Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) - Net Interest Income [Member] - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019	[1]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		$ 62	$ (251)	$ (797)	[1]	$ (424)
Gain (Loss) on Hedged Items		(44)	198	759	[1]	349
Securities available-for-sale [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		12	(404)	(1,144)	[1]	(661)
Gain (Loss) on Hedged Items		52	488	1,230	[1]	838
Deposits [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		0		120	[1]
Gain (Loss) on Hedged Items	[1]	(35)		(181)
Long-term Debt [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		50	153	227	[1]	237
Gain (Loss) on Hedged Items		$ (61)	$ (290)	$ (290)	[1]	$ (489)

[1] During the first quarter of 2020, $3.0 billion of fixed-rate senior debt obligations issued to HSBC North America were recharacterized as time deposits. The cumulative amount of fair value hedging adjustments associated with this debt was reclassified to deposits. See Note 14, "Related Party Transactions," for additional information.