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Summary of Significant Accounting Policies (Details 3) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Accounting Standards Update 2014-01 | Forecast member  
Accounting Pronouncements  
Decrease in net income available to common shareholders $ 4us-gaap_NewAccountingPronouncementOrChangeInAccountingPrincipleEffectOfChangeOnNetIncome
/ us-gaap_AdjustmentsForNewAccountingPronouncementsAxis
= cyn_AccountingStandardsUpdate201401Member
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
Core deposit intangibles | Minimum  
Goodwill and Intangibles  
Amortization period 4 years
Core deposit intangibles | Maximum  
Goodwill and Intangibles  
Amortization period 8 years
Client advisory contract | Minimum  
Goodwill and Intangibles  
Amortization period 4 years
Client advisory contract | Maximum  
Goodwill and Intangibles  
Amortization period 20 years