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Marketable and Other Securities - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($)
$ in Millions
Jun. 30, 2019
Dec. 31, 2018
Jun. 30, 2018
Dec. 31, 2017
Marketable Securities [Line Items]        
Cash and cash equivalents $ 17,072 $ 20,844    
Restricted cash 269 260    
Total 20,181 $ 23,496 $ 17,771 $ 17,848
Other current assets [Member]        
Marketable Securities [Line Items]        
Restricted cash 2,541      
Other assets [Member]        
Marketable Securities [Line Items]        
Restricted cash $ 568