Borrowings - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Line of Credit Facility [Line Items]
Other short-term borrowings	$ 8,405,000,000	$ 6,553,000,000
Weighted-average interest rate of short-term borrowings	5.48%	5.57%
Capacity of allowable commercial paper note issuance	$ 5,000,000,000
Commercial paper	0	$ 0
Secured Uncommitted Lines Of Credit
Line of Credit Facility [Line Items]
Other short-term borrowings	$ 700,000,000	1,650,000,000
Commercial paper | Maximum
Line of Credit Facility [Line Items]
Maturity term	270 days
Federal Reserve Bank Advances
Line of Credit Facility [Line Items]
Other short-term borrowings	$ 0	0
Total borrowing capacity	32,900,000,000	6,200,000,000
Federal Reserve Bank Term Funding Program (BTFP)
Line of Credit Facility [Line Items]
Other short-term borrowings		0
Total borrowing capacity		39,200,000,000
Repurchase Agreements
Line of Credit Facility [Line Items]
Other short-term borrowings	7,700,000,000	4,900,000,000
Line of Credit | TDAC
Line of Credit Facility [Line Items]
Other short-term borrowings	700,000,000	700,000,000
Line of Credit | Committed Lines Of Credit With External Banks
Line of Credit Facility [Line Items]
Other short-term borrowings	0
Total borrowing capacity	2,100,000,000
Line of Credit | Uncommitted Lines Of Credit With External Banks
Line of Credit Facility [Line Items]
Other short-term borrowings	0	0
Total borrowing capacity	1,600,000,000
Line of Credit | Secured Uncommitted Lines Of Credit
Line of Credit Facility [Line Items]
Other short-term borrowings	0	950,000,000
Federal Home Loan Bank Advances | Secured Credit Facility
Line of Credit Facility [Line Items]
Borrowings outstanding	$ 24,000,000,000	$ 26,400,000,000
Weighted average interest rate	5.33%	5.34%
Total borrowing capacity	$ 63,400,000,000	$ 63,100,000,000