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Income, Sales-Based And Other Taxes (Unrecognized Tax Benefits) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Income, Sales-Based And Other Taxes [Abstract]      
Balance at January 1 $ 8,986 $ 7,838 $ 7,663
Additions based on current year's tax positions 903 1,454 1,460
Additions for prior years' tax positions 496 448 464
Reductions for prior years' tax positions (190) (532) (249)
Reductions due to lapse of the statute of limitations (4) (117) (588)
Settlements with tax authorities (725) (43) (849)
Foreign exchange effects/other (70) (62) (63)
Balance at December 31 $ 9,396 $ 8,986 $ 7,838