Pledged and Restricted Assets - Type of Pledged Assets (Details) - USD ($) $ in Billions	Dec. 31, 2020	Dec. 31, 2019
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 47.5	$ 42.1
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	2.9	1.0
Government Sponsored Agency and Other Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	32.5	33.4
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 12.1	$ 7.7

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

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