Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
ASSETS
Cash and Due from Banks	$ 4,791,500,000	$ 4,654,200,000
Federal Reserve and Other Central Bank Deposits	34,326,200,000	40,030,400,000
Interest-Bearing Deposits with Banks	1,939,000,000	1,941,100,000
Federal Funds Sold	800,000,000
Balance at December 31	784,700,000	1,070,300,000
FAIR VALUE	24,473,000,000	22,879,300,000
LIABILITIES
Deposits	116,164,000,000	123,932,100,000
Federal Funds Purchased	3,045,400,000	1,896,900,000
Balance at December 31	784,700,000	567,200,000
Other Borrowings	6,567,800,000	7,592,300,000
Senior Notes	2,773,200,000	2,724,200,000
Unfunded Commitments	0	0
BOOK VALUE
ASSETS
Cash and Due from Banks	4,791,500,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	34,326,200,000	40,030,400,000
Interest-Bearing Deposits with Banks	1,939,000,000	1,941,100,000
Federal Funds Sold		32,000,000.0
Balance at December 31	784,700,000	1,070,300,000
FAIR VALUE	26,221,700,000	25,036,100,000
Loans
Held for Investment	47,438,300,000	42,749,000,000
Other Assets	1,476,600,000	1,476,900,000
LIABILITIES
Deposits	116,164,000,000	123,932,100,000
Federal Funds Purchased	3,045,400,000	1,896,900,000
Balance at December 31	784,700,000	567,200,000
Other Borrowings	6,567,800,000	7,592,300,000
Senior Notes	2,773,200,000	2,724,200,000
Long-Term Debt	4,065,000,000	2,066,200,000
Unfunded Commitments	178,800,000	218,900,000
Other Liabilities	74,900,000	73,200,000
FAIR VALUE
ASSETS
Cash and Due from Banks	4,791,500,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	34,326,200,000	40,030,400,000
Interest-Bearing Deposits with Banks	1,939,000,000	1,941,100,000
Federal Funds Sold		32,000,000.0
Balance at December 31	784,700,000	1,070,300,000
FAIR VALUE	24,473,000,000	22,879,300,000
Loans
Held for Investment	47,598,300,000	42,636,500,000
Other Assets	1,458,000,000	1,460,400,000
LIABILITIES
Deposits	116,207,600,000	123,926,900,000
Federal Funds Purchased	3,045,400,000	1,896,900,000
Balance at December 31	784,700,000	567,200,000
Other Borrowings	6,607,400,000	7,592,800,000
Senior Notes	2,798,100,000	2,729,800,000
Long-Term Debt	4,186,800,000	2,110,700,000
Unfunded Commitments	178,800,000	218,900,000
Other Liabilities	74,900,000	73,200,000
FAIR VALUE | LEVEL 1
ASSETS
Cash and Due from Banks	4,791,500,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Federal Funds Sold		0
Balance at December 31	0	0
FAIR VALUE	0	50,000,000.0
Loans
Held for Investment	0	0
Other Assets	86,100,000	94,700,000
LIABILITIES
Deposits	0	0
Federal Funds Purchased	0	0
Balance at December 31	0	0
Other Borrowings	0	0
Senior Notes	0	0
Long-Term Debt	0	0
Unfunded Commitments	0	0
Other Liabilities	0	0
FAIR VALUE | LEVEL 2
ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	34,326,200,000	40,030,400,000
Interest-Bearing Deposits with Banks	1,939,000,000	1,941,100,000
Federal Funds Sold		32,000,000.0
Balance at December 31	784,700,000	1,070,300,000
FAIR VALUE	24,473,000,000	22,829,300,000
Loans
Held for Investment	0	0
Other Assets	1,371,900,000	1,365,700,000
LIABILITIES
Deposits	116,207,600,000	123,926,900,000
Federal Funds Purchased	3,045,400,000	1,896,900,000
Balance at December 31	784,700,000	567,200,000
Other Borrowings	6,607,400,000	7,592,800,000
Senior Notes	2,798,100,000	2,729,800,000
Long-Term Debt	4,186,800,000	2,110,700,000
Unfunded Commitments	178,800,000	218,900,000
Other Liabilities	0	0
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
Federal Funds Sold		0
Balance at December 31	0	0
FAIR VALUE	0	0
Loans
Held for Investment	47,598,300,000	42,636,500,000
Other Assets	0	0
LIABILITIES
Deposits	0	0
Federal Funds Purchased	0	0
Balance at December 31	0	0
Other Borrowings	0	0
Senior Notes	0	0
Long-Term Debt	0	0
Unfunded Commitments	0	0
Other Liabilities	$ 74,900,000	$ 73,200,000