Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	$ (15,083)	$ (16,373)
OCI before reclassifications	[1]	21	24
Amounts reclassified from AOCI	[1]	93	187
Net current period Other comprehensive income/(loss)	[1]	114	211
Ending Balance	[1]	(14,969)	(16,162)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		118	219
Amortization of actuarial losses included in net periodic pension cost, tax		(32)	(60)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(101)	(15)
OCI before reclassifications		1	27
Net current period Other comprehensive income/(loss)		1	27
Ending Balance		(100)	12
Unrealized Gains and Losses on Certain Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(2)
OCI before reclassifications		1	2
Net current period Other comprehensive income/(loss)		1	2
Ending Balance		1	0
Unrealized Gains and Losses on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(62)	54
OCI before reclassifications		11	(2)
Amounts reclassified from AOCI		(2)	4
Net current period Other comprehensive income/(loss)		9	2
Ending Balance		(53)	56
Defined Benefit Pension Plans and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(14,920)	(16,410)
OCI before reclassifications		8	(3)
Amounts reclassified from AOCI	[2]	95	183
Net current period Other comprehensive income/(loss)		103	180
Ending Balance		$ (14,817)	$ (16,230)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the three months ended March 31, 2019 and 2018 totaling $118 and $219 (net of tax of ($32) and ($60)). These are included in the net periodic pension cost.