Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Other comprehensive loss	$ (52)	$ (536)
Net Effect of Exchange Rate Fluctuations
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,229)	(813)
Change before reclassifications	(81)	(564)
Other comprehensive loss	(81)	(564)
Balance at end of the period	(1,310)	(1,377)
Change in Certain Derivative Instruments
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(60)	(14)
Change before reclassifications	63	(2)
Amounts reclassified from accumulated other comprehensive income (loss)	(50)	11
Translation effect		(1)
Tax effect		(2)
Other comprehensive loss	13	6
Balance at end of the period	(47)	(8)
Employee Benefit Plans
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(983)	(1,016)
Change before reclassifications	3	(2)
Amounts reclassified from accumulated other comprehensive income (loss)	19	17
Translation effect	(2)	16
Other comprehensive loss	20	31
Balance at end of the period	(963)	(985)
Accumulated Other Comprehensive Loss.
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(2,272)	(1,843)
Change before reclassifications	(15)	(568)
Amounts reclassified from accumulated other comprehensive income (loss)	(31)	28
Translation effect	(2)	15
Tax effect		(2)
Other comprehensive loss	(48)	(527)
Balance at end of the period	$ (2,320)	$ (2,370)