Derivative Financial Instruments - Carrying Value of Hedged Items in Fair Value Hedge (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2020	Dec. 31, 2019
Securities available-for-sale [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged items	[1]	$ 9,024	$ 7,277
Active hedged asset adjustments		963	554
Discontinued hedged asset adjustments		763	428
Total hedged asset adjustments		1,726	982
Deposits [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	[1],[2]	5,252
Active hedged liability adjustments	[2]	252
Discontinued hedged liability adjustments	[2]	0
Total hedged liability adjustments	[2]	252
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]	2,244	10,975
Active hedged liability adjustments		260	285
Discontinued hedged liability adjustments		(16)	(32)
Total hedged liability adjustments		$ 244	$ 253

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

[2] During the first nine months of 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 14, "Related Party Transactions," for additional information.