|**Equity (Tables)**                                                                                                                                                                                                 | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
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|**Equity [Abstract]**                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Summary of Common Stock Purchases                                                                                                                                                                                   | The following table provides the number of shares of our common stock purchased and the cost of purchases under our publicly announced share purchase plans, including our accelerated share repurchase agreements:(SHARES IN MILLIONS, DOLLARS IN BILLIONS)2019(a)2018(b)2017c)Shares of common stock purchased213307150Cost of purchase$8.9$12.2$5.0(a)Represents shares purchased pursuant to the accelerated share repurchase agreement withGS&Co.entered into onFebruary 7, 2019, as well as other share repurchases. See above for additional information.(b)Represents shares purchased pursuant to the accelerated share repurchase agreement with Citibank entered into onMarch 12, 2018, as well as other share repurchases. See above for additional information.(c)Represents shares purchased pursuant to the accelerated share repurchase agreement with Citibank entered into onFebruary 2, 2017. See above for additional information.
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|The following table provides the number of shares of our common stock purchased and the cost of purchases under our publicly announced share purchase plans, including our accelerated share repurchase agreements:
|(SHARES IN MILLIONS, DOLLARS IN BILLIONS)                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Shares of common stock purchased                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Cost of purchase                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
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|(a)                                                                                                                                                                                                                 | Represents shares purchased pursuant to the accelerated share repurchase agreement withGS&Co.entered into onFebruary 7, 2019, as well as other share repurchases. See above for additional information.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
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|(b)                                                                                                                                                                                                                 | Represents shares purchased pursuant to the accelerated share repurchase agreement with Citibank entered into onMarch 12, 2018, as well as other share repurchases. See above for additional information.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

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