Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)			1 Months Ended	3 Months Ended								12 Months Ended
		Feb. 12, 2020	Dec. 31, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collateralized Securities Transactions [Abstract]
Cash on deposit with clearing organizations for trade facilitation purposes			$ 204,000,000.0	$ 204,000,000.0				$ 196,900,000				$ 204,000,000.0	$ 196,900,000
SCB LLC held U.S. Treasury Bills			$ 0	$ 0				$ 392,400,000				$ 0	$ 392,400,000
Deferred Sales Commissions, Net [Abstract]
Period of time the deferred sales commissions are amortized over for U.S. fund shares												5 years 6 months
Period of time the deferred sales commissions are amortized over for non-U.S. fund shares												4 years
Mutual Fund Underwriting Activities [Abstract]
Period over which receivables from brokers and dealers for sale of shares of company-sponsored mutual funds generally are realized												3 days
Long-term Incentive Compensation Plans [Abstract]
Employee allocation percentage maximum, percent			50.00%	50.00%								50.00%
Long-term incentive cash maximum per employee			$ 250,000	$ 250,000								$ 250,000
Long-term incentive awards vesting periods												4 years
AB Holding Units purchased in periods (in units)												6,000,000.0	9,300,000
Dollar amount paid for AB Holding Units acquired												$ 172,600,000	$ 268,000,000.0
Open-market purchases of AB Holding Units (in units)												2,900,000	6,500,000
Dollar amount paid for open-market purchases of AB Holding Units												$ 82,700,000	$ 183,200,000
Restricted AB Holding Units awarded to employees (in units)			5,400,000									7,700,000	8,700,000	6,200,000
Units issued upon exercise of options (in units)												511,894	889,119
Proceeds from stock options exercised												$ 11,511,000	$ 16,589,000	$ 20,110,000
Foreign Currency Translations [Abstract]
Net foreign currency transaction gains (losses)												$ (2,000,000.0)	$ (100,000)	$ (2,900,000)
Cash Distribution [Line Items]
Cash distribution, distribution declared (in dollars per unit)	[1],[2]			$ 0.93	$ 0.70	$ 0.63	$ 0.56	$ 0.71	$ 0.76	$ 0.69	$ 0.80
Percentage of General Partnership interest in company												1.00%
Cash distributions per unit paid to the General Partner and Unitholders (in dollars per unit)												$ 2.60	$ 3.16	$ 2.39
Cash Distribution
Cash Distribution [Line Items]
Cash distribution, declaration date												Feb. 12, 2020
Percentage of General Partnership interest in company												1.00%
Cash distribution, distribution date												Mar. 05, 2020
Cash distribution, date of record												Feb. 24, 2020
Employees based outside of the United States
Long-term Incentive Compensation Plans [Abstract]
Employee allocation percentage maximum, percent			100.00%	100.00%								100.00%
Long-term incentive cash maximum per employee			$ 100,000	$ 100,000								$ 100,000
Subsequent Event | Cash Distribution
Cash Distribution [Line Items]
Cash distribution, distribution declared (in dollars per unit)		$ 0.93
Furniture
Furniture, Equipment and Leasehold Improvements [Abstract]
Useful Life												8 years
Equipment | Minimum
Furniture, Equipment and Leasehold Improvements [Abstract]
Useful Life												3 years
Equipment | Maximum
Furniture, Equipment and Leasehold Improvements [Abstract]
Useful Life												6 years

[1] Cash distributions reflect the impact of our non-GAAP adjustments.

[2] Declared and paid during the following quarter.