Accumulated Other Comprehensive Loss (Summary of Changes in AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (9,892)	$ (7,684)	$ (9,892)	$ (7,684)	$ (9,519)	$ (9,333)	$ (6,937)	$ (7,525)
Amounts reclassified, pretax - Foreign Currency Translation	(1)	(3)	0	(3)
Tax (benefit) expense reclassified - Foreign Currency Translation	14	(74)	1	56
Other comprehensive (loss) income before reclassifications, net - Pension	(13)	18	(14)	26
Amounts reclassified, pretax - Pension	43	88	87	176
Tax (benefit) expense reclassified - Pension	(6)	(26)	(16)	(49)
Other comprehensive (loss) income before reclassifications, net - AFS Securities	0	0	0	0
Amounts reclassified, pretax - AFS Securities	0	0	0	0
Tax (benefit) expense reclassified - AFS Securities	0	0	0	0
Other comprehensive (loss) income before reclassifications, net - Unrealized Hedging (Losses) Gains	21	(245)	28	(200)
Amounts reclassified, pretax - Unrealized Hedging (Losses) Gains	16	(1)	20	(28)
Tax (benefit) expense reclassified - Unrealized Hedging (Losses) Gains	12	(60)	15	56
Other comprehensive (loss) income before reclassifications, net	(427)	(791)	109	(362)
Amounts reclassified, pretax	58	84	107	145
Tax (benefit) expense reclassified	(4)	(40)	(30)	63
Other Comprehensive Income (Loss), ASU 2016-01 adoption impact on foreign currency translation Arising During Period				0
Other Comprehensive Income (Loss), ASU 2018-02 adoption impact on Securities Arising During Period			0
Other Comprehensive Income (Loss), ASU 2018-02 adoption impact on foreign currency translation Arising During Period			(8)
Other Comprehensive Income (Loss), ASU 2018-02 adoption impact on Defined Benefit Plan Arising During Period			(737)
Other Comprehensive Income (Loss), ASU 2018-02 adoption impact on Derivatives Arising During Period			0
Reclassification from OCI, current period, ASU 2018-02 adoption impact			(745)
Other Comprehensive Income (Loss), ASU 2016-01 adoption impact on Defined Benefit Plan Arising During Period				0
Other Comprehensive Income (Loss), ASU 2016-01 adoption impact on Securities Arising During Period	0	0	0	(5)
Other Comprehensive Income (Loss), ASU 2016-01 adoption impact on Derivatives Arising During Period				0
Reclassification from OCI, current period, ASU 2016-01 adoption impact				(5)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(3,354)	(3,085)	(3,354)	(3,085)	(2,932)	(3,442)	(2,444)	(2,950)
Other comprehensive (loss) income before reclassifications, net - Foreign Currency Translation	(435)	(564)	95	(188)
Defined Benefit Pension and Post-retirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(6,398)	(4,499)	(6,398)	(4,499)	(6,422)	(5,718)	(4,579)	(4,652)
Unrealized Gains (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	0	0	0	0	0	0	0	5
Unrealized hedging (losses) gains
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (140)	$ (100)	$ (140)	$ (100)	$ (165)	$ (173)	$ 86	$ 72