Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance	[1]	$ (15,083)	$ (16,373)	$ (13,623)
OCI before reclassifications	[1]	(1,471)	517	(230)
Amounts reclassified from AOCI	[1]	401	773	477
Net current period OCI	[1]	(1,070)	1,290	247
Balance	[1]	(16,153)	(15,083)	(16,373)
Defined benefit pension plans & other postretirement benefits:
Amortization of actuarial losses included in net periodic pension cost, net of tax of ($570), ($367), and ($849)		464	878	542
Amortization of actuarial losses included in net periodic pension cost, tax		(133)	(242)	(272)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(101)	(15)	(143)
OCI before reclassifications		(27)	(86)	128
Amounts reclassified from AOCI
Net current period OCI		(27)	(86)	128
Balance		(128)	(101)	(15)
Unrealized Gains and Losses on Certain Investments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		0	(2)	(2)
OCI before reclassifications		1	2	1
Amounts reclassified from AOCI
Net current period OCI		1	2	1
Balance		1	0	(2)
Unrealized Gains and Losses on Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(62)	54	(127)
OCI before reclassifications		(48)	(146)	119
Amounts reclassified from AOCI		26	30	52
Net current period OCI		(22)	(116)	171
Balance		(84)	(62)	54
Defined Benefit Pension Plans and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(14,920)	(16,410)	(13,351)
OCI before reclassifications		(1,397)	747	(478)
Amounts reclassified from AOCI		375	743	425	[2]
Net current period OCI		(1,022)	1,490	(53)
Balance		$ (15,942)	(14,920)	(16,410)
Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance			(2,997)
Net current period OCI	[1]		(2,997)
Balance				$ (2,997)
Accounting Standards Update 2018-02 [Member] | Unrealized Gains and Losses on Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net current period OCI			10
Accounting Standards Update 2018-02 [Member] | Defined Benefit Pension Plans and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net current period OCI			(3,006)
Accounting Standards Update 2018-02 [Member] | AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net current period OCI			$ (1)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the years ended December 31, 2019, 2018, and 2017 totaling $464, $878, and $542 (net of tax of ($133), ($242), and ($272)), respectively. These are included in the net periodic pension cost. See Note 17.