Shareowners' Equity and Noncontrolling Interest (Summary of Changes in AOCI) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (6,937)	$ (8,333)	$ (7,525)	$ (8,334)
Other comprehensive (loss) income before reclassifications, net - Foreign Currency Translation	409	146
Amounts reclassified, pretax - Foreign Currency Translation	0	0
Tax (benefit) expense reclassified - Foreign Currency Translation	(130)	0
Other comprehensive (loss) income before reclassifications, net - Pension	(8)	0
Amounts reclassified, pretax - Pension	88	131
Tax (benefit) expense reclassified - Pension	23	48
Other comprehensive (loss) income before reclassifications, net - AFS Securities	0	(21)
Amounts reclassified, pretax - AFS Securities	0	383
Tax (benefit) expense reclassified - AFS Securities	0	147
Other comprehensive (loss) income before reclassifications, net - Unrealized Hedging (Losses) Gains	45	50
Amounts reclassified, pretax - Unrealized Hedging (Losses) Gains	27	(5)
Tax (benefit) expense reclassified - Unrealized Hedging (Losses) Gains	(4)	(1)
Other comprehensive (loss) income before reclassifications, net	429	150
Amounts reclassified, pretax	(61)	247
Tax (benefit) expense reclassified	103	98
Other Comprehensive Income (Loss), ASU 2016-01 adoption impact on foreign currency translation Arising During Period	0
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	(5)	0
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	(2,444)	(3,359)	(2,950)	(3,480)
Other comprehensive (loss) income before reclassifications, net - Foreign Currency Translation	376	121
Defined Benefit Pension and Post-retirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(4,579)	(4,962)	(4,652)	(5,045)
Unrealized Gains (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	0	96	5	353
Unrealized Hedging (Losses) Gains
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ 86	(108)	$ 72	$ (162)
Sales of significant investments in AFS securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified, pretax - Unrealized Hedging (Losses) Gains		$ 500