Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Cash and Cash Equivalents [Line Items]
Cash and due from banks	$ 4,009	$ 3,970
Russia
Cash and Cash Equivalents [Line Items]
Cash and due from banks	1,400	767
Western Europe
Cash and Cash Equivalents [Line Items]
Cash and due from banks	$ 1,900	$ 1,300

For banks and other depository institutions: Includes cash on hand (currency and coin), cash items in process of collection, noninterest bearing deposits due from other financial institutions (including corporate credit unions), and noninterest bearing balances with the Federal Reserve Banks, Federal Home Loan Banks and central banks.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant