SIGNIFICANT ACCOUNTING POLICIES - Assumption Updates and Model Changes (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019
Change in Accounting Estimate [Line Items]
Policyholders’ benefits	$ 2,788,000,000		$ 880,000,000
Policy charges and fee income	991,000,000		931,000,000
Interest credited to policyholders’ account balances	317,000,000		304,000,000
Earnings (loss) from operations, before income taxes	6,887,000,000		(924,000,000)
Net income (loss)	5,447,000,000		$ (709,000,000)
Long-term Lapses, Partial Withdrawal Rates and Election Assumptions Updates
Change in Accounting Estimate [Line Items]
Policyholders’ benefits	1,400,000,000
Amortization of deferred policy acquisition costs, net	1,100,000,000
Policy charges and fee income	46,000,000
Interest credited to policyholders’ account balances		$ (6,000,000)
Earnings (loss) from operations, before income taxes	(2,500,000,000)
Net income (loss)	(1,900,000,000)
5-year Historical Average Over A 10-year Period
Change in Accounting Estimate [Line Items]
Interest rate assumptions	$ 0.0225