Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2011 Entity Claim Segment Office Statement Y
Summary of Significant Accounting Policies
Number of offices for delivery of banking, trust and investment services		78
Number of investment advisory affiliates (in entities)		5
Number of unconsolidated subsidiaries		1
Amount recognized as troubled debt restructurings	$ 26.1
Number of separate but consecutive statements		2
Percentage of likelihood of fair value of a reporting unit being less than its carrying value in order to perform two-step		50.00%

- Definition

The amount of loans that were modified in trouble debt restructurings due to the adoption of new troubled debt restructuring accounting guidance.

+ Details

Name:	cyn_LoansModifiedInTroubleDebtRestucturingsDueToGuidanceAdoption
Namespace Prefix:	cyn
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the number of consolidated investment advisory affiliates.

+ Details

Name:	cyn_NumberOfConsolidatedInvestmentAdvisoryAffiliates
Namespace Prefix:	cyn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of offices in different locations through which the entity carries out its operations.

+ Details

Name:	cyn_NumberOfOffices
Namespace Prefix:	cyn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of subsidiaries which are not consolidated with the parent entity.

+ Details

Name:	cyn_NumberOfUnconsolidatedSubsidiaries
Namespace Prefix:	cyn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of separate consecutive statements.

+ Details

Name:	cyn_SeparateConsecutiveStatementsNumber
Namespace Prefix:	cyn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of likelihood of fair value of a reporting unit being less than its carrying value in order to perform two-step goodwill impairment test.

+ Details

Name:	cyn_TwoStepGoodwillImpairmentTestFairValueLessThanCarryingValueMinimumLikelihood
Namespace Prefix:	cyn
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration