Acquisition, Divestiture, and Discontinued Operations - Principal and Fair Value Amounts for Portfolio Loans at Carrying Value, and Portfolio Loans at Fair Value (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	$ 49	$ 72	$ 54
Portfolio [Member] \| Carrying Amount [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	23	26	26
Loans placed on nonaccrual status	5	8	8
Portfolio Loans at Fair Value [Member] \| Carrying Amount [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	0	1	0
Portfolio Loans at Fair Value [Member] \| Fair Value [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	0	1	0
Loans Held For Sale Fair Value [Member] \| Carrying Amount [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	0	0	5
Loans Held For Sale Fair Value [Member] \| Fair Value [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	$ 0	$ 0	$ 4

This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612

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- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5111-111524

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

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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.

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