{"cik":1528115,"taxonomy":"us-gaap","tag":"PreferredStockParOrStatedValuePerShare","label":"Preferred Stock, Par or Stated Value Per Share","description":"Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.","entityName":"ANNEXON, INC.","units":{"USD/shares":[{"end":"2019-12-31","val":0.001,"accn":"0001564590-20-054172","fy":2020,"fp":"Q3","form":"10-Q","filed":"2020-11-16"},{"end":"2019-12-31","val":0.001,"accn":"0001564590-21-015262","fy":2020,"fp":"FY","form":"10-K","filed":"2021-03-25","frame":"CY2019Q4I"},{"end":"2020-09-30","val":0.001,"accn":"0001564590-20-054172","fy":2020,"fp":"Q3","form":"10-Q","filed":"2020-11-16","frame":"CY2020Q3I"},{"end":"2020-12-31","val":0.001,"accn":"0001564590-21-015262","fy":2020,"fp":"FY","form":"10-K","filed":"2021-03-25"},{"end":"2020-12-31","val":0.001,"accn":"0001564590-22-008044","fy":2021,"fp":"FY","form":"10-K","filed":"2022-03-01","frame":"CY2020Q4I"},{"end":"2021-12-31","val":0.001,"accn":"0001564590-22-008044","fy":2021,"fp":"FY","form":"10-K","filed":"2022-03-01","frame":"CY2021Q4I"}]}}