Consolidated Company-Sponsored Investment Funds - Summary of Balance Sheet Amounts (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Condensed Balance Sheet Statements, Captions [Line Items]
Other assets	$ 341,821	$ 330,943
Total assets	9,327,774	8,706,092
Liabilities	5,382,087	4,363,430
Redeemable non-controlling interest	51,081	325,561
Partners' capital attributable to AB Unitholders	3,894,606	4,017,101
Total liabilities, redeemable non-controlling interest and capital	9,327,774	8,706,092
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	33,076	11,433
Investments	234,096	581,004
Other assets	7,897	19,810
Redeemable non-controlling interest	51,081	325,561
Reportable entities | Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	33,076	11,433
Investments	234,096	581,004
Other assets	7,897	19,810
Total assets	275,069	612,247
Liabilities	26,422	31,017
Redeemable non-controlling interest	51,081	325,561
Partners' capital attributable to AB Unitholders	197,566	255,669
Total liabilities, redeemable non-controlling interest and capital	275,069	612,247
Reportable entities | VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	28,657	9,623
Investments	128,941	404,624
Other assets	3,779	9,618
Total assets	161,377	423,865
Liabilities	6,438	12,147
Redeemable non-controlling interest	35,486	273,219
Partners' capital attributable to AB Unitholders	119,453	138,499
Total liabilities, redeemable non-controlling interest and capital	161,377	423,865
Reportable entities | VOEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	4,419	1,810
Investments	105,155	176,380
Other assets	4,118	10,192
Total assets	113,692	188,382
Liabilities	19,984	18,870
Redeemable non-controlling interest	15,595	52,342
Partners' capital attributable to AB Unitholders	78,113	117,170
Total liabilities, redeemable non-controlling interest and capital	$ 113,692	$ 188,382