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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Securities in an unrealized gain position:
Sale proceeds	$ 122	$ 432	$ 1,212	$ 938
Realized gains	9	6	40	47
Securities in an unrealized loss position:
Sales proceeds	15	25	23	25
Realized losses	$ 0	$ (4)	$ (1)	$ (5)