Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 34,086	$ 34,531
Balance	33,464	34,456
Net unrealized gains/(losses)on cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(7)	164
Other comprehensive (loss) gain before reclassifications	222	(215)
Loss reclassified from accumulated other comprehensive loss	37	13
Net current-period change in accumulated other comprehensive (loss) income	259	(202)
Balance	252	(38)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	0	(91)
Other comprehensive (loss) gain before reclassifications	1	16
Loss reclassified from accumulated other comprehensive loss	0	0
Net current-period change in accumulated other comprehensive (loss) income	1	16
Balance	1	(75)
Pension and other postretirement liability adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(326)	(403)
Other comprehensive (loss) gain before reclassifications	11	8
Loss reclassified from accumulated other comprehensive loss	0	0
Net current-period change in accumulated other comprehensive (loss) income	11	8
Balance	(315)	(395)
Total accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(333)	(330)
Other comprehensive (loss) gain before reclassifications	234	(191)
Loss reclassified from accumulated other comprehensive loss	37	13
Net current-period change in accumulated other comprehensive (loss) income	271	(178)
Balance	$ (62)	$ (508)