Earnings per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic EPS:
Net income attributable to City National Corporation	$ 71,808	$ 69,891	$ 201,873	$ 189,182
Less: Dividends on preferred stock	4,093	4,093	12,281	12,281
Net income available to common shareholders	67,715	65,798	189,592	176,901
Less: Earnings allocated to participating securities	576	644	1,664	1,801
Earnings allocated to common shareholders	$ 67,139	$ 65,154	$ 187,928	$ 175,100
Weighted-average common shares outstanding	55,829	55,031	55,668	54,893
Basic earnings per common share (in dollars per share)	$ 1.20	$ 1.18	$ 3.38	$ 3.19
Diluted EPS:
Earnings allocated to common shareholders	$ 67,143	$ 65,160	$ 187,943	$ 175,116
Weighted-average common shares outstanding	55,829	55,031	55,668	54,893
Dilutive effect of equity awards (in shares)	858	734	884	723
Weighted-average diluted common shares outstanding	56,687	55,765	56,552	55,616
Diluted earnings per common share (in dollars per share)	$ 1.18	$ 1.17	$ 3.32	$ 3.15
Stock options
Antidilutive securities not included in calculation of diluted EPS:
Antidilutive securities not included in calculation of diluted EPS (in shares)	400	700	400	700