Restrictions on Cash and Due from Banks (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Restrictions on Cash and Due from Banks
Average reserve balance maintained with Federal Reserve Bank	$ 145.8	$ 115.5

Represents the average reserve balance maintained with the Federal Reserve Bank.

No definition available.

Name:	cyn_AverageReservesMaintainedWithFederalReserveBank
Namespace Prefix:	cyn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration