Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 781,683	$ 779,498	$ 720,800
Other comprehensive (loss) income:
Foreign currency translation adjustments, before reclassification and tax:	5,986	(19,337)	28,123
Less: reclassification adjustment for losses included in net income upon liquidation	0	(100)	0
Foreign currency translation adjustments, before tax	5,986	(19,237)	28,123
Income tax expense	(383)	620	0
Foreign currency translation adjustments, net of tax	5,603	(18,617)	28,123
Unrealized gains on investments:
Unrealized gains arising during period	0	0	6
Income tax benefit	0	0	3
Unrealized gains on investments, net of tax	0	0	9
Changes in employee benefit related items:
Amortization of prior service cost	24	24	24
Recognized actuarial (loss) gain	(7,891)	1,586	(3,190)
Changes in employee benefit related items	(7,867)	1,610	(3,166)
Income tax benefit (expense)	274	(139)	(27)
Employee benefit related items, net of tax	(7,593)	1,471	(3,193)
Other	0	374	0
Other comprehensive (loss) gain	(1,990)	(16,772)	24,939
Less: Comprehensive income in consolidated entities attributable to non-controlling interests	29,788	21,864	59,379
Comprehensive income attributable to AB Unitholders	$ 749,905	$ 740,862	$ 686,360