Fair Value Option - Aggregate Differences (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Long-term beneficial interests
Performing loans, ninety days or more past due	$ 0	$ 0
Lending-related commitments, fair value option elected
Long-term beneficial interests
Contractual amount of lending-related commitments	10,900,000,000	7,400,000,000
Contractual lending-related commitments, fair value	(225,000,000)	(76,000,000)
Contractual principal outstanding
Loans
Nonaccrual loans	4,078,000,000	4,258,000,000
Total loans	53,350,000,000	44,954,000,000
Contractual principal outstanding \| Principal-protected debt
Long-term debt
Total long-term debt	29,380,000,000	26,297,000,000
Contractual principal outstanding \| Loans reported as trading assets
Loans
Nonaccrual loans	4,078,000,000	4,219,000,000
All other performing loans	46,105,000,000	38,157,000,000
Contractual principal outstanding \| Loans
Loans
Nonaccrual loans	0	39,000,000
All other performing loans	3,167,000,000	2,539,000,000
Fair value
Loans
Nonaccrual loans	1,159,000,000	1,371,000,000
Total loans	48,953,000,000	40,469,000,000
Long-term debt
Total long-term debt	50,096,000,000	47,519,000,000
Long-term beneficial interests
Total long-term beneficial interests	1,000,000	45,000,000
Fair value \| Principal-protected debt
Long-term debt
Total long-term debt	25,563,000,000	23,848,000,000
Fair value \| Nonprincipal-protected debt
Long-term debt
Total long-term debt	24,533,000,000	23,671,000,000
Long-term beneficial interests
Total long-term beneficial interests	1,000,000	45,000,000
Fair value \| Loans reported as trading assets
Loans
Nonaccrual loans	1,159,000,000	1,371,000,000
All other performing loans	44,718,000,000	36,590,000,000
Fair value \| Loans
Loans
Nonaccrual loans	0	0
All other performing loans	3,076,000,000	2,508,000,000
Fair value over/(under) contractual principal outstanding
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,919,000,000)	(2,887,000,000)
Total loans	(4,397,000,000)	(4,485,000,000)
Fair value over/(under) contractual principal outstanding \| Principal-protected debt
Long-term debt
Long-term debt, Fair value over/(under) contractual principal outstanding	(3,817,000,000)	(2,449,000,000)
Fair value over/(under) contractual principal outstanding \| Loans reported as trading assets
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,919,000,000)	(2,848,000,000)
All other performing loans	(1,387,000,000)	(1,567,000,000)
Fair value over/(under) contractual principal outstanding \| Loans
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	0	(39,000,000)
All other performing loans	$ (91,000,000)	$ (31,000,000)

Represents the portion of loans held as assets for which the fair value option has been elected, valued at fair value.

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Fair Value Options Other Performing Loans.

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- Definition

Guarantor Obligations, Net of Other Commitments, Current Carrying Value

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- Definition

Long Term Beneficial Interests.

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Long term beneficial interests.

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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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This item represents the aggregate fair value of loans held as assets that are in nonaccrual status for which the fair value option has been elected, if the entity's policy is to recognize interest income separately from other changes in fair value.

+ 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)(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

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
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