Schedule III Supplementary Insurance Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Supplementary Insurance Information, by Segment [Line Items]
Unclaimed Death Benefit Reserve Increase Before Taxes	$ 95.5
Waiver of Premium Benefit Reserve Increase (Decrease) Before Tax	85.0
Deferred Acquisition Costs	1,829.2		1,755.5
Reserves for Future Policy Contract Benefits	43,099.1		44,694.4
Unearned Premiums	413.8		426.7
Policy and Contract Benefits	1,511.0		1,484.6
Premium Income	7,624.7		7,716.1		7,514.2
Net Investment Income	2,492.1	[1]	2,515.2	[1]	2,519.6	[1]
Benefits and Change in Reserves for Future Benefits	6,595.7	[1]	6,722.2		7,209.5	[1]
Amortization of Deferred Acquisition Costs	418.9		378.7		365.7
All Other Expenses	2,134.0	[2]	2,165.0	[2]	2,369.5	[2]
Impairment of Deferred Acquisition Costs	0		0		196.0
Unum U.S.
Supplementary Insurance Information, by Segment [Line Items]
Unclaimed Death Benefit Reserve Increase Before Taxes	75.4		0		0
Deferred Acquisition Costs	1,051.5		1,024.3
Reserves for Future Policy Contract Benefits	11,788.4		12,449.3
Unearned Premiums	47.6		46.1
Policy and Contract Benefits	889.1		890.3
Premium Income	4,517.1		4,456.5		4,296.0
Net Investment Income	929.6	[1]	952.3	[1]	951.4	[1]
Benefits and Change in Reserves for Future Benefits	3,222.4	[1]	3,238.6		3,113.5	[1]
Amortization of Deferred Acquisition Costs	230.0		196.5		188.1
All Other Expenses	1,254.0	[2]	1,251.2	[2]	1,250.5	[2]
Premiums Written	3,068.0	[3]	3,045.0	[3]	2,965.8	[3]
Long-term Care
Supplementary Insurance Information, by Segment [Line Items]
Impairment of Deferred Acquisition Costs	0		0		769.6
Unum U.K.
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	34.3		38.8
Reserves for Future Policy Contract Benefits	2,594.3		2,487.1
Unearned Premiums	139.3		142.9
Policy and Contract Benefits	160.0		155.7
Premium Income	556.6		694.6		687.6
Net Investment Income	148.5	[1]	170.8	[1]	189.9	[1]
Benefits and Change in Reserves for Future Benefits	413.3	[1]	541.4		493.8	[1]
Amortization of Deferred Acquisition Costs	14.7		15.7		15.3
All Other Expenses	145.2	[2]	177.1	[2]	178.0	[2]
Premiums Written	448.1	[3]	466.3	[3]	480.0	[3]
Colonial Life
Supplementary Insurance Information, by Segment [Line Items]
Unclaimed Death Benefit Reserve Increase Before Taxes	20.1		0		0
Deferred Acquisition Costs	743.4		692.4
Reserves for Future Policy Contract Benefits	1,815.6		1,691.3
Unearned Premiums	30.0		29.9
Policy and Contract Benefits	193.7		149.8
Premium Income	1,232.2		1,194.5		1,135.3
Net Investment Income	145.4	[1]	138.6	[1]	132.4	[1]
Benefits and Change in Reserves for Future Benefits	667.0	[1]	627.3		589.4	[1]
Amortization of Deferred Acquisition Costs	174.2		166.5		151.2
All Other Expenses	271.8	[2]	265.3	[2]	257.5	[2]
Premiums Written	1,011.8	[3]	986.3	[3]	944.9	[3]
Closed Block
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	0		0
Reserves for Future Policy Contract Benefits	26,900.8		28,066.7
Unearned Premiums	196.9		207.8
Policy and Contract Benefits	268.2		288.8
Premium Income	1,318.8		1,370.5		1,395.3
Net Investment Income	1,272.3	[1]	1,230.5	[1]	1,189.7	[1]
Benefits and Change in Reserves for Future Benefits	2,293.0	[1]	2,314.9		3,012.8	[1]
Amortization of Deferred Acquisition Costs	0		0		11.1
All Other Expenses	282.6	[2]	290.7	[2]	496.4	[2]
Premiums Written	1,307.0	[3]	1,358.6	[3]	1,385.1	[3]
Impairment of Deferred Acquisition Costs					196.0
Corporate
Supplementary Insurance Information, by Segment [Line Items]
Premium Income	0		0		0
Net Investment Income	(3.7)	[1]	23.0	[1]	56.2	[1]
Benefits and Change in Reserves for Future Benefits	0	[1]	0		0	[1]
Amortization of Deferred Acquisition Costs	0		0		0
All Other Expenses	180.4	[2]	180.7	[2]	187.1	[2]
Premiums Written	0	[3]	0	[3]	0	[3]
Individual Disability - Closed Block
Supplementary Insurance Information, by Segment [Line Items]
Reserve Increase Due to Unlocking	0		0		183.5
Claim Reserve Total [Member] | Long-term Care
Supplementary Insurance Information, by Segment [Line Items]
Reserve Increase Due to Unlocking					248.1
Impairment of Deferred Acquisition Costs			573.6
Group Life | Unum U.S.
Supplementary Insurance Information, by Segment [Line Items]
Unclaimed Death Benefit Reserve Increase Before Taxes	49.1
Waiver of Premium Benefit Reserve Increase (Decrease) Before Tax	$ 85.0		$ 0		$ 0

[1] (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] (3)Includes commissions, interest and debt expense, deferral of acquisition costs, compensation expense, non-operating retirement related loss, and other expenses. Where not directly attributable to a segment, expenses are generally allocated based on activity levels, time information, and usage statistics. Included in 2011 in the Closed Block segment is an impairment charge of $196.0 million related to long-term care deferred policy acquisition costs.

[3] (4)Excludes life insurance.