Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, benefit obligation, increase (decrease) due to remeasurement			$ 2,400
Defined benefit plans				$ 38	$ 64
PRB plans	$ 5	$ 8		9	8
Defined contribution plans	221	228		730	668
Liability, Defined Benefit Plan, Current	314			314		$ 314
Liability, Defined Benefit Pension Plan, Noncurrent	9,742			9,742		10,342
Non-service pension (income) expense	(491)	(253)		(1,472)	(658)
Total net periodic benefit (income) expense				(1,073)	(325)
Marketable securities held in trusts	965			965		881
UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plans	0	0		0	0
Foreign Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plans	8	14		29	56
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	1,389			1,389		424
Liability, Defined Benefit Pension Plan, Noncurrent	8,638			8,638		9,131
Service cost	131	149		393	328
Interest cost	312	465		937	1,170
Expected return on plan assets	(869)	(827)		(2,608)	(2,162)
Amortization of prior service cost (credit)	(42)	13		(126)	39
Recognized actuarial net loss (gain)	109	86		327	255
Net settlement, curtailment and special termination benefit loss	1	8		4	35
Non-service pension (income) expense	(489)	(255)		(1,466)	(663)
Total net periodic benefit (income) expense	(358)	(106)		(1,073)	(335)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Liability, Defined Benefit Pension Plan, Noncurrent	1,039			1,039		1,072
Service cost	2	2		6	5
Interest cost	6	10		18	26
Expected return on plan assets	(5)	(4)		(15)	(9)
Amortization of prior service cost (credit)	(1)	(1)		(3)	(3)
Recognized actuarial net loss (gain)	(2)	(3)		(6)	(9)
Net settlement, curtailment and special termination benefit loss	0	0		0	0
Non-service pension (income) expense	(2)	2		(6)	5
Total net periodic benefit (income) expense	0	$ 4		0	$ 10
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	$ 65			$ 65		$ 139