Short-Term Borrowings - Outstanding and weighted-average interest rates of short-term borrowings (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Weighted-average interest rate as of year-end	0.31%	0.93%
Securities Sold Under Repurchase Agreements
Short-term Debt [Line Items]
Balance as of December 31	$ 1,575	$ 3,413	$ 1,102
Maximum outstanding as of any month-end	1,575	5,373	4,125
Average outstanding during the year	$ 667	$ 2,615	$ 1,616
Weighted-average interest rate as of year-end	0.00%	0.00%	0.00%
Weighted-average interest rate during the year	(0.00%)	0.14%	1.90%
Tax-Exempt Investment Program
Short-term Debt [Line Items]
Balance as of December 31	$ 0	$ 616	$ 823
Maximum outstanding as of any month-end	616	823	931
Average outstanding during the year	$ 523	$ 771	$ 898
Weighted-average interest rate as of year-end	0.00%	0.23%	1.75%
Weighted-average interest rate during the year	0.31%	0.78%	1.51%
Other
Short-term Debt [Line Items]
Balance as of December 31	$ 0	$ 3,302	$ 0
Maximum outstanding as of any month-end	0	25,665	0
Average outstanding during the year	$ 315	$ 8,251	$ 3
Weighted-average interest rate as of year-end	0.00%	1.35%	0.00%
Weighted-average interest rate during the year	0.00%	1.23%	0.01%

Short Term Debt Weighted Average Interest Rate During The Period

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Weighted average interest rate of short-term debt outstanding calculated at point in time.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1402
-Paragraph (a)

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For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, maximum month-end borrowings during the period.

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