Statutory Financial Information - Additional Details (Detail) In Millions, unless otherwise specified	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2011 United States Traditional Insurance Subsidiaries [Member] USD ($)	Dec. 31, 2011 Unum U.K. GBP (£)
Statutory Accounting Practices [Line Items]
Number of States that Adopted Accounting Principles materially different from NAIC	0
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments			$ 634.4	£ 187.0
Cash and Securities Segregated under Federal and Other Regulations	$ 294.3	$ 293.6