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	$ 914,000,000	$ 877,000,000	$ 996,000,000	$ 980,000,000	$ 938,000,000	$ 929,000,000	$ 1,873,000,000	$ 1,867,000,000	$ 2,787,000,000	$ 2,847,000,000	$ 3,778,000,000	$ 3,834,000,000	$ 3,686,000,000
Policyholders’ benefits	1,034,000,000	736,000,000	2,776,000,000	1,735,000,000	895,000,000	921,000,000	3,512,000,000	1,816,000,000	4,546,000,000	3,551,000,000	4,385,000,000	2,856,000,000	4,380,000,000
Interest credited to policyholders’ account balances	306,000,000			320,000,000	317,000,000	307,000,000		624,000,000	930,000,000	944,000,000	1,263,000,000	1,067,000,000
Net derivative gains (losses)	(1,472,000,000)	(6,038,000,000)	9,400,000,000	(453,000,000)	(237,000,000)	(1,633,000,000)	3,362,000,000	(1,870,000,000)	1,890,000,000	(2,323,000,000)	(4,012,000,000)	(250,000,000)	191,000,000
Income (loss) from continuing operations, before income taxes	(923,000,000)	(5,008,000,000)	6,859,000,000	(427,000,000)	438,000,000	(962,000,000)	1,851,000,000	(524,000,000)	928,000,000	(951,000,000)	(2,060,000,000)	2,490,000,000	1,243,000,000
Net income (loss)	(705,000,000)	$ (3,933,000,000)	5,425,000,000	(306,000,000)	$ 428,000,000	$ (739,000,000)	$ 1,492,000,000	$ (311,000,000)	787,000,000	$ (617,000,000)	$ (1,467,000,000)	$ 2,189,000,000	$ 1,201,000,000
Long-term Lapses, Partial Withdrawal Rates and Election Assumptions Updates
Change in Accounting Estimate [Line Items]
Policy charges and fee income	(23,000,000)		46,000,000	3,000,000
Policyholders’ benefits	193,000,000		1,400,000,000	875,000,000
Interest credited to policyholders’ account balances	5,000,000		(6,000,000)	(13,000,000)
Net derivative gains (losses)	(112,000,000)			(578,000,000)
Amortization of deferred policy acquisition costs, net	(35,000,000)		1,100,000,000	(46,000,000)
Income (loss) from continuing operations, before income taxes	(74,000,000)		(2,500,000,000)	(1,400,000,000)
Net income (loss)	(58,000,000)		(2,000,000,000.0)	$ (1,100,000,000)
Economic Scenario Generator
Change in Accounting Estimate [Line Items]
Income (loss) from continuing operations, before income taxes									201,000,000
Net income (loss)									$ 159,000,000
Credit Risk Adjustment, Fair Value Scenario Calibration
Change in Accounting Estimate [Line Items]
Gain (loss) on assumption updates and model changes, pre tax	$ 445,000,000
5-year Historical Average Over A 10-year Period
Change in Accounting Estimate [Line Items]
Interest rate assumptions			$ 0.0225