Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($)	Sep. 30, 2024	Dec. 31, 2023
FINANCIAL ASSETS
Cash and Due from Banks	$ 6,871,700,000	$ 4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,848,800,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,606,800,000	1,939,000,000
Securities Purchased under Agreements to Resell	981,600,000	784,700,000
Debt Securities - Held to Maturity	21,372,000,000	24,473,000,000
FINANCIAL LIABILITIES
Deposits	121,183,300,000	116,164,000,000
Federal Funds Purchased	2,761,900,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	170,800,000	784,700,000
Other Borrowings	6,903,200,000	6,567,800,000
Senior Notes	2,820,900,000	2,773,200,000
Unfunded Commitments	0	0
BOOK VALUE
FINANCIAL ASSETS
Cash and Due from Banks	6,871,700,000	4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,848,800,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,606,800,000	1,939,000,000
Securities Purchased under Agreements to Resell	981,600,000	784,700,000
Debt Securities - Held to Maturity	22,708,600,000	26,221,700,000
Loans
Held for Investment	41,765,500,000	47,438,300,000
Other Assets	1,450,500,000	1,476,600,000
FINANCIAL LIABILITIES
Deposits	121,183,300,000	116,164,000,000
Federal Funds Purchased	2,761,900,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	170,800,000	784,700,000
Other Borrowings	6,903,200,000	6,567,800,000
Senior Notes	2,820,900,000	2,773,200,000
Long-Term Debt	4,077,200,000	4,065,000,000
Unfunded Commitments	173,400,000	178,800,000
Other Liabilities	47,900,000	74,900,000
TOTAL ESTIMATED FAIR VALUE
FINANCIAL ASSETS
Cash and Due from Banks	6,871,700,000	4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,848,800,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,606,800,000	1,939,000,000
Securities Purchased under Agreements to Resell	981,600,000	784,700,000
Debt Securities - Held to Maturity	21,372,000,000	24,473,000,000
Loans
Held for Investment	41,488,700,000	47,598,300,000
Other Assets	1,446,000,000	1,458,000,000
FINANCIAL LIABILITIES
Deposits	123,302,500,000	116,207,600,000
Federal Funds Purchased	2,761,900,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	170,800,000	784,700,000
Other Borrowings	6,940,000,000	6,607,400,000
Senior Notes	2,869,100,000	2,798,100,000
Long-Term Debt	4,248,100,000	4,186,800,000
Unfunded Commitments	173,400,000	178,800,000
Other Liabilities	47,900,000	74,900,000
TOTAL ESTIMATED FAIR VALUE | LEVEL 1
FINANCIAL ASSETS
Cash and Due from Banks	6,871,700,000	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	87,900,000	86,100,000
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	40,848,800,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,606,800,000	1,939,000,000
Securities Purchased under Agreements to Resell	981,600,000	784,700,000
Debt Securities - Held to Maturity	21,372,000,000	24,473,000,000
Loans
Held for Investment	0	0
Other Assets	1,358,100,000	1,371,900,000
FINANCIAL LIABILITIES
Deposits	123,302,500,000	116,207,600,000
Federal Funds Purchased	2,761,900,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	170,800,000	784,700,000
Other Borrowings	6,940,000,000	6,607,400,000
Senior Notes	2,869,100,000	2,798,100,000
Long-Term Debt	4,248,100,000	4,186,800,000
Unfunded Commitments	173,400,000	178,800,000
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
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	0
Loans
Held for Investment	41,488,700,000	47,598,300,000
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	$ 47,900,000	$ 74,900,000