Loans and ACL - Types of Modifications and Impact to Allowance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Newly Designated TDRs \| Commercial \| Commercial and industrial
Financing Receivable, Modifications [Line Items]
ALLL Impact	$ 0	$ 3	$ 3
Newly Designated TDRs \| Commercial \| CRE
Financing Receivable, Modifications [Line Items]
ALLL Impact	0	1	0
Newly Designated TDRs \| Retail \| Residential mortgage
Financing Receivable, Modifications [Line Items]
ALLL Impact	16	25	28
Newly Designated TDRs \| Retail \| Direct
Financing Receivable, Modifications [Line Items]
ALLL Impact	0	0	0
Newly Designated TDRs \| Retail \| Indirect
Financing Receivable, Modifications [Line Items]
ALLL Impact	22	21	21
Newly Designated TDRs \| Revolving credit
Financing Receivable, Modifications [Line Items]
ALLL Impact	4	4	4
Newly Designated TDRs \| Rate \| Commercial \| Commercial and industrial
Financing Receivable, Modifications [Line Items]
TDRs	74	79	105
Newly Designated TDRs \| Rate \| Commercial \| CRE
Financing Receivable, Modifications [Line Items]
TDRs	32	14	12
Newly Designated TDRs \| Rate \| Retail \| Residential mortgage
Financing Receivable, Modifications [Line Items]
TDRs	250	357	431
Newly Designated TDRs \| Rate \| Retail \| Direct
Financing Receivable, Modifications [Line Items]
TDRs	8	10	14
Newly Designated TDRs \| Rate \| Retail \| Indirect
Financing Receivable, Modifications [Line Items]
TDRs	195	192	169
Newly Designated TDRs \| Rate \| Revolving credit
Financing Receivable, Modifications [Line Items]
TDRs	18	19	17
Newly Designated TDRs \| Structure \| Commercial \| Commercial and industrial
Financing Receivable, Modifications [Line Items]
TDRs	62	101	96
Newly Designated TDRs \| Structure \| Commercial \| CRE
Financing Receivable, Modifications [Line Items]
TDRs	3	10	16
Newly Designated TDRs \| Structure \| Retail \| Residential mortgage
Financing Receivable, Modifications [Line Items]
TDRs	30	46	53
Newly Designated TDRs \| Structure \| Retail \| Direct
Financing Receivable, Modifications [Line Items]
TDRs	2	3	1
Newly Designated TDRs \| Structure \| Retail \| Indirect
Financing Receivable, Modifications [Line Items]
TDRs	4	6	7
Newly Designated TDRs \| Structure \| Revolving credit
Financing Receivable, Modifications [Line Items]
TDRs	0	0	0
Re-Modification of Previously Designated TDRs
Financing Receivable, Modifications [Line Items]
ALLL Impact	0	0	0
Re-Modification of Previously Designated TDRs \| Rate
Financing Receivable, Modifications [Line Items]
TDRs	120	176	79
Re-Modification of Previously Designated TDRs \| Structure
Financing Receivable, Modifications [Line Items]
TDRs	$ 15	$ 44	$ 46

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

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&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=82895541&loc=d3e18845-111554

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