Guarantee Arrangements and Pledged Assets - Summary of Credit Ratings of Credit Risk Related Guarantees (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	271,105
Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	262,985
Investment Grade [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	227,091
Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	220,004
Non-Investment Grade [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	44,014
Non-Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	42,981
Single name CDS [Member]
Credit Derivatives [Line Items]
Average Life in years	2 years 6 months
Single name CDS [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	173,938
Single name CDS [Member] | Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	138,852
Single name CDS [Member] | Non-Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	35,086
Structured CDS [Member]
Credit Derivatives [Line Items]
Average Life in years	1 year 8 months 12 days
Structured CDS [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	47,806
Structured CDS [Member] | Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	43,798
Structured CDS [Member] | Non-Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	4,008
Index credit derivatives [Member]
Credit Derivatives [Line Items]
Average Life in years	3 years 2 months 12 days
Index credit derivatives [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	26,732
Index credit derivatives [Member] | Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	25,999
Index credit derivatives [Member] | Non-Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	733
Total return swaps [Member]
Credit Derivatives [Line Items]
Average Life in years	7 years 2 months 12 days
Total return swaps [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	14,509
Total return swaps [Member] | Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	11,355
Total return swaps [Member] | Non-Investment Grade [Member] | Sell-protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	3,154
Standby Letters of Credit [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	8,120
Average Life in years	1 year 3 months 18 days
Standby Letters of Credit [Member] | Investment Grade [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	7,087
Standby Letters of Credit [Member] | Non-Investment Grade [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	1,033