Equity, Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in Accumulated Other Comprehensive Loss, By Component
Beginning balance, accumulated other comprehensive loss, net of tax	$ 21,991
Ending balance, accumulated other comprehensive loss, net of tax	21,877
Accumulated Other Comprehensive Loss [Member]
Changes in Accumulated Other Comprehensive Loss, By Component
Beginning balance, accumulated other comprehensive loss, net of tax	(940)	$ (1,410)
Other comprehensive income before reclassifications	42	74
Amounts reclassified from accumulated other comprehensive loss	6	2
Other comprehensive income	48	76
Reclassification of stranded income tax effects of Tax Reform to retained earnings per ASU 2018-02	(91)	0
Ending balance, accumulated other comprehensive loss, net of tax	(983)	(1,334)
Foreign Currency Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Loss, By Component
Beginning balance, accumulated other comprehensive loss, net of tax	(507)	(1,021)
Other comprehensive income before reclassifications	42	74
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive income	42	74
Reclassification of stranded income tax effects of Tax Reform to retained earnings per ASU 2018-02	0	0
Ending balance, accumulated other comprehensive loss, net of tax	(465)	(947)
Defined Benefit Plans Items [Member]
Changes in Accumulated Other Comprehensive Loss, By Component
Beginning balance, accumulated other comprehensive loss, net of tax	(433)	(389)
Other comprehensive income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	6	2
Other comprehensive income	6	2
Reclassification of stranded income tax effects of Tax Reform to retained earnings per ASU 2018-02	(91)	0
Ending balance, accumulated other comprehensive loss, net of tax	$ (518)	$ (387)