Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 26, 2020
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Transition Report	false
Entity File Number	001-11294
Entity Registrant Name	Unum Group
Entity Central Index Key	0000005513
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	62-1598430
Entity Address, Address Line One	1 Fountain Square
Entity Address, City or Town	Chattanooga,
Entity Address, State or Province	TN
Entity Address, Postal Zip Code	37402
City Area Code	423
Local Phone Number	294-1011
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		203,662,044
NEW YORK STOCK EXCHANGE, INC. | Common Class A
Entity Information [Line Items]
Trading Symbol	UNM
Security Exchange Name	NYSE
Title of 12(b) Security	Common stock, $0.10 par value
NEW YORK STOCK EXCHANGE, INC. | 6.250% Junior Subordinated Notes due 2058
Entity Information [Line Items]
Trading Symbol	UNMA
Security Exchange Name	NYSE
Title of 12(b) Security	6.250% Junior Subordinated Notes due 2058