Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Feb. 24, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K/A
Amendment Flag	true
Amendment Description	TrustCo Bank Corp NY (the “Company”), is filing this Amendment No. 1 (“Amendment No. 1”) to its Annual Report on Form 10-K for the year ended December 31, 2019 (the “Original Filing”) for the sole purpose of filing Exhibit 4.1, which was inadvertently omitted from the Original Filing.
Document Period End Date	Dec. 31, 2019
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity Registrant Name	TRUSTCO BANK CORP N Y
Entity Incorporation, State or Country Code	NY
Entity File Number	000-10592
Entity Tax Identification Number	14-1630287
Entity Address, Address Line One	5 SARNOWSKI DRIVE
Entity Address, City or Town	GLENVILLE
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	12302
City Area Code	518
Local Phone Number	377-3311
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Small Business	false
Entity Public Float			$ 749
Entity Common Stock, Shares Outstanding		96,801,657
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0000357301
Document Annual Report	true
Title of 12(b) Security	Common Stock, $1.00 Par Value
Trading Symbol	TRST
Security Exchange Name	NASDAQ