Commercial and investor real estate loans subject to charge offs, maximum.

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Days For Commercial and Industrial Loans To Be Evaluated As Potential Charge Off

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Days For Consumer Close-Ended Loans To Be Evaluated As Potential Charge Off

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Day sfor consumer first lien postion loans to be evaluated as a potential charge off

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Days for home equity loans in a second lien position to be evaluated as potential charge off

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Days for Consumer Loans in an Open-Ended Position to be Evaluated for Potential Charge Off

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Days for Credit Cards to be Evaluated for Potential Charge Off

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Amount of increase (decrease) in allowance for credit loss on financing receivable.

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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.

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Amount of cumulative tax effect on beginning retained earnings from change in accounting principle.

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Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Modifications [Line Items]
Retained earnings		$ 3,770,000,000	$ 3,751,000,000
Commercial And Investor Real Estate Loans Subject To Charge Offs Maximum		$ 250,000
Days For Commercial and Investor Real Estate Loans To Be Evaluated As Potential Charge Off		180 days
Days For Consumer First Lien Postion Loans To Be Evaluated As Potential Charge Off		180 days
Days For Home Equity Loans In Second Lien Position To Be Evaluated As Potential Charge Off		120 days
Days For Consumer Close-Ended Loans To Be Evaluated As Potential Charge Off		120 days
Days for Consumer Loans in an Open-Ended Position to be Evaluated for Potential Charge Off		180 days
Days for Credit Cards to be Evaluated for Potential Charge Off		180 days
Provision for credit losses (1)		$ 878,000,000
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Modifications [Line Items]
Retained earnings		377,000,000
CECL [Member]
Financing Receivable, Modifications [Line Items]
Provision for credit losses (1)	$ 501,000,000
CumulativeEffectPeriodOfAdoptionAdjustmentAttributableToTheAllowance [Member]
Financing Receivable, Modifications [Line Items]
Retained earnings		375,000,000
CumulativeEffectPeriodOfAdoptionAdjustmentAttributableToOtherFinancialAssets [Member]
Financing Receivable, Modifications [Line Items]
Retained earnings		2,000,000
Retained Earnings (Deficit) [Member] \| Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Modifications [Line Items]
Retained earnings		$ (377,000,000)	$ 2,000,000	$ (2,000,000)
Retained Earnings (Deficit) [Member] \| CECL Day 1 Adjustment to the Allowance [Member]
Financing Receivable, Modifications [Line Items]
Retained earnings	375,000,000
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle	$ 126,000,000
Minimum [Member]
Financing Receivable, Modifications [Line Items]
Lessee, Operating Lease, Term of Contract		1 year
Maximum [Member]
Financing Receivable, Modifications [Line Items]
Lessee, Operating Lease, Term of Contract		20 years
Leasehold improvements \| Minimum [Member]
Financing Receivable, Modifications [Line Items]
Property, Plant and Equipment, Useful Life		7 years
Leasehold improvements \| Maximum [Member]
Financing Receivable, Modifications [Line Items]
Property, Plant and Equipment, Useful Life		40 years
Furniture and equipment \| Minimum [Member]
Financing Receivable, Modifications [Line Items]
Property, Plant and Equipment, Useful Life		3 years
Furniture and equipment \| Maximum [Member]
Financing Receivable, Modifications [Line Items]
Property, Plant and Equipment, Useful Life		10 years