Employee Incentive, Retirement, Deferred Compensation, and Career Achievement Plans (Stock-Based Compensation Expense and Related Income Tax Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 183	$ 197	$ 153
Income tax benefit on share-based compensation expense	(44)	(47)	(57)
Income tax benefit/(expense)	(1,144)	(1,055)	(1,296)
Accounting Standards Update 2016-09 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax benefit/(expense)	23	46	87
Stock option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	51	51	50
Restricted stock unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	120	136	94
Restricted stock unit [Member] \| Non-Officer Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense		36
Employee stock purchase plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 12	$ 10	$ 9

Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of noncash expense for share-based payment arrangement.

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