Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance	[1]	$ (13,623)	$ (12,748)	$ (13,903)
OCI before reclassifications	[1]	(230)	(1,434)	(51)
Amounts reclassified from AOCI	[1]	477	559	1,206
Net current period OCI	[1]	247	(875)	1,155
Balance	[1]	(13,376)	(13,623)	(12,748)
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)		542	524	1,038
Amortization of actuarial losses included in net periodic pension cost, tax		(272)	(288)	(570)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(143)	(39)	53
OCI before reclassifications		128	(104)	(92)
Amounts reclassified from AOCI
Net current period OCI		128	(104)	(92)
Balance		(15)	(143)	(39)
Unrealized Gains and Losses on Certain Investments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(2)	0	(8)
OCI before reclassifications		1	(2)	8
Amounts reclassified from AOCI
Net current period OCI		1	(2)	8
Balance		(1)	(2)	0
Unrealized Gains and Losses on Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(127)	(197)	(136)
OCI before reclassifications		119	(8)	(140)
Amounts reclassified from AOCI		52	78	79
Net current period OCI		171	70	(61)
Balance		44	(127)	(197)
Defined Benefit Pension Plans and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance		(13,351)	(12,512)	(13,812)
OCI before reclassifications		(478)	(1,320)	173
Amounts reclassified from AOCI	[2]	425	481	1,127
Net current period OCI		(53)	(839)	1,300
Balance		$ (13,404)	$ (13,351)	$ (12,512)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the years ended December 31, 2017, 2016, and 2015 totaling $542, $524, and $1,038 (net of tax of ($272), ($288), and ($570)), respectively. These are included in the net periodic pension cost of which a portion is allocated to production as inventoried costs. See Note 14.