Statutory Financial Information - Additional Details (Detail) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2012 United States Traditional Insurance Subsidiaries [Member] USD ($)	Dec. 31, 2012 Unum U.K. GBP (£)
Statutory Accounting Practices [Line Items]
Number of States that Adopted Accounting Principles materially different from NAIC	0
Statutory Accounting Practices, Future Dividend Payments Restrictions	P12M
Dividend Payment Restrictions Schedule, Description	.1
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments			$ 623.7	£ 144.7
Cash and Securities Segregated under Federal and Other Regulations	$ 277.5	$ 294.3