Postretirement Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Amount by which fair value of plan assets exceeds market-related value of plan assets (MRVA)	$ 3,674
Derivative net notional amount for fixed income as percentage of total plan assets	4.30%	4.40%
Derivative net notional amount for global equity, currency overlay and commodities as a percentage of total plan assets	3.60%	5.50%
Company contribution			$ 3,500
Expense for defined contribution plans	$ 1,533	$ 1,480	$ 1,522
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation (ABO) for all pension plans	75,787	69,376
Company contribution	$ 16	$ 16
Defined benefit plan, actual plan asset allocations	100.00%	100.00%
Pension Plans [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	49.00%	48.00%
Pension Plans [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	29.00%	28.00%
Pension Plans [Member] | Level 3 [Member] | Fixed Income Securities [Member] | Mortgage backed and asset backed
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	$ 10	$ (4)
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)	0
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Company contribution	$ 1	$ 2
Other Postretirement Benefits Plans [Member] | Fixed Income 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%