Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
ASSETS
Cash and Due from Banks	$ 5,308,700,000	$ 4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,269,900,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,372,100,000	1,939,000,000
Securities Purchased under Agreements to Resell	500,100,000	784,700,000
Debt Securities - Held to Maturity	21,641,400,000	24,473,000,000
Loans
Deposits	123,941,700,000	116,164,000,000
Deposits
Savings Certificates and Other Time	5,636,600,000	4,109,700,000
Non U.S. Offices — Interest-Bearing	67,084,700,000	63,971,100,000
Federal Funds Purchased	2,600,500,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	511,400,000	784,700,000
Other Borrowings	6,526,200,000	6,567,800,000
Senior Notes	2,743,500,000	2,773,200,000
Unfunded Commitments	0
TOTAL ESTIMATED FAIR VALUE
ASSETS
Cash and Due from Banks	5,308,700,000	4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,269,900,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,372,100,000	1,939,000,000
Securities Purchased under Agreements to Resell	500,100,000	784,700,000
Debt Securities - Held to Maturity	21,641,400,000	24,473,000,000
Loans
Held for Investment	47,179,400,000	47,598,300,000
Other Assets	1,490,300,000	1,458,000,000
Deposits	123,996,600,000	116,207,600,000
Deposits
Federal Funds Purchased	2,600,500,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	511,400,000	784,700,000
Other Borrowings	6,544,300,000	6,607,400,000
Senior Notes	2,771,300,000	2,798,100,000
Long-Term Debt	4,135,700,000	4,186,800,000
Unfunded Commitments	163,300,000	178,800,000
Other Liabilities	42,700,000	74,900,000
TOTAL ESTIMATED FAIR VALUE | LEVEL 1
ASSETS
Cash and Due from Banks	5,308,700,000	4,791,500,000
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	0
Loans
Held for Investment	0	0
Other Assets	95,200,000	86,100,000
Deposits	0	0
Deposits
Federal Funds Purchased	0	0
Securities Sold Under Agreements to Repurchase	0	0
Other Borrowings	0	0
Senior Notes	0	0
Long-Term Debt	0	0
Unfunded Commitments	0	0
Other Liabilities	0	0
TOTAL ESTIMATED FAIR VALUE | LEVEL 2
ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	40,269,900,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,372,100,000	1,939,000,000
Securities Purchased under Agreements to Resell	500,100,000	784,700,000
Debt Securities - Held to Maturity	21,641,400,000	24,473,000,000
Loans
Held for Investment	0	0
Other Assets	1,395,100,000	1,371,900,000
Deposits	123,996,600,000	116,207,600,000
Deposits
Federal Funds Purchased	2,600,500,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	511,400,000	784,700,000
Other Borrowings	6,544,300,000	6,607,400,000
Senior Notes	2,771,300,000	2,798,100,000
Long-Term Debt	4,135,700,000	4,186,800,000
Unfunded Commitments	163,300,000	178,800,000
Other Liabilities	0	0
TOTAL ESTIMATED FAIR VALUE | LEVEL 3
ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	0
Loans
Held for Investment	47,179,400,000	47,598,300,000
Other Assets	0	0
Deposits	0	0
Deposits
Federal Funds Purchased	0	0
Securities Sold Under Agreements to Repurchase	0	0
Other Borrowings	0	0
Senior Notes	0	0
Long-Term Debt	0	0
Unfunded Commitments	0	0
Other Liabilities	42,700,000	74,900,000
BOOK VALUE
ASSETS
Cash and Due from Banks	5,308,700,000	4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,269,900,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,372,100,000	1,939,000,000
Securities Purchased under Agreements to Resell	500,100,000	784,700,000
Debt Securities - Held to Maturity	23,497,900,000	26,221,700,000
Loans
Held for Investment	47,180,100,000	47,438,300,000
Other Assets	1,505,700,000	1,476,600,000
Deposits	123,941,700,000	116,164,000,000
Deposits
Federal Funds Purchased	2,600,500,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	511,400,000	784,700,000
Other Borrowings	6,526,200,000	6,567,800,000
Senior Notes	2,743,500,000	2,773,200,000
Long-Term Debt	4,069,000,000	4,065,000,000
Unfunded Commitments	163,300,000	178,800,000
Other Liabilities	$ 42,700,000	$ 74,900,000