Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) - Net Interest Income [Member] - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	$ 28	$ 159	$ 174	$ (638)
Gain (Loss) on Hedged Items	(34)	(172)	(177)	587
Securities available-for-sale [Member] \| Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	29	182	221	(962)
Gain (Loss) on Hedged Items	(4)	(135)	(144)	1,095
Deposits [Member] \| Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(3)	33	(35)	153
Gain (Loss) on Hedged Items	(13)	(69)	(5)	(250)
Long-term Debt [Member] \| Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	2	(56)	(12)	171
Gain (Loss) on Hedged Items	$ (17)	$ 32	$ (28)	$ (258)

Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986

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- Definition

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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