Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance	[1]	$ (16,153)	$ (15,083)	$ (16,373)
OCI before reclassifications	[1]	(1,817)	(1,471)	517
Amounts reclassified from AOCI	[1]	837	401	773
Net current period OCI	[1]	(980)	(1,070)	1,290
Balance	[1]	(17,133)	(16,153)	(15,083)
Defined benefit pension plans & other postretirement benefits:
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		917	464	878
Amortization of actuarial losses included in net periodic pension cost, tax		(52)	(133)	(242)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(128)	(101)	(15)
OCI before reclassifications		98	(27)	(86)
Amounts reclassified from AOCI
Net current period OCI		98	(27)	(86)
Balance		(30)	(128)	(101)
Unrealized Gains and Losses on Certain Investments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		1	0	(2)
OCI before reclassifications			1	2
Amounts reclassified from AOCI
Net current period OCI			1	2
Balance		1	1	0
Unrealized Gains and Losses on Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(84)	(62)	54
OCI before reclassifications		14	(48)	(146)
Amounts reclassified from AOCI		27	26	30
Net current period OCI		41	(22)	(116)
Balance		(43)	(84)	(62)
Defined Benefit Pension Plans and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(15,942)	(14,920)	(16,410)
OCI before reclassifications		(1,929)	(1,397)	747
Amounts reclassified from AOCI		810	375	743	[2]
Net current period OCI		(1,119)	(1,022)	1,490
Balance		$ (17,061)	$ (15,942)	$ (14,920)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the years ended December 31, 2020, 2019, and 2018 totaling $917, $464, and $878 (net of tax of ($52), ($133), and ($242)), respectively. These are included in the net periodic pension cost. See Note 16.