Fair Value Measurements - Change in Fair Values of Level 3 Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Trading Account Assets [Member] \| Other Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Gains (Losses) Included in Earnings		$ 4
Settlements		(4)
Unrealized Gains (Losses) Included in Earnings		(1)
Trading Account Assets [Member] \| States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		3
Sales		(3)
Trading Account Assets [Member] \| Other Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Gains (Losses) Included in Earnings		4
Sales		(4)
Securities Available for Sale [Member] \| Other Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Purchases	10
Ending Balance	10
Other Investments [Member] \| Principal Investments Direct [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	141	191
Gains (Losses) Included in Earnings	18	(11)
Purchases	1	8
Sales	(58)	(47)
Ending Balance	102	141
Unrealized Gains (Losses) Included in Earnings	13	(23)
Other Investments [Member] \| Principal Investments Indirect [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	413	436
Gains (Losses) Included in Earnings	57	58
Purchases	8	23
Sales	(176)	(104)
Ending Balance	302	413
Unrealized Gains (Losses) Included in Earnings	(26)	18
Other Investments [Member] \| Equity and Mezzanine Investments Direct [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Unrealized Gains (Losses) Included in Earnings		8
Other Investments [Member] \| Equity and Mezzanine Investments Indirect [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	23	41
Gains (Losses) Included in Earnings	(1)	2
Settlements	(12)	(20)
Ending Balance	10	23
Unrealized Gains (Losses) Included in Earnings	(1)	2
Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	25	19
Gains (Losses) Included in Earnings	4	(10)
Purchases	4	1
Sales	(3)	(2)
Transfers into Level 3	7	46
Transfers out of Level 3	(24)	(29)
Ending Balance	13	25
Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		1
Gains (Losses) Included in Earnings		(1)
Transfers into Level 3	1
Transfers out of Level 3	(1)
Credit [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	3	4
Gains (Losses) Included in Earnings	(17)	(8)
Settlements	16	7
Ending Balance	$ 2	$ 3

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Fair value measurement with unobservable inputs reconciliation recurring basis asset and liabilities value.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ 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 (c)(1)

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ 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 (c)(2)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ 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 c

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ 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 (c)(2)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ 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 (c)(3)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ 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 (c)(3)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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