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Revenues (Changes) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Significant changes to contract liabilities    
Total contract liabilities, at beginning of period $ 529 $ 486
Decrease due to recognition of revenues for goods and services (41) (37)
Increase due to goods and services transferred over time 46 38
Total contract liabilities, at end of period $ 534 $ 487