Derivative Financial Instruments - Carrying Value of Hedged Items in Fair Value Hedge (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Securities available-for-sale [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged items	[1]	$ 7,966	$ 7,277
Active hedged asset adjustments		681	554
Discontinued hedged asset adjustments		738	428
Total hedged asset adjustments		1,419	982
Deposits [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	[1],[2]	5,214
Active hedged liability adjustments	[2]	214
Discontinued hedged liability adjustments	[2]	0
Total hedged liability adjustments	[2]	214
Fixed-rate senior debt obligations recharacterized as time deposits		5,000
Long-term Debt [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	[1]	2,227	10,975
Active hedged liability adjustments		242	285
Discontinued hedged liability adjustments		(15)	(32)
Total hedged liability adjustments		$ 227	$ 253

[1] The carrying amount of securities AFS represents the amortized cost basis.

[2] During 2020, $5.0 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 23, "Related Party Transactions," for additional information.