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REVENUE - Rollforward (Details)
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
Revenue from Contract with Customer [Abstract]  
Balance at January 1 (after adopting ASU 2016-13) $ 5
Provision for expected credit losses during the period 3
Write-offs charged against the allowance (2)
Recoveries of amounts previously written off 1
Balance at end of year $ 7