Segment Information Segments - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Integer Rate	Dec. 31, 2015 GBP (£) Integer	Dec. 31, 2014 USD ($)	Dec. 31, 2014 GBP (£)	Dec. 31, 2015 GBP (£) Rate
Supplementary Insurance Information, by Segment
Number of Operating Segments | Integer	3	3
Effective Date of Business Acquisition	Sep. 03, 2015	Sep. 03, 2015
Percentage Ownership of Acquired Business | Rate	100.00%				100.00%
Name of Acquired Businesses	National Dental Plan Limited and associated companies (National Dental)	National Dental Plan Limited and associated companies (National Dental)
Total Cash Purchase Price to Acquire Business	$ 54,300,000	£ 35.9
Total Revenues of Acquired Business			$ 24,200,000	£ 14.7
Assets of Acquiree at Acquisition Date	28,100,000	18.6
Liabilities of Acquiree at Acquisition Date	7,500,000	£ 5.0
Goodwill	230,900,000		198,700,000
Unum U.K.
Supplementary Insurance Information, by Segment
Goodwill	33,700,000				£ 22.3
Unum U.S.
Supplementary Insurance Information, by Segment
Goodwill	$ 187,600,000		$ 187,600,000.0