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Summary of Significant Accounting Policies and Recent Accounting Pronouncements, Cash, Cash Equivalents and Restricted Cash (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Accounting Policies [Abstract]        
Cash and cash equivalents $ 619 $ 900 $ 985  
Other current assets 3 3 3  
Other assets and deferred charges 0 1 1  
Cash, cash equivalents and restricted cash in the statement of cash flows $ 622 $ 904 $ 989 $ 481