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Cash, Cash Equivalents and Restricted Cash - Schedule of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($)
$ in Millions
Sep. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]        
Cash and cash equivalents $ 1,344 $ 1,553 $ 1,694  
Restricted cash in other current assets 4   0  
Restricted cash in other noncurrent assets 37   42  
Total cash, cash equivalents and restricted cash $ 1,385 $ 1,597 $ 1,736 $ 1,555