Segment Information Deferred Acquisition Costs by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	$ 1,901.3
Deferred Policy Acquisition Cost, Amortization Expense	(482.3)	$ (440.8)	$ (418.9)
Deferred Acquisition Costs at End of Year	2,008.5	1,901.3
Operating Segments
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	1,901.3	1,829.2	1,755.5
Deferral of Acquisition Costs	569.7	524.0	466.8
Deferred Policy Acquisition Cost, Amortization Expense	(482.3)	(440.8)	(418.9)
Adjustment Related to Unrealized Investment (Gain) Loss	21.4	(9.2)	25.4
Deferred Policy Acquisition Costs Foreign Currency Translation Adjustment And Other	(1.6)	(1.9)	0.4
Deferred Acquisition Costs at End of Year	2,008.5	1,901.3	1,829.2
Operating Segments | Unum U.S.
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	1,096.5	1,051.5	1,024.3
Deferral of Acquisition Costs	307.3	292.7	252.0
Deferred Policy Acquisition Cost, Amortization Expense	(272.3)	(248.1)	(230.0)
Adjustment Related to Unrealized Investment (Gain) Loss	4.9	0.4	5.2
Deferred Policy Acquisition Costs Foreign Currency Translation Adjustment And Other	0.0	0.0	0.0
Deferred Acquisition Costs at End of Year	1,136.4	1,096.5	1,051.5
Operating Segments | Unum U.K.
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	30.4	34.3	38.8
Deferral of Acquisition Costs	9.6	10.5	9.8
Deferred Policy Acquisition Cost, Amortization Expense	(11.3)	(12.5)	(14.7)
Adjustment Related to Unrealized Investment (Gain) Loss	0.0	0.0	0.0
Deferred Policy Acquisition Costs Foreign Currency Translation Adjustment And Other	(1.6)	(1.9)	0.4
Deferred Acquisition Costs at End of Year	27.1	30.4	34.3
Operating Segments | Colonial Life
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	774.4	743.4	692.4
Deferral of Acquisition Costs	252.8	220.8	205.0
Deferred Policy Acquisition Cost, Amortization Expense	(198.7)	(180.2)	(174.2)
Adjustment Related to Unrealized Investment (Gain) Loss	16.5	(9.6)	20.2
Deferred Policy Acquisition Costs Foreign Currency Translation Adjustment And Other	0.0	0.0	0.0
Deferred Acquisition Costs at End of Year	$ 845.0	$ 774.4	$ 743.4