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Revenue Recognition - Narratives (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Revenue from Contract with Customer [Abstract]      
Allowance for credit losses, period increase (decrease) $ 7    
Allowance for credit losses 131   $ 138
Provisions for doubtful receivables 41 $ 69  
Contract assets 205   279
Deferred revenue 131   279
Contract with Customer, Liability, Current 8   21
Contract with Customer, Liability, Noncurrent $ 26   $ 26