Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	$ (16,162)	$ (13,415)	$ (16,373)	$ (13,623)
OCI before reclassifications	[1]	(173)	61	(149)	149
Amounts reclassified from AOCI	[1]	196	120	383	240
Net current period Other comprehensive income/(loss)	[1]	23	181	234	389
Ending Balance	[1]	(16,139)	(13,234)	(16,139)	(13,234)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		219	131	438	263
Amortization of actuarial losses included in net periodic pension cost, tax		(62)	(73)	(122)	(145)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		12	(109)	(15)	(143)
OCI before reclassifications		(84)	43	(57)	77
Net current period Other comprehensive income/(loss)		(84)	43	(57)	77
Ending Balance		(72)	(66)	(72)	(66)
Unrealized Gains and Losses on Certain Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		0	(1)	(2)	(2)
OCI before reclassifications		1	(1)	3
Net current period Other comprehensive income/(loss)		1	(1)	3
Ending Balance		1	(2)	1	(2)
Unrealized Gains and Losses on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		56	(59)	54	(127)
OCI before reclassifications		(91)	19	(93)	71
Amounts reclassified from AOCI		6	18	10	34
Net current period Other comprehensive income/(loss)		(85)	37	(83)	105
Ending Balance		(29)	(22)	(29)	(22)
Defined Benefit Pension Plans and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(16,230)	(13,246)	(16,410)	(13,351)
OCI before reclassifications		1		(2)	1
Amounts reclassified from AOCI	[2]	190	102	373	206
Net current period Other comprehensive income/(loss)		191	102	371	207
Ending Balance		$ (16,039)	$ (13,144)	$ (16,039)	$ (13,144)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the six and three months ended June 30, 2017 totaling $263 and $131 (net of tax of $(145) and ($73)) and for the six and three months ended June 30, 2018 totaling $438 and $219 (net of tax of ($122) and $(62)). These are included in the net periodic pension cost.