Deposits Narrative Data (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deposits [Abstract]
Time Deposits, $250,000 or More	$ 8.7	$ 54.8

The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more representing the amount that meets or exceed the FDIC insurance limit.

No definition available.

Name:	unb_TimeDeposits250000orMore
Namespace Prefix:	unb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant