Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	$ (16,373)	$ (13,623)
OCI before reclassifications	[1]	24	88
Amounts reclassified from AOCI	[1]	187	120
Net current period Other comprehensive income/(loss)	[1]	211	208
Ending Balance	[1]	(16,162)	(13,415)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		219	132
Amortization of actuarial losses included in net periodic pension cost, tax		(60)	(72)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(15)	(143)
OCI before reclassifications		27	34
Amounts reclassified from AOCI
Net current period Other comprehensive income/(loss)		27	34
Ending Balance		12	(109)
Unrealized Gains and Losses on Certain Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(2)	(2)
OCI before reclassifications		2	1
Amounts reclassified from AOCI
Net current period Other comprehensive income/(loss)		2	1
Ending Balance		0	(1)
Unrealized Gains and Losses on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		54	(127)
OCI before reclassifications		(2)	52
Amounts reclassified from AOCI		4	16
Net current period Other comprehensive income/(loss)		2	68
Ending Balance		56	(59)
Defined Benefit Pension Plans and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(16,410)	(13,351)
OCI before reclassifications		(3)	1
Amounts reclassified from AOCI	[2]	183	104
Net current period Other comprehensive income/(loss)		180	105
Ending Balance		$ (16,230)	$ (13,246)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the three months ended March 31, 2018 and 2017 totaling $219 and $132 (net of tax of ($60) and ($72)). These are included in the net periodic pension cost.