Shareholders' Equity (Accumulated other comprehensive income) (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2021		Jun. 30, 2020		Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	$ (16,952)		$ (16,333)		$ (17,133)	$ (16,153)
OCI before reclassifications	[1]	76		121		53	(231)
Amounts reclassified from AOCI	[1]	215		187		419	359
Net current period Other comprehensive income/(loss)	[1]	291		308		472	128
Ending Balance	[1]	(16,661)		(16,025)		(16,661)	(16,025)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		235		197		463	390
Amortization of actuarial losses included in net periodic pension cost, tax		(57)		(50)		(122)	(103)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(66)		(205)		(30)	(128)
OCI before reclassifications		14		44		(22)	(33)
Net current period Other comprehensive income/(loss)		14		44		(22)	(33)
Ending Balance		(52)		(161)		(52)	(161)
Unrealized Gains and Losses on Certain Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		1		1		1	1
Ending Balance		1		1		1	1
Unrealized Gains and Losses on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(34)		(357)		(43)	(84)
OCI before reclassifications		54		89		65	(186)
Amounts reclassified from AOCI				10		(2)	12
Net current period Other comprehensive income/(loss)		54		99		63	(174)
Ending Balance		20		(258)		20	(258)
Defined Benefit Pension Plans and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(16,853)		(15,772)		(17,061)	(15,942)
OCI before reclassifications		8		(12)		10	(12)
Amounts reclassified from AOCI		215	[2]	177	[2]	421	347
Net current period Other comprehensive income/(loss)		223		165		431	335
Ending Balance		$ (16,630)		$ (15,607)		$ (16,630)	$ (15,607)

[1] Net of tax.

[2] Primarily relates to amortization of actuarial losses for the six and three months ended June 30, 2020 $390 and $197 (net of tax of ($103) and ($50)) and six and three months ended June 30, 2021 totaling $463 and $235 (net of tax of ($122) and ($57)). These are included in the net periodic pension cost.