Borrowings - Narrative (Details) - USD ($)		9 Months Ended
		Sep. 30, 2023	Dec. 31, 2022
Line of Credit Facility [Line Items]
Other short-term borrowings	[1]	$ 7,550,000,000	$ 4,650,000,000
Weighted-average interest rate of short-term borrowings		5.39%	4.97%
Capacity of allowable commercial paper note issuance		$ 5,000,000,000
Commercial paper		85,000,000	$ 250,000,000
Secured Uncommitted Lines Of Credit
Line of Credit Facility [Line Items]
Other short-term borrowings		$ 950,000,000
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		7,200,000,000	7,800,000,000
Federal Reserve Bank Term Funding Program (BTFP)
Line of Credit Facility [Line Items]
Other short-term borrowings		0
Total borrowing capacity		40,200,000,000
Repurchase Agreements
Line of Credit Facility [Line Items]
Other short-term borrowings		6,500,000,000	4,400,000,000
Line of Credit | TDAC
Line of Credit Facility [Line Items]
Other short-term borrowings		0	0
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		1,800,000,000
Line of Credit | Secured Uncommitted Lines Of Credit
Line of Credit Facility [Line Items]
Other short-term borrowings		950,000,000
Federal Home Loan Bank Advances | Secured Credit Facility
Line of Credit Facility [Line Items]
Borrowings outstanding		$ 31,800,000,000	$ 12,400,000,000
Weighted average interest rate		5.17%	4.88%
Total borrowing capacity		$ 55,600,000,000	$ 68,600,000,000

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.