Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($)	Sep. 30, 2025	Dec. 31, 2024
FINANCIAL ASSETS
Cash and Due from Banks	$ 5,346,200,000	$ 4,677,200,000
Federal Reserve and Other Central Bank Deposits	49,374,000,000	38,775,400,000
Interest-Bearing Deposits with Banks	1,990,000,000	1,944,700,000
Federal Funds Sold and Securities Purchased under Agreements to Resell	1,856,300,000	451,000,000.0
Debt Securities - Held to Maturity	21,838,300,000	20,654,500,000
FINANCIAL LIABILITIES
Deposits	135,801,100,000	122,482,700,000
Federal Funds Purchased	1,751,900,000	2,159,500,000
Securities Sold Under Agreements to Repurchase	371,500,000	462,000,000.0
Other Borrowings	6,580,000,000	6,521,000,000
Senior Notes	2,847,200,000	2,769,700,000
Unfunded Commitments	29,300,000	0
BOOK VALUE
FINANCIAL ASSETS
Cash and Due from Banks	5,346,200,000	4,677,200,000
Federal Reserve and Other Central Bank Deposits	49,374,000,000	38,775,400,000
Interest-Bearing Deposits with Banks	1,990,000,000	1,944,700,000
Federal Funds Sold and Securities Purchased under Agreements to Resell	1,856,300,000	451,000,000.0
Debt Securities - Held to Maturity	22,974,900,000	22,296,700,000
Loans
Held for Investment	42,785,000,000	43,222,500,000
Other Assets	1,579,500,000	1,506,400,000
FINANCIAL LIABILITIES
Deposits	135,801,100,000	122,482,700,000
Federal Funds Purchased	1,751,900,000	2,159,500,000
Securities Sold Under Agreements to Repurchase	371,500,000	462,000,000.0
Other Borrowings	6,580,000,000	6,521,000,000
Senior Notes	2,847,200,000	2,769,700,000
Long-Term Debt	4,094,300,000	4,081,300,000
Unfunded Commitments	319,200,000	227,100,000
Other Liabilities	47,800,000	50,600,000
TOTAL ESTIMATED FAIR VALUE
FINANCIAL ASSETS
Cash and Due from Banks	5,346,200,000	4,677,200,000
Federal Reserve and Other Central Bank Deposits	49,374,000,000	38,775,400,000
Interest-Bearing Deposits with Banks	1,990,000,000	1,944,700,000
Federal Funds Sold and Securities Purchased under Agreements to Resell	1,856,300,000	451,000,000.0
Debt Securities - Held to Maturity	21,838,300,000	20,654,500,000
Loans
Held for Investment	42,626,600,000	42,803,200,000
Other Assets	1,574,700,000	1,499,200,000
FINANCIAL LIABILITIES
Deposits	134,847,000,000	122,536,500,000
Federal Funds Purchased	1,751,900,000	2,159,500,000
Securities Sold Under Agreements to Repurchase	371,500,000	462,000,000.0
Other Borrowings	6,602,900,000	6,545,300,000
Senior Notes	2,895,300,000	2,800,300,000
Long-Term Debt	4,197,600,000	4,164,400,000
Unfunded Commitments	319,200,000	227,100,000
Other Liabilities	47,800,000	50,600,000
TOTAL ESTIMATED FAIR VALUE | LEVEL 1
FINANCIAL ASSETS
Cash and Due from Banks	5,346,200,000	4,677,200,000
Federal Reserve and Other Central Bank Deposits	0
Interest-Bearing Deposits with Banks	0
Federal Funds Sold and Securities Purchased under Agreements to Resell	0
Debt Securities - Held to Maturity	0
Loans
Held for Investment	0
Other Assets	87,800,000	83,300,000
FINANCIAL LIABILITIES
Deposits	0	0
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
FINANCIAL ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	49,374,000,000	38,775,400,000
Interest-Bearing Deposits with Banks	1,990,000,000	1,944,700,000
Federal Funds Sold and Securities Purchased under Agreements to Resell	1,856,300,000	451,000,000.0
Debt Securities - Held to Maturity	21,838,300,000	20,654,500,000
Loans
Held for Investment	0	0
Other Assets	1,486,900,000	1,415,900,000
FINANCIAL LIABILITIES
Deposits	134,847,000,000	122,536,500,000
Federal Funds Purchased	1,751,900,000	2,159,500,000
Securities Sold Under Agreements to Repurchase	371,500,000	462,000,000.0
Other Borrowings	6,602,900,000	6,545,300,000
Senior Notes	2,895,300,000	2,800,300,000
Long-Term Debt	4,197,600,000	4,164,400,000
Unfunded Commitments	319,200,000	227,100,000
Other Liabilities	0	0
TOTAL ESTIMATED FAIR VALUE | LEVEL 3
FINANCIAL ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Federal Funds Sold and Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	0
Loans
Held for Investment	42,626,600,000	42,803,200,000
Other Assets	0	0
FINANCIAL LIABILITIES
Deposits	0	0
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	$ 47,800,000	$ 50,600,000