Segment Results (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) item	Sep. 30, 2014 USD ($)
Segment Results
Number of reportable segments | item			3
Earnings Summary:
Net interest income	$ 232,257	$ 215,776	$ 685,347	$ 634,676
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	(6,000)	(8,000)	4,000	(9,000)
(Reversal of) provision for losses on acquired impaired loans	1,148	589	2,736	3,783
Noninterest income	104,871	107,917	328,850	310,264
Depreciation and amortization	10,719	9,702	37,812	28,356
Noninterest expense	227,324	213,212	666,333	626,992
Income before income taxes	103,937	108,190	303,316	294,809
Provision for income taxes	32,208	37,452	100,489	103,571
Net income	71,729	70,738	202,827	191,238
Less: Net (loss) income attributable to noncontrolling interest	(79)	847	954	2,056
Net income attributable to City National Corporation	71,808	69,891	201,873	189,182
Selected Average Balances:
Loans and leases, excluding acquired impaired loans	21,969,592	18,837,760	21,224,326	18,050,616
Acquired impaired loans	420,308	580,200	455,786	639,592
Total assets	34,451,160	30,896,357	33,205,126	30,097,514
Deposits	30,106,057	26,830,633	28,854,337	26,043,449
Goodwill	637,918	642,255	636,660	642,498
Customer-relationship intangibles, net	31,714	37,024	32,918	38,505
Other segment
Earnings Summary:
Net interest income	5,494	10,521	21,114	30,541
Noninterest income	(16,931)	(12,278)	(45,412)	(26,652)
Depreciation and amortization	6,398	5,119	24,502	14,665
Noninterest expense	(20,915)	(19,869)	(68,315)	(56,308)
Income before income taxes	3,080	12,993	19,515	45,532
Provision for income taxes	954	4,533	6,486	16,109
Net income	2,126	8,460	13,029	29,423
Net income attributable to City National Corporation	2,126	8,460	13,029	29,423
Selected Average Balances:
Loans and leases, excluding acquired impaired loans	56,038	60,002	57,460	57,583
Total assets	11,330,543	10,675,661	10,761,541	10,586,949
Deposits	54,447	277,930	104,932	254,929
Commercial and Private Banking
Earnings Summary:
Net interest income	226,171	204,803	662,184	602,879
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	(6,000)	(8,000)	4,000	(9,000)
(Reversal of) provision for losses on acquired impaired loans	1,148	589	2,736	3,783
Noninterest income	51,675	50,906	158,718	135,498
Depreciation and amortization	2,482	2,786	7,688	8,381
Noninterest expense	188,367	175,844	563,775	517,022
Income before income taxes	91,849	84,490	242,703	218,191
Provision for income taxes	28,440	29,478	80,661	77,192
Net income	63,409	55,012	162,042	140,999
Net income attributable to City National Corporation	63,409	55,012	162,042	140,999
Selected Average Balances:
Loans and leases, excluding acquired impaired loans	21,913,554	18,777,758	21,166,866	17,993,033
Acquired impaired loans	420,308	580,200	455,786	639,592
Total assets	22,390,469	19,482,692	21,704,604	18,814,041
Deposits	29,953,606	26,481,108	28,654,702	25,710,863
Goodwill	393,176	393,176	393,176	393,176
Customer-relationship intangibles, net	1,315	2,335	1,460	2,717
Wealth Management
Earnings Summary:
Net interest income	592	452	2,049	1,256
Noninterest income	70,127	69,289	215,544	201,418
Depreciation and amortization	1,839	1,797	5,622	5,310
Noninterest expense	59,872	57,237	170,873	166,278
Income before income taxes	9,008	10,707	41,098	31,086
Provision for income taxes	2,814	3,441	13,342	10,270
Net income	6,194	7,266	27,756	20,816
Less: Net (loss) income attributable to noncontrolling interest	(79)	847	954	2,056
Net income attributable to City National Corporation	6,273	6,419	26,802	18,760
Selected Average Balances:
Total assets	730,148	738,004	738,981	696,524
Deposits	98,004	71,595	94,703	77,657
Goodwill	244,742	249,079	243,484	249,322
Customer-relationship intangibles, net	$ 30,399	$ 34,689	$ 31,458	$ 35,788