Employee Benefit Plans (Pension and Postretirement Plans) (Details) $ in Millions		1 Months Ended	12 Months Ended
	Apr. 03, 2020 USD ($)	Aug. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, number of plan participants	3,400
Defined benefit plan, benefit obligation, (increase) decrease due to remeasurement	$ 2,400
Actuarial loss (gain)		$ 425
Remeasurement losses		605
Benefit obligation gain for change in benefit plan		$ 180	$ (51)	$ (93)	$ 105
Reduction in PBO discount rate, in bps		124
Actual asset returns		17.00%
Net settlement and curtailment gain (loss)		$ 98
Plan amendments			$ 2,100
Percentage Of Projected Benefit Obligation Comprised Of Domestic Plan Benefits			85.00%	82.00%
Percentage Of Projected Benefit Obligation Comprised Of Foreign Plan Benefits			12.00%	17.00%
Other pension and PRB related liabilities			$ 139	$ 21
Defined Benefit Plan, Accumulated Benefit Obligation			70,200	37,700
Fair value of plan assets			62,318	36,225
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			$ 1,649	$ 1,671	1,538
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Percent Of Plan Assets Concentrated in Individual Investment			5.00%
Nonqualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage Of Projected Benefit Obligation Comprised Of Domestic Plan Benefits			3.00%	1.00%
UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Discretionary Pension Contributions			$ 750
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discretionary Pension Contributions			51
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year			50
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)			114	$ (11)
Benefit obligation gain for change in benefit plan			48	2
Net settlement and curtailment gain (loss)			(1)	0	$ 0
Plan amendments			$ (7)	$ 0
Expected return on plan assets, net cost			5.70%	7.00%	7.00%
Fair value of plan assets			$ 381	$ 20	$ 20
Other Postretirement Benefits Plan [Member] | Asset Held in Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			149	0
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)			7,029	4,247
Benefit obligation gain for change in benefit plan			397	124
Net settlement and curtailment gain (loss)			(45)	59	$ (3)
Plan amendments			$ (2,088)	$ 0
Expected return on plan assets, net cost			6.50%	6.80%	6.90%
Derivative, Fair Value, Net			$ 176	$ 75
Fair value of plan assets			$ 62,318	36,225	$ 32,150
Pension Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Range Of Growth Seeking Assets In Company's Overall Investment Strategy			55.00%
Range Of Income Generating Assets In Company's Overall Investment Strategy			50.00%
Pecentage Of Interest Rate Sensitivity Of Pension Plan Liabilities Fixed Income Portfolio Designed To Hedge			70.00%
Pension Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Range Of Growth Seeking Assets In Company's Overall Investment Strategy			50.00%
Range Of Income Generating Assets In Company's Overall Investment Strategy			45.00%
Pecentage Of Interest Rate Sensitivity Of Pension Plan Liabilities Fixed Income Portfolio Designed To Hedge			30.00%
VEBA [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			$ 0	$ 0