Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	$ (16,661)		$ (16,025)		$ (17,133)	$ (16,153)
OCI before reclassifications	[1]	1,501		87		1,554	(144)
Amounts reclassified from AOCI	[1]	342		159		761	518
Net current period Other comprehensive income/(loss)	[1]	1,843		246		2,315	374
Ending Balance	[1]	(14,818)		(15,779)		(14,818)	(15,779)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		227		172		690	562
Amortization of actuarial losses included in net periodic pension cost, tax		(60)		(76)		(182)	(179)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(52)		(161)		(30)	(128)
OCI before reclassifications		(41)		48		(63)	15
Net current period Other comprehensive income/(loss)		(41)		48		(63)	15
Ending Balance		(93)		(113)		(93)	(113)
Unrealized Gains and Losses on Certain Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		1		1		1	1
Ending Balance		1		1		1	1
Unrealized Gains and Losses on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		20		(258)		(43)	(84)
OCI before reclassifications		(1)		79		64	(107)
Amounts reclassified from AOCI		(4)		8		(6)	20
Net current period Other comprehensive income/(loss)		(5)		87		58	(87)
Ending Balance		15		(171)		15	(171)
Defined Benefit Pension Plans and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(16,630)		(15,607)		(17,061)	(15,942)
OCI before reclassifications		1,543		(40)		1,553	(52)
Amounts reclassified from AOCI		346	[2]	151	[2]	767	498
Net current period Other comprehensive income/(loss)		1,889		111		2,320	446
Ending Balance		$ (14,741)		$ (15,496)		$ (14,741)	$ (15,496)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the nine and three months ended September 30, 2020 $562 and $172 (net of tax of ($179) and ($76)) and nine and three months ended September 30, 2021 totaling $690 and $227 (net of tax of ($182) and ($60)). These are included in the net periodic pension cost.