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Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 187.0	$ 132.0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	95.0	57.0
Troubled Debt Restructuring, Charge-offs	20.9	18.6
Troubled Debt Restructurings, Recorded Balance Modified During The Period	83.0	37.0
US Government Agency Insured Loans | Residential Mortgage [Member] | Loans to individuals [Member] | Accruing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 152.0	$ 92.0

X

- Definition

Represents the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructuring and are performing according to modified terms.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ 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=121611835&loc=SL6953676-111524

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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=121611835&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=121585226&loc=d3e18845-111554

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- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: 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=121585226&loc=d3e18845-111554

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