Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	$ (21)	$ 6
Total before tax	(236)	(307)
Income tax expense	121	144
Net of tax	(115)	(163)
Reclassification out of Accumulated Other Comprehensive Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	44	51
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
Reclassification out of Accumulated Other Comprehensive Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	47	54
Income tax expense	(12)	(21)
Net of tax	$ 35	$ 33