Segment Results (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) item	Jun. 30, 2014 USD ($)
Segment Results
Number of reportable segments | item			3
Earnings Summary:
Net interest income	$ 236,510	$ 219,102	$ 453,090	$ 418,900
(Reversal of) provision for credit losses on loans and leases, excluding covered loans	10,000	(1,000)	10,000	(1,000)
(Reversal of) provision for losses on covered loans	1,091	(1,461)	1,588	3,194
Noninterest income	112,904	101,099	223,979	202,347
Depreciation and amortization	10,734	9,339	27,093	18,654
Noninterest expense	220,926	212,243	439,009	413,780
Income before income taxes	106,663	101,080	199,379	186,619
Provision for income taxes	37,684	35,109	68,281	66,119
Net income	68,979	65,971	131,098	120,500
Less: Net income attributable to noncontrolling interest	480	510	1,033	1,209
Net income attributable to City National Corporation	68,499	65,461	130,065	119,291
Selected Average Balances:
Loans and leases, excluding covered loans	21,281,468	17,959,191	20,845,516	17,650,520
Covered loans	455,406	643,690	473,819	669,781
Total assets	32,880,515	29,965,898	32,571,783	29,691,472
Deposits	28,623,323	25,912,081	28,218,104	25,643,332
Goodwill	636,172	642,622	636,021	642,622
Customer-relationship intangibles, net	32,883	38,470	33,530	39,258
Other segment
Earnings Summary:
Net interest income	8,071	10,288	15,620	20,020
Noninterest income	(12,971)	(6,141)	(28,482)	(14,374)
Depreciation and amortization	6,321	4,799	18,104	9,546
Noninterest expense	(21,078)	(18,917)	(47,480)	(36,439)
Income before income taxes	9,857	18,265	16,514	32,539
Provision for income taxes	3,498	6,376	5,685	11,604
Net income	6,359	11,889	10,829	20,935
Net income attributable to City National Corporation	6,359	11,889	10,829	20,935
Selected Average Balances:
Loans and leases, excluding covered loans	59,732	57,683	58,183	56,353
Total assets	10,391,313	10,566,732	10,472,326	10,541,858
Deposits	90,959	254,272	130,593	243,238
Commercial and Private Banking
Earnings Summary:
Net interest income	227,792	208,340	436,013	398,078
(Reversal of) provision for credit losses on loans and leases, excluding covered loans	10,000	(1,000)	10,000	(1,000)
(Reversal of) provision for losses on covered loans	1,091	(1,461)	1,588	3,194
Noninterest income	55,546	38,511	107,043	84,592
Depreciation and amortization	2,492	2,774	5,206	5,595
Noninterest expense	185,756	174,324	375,486	341,180
Income before income taxes	83,999	72,214	150,776	133,701
Provision for income taxes	29,811	25,210	51,905	47,679
Net income	54,188	47,004	98,871	86,022
Net income attributable to City National Corporation	54,188	47,004	98,871	86,022
Selected Average Balances:
Loans and leases, excluding covered loans	21,221,481	17,901,508	20,787,046	17,594,167
Covered loans	455,406	643,690	473,819	669,781
Total assets	21,747,378	18,705,693	21,355,970	18,473,951
Deposits	28,434,220	25,584,025	27,994,486	25,319,356
Goodwill	393,177	393,177	393,177	393,177
Customer-relationship intangibles, net	1,419	2,692	1,534	2,912
Wealth Management
Earnings Summary:
Net interest income	647	474	1,457	802
Noninterest income	70,329	68,729	145,418	132,129
Depreciation and amortization	1,921	1,766	3,783	3,513
Noninterest expense	56,248	56,836	111,003	109,039
Income before income taxes	12,807	10,601	32,089	20,379
Provision for income taxes	4,375	3,523	10,691	6,836
Net income	8,432	7,078	21,398	13,543
Less: Net income attributable to noncontrolling interest	480	510	1,033	1,209
Net income attributable to City National Corporation	7,952	6,568	20,365	12,334
Selected Average Balances:
Loans and leases, excluding covered loans	255		287
Total assets	741,824	693,473	743,487	675,663
Deposits	98,144	73,784	93,025	80,738
Goodwill	242,995	249,445	242,844	249,445
Customer-relationship intangibles, net	$ 31,464	$ 35,778	$ 31,996	$ 36,346