Allowance For Credit Losses (TDRs on Financing Receivables) (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($) obligor	Dec. 31, 2019 USD ($) obligor
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	689	543
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 440	$ 374
Increase in Allowance at Modification	$ 11	$ 9
Commercial And Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	151	97
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 250	$ 259
Increase in Allowance at Modification	$ 0	$ 3
Commercial Real Estate Mortgage - Owner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	21	51
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 16	$ 29
Increase in Allowance at Modification	$ 0	$ 0
Commercial Real Estate Construction - Owner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	1	1
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 1	$ 2
Increase in Allowance at Modification	$ 0	$ 0
Commercial investor real estate mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	11	12
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 78	$ 26
Increase in Allowance at Modification	$ 0	$ 0
Commercial Investor Real Estate Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	4	12
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 5	$ 18
Increase in Allowance at Modification	$ 0	$ 2
Residential First Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	378	159
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 85	$ 32
Increase in Allowance at Modification	$ 11	$ 4
Home Equity Lines of Credit[Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	0	0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0
Increase in Allowance at Modification	$ 0	$ 0
Home Equity Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	43	99
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 4	$ 7
Increase in Allowance at Modification	$ 0	$ 0
Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	14	37
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0
Increase in Allowance at Modification	$ 0	$ 0
Indirect-vehicles and other consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	66	75
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 1	$ 1
Increase in Allowance at Modification	$ 0	$ 0
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	173	149
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 267	$ 290
Increase in Allowance at Modification	$ 0	$ 3
Total Investor Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	15	24
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 83	$ 44
Increase in Allowance at Modification	$ 0	$ 2
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Obligors \| obligor	501	370
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 90	$ 40
Increase in Allowance at Modification	$ 11	$ 4

Amount of other addition (reduction) in allowance reserve for credit loss.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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-Paragraph 33
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