Time Deposits - Additional Information (Details - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Time Deposits
Time Deposits 250000 Or More	$ 3,777,000	$ 5,333,000
Certificates of deposit had been obtained through the National CD Rateline program	$ 6,800,000

The aggregate interest expense incurred on time deposits, including certificates of deposits, in domestic offices obtained through the National CD Rateline program.

No definition available.

Name:	cnnb_InterestExpenseTimeDepositsThroughNationalCdRatelineProgram
Namespace Prefix:	cnnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration