Equity, Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax
Beginning balance, accumulated other comprehensive income (loss), net of tax	$ 20,024
Ending balance, accumulated other comprehensive income (loss), net of tax	21,991	$ 20,024
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax
Beginning balance, accumulated other comprehensive income (loss), net of tax	(1,410)	(933)	$ (367)
Other comprehensive income (loss) before reclassifications	458	(484)	(585)
Amounts reclassified from accumulated other comprehensive income (loss)	12	7	19
Net other comprehensive income (loss)	470	(477)	(566)
Ending balance, accumulated other comprehensive income (loss), net of tax	(940)	(1,410)	(933)
Foreign Currency Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax
Beginning balance, accumulated other comprehensive income (loss), net of tax	(1,021)	(605)	1
Other comprehensive income (loss) before reclassifications	514	(416)	(606)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Net other comprehensive income (loss)	514	(416)	(606)
Ending balance, accumulated other comprehensive income (loss), net of tax	(507)	(1,021)	(605)
Defined Benefit Plan Items Adjustment [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax
Beginning balance, accumulated other comprehensive income (loss), net of tax	(389)	(328)	(368)
Other comprehensive income (loss) before reclassifications	(56)	(68)	21
Amounts reclassified from accumulated other comprehensive income (loss)	12	7	19
Net other comprehensive income (loss)	(44)	(61)	40
Ending balance, accumulated other comprehensive income (loss), net of tax	$ (433)	$ (389)	$ (328)