Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	$ (16,139)	$ (13,234)	$ (16,373)	$ (13,623)
OCI before reclassifications	[1]	(3)	84	(152)	233
Amounts reclassified from AOCI	[1]	193	114	576	354
Net current period Other comprehensive income/(loss)	[1]	190	198	424	587
Ending Balance	[1]	(15,949)	(13,036)	(15,949)	(13,036)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		219	131	657	394
Amortization of actuarial losses included in net periodic pension cost, tax		(60)	(72)	(182)	(217)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(72)	(66)	(15)	(143)
OCI before reclassifications		2	44	(55)	121
Net current period Other comprehensive income/(loss)		2	44	(55)	121
Ending Balance		(70)	(22)	(70)	(22)
Unrealized Gains and Losses on Certain Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		1	(2)	(2)	(2)
OCI before reclassifications				3
Net current period Other comprehensive income/(loss)				3
Ending Balance		1	(2)	1	(2)
Unrealized Gains and Losses on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(29)	(22)	54	(127)
OCI before reclassifications		(4)	40	(97)	111
Amounts reclassified from AOCI		9	10	19	44
Net current period Other comprehensive income/(loss)		5	50	(78)	155
Ending Balance		(24)	28	(24)	28
Defined Benefit Pension Plans and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(16,039)	(13,144)	(16,410)	(13,351)
OCI before reclassifications		(1)		(3)	1
Amounts reclassified from AOCI	[2]	184	104	557	310
Net current period Other comprehensive income/(loss)		183	104	554	311
Ending Balance		$ (15,856)	$ (13,040)	$ (15,856)	$ (13,040)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the nine and three months ended September 30, 2017 totaling $394 and $131 (net of tax of ($217) and ($72)) and for the nine and three months ended September 30, 2018 totaling $657 and $219 (net of tax of ($182) and ($60)). These are included in the net periodic pension cost.