Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassifications out of accumulated other comprehensive income loss by component
Other income, net	$ 44	$ 16	$ 39	$ 37
Total before tax	502	237	(5,525)	473
Income tax benefit	(131)	55	(269)	(66)
Net (loss) income	371	292	(5,794)	407
Decrease (Increase) in Net Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income, net	56	45	113	89
Decrease (Increase) in Net Income | Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Other income, net	2	3	4	6
Decrease (Increase) in Net Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	58	48	117	95
Income tax benefit	(14)	(12)	(29)	(24)
Net (loss) income	$ 44	$ 36	$ 88	$ 71