Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 861,783	$ 781,683	$ 779,498
Other comprehensive income:
Foreign currency translation adjustments, before reclassification and tax:	23,882	5,986	(19,337)
Less: reclassification adjustment for losses included in net income upon liquidation	(216)	0	(100)
Foreign currency translation adjustments, before tax	24,098	5,986	(19,237)
Income tax (expense) benefit	(854)	(383)	620
Foreign currency translation adjustments, net of tax	23,244	5,603	(18,617)
Changes in employee benefit related items:
Amortization of prior service cost	24	24	24
Recognized actuarial (loss) gain	(4,280)	(7,891)	1,586
Changes in employee benefit related items	(4,256)	(7,867)	1,610
Income tax benefit (expense)	(187)	274	(139)
Employee benefit related items, net of tax	(4,443)	(7,593)	1,471
Other	0	0	374
Other comprehensive gain (loss)	18,801	(1,990)	(16,772)
Less: Comprehensive (loss) income in consolidated entities attributable to non-controlling interests	(4,169)	29,788	21,864
Comprehensive income attributable to AB Unitholders	$ 884,753	$ 749,905	$ 740,862