Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Footnote Information) (Details) - USD ($)	3 Months Ended	6 Months Ended
Mar. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Abstract]
Deposits at the Federal Reserve Bank earning interest at the Federal Funds target rate		$ 16,400,000,000	$ 13,700,000,000
Interest-earning deposits in other financial institutions		5,800,000,000	3,000,000,000.0
Fair value of securities purchased under agreements to resell		777,000,000	$ 232,000,000
Securities received as collateral, amount repledged and sold	$ 0	$ 0

Interest bearing Deposits in Federal Reserve Banks

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- References

No definition available.

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- Definition

Fair value of collateral permitted, by contact or custom, to be sold or re-pledged.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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- Definition

For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=117340910&loc=d3e59706-112781

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.2)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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- Definition

The fair value of collateral received that has been sold or re-pledged and is owed to the debtor (transferor) upon settlement of the related contractual obligation under which it was received.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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