Consolidated Company-Sponsored Investment Funds (Summary of Balance Sheet Amounts) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Condensed Balance Sheet Statements, Captions [Line Items]
Other assets	$ 446,460	$ 330,943
Total assets	10,443,237	8,706,092
Liabilities	6,292,486	4,363,430
Redeemable non-controlling interest	224,900	325,561
Partners' capital attributable to AB Unitholders	3,925,851	4,017,101
Total liabilities, redeemable non-controlling interest and capital	10,443,237	8,706,092
Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	87,277	11,433
Investments	443,472	581,004
Other assets	39,538	19,810
Redeemable non-controlling interest	224,900	325,561
Reportable entities | Company-sponsored investment funds
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	87,277	11,433
Investments	443,472	581,004
Other assets	39,538	19,810
Total assets	570,287	612,247
Liabilities	104,875	31,017
Redeemable non-controlling interest	224,900	325,561
Partners' capital attributable to AB Unitholders	240,512	255,669
Total liabilities, redeemable non-controlling interest and capital	570,287	612,247
Reportable entities | VIEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	83,067	9,623
Investments	273,445	404,624
Other assets	20,444	9,618
Total assets	376,956	423,865
Liabilities	73,325	12,147
Redeemable non-controlling interest	179,090	273,219
Partners' capital attributable to AB Unitholders	124,541	138,499
Total liabilities, redeemable non-controlling interest and capital	376,956	423,865
Reportable entities | VOEs
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	4,210	1,810
Investments	170,027	176,380
Other assets	19,094	10,192
Total assets	193,331	188,382
Liabilities	31,550	18,870
Redeemable non-controlling interest	45,810	52,342
Partners' capital attributable to AB Unitholders	115,971	117,170
Total liabilities, redeemable non-controlling interest and capital	$ 193,331	$ 188,382