Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Financing Receivable, Troubled Debt Restructuring [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 145.0		$ 145.0		$ 166.0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	70.0		70.0		71.0
Financing Receivable, Troubled Debt Restructuring, Postmodification	6.2	$ 31.0	40.0	$ 76.0
Permanent mortgages guaranteed by US government agencies [Member] \| Accruing [Member] \| Residential mortgage [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 93.0		$ 93.0		$ 86.0

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

No definition available.

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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

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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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