Stockholders' Equity and Noncontrolling Interests - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Loss, Net of Tax [Roll Forward]
Balance at beginning of period	$ 45,957	$ 42,777
Other comprehensive income (loss), net of tax	(656)	185
Balance at end of period	44,317	44,638
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Loss, Net of Tax [Roll Forward]
Balance at beginning of period	(2,277)	(2,250)
Other comprehensive income (loss), net of tax	(814)	125
Balance at end of period	(3,091)	(2,125)
Defined benefit plans [Member]
Accumulated Other Comprehensive Loss, Net of Tax [Roll Forward]
Balance at beginning of period	(8,857)	(6,737)
Other comprehensive income (loss) before reclassification adjustment, net of tax and impact of adoption of accounting standards	263	(1)
Reclassification adjustment, net of tax	54	37
Other comprehensive income (loss), net of tax	317	36
Balance at end of period	$ (8,540)	$ (6,701)