Long-term Incentive Compensation Plans - Summary of Share-based Compensation, Employee Stock Purchase Plan, Activity (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Share-Based Payment Arrangement [Abstract]
Total amount of AB Holding Units Purchased/Retained (in shares)	0.6	0.4	0.8	1.2
Total Cash Paid for AB Holding Units Purchased/Retained	$ 19.9	$ 13.2	$ 28.7	$ 43.7
Open Market Purchases of AB Holding Units Purchased (in shares)	0.5	0.3	0.6	1.0
Total Cash Paid for Open Market Purchases of AB Holding Units	$ 16.9	$ 12.3	$ 21.6	$ 38.4