Schedule III Supplementary Insurance Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs	$ 1,901.3	$ 1,829.2	$ 1,901.3		$ 1,829.2
Reserves for Future Policy Contract Benefits	45,929.4	43,099.1	45,929.4		43,099.1
Unearned Premiums	396.6	413.8	396.6		413.8
Policy and Contract Benefits	1,529.3	1,511.0	1,529.3		1,511.0
Premium Income			7,797.2		7,624.7		7,716.1
Net Investment Income			2,477.4	[1]	2,492.1	[1]	2,515.2	[1]
Benefits and Change in Reserves for Future Benefits			7,310.8	[2]	6,595.7	[2]	6,722.2
Amortization of Deferred Acquisition Costs			440.8		418.9		378.7
All Other Expenses			2,230.9	[3]	2,134.0	[3]	2,165.0	[3]
Reserve Increase for Long-term Care	698.2		698.2
Unclaimed Death Benefit Reserve Increase Before Taxes		95.5			95.5
Waiver of Premium Benefit Reserve Increase (Decrease) Before Tax		(85.0)
Unum U.S.
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs	1,096.5	1,051.5	1,096.5		1,051.5
Reserves for Future Policy Contract Benefits	11,828.0	11,788.4	11,828.0		11,788.4
Unearned Premiums	46.6	47.6	46.6		47.6
Policy and Contract Benefits	953.7	889.1	953.7		889.1
Premium Income			4,659.7		4,517.1		4,456.5
Net Investment Income			890.3	[1]	929.6	[1]	952.3	[1]
Benefits and Change in Reserves for Future Benefits			3,288.1	[2]	3,222.4	[2]	3,238.6
Amortization of Deferred Acquisition Costs			248.1		230.0		196.5
All Other Expenses			1,279.6	[3]	1,254.0	[3]	1,251.2	[3]
Premiums Written			3,144.1	[4]	3,068.0	[4]	3,045.0	[4]
Unclaimed Death Benefit Reserve Increase Before Taxes					75.4
Waiver of Premium Benefit Reserve Increase (Decrease) Before Tax					85.0
Unum U.K.
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs	30.4	34.3	30.4		34.3
Reserves for Future Policy Contract Benefits	2,596.7	2,594.3	2,596.7		2,594.3
Unearned Premiums	130.6	139.3	130.6		139.3
Policy and Contract Benefits	127.6	160.0	127.6		160.0
Premium Income			607.2		556.6		694.6
Net Investment Income			151.0	[1]	148.5	[1]	170.8	[1]
Benefits and Change in Reserves for Future Benefits			431.0	[2]	413.3	[2]	541.4
Amortization of Deferred Acquisition Costs			12.5		14.7		15.7
All Other Expenses			166.9	[3]	145.2	[3]	177.1	[3]
Premiums Written			479.9	[4]	448.1	[4]	466.3	[4]
Colonial Life
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs	774.4	743.4	774.4		743.4
Reserves for Future Policy Contract Benefits	1,919.7	1,815.6	1,919.7		1,815.6
Unearned Premiums	30.8	30.0	30.8		30.0
Policy and Contract Benefits	191.4	193.7	191.4		193.7
Premium Income			1,273.7		1,232.2		1,194.5
Net Investment Income			146.7	[1]	145.4	[1]	138.6	[1]
Benefits and Change in Reserves for Future Benefits			660.6	[2]	667.0	[2]	627.3
Amortization of Deferred Acquisition Costs			180.2		174.2		166.5
All Other Expenses			279.5	[3]	271.8	[3]	265.3	[3]
Premiums Written			1,042.7	[4]	1,011.8	[4]	986.3	[4]
Unclaimed Death Benefit Reserve Increase Before Taxes					20.1
Closed Block
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs	0	0	0		0
Reserves for Future Policy Contract Benefits	29,585.0	26,900.8	29,585.0		26,900.8
Unearned Premiums	188.6	196.9	188.6		196.9
Policy and Contract Benefits	256.6	268.2	256.6		268.2
Premium Income			1,256.6		1,318.8		1,370.5
Net Investment Income			1,284.1	[1]	1,272.3	[1]	1,230.5	[1]
Benefits and Change in Reserves for Future Benefits			2,931.1	[2]	2,293.0	[2]	2,314.9
Amortization of Deferred Acquisition Costs			0		0		0
All Other Expenses			277.0	[3]	282.6	[3]	290.7	[3]
Premiums Written			1,248.6	[4]	1,307.0	[4]	1,358.6	[4]
Reserve Increase for Long-term Care			698.2
Corporate and Other Segment
Supplementary Insurance Information, by Segment
Premium Income			0		0		0
Net Investment Income			5.3	[1]	(3.7)	[1]	23.0	[1]
Benefits and Change in Reserves for Future Benefits			0	[2]	0	[2]	0
Amortization of Deferred Acquisition Costs			0		0		0
All Other Expenses			227.9	[3]	180.4	[3]	180.7	[3]
Premiums Written			0	[4]	0	[4]	0	[4]
Non-operating retirement related loss due to settlement			$ 64.4

[1] Net investment income is allocated based upon segmentation. Each segment has its own specifically identified assets and receives the investment income generated by those assets.

[2] Included in 2014 is a reserve charge of $698.2 million in the Closed Block segment related to our long-term care business. Included in 2013 are unclaimed death benefits reserve increases of $75.4 million in the Unum US segment and $20.1 million in the Colonial Life segment and a group life waiver of premium benefit reserve reduction of $85.0 million in the Unum US segment.

[3] Includes commissions; interest and debt expense; deferral of acquisition costs; compensation expense; non-operating retirement related loss, which in 2014 included a settlement loss of $64.4 million in the Corporate segment related to a pension plan amendment; and other expenses. Where not directly attributable to a segment, expenses are generally allocated based on activity levels, time information, and usage statistics.

[4] Excludes life insurance.