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Revenue - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Contract Balance          
Software license contracts term (in years)     1 year    
Deferred revenue $ 467   $ 467   $ 498
Deferred income recognized as revenue 90 $ 100 410 $ 370  
Operating lease revenue $ 148 $ 153 $ 433 $ 428