SIGNIFICANT ACCOUNTING POLICIES - Variable Interest Entities (Details) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2020 USD ($) joint_venture	Dec. 31, 2019 USD ($) joint_venture	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)
Variable Interest Entity [Line Items]
Assets		$ 262,496	$ 249,818	$ 254,018	$ 240,681	$ 220,779
Liabilities		243,549	234,406	$ 234,893	$ 218,889	$ 205,224
Redeemable non-controlling interest	[1],[2]	$ 95	$ 365
Consolidated Variable Interest Entities
Variable Interest Entity [Line Items]
Number of consolidated real estate joint ventures | joint_venture		1	1
Assets		$ 31	$ 32
Non-consolidated Vairable Interest Entities
Variable Interest Entity [Line Items]
Assets		156,700	160,200
Investment assets		1,300	1,200
Variable interest entity, maximum loss exposure		1,300	1,200
Variable interest entity, unfunded commitments		1,200	1,100
Operating income (loss)		$ (4)	$ (5)
Number of nonconsolidated real estate joint ventures | joint_venture		1	1
Special Purpose Entity
Variable Interest Entity [Line Items]
Investment assets		$ 18
AB-Sponsored Investment Funds | Consolidated Variable Interest Entities
Variable Interest Entity [Line Items]
Assets		169	$ 424
Liabilities		7	12
Redeemable non-controlling interest		39	273
AB-Sponsored Investment Funds | VOE Consolidation Model
Variable Interest Entity [Line Items]
Assets		102	188
Liabilities		23	19
Redeemable non-controlling interest		18	52
AB-Sponsored Investment Funds | Non-consolidated Vairable Interest Entities
Variable Interest Entity [Line Items]
Assets		68,900	79,300
Variable interest entity, maximum loss exposure		$ 7	$ 8

[1] See Note 12 for details of Redeemable noncontrolling interest.

[2] See Note 2 for details of balances with variable interest entities.