Loan Servicing - Residential MSR Sensitivity (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Residential MSRs
Servicing Assets at Fair Value [Line Items]
Composition of loans serviced for others	100.00%	100.00%
Weighted average life	6 years 10 months 24 days	6 years 4 months 24 days
Residential MSRs \| Min
Servicing Assets at Fair Value [Line Items]
Prepayment speed	6.00%	7.10%
OAS	8.30%	8.40%
Residential MSRs \| Max
Servicing Assets at Fair Value [Line Items]
Prepayment speed	8.70%	10.10%
OAS	8.90%	8.90%
Residential MSRs \| Weighted Average
Servicing Assets at Fair Value [Line Items]
Prepayment speed	7.90%	9.10%
Effect on fair value of a 10% increase	$ (28)	$ (31)
Effect on fair value of a 20% increase	$ (55)	$ (60)
OAS	8.50%	8.50%
Effect on fair value of a 10% increase	$ (30)	$ (28)
Effect on fair value of a 20% increase	$ (58)	$ (54)
Fixed-rate residential mortgage loans
Servicing Assets at Fair Value [Line Items]
Composition of loans serviced for others	99.20%	99.10%
Adjustable-rate residential mortgage loans
Servicing Assets at Fair Value [Line Items]
Composition of loans serviced for others	0.80%	0.90%

Option adjusted spread assumption used in valuing MSRs

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- Definition

Composition Of Mortgage Loans Serviced For Others

+ References

No definition available.

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- Definition

Effect on fair value of a 10% increase in weighted average OAS

+ References

No definition available.

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- Definition

Effect on fair value of a 20% increase in weighted average OAS

+ References

No definition available.

+ Details

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- Definition

Weighted average life of securitized assets regardless of when the transfer occurred, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

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- Definition

Estimated rate of prepayment of principal on financial assets regardless of when the transfer occurred.

+ References

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- Definition

The hypothetical financial impact of a 10 percent adverse change of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

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- Definition

The hypothetical financial impact of a 20 percent adverse change of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

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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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