Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 34,086	$ 34,531
Balance	31,945	34,474
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	(16)	(132)
Loss reclassified from accumulated other comprehensive loss	72	35
Net current-period change in accumulated other comprehensive (loss) income	56	(97)
Balance	49	67
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	0	(91)
Other comprehensive (loss) gain before reclassifications	1	20
Loss reclassified from accumulated other comprehensive loss	0	0
Net current-period change in accumulated other comprehensive (loss) income	1	20
Balance	1	(71)
Pension and other postretirement liability adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(326)	(403)
Other comprehensive (loss) gain before reclassifications	21	23
Loss reclassified from accumulated other comprehensive loss	0	0
Net current-period change in accumulated other comprehensive (loss) income	21	23
Balance	(305)	(380)
Total accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(333)	(330)
Other comprehensive (loss) gain before reclassifications	6	(89)
Loss reclassified from accumulated other comprehensive loss	72	35
Net current-period change in accumulated other comprehensive (loss) income	78	(54)
Balance	$ (255)	$ (384)