SIGNIFICANT ACCOUNTING POLICIES - Assumption Updates and Model Changes (Details) - USD ($)	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in Accounting Estimate [Line Items]
Policy charges and fee income	$ 853,000,000	$ 824,000,000	$ 905,000,000	$ 899,000,000	$ 863,000,000	$ 857,000,000	$ 1,729,000,000	$ 1,720,000,000	$ 2,582,000,000	$ 2,619,000,000	$ 3,487,000,000	$ 3,515,000,000	$ 3,289,000,000
Policyholders’ benefits	950,000,000	691,000,000	2,626,000,000	1,642,000,000	861,000,000	853,000,000	3,317,000,000	1,714,000,000	4,267,000,000	3,356,000,000	4,088,000,000	2,960,000,000	3,481,000,000
Interest credited to policyholders’ account balances	277,000,000		289,000,000	296,000,000	291,000,000	272,000,000		563,000,000	845,000,000	859,000,000	1,149,000,000	979,000,000
Net derivative gains (losses)		(5,908,000,000)	9,532,000,000	(343,000,000)	(179,000,000)	(1,558,000,000)	3,624,000,000	(1,737,000,000)	2,097,000,000	(2,080,000,000)	(3,831,000,000)	(1,034,000,000)	854,000,000
Income (loss) from operations, before income taxes	(1,193,000,000)	(5,113,000,000)	7,207,000,000	(439,000,000)	321,000,000	(1,016,000,000)	2,094,000,000	(695,000,000)	901,000,000	(1,134,000,000)	(2,463,000,000)	(1,472,000,000)	1,488,000,000
Net income (loss)	(944,000,000)	$ (4,086,000,000)	5,750,000,000	(264,000,000)	$ 268,000,000	$ (849,000,000)	$ 1,664,000,000	$ (581,000,000)	720,000,000	$ (845,000,000)	$ (1,884,000,000)	$ (902,000,000)	$ 2,791,000,000
Long-term Lapses Partial Withdrawal Rates And Election Assumptions Updates
Change in Accounting Estimate [Line Items]
Policy charges and fee income	(21,000,000)		54,000,000	(11,000,000)
Policyholders’ benefits	175,000,000		1,300,000,000	886,000,000
Interest credited to policyholders’ account balances	(8,000,000)		(6,000,000)	(14,000,000)
Net derivative gains (losses)	106,000,000			(548,000,000)
Amortization of deferred policy acquisition costs, net	26,000,000		840,000,000	(77,000,000)
Income (loss) from operations, before income taxes	(124,000,000)		(2,100,000,000)	(1,400,000,000)
Net income (loss)	(98,000,000)		(1,700,000,000)	$ (1,100,000,000)
Economic Scenario Generator
Change in Accounting Estimate [Line Items]
Income (loss) from operations, before income taxes									165,000,000
Net income (loss)									$ 130,000,000
Credit Risk Adjustment, Fair Value Scenario Calibration
Change in Accounting Estimate [Line Items]
Gain (loss) on assumption updates and model changes, pre tax	$ 421,000,000
5-year Historical Average Over A 10-year Period
Change in Accounting Estimate [Line Items]
Interest rate assumptions			$ 0.0225