Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	$ (17,133)	$ (16,153)
OCI before reclassifications	[1]	(23)	(352)
Amounts reclassified from AOCI	[1]	204	172
Net current period Other comprehensive income/(loss)	[1]	181	(180)
Ending Balance	[1]	(16,952)	(16,333)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		228	193
Amortization of actuarial losses included in net periodic pension cost, tax		(65)	(53)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(30)	(128)
OCI before reclassifications		(36)	(77)
Net current period Other comprehensive income/(loss)		(36)	(77)
Ending Balance		(66)	(205)
Unrealized Gains and Losses on Certain Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		1	1
Ending Balance		1	1
Unrealized Gains and Losses on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(43)	(84)
OCI before reclassifications		11	(275)
Amounts reclassified from AOCI		(2)	2
Net current period Other comprehensive income/(loss)		9	(273)
Ending Balance		(34)	(357)
Defined Benefit Pension Plans and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(17,061)	(15,942)
OCI before reclassifications		2
Amounts reclassified from AOCI		206	170
Net current period Other comprehensive income/(loss)		208	170
Ending Balance		$ (16,853)	$ (15,772)

[1] Net of tax.