Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
ASSETS
Cash and Due from Banks	$ 4,955,700,000	$ 4,654,200,000
Federal Reserve and Other Central Bank Deposits	32,316,800,000	40,030,400,000
Interest-Bearing Deposits with Banks	2,122,500,000	1,941,100,000
Securities Purchased under Agreements to Resell	384,300,000	1,070,300,000
Debt Securities - Held to Maturity	22,449,700,000	22,879,300,000
Deposits
Savings Certificates and Other Time	4,038,600,000	1,981,300,000
Non U.S. Offices Interest-Bearing	60,826,900,000	65,481,900,000
Federal Funds Purchased	5,539,300,000	1,896,900,000
Securities Sold Under Agreements to Repurchase	545,900,000	567,200,000
Other Borrowings	6,870,900,000	7,592,300,000
Senior Notes	2,688,900,000	2,724,200,000
Unfunded Commitments	0	0
BOOK VALUE
ASSETS
Cash and Due from Banks	4,955,700,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	32,316,800,000	40,030,400,000
Interest-Bearing Deposits with Banks	2,122,500,000	1,941,100,000
Federal Funds Sold		32,000,000.0
Securities Purchased under Agreements to Resell	384,300,000	1,070,300,000
Debt Securities - Held to Maturity	24,920,400,000	25,036,100,000
Loans
Held for Investment	43,410,200,000	42,749,000,000
Other Assets	1,502,100,000	1,476,900,000
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	45,300,400,000	56,468,900,000
Savings Certificates and Other Time	4,038,600,000	1,981,300,000
Non U.S. Offices Interest-Bearing	60,826,900,000	65,481,900,000
Federal Funds Purchased	5,539,300,000	1,896,900,000
Securities Sold Under Agreements to Repurchase	545,900,000	567,200,000
Other Borrowings	6,870,900,000	7,592,300,000
Senior Notes	2,688,900,000	2,724,200,000
Long-Term Debt	4,060,700,000	2,066,200,000
Unfunded Commitments	205,500,000	218,900,000
Other Liabilities	89,500,000	73,200,000
TOTAL ESTIMATED FAIR VALUE
ASSETS
Cash and Due from Banks	4,955,700,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	32,316,800,000	40,030,400,000
Interest-Bearing Deposits with Banks	2,122,500,000	1,941,100,000
Federal Funds Sold		32,000,000.0
Securities Purchased under Agreements to Resell	384,300,000	1,070,300,000
Debt Securities - Held to Maturity	22,449,700,000	22,879,300,000
Loans
Held for Investment	43,384,400,000	42,636,500,000
Other Assets	1,485,400,000	1,460,400,000
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	45,300,400,000	56,468,900,000
Savings Certificates and Other Time	4,070,400,000	1,976,100,000
Non U.S. Offices Interest-Bearing	60,826,900,000	65,481,900,000
Federal Funds Purchased	5,539,300,000	1,896,900,000
Securities Sold Under Agreements to Repurchase	545,900,000	567,200,000
Other Borrowings	6,888,100,000	7,592,800,000
Senior Notes	2,646,600,000	2,729,800,000
Long-Term Debt	4,026,100,000	2,110,700,000
Unfunded Commitments	205,500,000	218,900,000
Other Liabilities	89,500,000	73,200,000
TOTAL ESTIMATED FAIR VALUE | LEVEL 1
ASSETS
Cash and Due from Banks	4,955,700,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Federal Funds Sold		0
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	50,000,000.0
Loans
Held for Investment	0	0
Other Assets	89,400,000	94,700,000
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	45,300,400,000	56,468,900,000
Savings Certificates and Other Time	0	0
Non U.S. Offices Interest-Bearing	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
ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	32,316,800,000	40,030,400,000
Interest-Bearing Deposits with Banks	2,122,500,000	1,941,100,000
Federal Funds Sold		32,000,000.0
Securities Purchased under Agreements to Resell	384,300,000	1,070,300,000
Debt Securities - Held to Maturity	22,449,700,000	22,829,300,000
Loans
Held for Investment	0	0
Other Assets	1,396,000,000	1,365,700,000
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0	0
Savings Certificates and Other Time	4,070,400,000	1,976,100,000
Non U.S. Offices Interest-Bearing	60,826,900,000	65,481,900,000
Federal Funds Purchased	5,539,300,000	1,896,900,000
Securities Sold Under Agreements to Repurchase	545,900,000	567,200,000
Other Borrowings	6,888,100,000	7,592,800,000
Senior Notes	2,646,600,000	2,729,800,000
Long-Term Debt	4,026,100,000	2,110,700,000
Unfunded Commitments	205,500,000	218,900,000
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
Federal Funds Sold		0
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	0
Loans
Held for Investment	43,384,400,000	42,636,500,000
Other Assets	0	0
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0	0
Savings Certificates and Other Time	0	0
Non U.S. Offices Interest-Bearing	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	$ 89,500,000	$ 73,200,000