Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	$ (1,968)
Other comprehensive income (loss)	107	$ (150)	$ 351
Balance at end of the period	(1,843)	(1,968)
Net Effect of Exchange Rate Fluctuations
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(889)	(723)
Change before reclassifications	76	(166)
Other comprehensive income (loss)	76	(166)
Balance at end of the period	(813)	(889)	(723)
Change in Certain Derivative Instruments
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(18)	(12)
Change before reclassifications	(74)	(4)
Amounts reclassified from accumulated other comprehensive income	75	(1)
Translation effect	1	(1)
Tax effect	2
Other comprehensive income (loss)	4	(6)
Balance at end of the period	(14)	(18)	(12)
Employee Benefit Plans
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,061)	(1,091)
Change before reclassifications	(21)	(114)
Amounts reclassified from accumulated other comprehensive income	70	131
Translation effect	(7)	16
Tax effect	3	(3)
Other comprehensive income (loss)	45	30
Balance at end of the period	(1,016)	(1,061)	(1,091)
Accumulated Other Comprehensive Loss.
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,968)	(1,826)
Change before reclassifications	(19)	(284)
Amounts reclassified from accumulated other comprehensive income	145	130
Translation effect	(6)	15
Tax effect	5	(3)
Other comprehensive income (loss)	125	(142)
Balance at end of the period	$ (1,843)	$ (1,968)	$ (1,826)