Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Changes in accumulated other comprehensive income (loss), net of income taxes
Beginning of the period	$ 31,088
Net current period comprehensive income (loss)	(921)	$ 116
End of the period	30,218
Cumulative Foreign Currency Translation Adjustments
Changes in accumulated other comprehensive income (loss), net of income taxes
Beginning of the period	(4,924)	(4,912)
Other comprehensive income (loss) before reclassifications	(1,144)	122
Net current period comprehensive income (loss)	(1,144)	122
End of the period	(6,068)	(4,790)
Net Actuarial (Losses) and Prior Service (Costs) and Credits
Changes in accumulated other comprehensive income (loss), net of income taxes
Beginning of the period	(3,540)	(2,726)
Other comprehensive income (loss) before reclassifications	7	(1)
Amounts reclassified from accumulated other comprehensive income	50	24
Net current period comprehensive income (loss)	57	23
End of the period	(3,483)	(2,703)
Cumulative Gains (Losses) on Derivative Instruments Designated as Cash Flow Hedges
Changes in accumulated other comprehensive income (loss), net of income taxes
Beginning of the period	(1)	52
Other comprehensive income (loss) before reclassifications	176	(17)
Amounts reclassified from accumulated other comprehensive income	(10)	(12)
Net current period comprehensive income (loss)	166	(29)
End of the period	$ 165	$ 23