Equity Activity - AOCI Rollforward (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) (net of tax)
Balance at the Beginning of the Period		$ 17,725	$ 18,392
Other comprehensive income/(loss)		430	688
Balance at the End of the Period		18,290	18,448
Accumulated Other Comprehensive Income/(Loss)
Accumulated Other Comprehensive Income (Loss) (net of tax)
Balance at the Beginning of the Period		(26,592)	(29,398)
Other comprehensive income before reclassifications		(65)	284
Amount reclassified from accumulated other comprehensive income		495	404
Other comprehensive income/(loss)		430	688
Balance at the End of the Period		(28,583)	(28,710)
Accumulated Other Comprehensive Income/(Loss) | Accounting Standards Updates 2016-01 (Financial Instruments), 2017-12 (Hedging) and 2018-02 (Stranded Tax Effects)
Accumulated Other Comprehensive Income (Loss) (net of tax)
Cumulative Effect Of Prospective Application Of New Accounting Principle, Net Of Tax	[1]	(2,422)
Net Unrealized Gains/(Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) (net of tax)
Balance at the Beginning of the Period		35	319
Other comprehensive income before reclassifications		51	(25)
Amount reclassified from accumulated other comprehensive income		(41)	(64)
Other comprehensive income/(loss)		10	(89)
Balance at the End of the Period		50	230
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Accounting Standards Updates 2016-01 (Financial Instruments), 2017-12 (Hedging) and 2018-02 (Stranded Tax Effects)
Accumulated Other Comprehensive Income (Loss) (net of tax)
Cumulative Effect Of Prospective Application Of New Accounting Principle, Net Of Tax		5
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) (net of tax)
Balance at the Beginning of the Period		(2,834)	(3,603)
Other comprehensive income before reclassifications		(115)	270
Amount reclassified from accumulated other comprehensive income		0	0
Other comprehensive income/(loss)		(115)	270
Balance at the End of the Period		(2,903)	(3,333)
Foreign Currency Translation Adjustments | Accounting Standards Updates 2016-01 (Financial Instruments), 2017-12 (Hedging) and 2018-02 (Stranded Tax Effects)
Accumulated Other Comprehensive Income (Loss) (net of tax)
Cumulative Effect Of Prospective Application Of New Accounting Principle, Net Of Tax		46
Net Change Retirement-Related Benefit Plans
Accumulated Other Comprehensive Income (Loss) (net of tax)
Balance at the Beginning of the Period		(23,796)	(26,116)
Other comprehensive income before reclassifications		0	40
Amount reclassified from accumulated other comprehensive income		537	466
Other comprehensive income/(loss)		537	507
Balance at the End of the Period		(25,730)	(25,609)
Net Change Retirement-Related Benefit Plans | Accounting Standards Updates 2016-01 (Financial Instruments), 2017-12 (Hedging) and 2018-02 (Stranded Tax Effects)
Accumulated Other Comprehensive Income (Loss) (net of tax)
Cumulative Effect Of Prospective Application Of New Accounting Principle, Net Of Tax		(2,471)
Net Unrealized Gains/(Losses) on Available-For-Sale Securities
Accumulated Other Comprehensive Income (Loss) (net of tax)
Balance at the Beginning of the Period		3	2
Other comprehensive income before reclassifications		(2)	(1)
Amount reclassified from accumulated other comprehensive income		0	1
Other comprehensive income/(loss)		(2)	0
Balance at the End of the Period		(1)	$ 2
Net Unrealized Gains/(Losses) on Available-For-Sale Securities | Accounting Standards Updates 2016-01 (Financial Instruments), 2017-12 (Hedging) and 2018-02 (Stranded Tax Effects)
Accumulated Other Comprehensive Income (Loss) (net of tax)
Cumulative Effect Of Prospective Application Of New Accounting Principle, Net Of Tax		$ (2)

[1] Reflects the adoption of the FASB guidance on stranded tax effects, hedging and financial instruments. Refer to note 2, "Accounting Changes".