Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 29, 2022	Jun. 30, 2021
Entity Information [Line Items]
Document Type	10-K/A
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Registrant Name	QUANERGY SYSTEMS, INC.
Entity Central Index Key	0001794621
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Small Business	true
Entity File Number	001-39222
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	88-0535845
Entity Address, Address Line One	433 Lakeside Drive
Entity Address, City or Town	Sunnyvale
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94085
City Area Code	408
Local Phone Number	245-9500
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	QNGY
Security Exchange Name	NYSE
Entity Public Float			$ 273,516,000
Entity Common Stock, Shares Outstanding		86,504,955
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	true
Auditor Firm ID	100
Auditor Location	New York, New York
Auditor Name	WithumSmith+Brown, PC
Warrant
Entity Information [Line Items]
Title of 12(b) Security	Warrants, each whole warrant exercisable for one share of Common Stock at an exercise price of $11.50 per share
Trading Symbol	QNGY WS
Security Exchange Name	NYSE