Amount of cash subject to withdrawal restrictions, restricted deposits held as compensating balances, and cash and securities segregated in compliance with regulations (such as cash deposited in a special reserve account for the exclusive benefit of customers).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Amount of dividends available for payment after computation of statutory restrictions on capital surplus.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

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Statutory Financial Information - Additional Details (Detail) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2014 GBP (£)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 GBP (£)	Dec. 31, 2014 GBP (£)
Fairwind Insurance Company
Statutory Accounting Practices
Statutory Accounting Practices, Permitted Practice, Amount	$ 208.0	$ 200.0
Unum Limited
Statutory Accounting Practices
Statutory Net Income \| £			£ 50.7
Statutory Combined Capital and Surplus \| £						£ 445.9
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments \| £					£ 147.8
United States Traditional Insurance Subsidiaries
Statutory Accounting Practices
Statutory Net Income	653.7	623.1		$ 584.5
Statutory Combined Capital and Surplus	3,470.3	3,462.8
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments	663.6
Cash and Securities Segregated under Federal and Other Regulations	$ 284.1	$ 279.1