Liability for Unpaid Claims - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Unclaimed Death Benefit Reserve Increase (Decrease) Before Taxes	$ 95.5
Waiver of Premium Benefit Reserve Increase (Decrease) Before Tax	85.0
Impairment of Intangible Assets, Finite-lived	0	0	196.0
Unum U.S.
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Unclaimed Death Benefit Reserve Increase (Decrease) Before Taxes	75.4	0	0
Unum U.S. | Group Life
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Unclaimed Death Benefit Reserve Increase (Decrease) Before Taxes	49.1
Waiver of Premium Benefit Reserve Increase (Decrease) Before Tax	85.0	0	0
Unum U.S. | VoluntaryLife [Domain]
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Unclaimed Death Benefit Reserve Increase (Decrease) Before Taxes	26.3
Colonial Life
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Unclaimed Death Benefit Reserve Increase (Decrease) Before Taxes	20.1	0	0
Colonial Life | Colonial_Voluntary_Life [Domain]
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Unclaimed Death Benefit Reserve Increase (Decrease) Before Taxes	20.1
Closed Block
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Impairment of Intangible Assets, Finite-lived			196.0
Long-term Care
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Impairment of Intangible Assets, Finite-lived	0	0	769.6
Individual Disability - Closed Block
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Reserve Increase Due to Unlocking	0	0	183.5
Claim Reserve Prior Year [Member] | Unum U.S. | Group Life
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Waiver of Premium Benefit Reserve Increase (Decrease) Before Tax	78.0
Claim Reserve Prior Year [Member] | Long-term Care
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Reserve Increase Due to Unlocking		215.0
Claim Reserve Prior Year [Member] | Individual Disability - Closed Block
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Reserve Increase Due to Unlocking		176.0
Claim Reserve Total [Member] | Long-term Care
Liability for Unpaid Claims and CAE Narrative Information [Line Items]
Impairment of Intangible Assets, Finite-lived		573.6
Reserve Increase Due to Unlocking			$ 248.1