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EMPLOYEE RETIREMENT PLANS - Changes in the Fair Value of the Qualified Defined-benefit Pension Plan Level 3 Assets (Details) - Qualified - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Changes in the fair value of plan level 3 assets    
Balance at the beginning of the period $ 19 $ 59
Purchases 0 4
Sales (18) (41)
Unrealized (losses) gains 0 (3)
Balance at the end of the period $ 1 $ 19