustment | Closed Block | Accounting Standards Update 2018-12 | Long-term Care
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB																	(3,465.4)
Effect of Change in Discount Rate Assumptions																	9,922.9
Revision of Prior Period, Accounting Standards Update, Adjustment | Closed Block | Accounting Standards Update 2018-12 | Other Insurance Product Line
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Removal of Shadow Adjustments, LFPB																	(600.2)
Effect of Change in Discount Rate Assumptions																	2,561.9
Revision of Prior Period, Accounting Standards Update, Adjustment | Retained Earnings | Accounting Standards Update 2018-12
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest																	(20.6)
Revision of Prior Period, Accounting Standards Update, Adjustment | Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2018-12
Cumulative Effect on Opening Balance in Period of Adoption [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest																	$ (6,684.4)

[1] 1The change in other assets is driven by the cost of reinsurance associated with the second phase of our Closed Block individual disability reinsurance transaction which was completed in the first quarter of 2021. In accordance with the provisions of the ASU related to non-contemporaneous reinsurance, we were then required to establish the ceded reserves using an upper-medium grade fixed-income instrument as of the reinsurance transaction date in March 2021 which resulted in higher ceded reserves compared to that which was reported historically.

[2] 2We previously reported policy and contract benefits and reserves for future policy and contract benefits liabilities in our consolidated balance sheet as of June 30, 2022 of $1,815.9 million and $43,088.0 million, respectively, resulting in total policyholder liabilities of $44,903.9 million. These balances were reclassified into new line items, future policy benefits and policyholders' account balances, which would have reported balances of $39,154.8 million and $5,749.1 million, respectively, as of June 30, 2022, resulting in total policyholder liabilities of $44,903.9 million under the historical accounting method.

[3] 1We previously reported policy and contract benefits and reserves for future policy and contract benefits liabilities in our consolidated balance sheet as of December 31, 2022 of $1,839.8 million and 42,330.2 million, respectively, resulting in total policyholder liabilities of $44,170.0 million. These balances were reclassified into new line items, future policy benefits and policyholders' account balances, which would have reported balances of $38,443.2 million and $5,726.8 million, respectively, as of December 31, 2022, resulting in total policyholder liabilities of $44,170.0 million under the historical accounting method.

[4] 5These amounts represent the portion of reinsurance recoverable related to the liability for future policy benefits. These amounts include the adjustments for the removal of shadow adjustments and for the effect of change in discount rate assumptions for the liability for future policy benefits ceded to third party reinsurers.

[5] 1Unum US excludes dental & vision and medical stop-loss product lines and Closed Block excludes our participating fund account, which represents policies issued by one of our subsidiaries prior to its 1986 conversion from a mutual stock life insurance company. The liabilities associated with these products are included within Other products.

[6] 1 Previously disclosed as Benefits and Change in Reserves for Future Benefits

[7] 1We previously reported policy and contract benefits and reserves for future policy and contract benefits liabilities in our consolidated balance sheet as of December 31, 2020 of $1,855.4 million and $49,653.0 million, respectively, resulting in total policyholder liabilities of $51,508.4 million. These balances were reclassified into new line items, future policy benefits and policyholders' account balances, which would have reported balances of $45,704.4 million and $5,804.0 million as of December 31, 2020, respectively, resulting in total policyholder liabilities of $51,508.4 million under the historical accounting method. These balances were reclassified to more closely align with the new disclosure requirements of ASU 2018-12.

[8] 2Shadow adjustments represent the adjustments related to unrealized investment gains and losses previously included in the reserves balance prior to the adoption of ASU 2018-12.

[9] 3Adjustment for loss contracts represents the adjustment for those cohorts whose net premium ratio exceeded 100 percent as of the transition date. For those cohorts, the net premiums were set equal to the gross premiums and the difference was recorded as a transition adjustment to the liability for future policy benefits.

[10] 4This amount reflects the effect of the reclassification of certain unearned premium. This amount was reclassified to more closely align with the presentation of liabilities under ASU 2018-12 and had no impact to stockholders' equity.

[11] 1The $12.3 million removal of shadow adjustments is related to the Unum US voluntary benefits product line.