Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassifications out of accumulated other comprehensive income loss by component
Other income, net	$ (44)	$ (8)	$ (5)	$ 29
Total before tax	410	329	(5,115)	802
Income tax benefit	(108)	(57)	(377)	(123)
Net (loss) income	302	272	(5,492)	679
Decrease (Increase) in Net Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income, net	54	45	167	134
Decrease (Increase) in Net Income | Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Other income, net	3	3	7	9
Decrease (Increase) in Net Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	57	48	174	143
Income tax benefit	(14)	(11)	(43)	(35)
Net (loss) income	$ 43	$ 37	$ 131	$ 108