Schedule III Supplementary Insurance Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	$ 2,300.9		$ 2,521.1
Reserves for Future Policy Contract Benefits	43,051.9		39,715.0
Unearned Premiums	433.2		436.7
Policy and Contract Benefits	1,494.0		1,565.0
Premium Income	7,514.2		7,431.4		7,475.5
Net Investment Income	2,519.6	[1]	2,495.5	[1]	2,346.6	[1]
Benefits and Change in Reserves for Future Benefits	7,209.5		6,354.1		6,291.6
Amortization of Deferred Acquisition Costs	533.8		547.1		526.2
All Other Expenses	2,277.5	[2]	1,960.7	[2]	1,980.9	[2]
Unum U.S.
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	1,392.3		1,362.2
Reserves for Future Policy Contract Benefits	12,280.2		11,799.2
Unearned Premiums	43.4		39.6
Policy and Contract Benefits	889.2		910.8
Premium Income	4,296.0		4,255.4		4,278.4
Net Investment Income	951.4	[1]	941.5	[1]	934.3	[1]
Benefits and Change in Reserves for Future Benefits	3,113.5		3,124.4		3,192.1
Amortization of Deferred Acquisition Costs	298.7		307.9		293.8
All Other Expenses	1,137.0	[2]	1,118.3	[2]	1,128.0	[2]
Premiums Written	2,965.8	[3]	2,938.9	[3]	2,997.0	[3]
Unum U.K.
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	59.4		58.2
Reserves for Future Policy Contract Benefits	2,172.5		2,053.9
Unearned Premiums	143.2		141.2
Policy and Contract Benefits	135.6		141.6
Premium Income	687.6		650.6		686.1
Net Investment Income	189.9	[1]	170.5	[1]	124.5	[1]
Benefits and Change in Reserves for Future Benefits	493.8		435.8		373.6
Amortization of Deferred Acquisition Costs	29.2		27.0		30.5
All Other Expenses	162.8	[2]	150.7	[2]	159.3	[2]
Premiums Written	480.0	[3]	469.4	[3]	508.6	[3]
Colonial Life
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	849.2		805.0
Reserves for Future Policy Contract Benefits	1,598.1		1,507.2
Unearned Premiums	28.5		26.8
Policy and Contract Benefits	134.7		118.4
Premium Income	1,135.3		1,075.7		1,015.1
Net Investment Income	132.4	[1]	122.5	[1]	114.3	[1]
Benefits and Change in Reserves for Future Benefits	589.4		534.7		480.6
Amortization of Deferred Acquisition Costs	189.0		187.2		178.5
All Other Expenses	207.7	[2]	194.8	[2]	189.9	[2]
Premiums Written	944.9	[3]	901.9	[3]	851.5	[3]
Closed Block
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	0		295.7
Reserves for Future Policy Contract Benefits	27,001.1		24,354.7
Unearned Premiums	218.1		229.1
Policy and Contract Benefits	334.5		394.2
Premium Income	1,395.3		1,449.7		1,495.9
Net Investment Income	1,189.7	[1]	1,166.4	[1]	1,106.8	[1]
Benefits and Change in Reserves for Future Benefits	3,012.8	[4]	2,259.2		2,245.3
Amortization of Deferred Acquisition Costs	16.9		25.0		23.4
All Other Expenses	582.9	[2]	327.9	[2]	340.7	[2]
Premiums Written	1,385.1	[3]	1,430.4	[3]	1,484.0	[3]
Corporate
Supplementary Insurance Information, by Segment [Line Items]
Premium Income	0		0		0
Net Investment Income	56.2	[1]	94.6	[1]	66.7	[1]
Benefits and Change in Reserves for Future Benefits	0		0		0
Amortization of Deferred Acquisition Costs	0		0		0
All Other Expenses	187.1	[2]	169.0	[2]	163.0	[2]
Premiums Written	$ 0	[3]	$ 0	[3]	$ 0	[3]

[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] Includes commissions, interest and debt expense, deferral of acquisition costs, compensation expense, and other expenses. Also included in 2011 in the Closed Block segment is an impairment charge of $289.8 million related to long-term care deferred policy acquisition costs. Where not directly attributable to a segment, expenses are generally allocated based on activity levels, time information, and usage statistics.

[3] Excludes life insurance.

[4] Included in 2011 in the Closed Block segment is a reserve charge of $573.6 million related to our long-term care business and a reserve charge of $183.5 million related to our individual disability business.