Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Summary of Credit Ratings of Credit Risk Related Guarantees (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021		Dec. 31, 2020
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions		$ 24,660	[1]	$ 28,045
Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions		$ 15,963
Single name credit default swap [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Average Life in years	[2]	2 years 7 months 6 days
Credit Ratings of the Obligors or the Transactions	[2]	$ 11,057
Index credit derivatives [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Average Life in years	[2]	3 years 3 months 18 days
Credit Ratings of the Obligors or the Transactions	[2]	$ 4,674
Total return swaps [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Average Life in years	[2]	5 years 7 months 6 days
Credit Ratings of the Obligors or the Transactions	[2]	$ 232
Standby Letters of Credit [Member]
Credit Derivatives [Line Items]
Average Life in years	[1]	1 year 2 months 12 days
Credit Ratings of the Obligors or the Transactions	[1]	$ 8,697
External Credit Rating, Investment Grade [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[1]	16,359
External Credit Rating, Investment Grade [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions		9,880
External Credit Rating, Investment Grade [Member] | Single name credit default swap [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[2]	8,767
External Credit Rating, Investment Grade [Member] | Index credit derivatives [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[2]	1,062
External Credit Rating, Investment Grade [Member] | Total return swaps [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[2]	51
External Credit Rating, Investment Grade [Member] | Standby Letters of Credit [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[1]	6,479
External Credit Rating, Non Investment Grade [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[1]	8,301
External Credit Rating, Non Investment Grade [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions		6,083
External Credit Rating, Non Investment Grade [Member] | Single name credit default swap [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[2]	2,290
External Credit Rating, Non Investment Grade [Member] | Index credit derivatives [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[2]	3,612
External Credit Rating, Non Investment Grade [Member] | Total return swaps [Member] | Sell Protection Credit Derivatives [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[2]	181
External Credit Rating, Non Investment Grade [Member] | Standby Letters of Credit [Member]
Credit Derivatives [Line Items]
Credit Ratings of the Obligors or the Transactions	[1]	$ 2,218

[1] External ratings for most of the obligors are not available. Presented above are the internal credit ratings which are developed using similar methodologies and rating scale equivalent to external credit ratings for purposes of classification as investment grade and non-investment grade.

[2] The credit ratings in the table represent external credit ratings for classification as investment grade and non-investment grade.