Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) - Net Interest Income [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	[1]	$ (859)	$ (173)
Gain (Loss) on Hedged Items	[1]	803	151
Securities available-for-sale [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	[1]	(1,156)	(257)
Gain (Loss) on Hedged Items	[1]	1,178	350
Deposits [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	[1]	120
Gain (Loss) on Hedged Items	[1]	(146)
Long-term Debt [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	[1]	177	84
Gain (Loss) on Hedged Items	[1]	$ (229)	$ (199)

[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.