Long-term Incentive Compensation Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)				5,922,324
Weighted average grant date fair value (in dollars per share)				$ 35.29
Grant date fair value of vested shares				$ 244.4	$ 235.8	$ 246.2
Number of unvested restricted AB Holding Units (in shares)	12,419,251	13,447,555		12,419,251	13,447,555
Number of restricted AB Units without a service requirement (in shares)	9,189,286			9,189,286
Number of restricted AB Units with a service requirement (in shares)	3,229,965			3,229,965
Director | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive compensation charge				$ 1.0	$ 1.0	$ 1.2
Granted (in shares)				29,952	30,102	30,870
Weighted average grant date fair value (in dollars per share)				$ 34.06	$ 33.89	$ 38.55
Minimum | Director | 2017 Grant 1 | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive awards vesting periods				3 years
Incentive Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation arrangement with individual, fair value of shares issued				$ 184.3	$ 170.2	$ 164.3
Long-term incentive compensation charge				$ 208.0	$ 183.0	$ 160.1
Period of recognition (in years)				5 years 4 months 20 days
Unrecognized compensation cost	$ 93.5			$ 93.5
Incentive Compensation Plan | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	4,400,000	5,000,000.0	3,800,000	4,700,000	5,200,000	4,200,000
Additional AB restricted units granted (in shares)					300,000	200,000	400,000
Incentive Compensation Plan | Minimum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)					$ 30.56	$ 30.56	$ 38.84
Incentive Compensation Plan | Maximum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)					$ 36.19	$ 38.84	$ 50.94
2017 Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of awards authorized for issuance (in shares)				60,000,000
Number of newly-issued units (in shares)				30,000,000
Granted AB holding unit net of forfeitures (in shares)	35,854,070	32,738,157		35,854,070	32,738,157
AB Holding units available for future grant (in shares)	24,145,930	27,261,843		24,145,930	27,261,843
Long Term Incentive Plan | Employee | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive awards vesting periods				3 years
Long Term Incentive Plan | Employee | Restricted Stock Units (RSUs) | 33.3% of Options and 25% of Restricted AB Holding Units, Second Anniversary Vesting Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage for the term of award				33.30%
Long Term Incentive Plan | Employee | Restricted Stock Units (RSUs) | 33.3% of Options and 25% of Restricted AB Holding Units, First Anniversary Vesting Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage for the term of award				33.30%
Long Term Incentive Plan | Employee | Restricted Stock Units (RSUs) | 33.3% of Options and 25% of Restricted AB Holding Units, Third Anniversary Vesting Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage for the term of award				33.30%
Employment and Separation Agreements | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive compensation charge				$ 17.6	$ 30.1	$ 35.0
Granted (in shares)				1,200,000	500,000	500,000
Employment and Separation Agreements | Minimum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive awards vesting periods				2 years
Weighted average grant date fair value (in dollars per share)				$ 28.46	$ 27.86	$ 34.86
Employment and Separation Agreements | Maximum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive awards vesting periods				10 years
Weighted average grant date fair value (in dollars per share)				$ 37.26	$ 38.58	$ 49.90