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Supplemental Financial Information (Share-Based Compensation) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense		$ 208	$ 151	$ 636	$ 458
Restricted share units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense		143	94	437	279
Unrecognized pretax compensation expense on nonvested awards		1,200		1,200
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense		57	50	176	155
Unrecognized pretax compensation expense on nonvested awards		529		529
Employee stock purchase plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense		$ 8	$ 7	$ 23	$ 24
Management Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options granted (in shares)	41.9
Weighted-average fair value of stock options granted (in dollars per share)	$ 7.91
Management Grant [Member] \| Restricted share units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted share units granted (in shares)	12.4
Weighted-average fair value of restricted share units granted (in dollars per share)	$ 39.88