Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
ASSETS
Cash and Due from Banks	$ 5,119.8	$ 3,056.8
Federal Reserve and Other Central Bank Deposits	37,933.6	64,582.2
Interest-Bearing Deposits with Banks	2,526.3	1,949.4
Securities Purchased under Agreements to Resell	1,171.8	686.4
Debt Securities - Held to Maturity	18,925.5	23,315.4
Deposits
Savings Certificates and Other Time	785.0	842.7
Non U.S. Offices Interest-Bearing	69,951.1	75,767.1
Federal Funds Purchased	389.2	0.2
Securities Sold Under Agreements to Repurchase	799.4	531.9
Other Borrowings	3,514.9	3,583.8
Senior Notes	3,305.8	2,505.5
BOOK VALUE
ASSETS
Cash and Due from Banks	5,119.8	3,056.8
Federal Reserve and Other Central Bank Deposits	37,933.6	64,582.2
Interest-Bearing Deposits with Banks	2,526.3	1,949.4
Federal Funds Sold	10.0
Securities Purchased under Agreements to Resell	1,171.8	686.4
Debt Securities - Held to Maturity	20,112.6	23,564.5
Loans (excluding Leases)
Held for Investment	41,058.6	40,319.3
Held for Sale		12.3
Other Assets	1,304.0	1,275.3
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	62,938.5	83,318.6
Savings Certificates and Other Time	785.0	842.7
Non U.S. Offices Interest-Bearing	69,951.1	75,767.1
Federal Funds Purchased	389.2	0.2
Securities Sold Under Agreements to Repurchase	799.4	531.9
Other Borrowings	3,514.9	3,583.8
Senior Notes	3,305.8	2,505.5
Long-Term Debt	1,094.1	1,145.7
Unfunded Commitments	276.7	289.3
Other Liabilities	84.1	75.5
TOTAL ESTIMATED FAIR VALUE
ASSETS
Cash and Due from Banks	5,119.8	3,056.8
Federal Reserve and Other Central Bank Deposits	37,933.6	64,582.2
Interest-Bearing Deposits with Banks	2,526.3	1,949.4
Federal Funds Sold	10.0
Securities Purchased under Agreements to Resell	1,171.8	686.4
Debt Securities - Held to Maturity	18,925.5	23,315.4
Loans (excluding Leases)
Held for Investment	40,818.8	40,208.2
Held for Sale		24.5
Other Assets	1,292.8	1,279.8
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	62,938.5	83,318.6
Savings Certificates and Other Time	778.6	843.8
Non U.S. Offices Interest-Bearing	69,951.1	75,767.1
Federal Funds Purchased	389.2	0.2
Securities Sold Under Agreements to Repurchase	799.4	531.9
Other Borrowings	3,513.0	3,583.9
Senior Notes	3,515.5	2,591.4
Long-Term Debt	1,083.0	1,189.4
Unfunded Commitments	276.7	289.3
Other Liabilities	84.1	75.5
TOTAL ESTIMATED FAIR VALUE | LEVEL 1
ASSETS
Cash and Due from Banks	5,119.8	3,056.8
Federal Reserve and Other Central Bank Deposits	0.0	0.0
Interest-Bearing Deposits with Banks	0.0	0.0
Federal Funds Sold	0.0
Securities Purchased under Agreements to Resell	0.0	0.0
Debt Securities - Held to Maturity	56.5	47.0
Loans (excluding Leases)
Held for Investment	0.0	0.0
Held for Sale		0.0
Other Assets	111.2	119.1
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	62,938.5	83,318.6
Savings Certificates and Other Time	0.0	0.0
Non U.S. Offices Interest-Bearing	0.0	0.0
Federal Funds Purchased	0.0	0.0
Securities Sold Under Agreements to Repurchase	0.0	0.0
Other Borrowings	0.0	0.0
Senior Notes	0.0	0.0
Long-Term Debt	0.0	0.0
Unfunded Commitments	0.0	0.0
Other Liabilities	0.0	0.0
TOTAL ESTIMATED FAIR VALUE | LEVEL 2
ASSETS
Cash and Due from Banks	0.0	0.0
Federal Reserve and Other Central Bank Deposits	37,933.6	64,582.2
Interest-Bearing Deposits with Banks	2,526.3	1,949.4
Federal Funds Sold	10.0
Securities Purchased under Agreements to Resell	1,171.8	686.4
Debt Securities - Held to Maturity	18,869.0	23,268.4
Loans (excluding Leases)
Held for Investment	0.0	0.0
Held for Sale		24.5
Other Assets	1,181.6	1,160.7
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0.0	0.0
Savings Certificates and Other Time	778.6	843.8
Non U.S. Offices Interest-Bearing	69,951.1	75,767.1
Federal Funds Purchased	389.2	0.2
Securities Sold Under Agreements to Repurchase	799.4	531.9
Other Borrowings	3,513.0	3,583.9
Senior Notes	3,515.5	2,591.4
Long-Term Debt	1,083.0	1,189.4
Unfunded Commitments	276.7	289.3
Other Liabilities	0.0	0.0
TOTAL ESTIMATED FAIR VALUE | LEVEL 3
ASSETS
Cash and Due from Banks	0.0	0.0
Federal Reserve and Other Central Bank Deposits	0.0	0.0
Interest-Bearing Deposits with Banks	0.0	0.0
Federal Funds Sold	0.0
Securities Purchased under Agreements to Resell	0.0	0.0
Debt Securities - Held to Maturity	0.0	0.0
Loans (excluding Leases)
Held for Investment	40,818.8	40,208.2
Held for Sale		0.0
Other Assets	0.0	0.0
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0.0	0.0
Savings Certificates and Other Time	0.0	0.0
Non U.S. Offices Interest-Bearing	0.0	0.0
Federal Funds Purchased	0.0	0.0
Securities Sold Under Agreements to Repurchase	0.0	0.0
Other Borrowings	0.0	0.0
Senior Notes	0.0	0.0
Long-Term Debt	0.0	0.0
Unfunded Commitments	0.0	0.0
Other Liabilities	$ 84.1	$ 75.5