Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plans	$ 7	$ 8
PRB plans	0	0
Defined contribution plans	271	213
Liability, Defined Benefit Pension Plan, Noncurrent	9,808		$ 10,342
Non-service pension (income) expense	(491)	(168)
Total net periodic benefit (income) expense	(358)	(130)
Marketable securities held in trusts	879		881
UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plans	0	0
Foreign Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plans	7	8
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Liability, Defined Benefit Pension Plan, Noncurrent	8,669		9,131
Service cost	131	37
Interest cost	312	253
Expected return on plan assets	(868)	(521)
Amortization of prior service cost (credit)	(42)	13
Recognized actuarial net loss (gain)	109	86
Net settlement and curtailment loss (gain)	0	0
Non-service pension (income) expense	(489)	(169)
Total net periodic benefit (income) expense	(358)	(132)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Liability, Defined Benefit Pension Plan, Noncurrent	1,073		1,072
Service cost	2	1
Interest cost	6	6
Expected return on plan assets	(5)	(1)
Amortization of prior service cost (credit)	(1)	(1)
Recognized actuarial net loss (gain)	(2)	(3)
Net settlement and curtailment loss (gain)	0	0
Non-service pension (income) expense	(2)	1
Total net periodic benefit (income) expense	0	$ 2
Other pension and PRB related items
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Liability, Defined Benefit Pension Plan, Noncurrent	$ 66		$ 139