Risks and Uncertainties Narratvie Data (Details)	3 Months Ended
Mar. 31, 2020 Rate
Risks and Uncertainties [Line Items]
Maximum term for payment deferrals	180 days
PPP loan term	2 years
PPP loan interest rate	1.00%

Maximum number of days for which payments will be deferred for financing receivables modified in accordance with payment deferral guidelines outlined in the CARES Act.

No definition available.

Name:	unb_FinancingReceivableModificationsMaximumTermPaymentDeferral
Namespace Prefix:	unb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration