Consolidated Company-Sponsored Investment Funds - Summary of Balance Sheet Amounts (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Condensed Balance Sheet Statements, Captions [Line Items]
Total assets	$ 9,617,114	$ 9,697,840
Liabilities	5,507,910	5,483,958
Redeemable non-controlling interest	117,804	102,359
Partners' capital attributable to AB Unitholders	3,991,400	4,111,523	$ 3,937,831
Total liabilities, redeemable non-controlling interest and capital	9,617,114	9,697,840
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	32,904	36,506
Investments	276,199	302,582
Other assets	12,797	12,244
Total assets	321,900	351,332
Liabilities	32,594	30,620
Redeemable non-controlling interest	117,804	102,359
Partners' capital attributable to AB Unitholders	171,502	218,353
Total liabilities, redeemable non-controlling interest and capital	321,900	351,332
VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	32,904	36,370
Investments	276,199	242,541
Other assets	12,797	4,859
Total assets	321,900	283,770
Liabilities	32,594	7,741
Redeemable non-controlling interest	117,804	82,753
Partners' capital attributable to AB Unitholders	171,502	193,276
Total liabilities, redeemable non-controlling interest and capital	321,900	283,770
VOEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	0	136
Investments	0	60,041
Other assets	0	7,385
Total assets	0	67,562
Liabilities	0	22,879
Redeemable non-controlling interest	0	19,606
Partners' capital attributable to AB Unitholders	0	25,077
Total liabilities, redeemable non-controlling interest and capital	$ 0	$ 67,562