Fair Value Option Elected, Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Loans Receivable, Fair Value Disclosure	$ 196	$ 222
Trading Loans [Member]
Loans Receivable, Fair Value Disclosure	2,149	2,517
Aggregate Unpaid Principal Balance Under the Fair Value Option	(2,111)	(2,488)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	38	29
Loans Held For Sale [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans Receivable, Fair Value Disclosure	1
Aggregate Unpaid Principal Balance Under the Fair Value Option	(1)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	0
Loans Held For Sale [Member] \| Performing Financial Instruments [Member]
Loans Receivable, Fair Value Disclosure	1,576	3,540
Aggregate Unpaid Principal Balance Under the Fair Value Option	(1,533)	(3,516)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	43	24
Loans Held For Investment [Member] \| Performing Financial Instruments [Member]
Loans Receivable, Fair Value Disclosure	192	219
Aggregate Unpaid Principal Balance Under the Fair Value Option	(198)	(225)
Fair Value, Option, Loans Held as Assets, Aggregate Difference	(6)	(6)
Loans Held For Investment [Member] \| Nonperforming Financing Receivable [Member]
Loans Receivable, Fair Value Disclosure	4	3
Aggregate Unpaid Principal Balance Under the Fair Value Option	(6)	(4)
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregated Difference	(2)	(1)
Brokered Time Deposits [Member]
Obligations, Fair Value Disclosure	236	78
Aggregate Unpaid Principal Balance Under the Fair Value Option	(233)	(80)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	3	(2)
Long-term Debt [Member]
Obligations, Fair Value Disclosure	530	963
Aggregate Unpaid Principal Balance Under the Fair Value Option	(517)	(924)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	$ 13	$ 39

Aggregate Unpaid Principal Balance Under the Fair Value Option, Asset

No definition available.

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- Definition

Fair value of obligations measured on a recurring basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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Period Type:	instant

- Definition

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of loans and long-term receivables (other than securities categorized as trading, available-for-sale or held-to-maturity) that have contractual principal amounts and for which the fair value option has been elected.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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- Definition

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of long-term debt instruments that have contractual principal amounts and for which the fair value option has been elected.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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- Definition

For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are in nonaccrual status.

+ References

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)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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- Definition

+ References

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)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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