Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance	[1]	$ (16,373)	$ (13,623)	$ (12,748)
OCI before reclassifications	[1]	517	(230)	(1,434)
Amounts reclassified from AOCI	[1]	773	477	559
Net current period OCI	[1]	1,290	247	(875)
Balance	[1]	(15,083)	(16,373)	(13,623)
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)		878	542	524
Amortization of actuarial losses included in net periodic pension cost, tax		(242)	(272)	(288)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(15)	(143)	(39)
OCI before reclassifications		(86)	128	(104)
Amounts reclassified from AOCI
Net current period OCI		(86)	128	(104)
Balance		(101)	(15)	(143)
Unrealized Gains and Losses on Certain Investments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(2)	(2)	0
OCI before reclassifications		2	1	(2)
Amounts reclassified from AOCI
Net current period OCI		2	1	(2)
Balance		0	(2)	(2)
Unrealized Gains and Losses on Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		54	(127)	(197)
OCI before reclassifications		(146)	119	(8)
Amounts reclassified from AOCI		30	52	78
Net current period OCI		(116)	171	70
Balance		(62)	54	(127)
Defined Benefit Pension Plans and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(16,410)	(13,351)	(12,512)
OCI before reclassifications		747	(478)	(1,320)
Amounts reclassified from AOCI		743	425	481	[2]
Net current period OCI		1,490	(53)	(839)
Balance		(14,920)	(16,410)	$ (13,351)
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] | Accumulated Net Investment Gain (Loss) Attributable to 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, 2018, 2017, and 2016 totaling $878, $542, and $524 (net of tax of ($242), ($272), and ($288)), respectively. These are included in the net periodic pension cost. See Note 17.