Cover	Dec. 16, 2025
Document Information [Line Items]
Document Type	8-K
Amendment Flag	false
Document Period End Date	Dec. 16, 2025
Current Fiscal Year End Date	--12-31
Entity File Number	001-40773
Entity Registrant Name	Concord Acquisition Corp II
Entity Central Index Key	0001851959
Entity Tax Identification Number	86-2171101
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	477 Madison Avenue
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10022
City Area Code	212
Local Phone Number	883-4330
Written Communications	false
Soliciting Material	false
Pre-commencement Tender Offer	false
Pre-commencement Issuer Tender Offer	false
Entity Emerging Growth Company	true
Elected Not To Use the Extended Transition Period	false
Units Each Consisting Of One Share Of Class Common Stock And Onethird Of One Warrant [Member]
Document Information [Line Items]
Title of 12(b) Security	Units, each consisting of one share of Class A Common Stock and one-third of one Warrant
Trading Symbol	CNDA.U
Class Common Stock Par Value 0. 0001 Per Share [Member]
Document Information [Line Items]
Title of 12(b) Security	Class A Common Stock, par value $0.0001 per share
Trading Symbol	CNDA
Warrants Each Whole Warrant Exercisable For One Share Of Class Common Stock At Exercise Price Of 11. 50 [Member]
Document Information [Line Items]
Title of 12(b) Security	Warrants, each whole warrant exercisable for one share of Class A Common Stock at an exercise price of $11.50
Trading Symbol	CNDA.WS