Consolidated Company-Sponsored Investment Funds - Summary of Balance Sheet Amounts (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Condensed Balance Sheet Statements, Captions [Line Items]
Other assets	$ 338,115	$ 264,418
Total assets	9,236,134	9,697,840
Liabilities	5,176,111	5,483,958
Redeemable non-controlling interest	17,803	102,359
Partners' capital attributable to AB Unitholders	4,042,220	4,111,523	$ 3,894,606
Total liabilities, redeemable non-controlling interest and capital	9,236,134	9,697,840
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	30,456	36,506
Investments	166,940	302,582
Other assets	8,288	12,244
Total assets	205,684	351,332
Liabilities	11,317	30,620
Redeemable non-controlling interest	17,803	102,359
Partners' capital attributable to AB Unitholders	176,564	218,353
Total liabilities, redeemable non-controlling interest and capital	205,684	351,332
VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	30,456	36,370
Investments	166,940	242,541
Other assets	8,288	4,859
Total assets	205,684	283,770
Liabilities	11,317	7,741
Redeemable non-controlling interest	17,803	82,753
Partners' capital attributable to AB Unitholders	176,564	193,276
Total liabilities, redeemable non-controlling interest and capital	205,684	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