Income Taxes - Summary of Income Taxes (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Computation of equity in net income attributable to AB Unitholders [Abstract]
Multiplied by: weighted average equity ownership interest									35.60%	35.40%	35.70%
Equity in net income attributable to AB Unitholders	$ 101,415,000	$ 73,874,000	$ 63,201,000	$ 69,914,000	$ 87,909,000	$ 66,722,000	$ 59,023,000	$ 52,638,000	$ 308,404,000	$ 266,292,000	$ 270,647,000
Computation of income tax [Abstract]
AB qualifying revenues									$ 2,704,137,000	$ 2,640,169,000	$ 2,647,254,000
Multiplied by: weighted average equity ownership interest for calculating tax									30.10%	29.40%	29.90%
Multiplied by: federal tax									3.50%	3.50%	3.50%
Federal income taxes									$ 28,522,000	$ 27,197,000	$ 27,674,000
State income taxes									502,000	532,000	576,000
Total income taxes									$ 29,024,000	$ 27,729,000	28,250,000
Changes in components for calculation of income tax [Abstract]
Increase in net income attributable to AB Unitholders (percent)									15.10%	(0.70%)
Increase in equity in net income attributable to AB Unitholders (percent)									15.80%	(1.60%)
Increase (decrease) in AB qualifying revenue (percent)									2.40%	(0.30%)
Increase (decrease) in income taxes (percent)									4.70%	(1.80%)
Unrecognized tax benefits	$ 0				$ 0				$ 0	$ 0
Variable Interest Entity, Primary Beneficiary
Computation of equity in net income attributable to AB Unitholders [Abstract]
Net income attributable to AB Unitholders									$ 865,952,000	$ 752,042,000	$ 757,588,000