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New Accounting Pronouncements - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Operating income (loss) $ (4) $ 0    
Total cash, cash equivalents and restricted cash 940 1,164 $ 1,089 $ 974
Accounting Standards Update 2017-07        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Operating income (loss) $ 2 1    
Scenario, Adjustment | Accounting Standards Update 2016-18        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Total cash, cash equivalents and restricted cash   $ 1