INVESTMENT OPERATIONS - Schedule of Fair Value (Proceeds) and Gains/Losses Realized on Securities Sold in an Unrealized Gain/Loss Position (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Securities in an unrealized gain position:
Sales proceeds	$ 232	$ 515	$ 1,443	$ 1,454
Realized gains	5	3	45	50
Securities in an unrealized loss position:
Sales proceeds	12	8	35	33
Realized losses	$ 0	$ 0	$ (1)	$ (5)