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Revenues (Contract liabilities) (Details) - USD ($)
$ in Millions
Mar. 31, 2020
Dec. 31, 2019
Mar. 31, 2019
Dec. 31, 2018
Contract balances        
Deferred contract revenues, recorded in other current liabilities $ 113 $ 100    
Deferred contract revenues, recorded in other long-term liabilities 421 429    
Total contract liabilities $ 534 $ 529 $ 487 $ 486