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Income Taxes, Reconciliation of Unrecognized Tax Benefits (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Tax Disclosure [Abstract]        
Unrecognized tax benefits $ 941 $ 936 $ 964 $ 989
Tax refund claim not presented in our balance sheets (274) (433)    
Other 77 (5)    
Uncertain tax position liabilities presented in our balance sheets $ 744 $ 498