Risks and Uncertainties Narratvie Data (Details) $ in Millions	6 Months Ended
Jun. 30, 2020 USD ($) loans Rate
Risks and Uncertainties [Line Items]
Maximum term for payment deferrals	180 days
Number of loans receiving payment deferrals \| loans	406
Outstanding balance of loans receiving payment deferrals \| $	$ 173.3
PPP loan term	2 years
PPP loan interest rate \| Rate	1.00%

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Number of loans for which payments were deferred for financing receivables modified in accordance with payment deferral guidelines outlined in the CARES Act.

+ References

No definition available.

+ Details

Name:	unb_FinancingReceivableModificationsNumberofPaymentDeferrals
Namespace Prefix:	unb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Outstanding balance of loans for which payments were deferred for financing receivables modified in accordance with payment deferral guidelines outlined in the CARES Act.

+ References

No definition available.

+ Details

Name:	unb_FinancingReceivableModificationsOutstandingBalanceofPaymentDeferrals
Namespace Prefix:	unb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Contractual interest rate on the Paycheck Protection Program loans.

+ References

No definition available.

+ Details

Name:	unb_PaycheckProtectionProgramInterestRate
Namespace Prefix:	unb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual term of Paycheck Protection Program loans.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ConcentrationRiskLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration