Postretirement Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Amount by which fair value of plan assets exceeds market-related value of plan assets (MRVA)	$ 6,805
Derivative net notional amount for fixed income as percentage of total plan assets	8.30%	4.30%
Derivative net notional amount for global equity, currency overlay and commodities as a percentage of total plan assets	0.40%	3.60%
Expense for defined contribution plans	$ 1,351	$ 1,533	$ 1,480
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation (ABO) for all pension plans	80,694	75,787
Company contribution	3,013	16
Defined Benefit Plan, Plan Assets, Amount	$ 68,696	$ 61,711	56,102
Defined benefit plan, actual plan asset allocations	100.00%	100.00%
Pension Plans [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	49.00%	49.00%
Pension Plans [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	30.00%	29.00%
Pension Plans [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 14,978	$ 11,504
Pension Plans [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	240	472	318
Pension Plans [Member] | Level 3 [Member] | Debt Securities [Member] | Corporate Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	2
Pension Plans [Member] | Level 3 [Member] | Debt Securities [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2
Pension Plans [Member] | Level 3 [Member] | Debt Securities [Member] | Mortgage backed and asset backed securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	1	10
Pension Plans [Member] | Level 3 [Member] | Debt Securities [Member] | Municipal [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	3
Pension Plans [Member] | Level 3 [Member] | Debt Securities [Member] | Sovereign Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	(1)
Pension Plans [Member] | Level 3 [Member] | Equity Securities [Member] | Non United States Common And Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held		(1)
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Company contribution		1
Defined Benefit Plan, Plan Assets, Amount	$ 160	$ 149	$ 132
Other Postretirement Benefits Plans [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	40.00%
Other Postretirement Benefits Plans [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	60.00%
Non-Cash Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Company contribution	$ 3,000