Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	$ (1,826)
Other comprehensive income (loss)	(150)	$ 351	$ (159)
Balance at end of the period	(1,968)	(1,826)
Net Effect of Exchange Rate Fluctuations
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(723)	(788)
Change before reclassifications	(166)	65
Other comprehensive income (loss)	(166)	65
Balance at end of the period	(889)	(723)	(788)
Change in Certain Derivative Instruments
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(12)	(4)
Change before reclassifications	(4)	(3)
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	(6)
Translation effect	(1)
Tax effect		1
Other comprehensive income (loss)	(6)	(8)
Balance at end of the period	(18)	(12)	(4)
Employee Benefit Plans
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,091)	(1,380)
Change before reclassifications	(114)	(8)
Amounts reclassified from accumulated other comprehensive income (loss)	131	285
Translation effect	16	32
Tax effect	(3)	(20)
Other comprehensive income (loss)	30	289
Balance at end of the period	(1,061)	(1,091)	(1,380)
Accumulated Other Comprehensive Loss.
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,826)	(2,172)
Change before reclassifications	(284)	54
Amounts reclassified from accumulated other comprehensive income (loss)	130	279
Translation effect	15	32
Tax effect	(3)	(19)
Other comprehensive income (loss)	(142)	346
Balance at end of the period	$ (1,968)	$ (1,826)	$ (2,172)