Loans and Related Allowance for Credit Losses (Narrative) (Details) - USD ($) $ in Billions	9 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Increase (decrease) in financing receivable and off-balance sheet, credit loss, allowance	$ 2.7
Nonperforming Financial Instruments [Member]
Troubled debt restructurings (TDRs)	0.8	$ 0.9
Performing, including Consumer Credit Card TDRs [Member]
Troubled debt restructurings (TDRs)	0.8	0.8
Federal Reserve Bank [Member]
Loans pledged as collateral for the ability to borrow	30.5	16.9
Federal Home Loan Bank [Member]
Loans pledged as collateral for the ability to borrow	68.9	$ 68.0
Total commercial
Increase (decrease) in commercial reserves	2.2
Total consumer
Increase (decrease) in consumer reserves	$ 0.5

Financing Receivable And Off-Balance Sheet, Credit Loss, Allowance, Increase (Decrease) In Commercial Reserves

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- Definition

Financing Receivable And Off-Balance Sheet, Credit Loss, Allowance, Increase (Decrease) In Consumer Reserves

+ References

No definition available.

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- Definition

Increase (Decrease) In Financing Receivable And Off-Balance Sheet, Credit Loss, Allowance

+ References

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- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18845-111554

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- Definition

The sum of the carrying amounts, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of related debt obligations, primarily secured borrowings and repurchase agreements, and for which the transferees are not permitted to sell or re-pledge them to an unrelated party.

+ 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 (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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