Short-Term Borrowings - Components of Short-Term Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Balance at year end, Securities Sold Under Repurchase Agreements	$ 0	$ 0
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Balance at year end, Federal Funds Purchase	0	200	$ 0
Average during the year	455	61	537
Maximum month-end balance	$ 2,285	$ 1,000	$ 3,197
Weighted-average rate during the year	1.24%	2.12%	1.68%
Weighted-average rate at December 31	0.00%	1.56%	0.00%
Securities Sold under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Balance at year end, Securities Sold Under Repurchase Agreements	$ 220	$ 187	$ 319
Average during the year	215	203	391
Maximum month-end balance	$ 267	$ 283	$ 614
Weighted-average rate during the year	0.11%	0.22%	0.09%
Weighted-average rate at December 31	0.04%	0.09%	0.09%
Other Short Term Borrowings [Member]
Short-term Debt [Line Items]
Balance at year end, Other Short-Term Borrowings	$ 759	$ 705	$ 544
Average during the year	1,452	730	915
Maximum month-end balance	$ 4,606	$ 847	$ 1,133
Weighted-average rate during the year	0.85%	2.31%	2.34%
Weighted-average rate at December 31	0.60%	1.99%	2.92%

Short Term Debt Weighted Average Interest Rate During Year

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- Definition

Amount of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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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.

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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.

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

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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, average borrowings during the period.

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No definition available.

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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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