Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Notional Value, Assets	$ 158,922	$ 113,188
Fair Value, Assets	2,219	2,543
Notional Value, Liabilities	144,621	122,497
Fair Value, Liabilities	2,049	2,610
Interest Rate Contracts [Member] \| Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	37,701	38,501
Fair Value, Assets	$ 794	$ 930
Derivative Asset Average Remaining Maturity Period	5 years 3 months 8 days	4 years 26 days
Notional Value, Liabilities	$ 56,518	$ 39,403
Fair Value, Liabilities	$ 561	$ 632
Derivative Liability Average Remaining Maturity Period	3 years 9 months 22 days	4 years 10 months 21 days
Interest Rate Contracts [Member] \| Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 59,030	$ 36,671
Fair Value, Assets	$ 582	$ 612
Derivative Asset Average Remaining Maturity Period	3 years 7 months 17 days	4 years 11 months 26 days
Notional Value, Liabilities	$ 34,153	$ 40,324
Fair Value, Liabilities	$ 694	$ 996
Derivative Liability Average Remaining Maturity Period	5 years 7 months 17 days	4 years 26 days
Interest Rate Contracts [Member] \| Options [Member] \| Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 29,624	$ 14,545
Fair Value, Assets	$ 18	$ 51
Derivative Asset Average Remaining Maturity Period	1 year 7 months 17 days	1 year 10 months 6 days
Notional Value, Liabilities	$ 505	$ 125
Fair Value, Liabilities	$ 10	$ 2
Derivative Liability Average Remaining Maturity Period	4 years 5 months 20 days	1 year 4 months 13 days
Interest Rate Contracts [Member] \| Options [Member] \| Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 505	$ 125
Fair Value, Assets	$ 11	$ 3
Derivative Asset Average Remaining Maturity Period	4 years 5 months 20 days	1 year 4 months 13 days
Notional Value, Liabilities	$ 27,283	$ 13,518
Fair Value, Liabilities	$ 16	$ 50
Derivative Liability Average Remaining Maturity Period	1 year 6 months 10 days	1 year 8 months 12 days
Interest Rate Contracts [Member] \| Futures [Member] \| Purchased [Member]
Derivative [Line Items]
Notional Value, Assets		$ 306
Derivative Asset Average Remaining Maturity Period		1 year 11 months 15 days
Notional Value, Liabilities		$ 7,111
Fair Value, Liabilities		$ 7
Derivative Liability Average Remaining Maturity Period		10 months 25 days
Interest Rate Contracts [Member] \| Futures [Member] \| Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 4,273
Fair Value, Assets	$ 1
Derivative Asset Average Remaining Maturity Period	1 year 5 months 12 days
Foreign Exchange Rate Contracts [Member] \| Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 24,501	$ 20,664
Fair Value, Assets	$ 732	$ 849
Derivative Asset Average Remaining Maturity Period	9 months 14 days	6 months 29 days
Notional Value, Liabilities	$ 22,874	$ 19,640
Fair Value, Liabilities	$ 687	$ 825
Derivative Liability Average Remaining Maturity Period	9 months 25 days	7 months 6 days
Foreign Exchange Option [Member] \| Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,288	$ 2,376
Fair Value, Assets	$ 81	$ 98
Derivative Asset Average Remaining Maturity Period	1 year 5 months 20 days	1 year 8 months 2 days
Foreign Exchange Option [Member] \| Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 3,288	$ 2,376
Fair Value, Liabilities	$ 81	$ 98
Derivative Liability Average Remaining Maturity Period	1 year 5 months 20 days	1 year 8 months 2 days

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

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+ References

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- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

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- Definition

Derivative asset average remaining maturity period.

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- Definition

Derivative liability average remaining maturity period.

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