Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 34,616	$ 34,573	$ 33,704	$ 33,070	$ 34,573	$ 33,070
Other comprehensive income	41		21		62	3
Ending balance	34,871	34,616	33,907	33,704	34,871	33,907
Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(3)	(2)	(2)	(2)	(2)	(2)
OCI before reclassifications	0		0		(1)	0
Amounts reclassified from AOCI	0		0		0	0
Other comprehensive income	0		0		(1)	0
Ending balance	(3)	(3)	(2)	(2)	(3)	(2)
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(3,135)	(3,165)	(2,978)	(2,960)	(3,165)	(2,960)
OCI before reclassifications	2		(1)		(5)	(39)
Amounts reclassified from AOCI	37		22		74	42
Other comprehensive income	39		21		69	3
Ending balance	(3,096)	(3,135)	(2,957)	(2,978)	(3,096)	(2,957)
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(35)	(27)	(31)	(33)	(27)	(33)
OCI before reclassifications	2		2		(6)	4
Amounts reclassified from AOCI	0		0		0	0
Other comprehensive income	2		2		(6)	4
Ending balance	(33)	(35)	(29)	(31)	(33)	(29)
AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			(1)	0		0
OCI before reclassifications			(1)			(2)
Amounts reclassified from AOCI			0			0
Other comprehensive income			(1)			(2)
Ending balance			(2)	(1)		(2)
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(3,173)	(3,194)	(3,012)	(2,995)	(3,194)	(2,995)
OCI before reclassifications	4		0		(12)	(37)
Amounts reclassified from AOCI	37		22		74	42
Other comprehensive income	41	21	22	(17)	62	5
Ending balance	$ (3,132)	$ (3,173)	$ (2,990)	$ (3,012)	$ (3,132)	$ (2,990)