BORROWINGS - Summary of Short-Term Borrowings (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Securities sold under repurchase agreements	$ 407	$ 403
Federal Home Loan Bank advances	1,030	1,280
Subordinated notes	126	121
Total short-term borrowings	$ 1,563	$ 1,804

Amount of short-term subordinated notes with no maturity date or original maturities of less than one year.

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Amount of advance from Federal Home Loan Bank (FHLBank) maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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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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