Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	$ (16)	$ 7	$ (37)	$ 13
Total before tax	(237)	(40)	(473)	(347)
Income tax expense	(55)	23	66	167
Net of tax	(292)	(17)	(407)	(180)
Reclassification out of Accumulated Other Comprehensive Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	46	52	90	103
Reclassification out of Accumulated Other Comprehensive Income | Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	3	3	6	6
Reclassification out of Accumulated Other Comprehensive Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	49	55	96	109
Income tax expense	(12)	(23)	(24)	(44)
Net of tax	$ 37	$ 32	$ 72	$ 65