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Investment Securities - Narrative (Details)
3 Months Ended
Mar. 31, 2024
USD ($)
security
Mar. 31, 2023
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]        
Allowance for credit losses on HTM investment securities $ 1,000,000   $ 1,000,000  
Allowance for credit losses on available-for-sale securities $ 0 $ 2,000,000 0 $ 2,000,000
Percentage of investment portfolio considered investment grade 99.00%      
Provision $ 0      
Charge-offs 0      
Charge-offs 0 $ 0    
Marketable securities, unrealized gain (loss) $ (6,580,000,000)      
Number of securities in loss position | security 1,731      
Asset pledged as collateral        
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]        
Debt securities $ 81,510,000,000   $ 71,300,000,000