Strategic Initiatives - Branch Closings (Details) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($) branch	Mar. 31, 2020 branch	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) branch
Restructuring Cost and Reserve [Line Items]
Number of branches closing | branch	30	60			20
Lease impairment charges			$ 63	$ 76	$ 13
Notional value of derivative contracts			1,395,345	2,021,133
Interest rate contracts
Restructuring Cost and Reserve [Line Items]
Notional value of derivative contracts			246,092	509,403
Write Down of Lease Right-of-use Assets, Net of Estimated Sublease Income | Occupancy Expense, Net
Restructuring Cost and Reserve [Line Items]
Lease impairment charges	$ 29			67
Write Down of Leasehold Improvement Assets | Occupancy Expense, Net
Restructuring Cost and Reserve [Line Items]
Fixed asset impairment charges	18		18	16
Write Down of Equipment Assets | Occupancy Expense, Net
Restructuring Cost and Reserve [Line Items]
Fixed asset impairment charges	$ 3
Write Down Owned Office Space Properties to Fair Value | Occupancy Expense, Net
Restructuring Cost and Reserve [Line Items]
Lease impairment charges			13
Lease Termination and Associated Costs | Occupancy Expense, Net
Restructuring Cost and Reserve [Line Items]
Lease impairment charges			40	9
Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Trading losses associated with exit of certain derivative contracts			35	67
Allocated restructuring costs from affiliates			86	64
Restructuring Plan | Interest rate contracts
Restructuring Cost and Reserve [Line Items]
Notional value of derivative contracts			25,900	64,600
HSBC Group Restructuring Activities
Restructuring Cost and Reserve [Line Items]
Allocated restructuring costs from affiliates			$ 53	$ 16