Consolidated Company-Sponsored Investment Funds - Summary of Balance Sheet Amounts (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Condensed Balance Sheet Statements, Captions [Line Items]
Other assets	$ 292,024	$ 330,943
Total assets	9,319,932	8,706,092
Liabilities	5,325,111	4,363,430
Redeemable non-controlling interest	56,990	325,561
Partners' capital attributable to AB Unitholders	3,937,831	4,017,101
Total liabilities, redeemable non-controlling interest and capital	9,319,932	8,706,092
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	29,207	11,433
Investments	228,176	581,004
Other assets	13,726	19,810
Redeemable non-controlling interest	56,990	325,561
Reportable entities | Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	29,207	11,433
Investments	228,176	581,004
Other assets	13,726	19,810
Total assets	271,109	612,247
Liabilities	29,891	31,017
Redeemable non-controlling interest	56,990	325,561
Partners' capital attributable to AB Unitholders	184,228	255,669
Total liabilities, redeemable non-controlling interest and capital	271,109	612,247
Reportable entities | VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	27,379	9,623
Investments	137,727	404,624
Other assets	3,951	9,618
Total assets	169,057	423,865
Liabilities	6,521	12,147
Redeemable non-controlling interest	38,733	273,219
Partners' capital attributable to AB Unitholders	123,803	138,499
Total liabilities, redeemable non-controlling interest and capital	169,057	423,865
Reportable entities | VOEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	1,828	1,810
Investments	90,449	176,380
Other assets	9,775	10,192
Total assets	102,052	188,382
Liabilities	23,370	18,870
Redeemable non-controlling interest	18,257	52,342
Partners' capital attributable to AB Unitholders	60,425	117,170
Total liabilities, redeemable non-controlling interest and capital	$ 102,052	$ 188,382