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Revenues (Changes) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Significant changes to contract liabilities    
Total contract liabilities, at beginning of period $ 486 $ 625
Decrease due to recognition of revenues for goods and services (114) (239)
Increase due to goods and services transferred over time 157 100
Total contract liabilities, at end of period $ 529 $ 486