Selected Operating Statement Data by Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information
Premium Income	$ 1,943.6	$ 1,905.8	$ 3,882.1	$ 3,836.7
Net Investment Income	629.1	626.1	1,241.6	1,247.2
Other Income	54.9	56.7	108.7	119.2
Operating Revenue	2,627.6	2,588.6	5,232.4	5,203.1
Operating Income (Loss)	335.2	311.1	656.8	619.5
Unum US
Segment Reporting Information
Premium Income	1,157.7	1,131.5	2,310.2	2,271.2
Net Investment Income	221.2	231.1	447.6	466.8
Other Income	30.3	32.1	61.2	68.8
Operating Revenue	1,409.2	1,394.7	2,819.0	2,806.8
Operating Income (Loss)	218.8	214.0	429.6	422.1
Unum UK
Segment Reporting Information
Premium Income	154.0	137.6	305.7	281.4
Net Investment Income	44.3	45.4	77.9	76.2
Other Income	0.2	(0.1)	0.1	0
Operating Revenue	198.5	182.9	383.7	357.6
Operating Income (Loss)	39.6	33.5	76.1	64.8
Colonial Life
Segment Reporting Information
Premium Income	316.8	307.9	633.2	615.0
Net Investment Income	36.2	34.3	73.1	74.0
Other Income	0.1	0.1	0	0.1
Operating Revenue	353.1	342.3	706.3	689.1
Operating Income (Loss)	75.3	71.1	154.7	146.5
Closed Block
Segment Reporting Information
Premium Income	315.1	328.8	633.0	669.1
Net Investment Income	326.5	316.1	642.8	629.2
Other Income	24.5	23.8	46.1	47.9
Operating Revenue	666.1	668.7	1,321.9	1,346.2
Operating Income (Loss)	37.3	29.6	66.4	56.9
Corporate
Segment Reporting Information
Premium Income	0	0	0	0
Net Investment Income	0.9	(0.8)	0.2	1.0
Other Income	(0.2)	0.8	1.3	2.4
Operating Revenue	0.7	0	1.5	3.4
Operating Income (Loss)	$ (35.8)	$ (37.1)	$ (70.0)	$ (70.8)