Derivative Financial Instruments - Carrying Value of Hedged Items in Fair Value Hedge (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Securities available-for-sale [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged items	[1]		$ 9,547	$ 7,277
Active hedged asset adjustments			1,167	554
Discontinued hedged asset adjustments			780	428
Total hedged asset adjustments			1,947	982
Deposits [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	[1],[2]		3,234
Active hedged liability adjustments	[2]		234
Discontinued hedged liability adjustments	[2]		0
Total hedged liability adjustments	[2]		234
Fixed-rate senior debt obligations recharacterized as time deposits		$ 3,000
Long-term Debt [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	[1]		5,932	10,975
Active hedged liability adjustments			328	285
Discontinued hedged liability adjustments			(19)	(32)
Total hedged liability adjustments			$ 309	$ 253

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

[2] 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.