Loans and ACL - Types of Modifications and Impact to Allowance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Newly Designated TDRs \| Commercial: \| Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	$ 2	$ 0	$ 3
Newly Designated TDRs \| Commercial: \| CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	0	0	0
Newly Designated TDRs \| Commercial: \| Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	5	0	1
Newly Designated TDRs \| Consumer: \| Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	13	16	25
Newly Designated TDRs \| Consumer: \| Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	0	0	0
Newly Designated TDRs \| Consumer: \| Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	25	22	21
Newly Designated TDRs \| Consumer: \| Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	0	0	0
Newly Designated TDRs \| Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	5	4	4
Newly Designated TDRs \| Rate \| Commercial: \| Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	56	74	79
Newly Designated TDRs \| Rate \| Commercial: \| CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1	31	6
Newly Designated TDRs \| Rate \| Commercial: \| Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	36	1	8
Newly Designated TDRs \| Rate \| Consumer: \| Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	296	250	357
Newly Designated TDRs \| Rate \| Consumer: \| Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	8	8	10
Newly Designated TDRs \| Rate \| Consumer: \| Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	209	191	188
Newly Designated TDRs \| Rate \| Consumer: \| Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	4	4	4
Newly Designated TDRs \| Rate \| Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	24	18	19
Newly Designated TDRs \| Structure \| Commercial: \| Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	11	62	101
Newly Designated TDRs \| Structure \| Commercial: \| CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1	2	8
Newly Designated TDRs \| Structure \| Commercial: \| Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	1	2
Newly Designated TDRs \| Structure \| Consumer: \| Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	27	30	46
Newly Designated TDRs \| Structure \| Consumer: \| Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	3	2	3
Newly Designated TDRs \| Structure \| Consumer: \| Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	8	4	6
Newly Designated TDRs \| Structure \| Consumer: \| Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0	0
Newly Designated TDRs \| Structure \| Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0	0
Re-Modification of Previously Designated TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL Impact	0	0	0
Re-Modification of Previously Designated TDRs \| Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	53	120	176
Re-Modification of Previously Designated TDRs \| Structure
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	$ 23	$ 15	$ 44

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.

No definition available.

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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=118936363&loc=SL6953676-111524

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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=118939409&loc=d3e18845-111554

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