Summary of Significant Accounting Policies - Schedule of Repurchase Activity (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Total amount of AB Holding Units Purchased (in units)	5.6	5.4
Total Cash Paid for AB Holding Units Purchased	$ 262.3	$ 149.0
Open-market purchases of AB Holding Units Purchased (in units)	2.6	3.1
Total Cash Paid for Open Market Purchases of AB Holding Units	$ 117.9	$ 74.0