Derivatives and Hedging Activities - Gain (Loss) from Interest Rate Hedges and Related Hedged Borrowings and Deposits (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Interest expense	$ 8,938	$ 17,376	$ 15,912
Interest Rate Contract [Member] \| Fair Value Hedging [Member] \| Derivative Contracts Accounted for as Hedges [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	3,862	3,196	(1,854)
Gain (Loss) Recognized On Hedged Borrowings and Deposits	$ (4,557)	$ (3,657)	$ 1,295

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Amount of the cost of borrowed funds accounted for as interest expense.

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