Investment Objectives and Goals - AMG GW&K Muni Income ETF	Dec. 31, 2025
Prospectus [Line Items]
Risk/Return [Heading]	AMG GW&K Muni Income ETF
Objective [Heading]	Investment Objective
Objective, Primary [Text Block]	The investment objective of AMG GW&K Muni Income ETF (the “Fund”) is to seek current income exempt from federal income tax, consistent with preservation of capital.
Objective, Secondary [Text Block]	Capital appreciation is a secondary objective.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-Section 2
-Subsection a

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-Section 2
-Subsection a

Name:	oef_ObjectivePrimaryTextBlock
Namespace Prefix:	oef_
Data Type:	dtr-types:textBlockItemType
Balance Type:	na
Period Type:	duration

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-Section 2
-Subsection a

Name:	oef_ObjectiveSecondaryTextBlock
Namespace Prefix:	oef_
Data Type:	dtr-types:textBlockItemType
Balance Type:	na
Period Type:	duration

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-Section 1
-Subsection a

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Section 2
-Name Form N-1A
-Subsection a

Name:	dei_LegalEntityAxis=afii_S000095116Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: