Quarterly report pursuant to Section 13 or 15(d)

Outstanding Loans and Leases and Allowance for Credit Losses - Allowance for Credit Losses (Details)

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Outstanding Loans and Leases and Allowance for Credit Losses - Allowance for Credit Losses (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2023
Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Line Items]                
Allowance for credit losses     $ 14,693 $ 21,506 $ 14,693 $ 21,506    
Allowance for credit losses, period increase (decrease)         (6,000)      
Loan and leases receivable, allowance, period increase (decrease)         (5,600)      
Reserve for unfunded lending commitments, period increase (decrease)         (340)      
Increase in provision for credit losses     2,000   15,400      
Provision for credit losses     (624) 1,389 (4,105) 11,267    
Outstanding loans and leases, period increase (decrease), excluding loans accounted for under the fair value option         (1,000)      
Scenario, Forecast                
Financing Receivable, Allowance for Credit Loss [Line Items]                
Unemployment rate, economic outlook 5.00% 5.00%            
U.S. gross domestic product, economic outlook             1.90% 1.80%
Consumer real estate                
Financing Receivable, Allowance for Credit Loss [Line Items]                
Allowance for credit losses     653 993 653 993    
Loan and leases receivable, allowance, period increase (decrease)         (342)      
Outstanding loans and leases, period increase (decrease), excluding loans accounted for under the fair value option         (5,200)      
Credit card and other consumer                
Financing Receivable, Allowance for Credit Loss [Line Items]                
Allowance for credit losses     6,639 9,836 6,639 9,836    
Loan and leases receivable, allowance, period increase (decrease)         (2,600)      
Commercial                
Financing Receivable, Allowance for Credit Loss [Line Items]                
Allowance for credit losses     $ 7,401 $ 10,677 7,401 $ 10,677    
Loan and leases receivable, allowance, period increase (decrease)         (3,100)      
Commercial, excluding small business                
Financing Receivable, Allowance for Credit Loss [Line Items]                
Outstanding loans and leases, period increase (decrease), excluding loans accounted for under the fair value option         $ 17,900