Short-Term Borrowings - Outstanding and Weighted-Average Interest Rates of Short-Term Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Short-term Debt [Line Items]
Weighted-average interest rate as of year-end	1.52%	0.83%
Securities Sold Under Repurchase Agreements
Short-term Debt [Line Items]
Balance as of December 31	$ 1,867	$ 1,177	$ 1,575
Maximum outstanding as of any month-end	4,690	11,517	1,575
Average outstanding during the year	$ 3,904	$ 3,633	$ 667
Weighted-average interest rate as of year-end	0.08%	2.31%	0.00%
Weighted-average interest rate during the year	0.87%	0.39%	(0.00%)
Federal Funds Purchased
Short-term Debt [Line Items]
Balance as of December 31	$ 1,000	$ 0	$ 0
Maximum outstanding as of any month-end	1,000	0	0
Average outstanding during the year	$ 65	$ 0	$ 0
Weighted-average interest rate as of year-end	2.03%	0.00%	0.00%
Weighted-average interest rate during the year	4.82%	0.00%	0.00%
Tax-Exempt Investment Program
Short-term Debt [Line Items]
Balance as of December 31	$ 0	$ 0	$ 0
Maximum outstanding as of any month-end	0	0	616
Average outstanding during the year	$ 0	$ 0	$ 523
Weighted-average interest rate as of year-end	0.00%	0.00%	0.00%
Weighted-average interest rate during the year	0.00%	0.00%	0.31%
Other
Short-term Debt [Line Items]
Balance as of December 31	$ 2,500	$ 2,000	$ 0
Maximum outstanding as of any month-end	4,500	8,525	0
Average outstanding during the year	$ 784	$ 696	$ 315
Weighted-average interest rate as of year-end	3.43%	4.18%	0.00%
Weighted-average interest rate during the year	5.15%	0.01%	0.00%