Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
ASSETS
Cash and Due from Banks	$ 4,799.3	$ 4,389.5
Federal Reserve and Other Central Bank Deposits	54,232.9	55,503.6
Interest-Bearing Deposits with Banks	3,848.4	4,372.6
Securities Purchased under Agreements to Resell	947.8	1,596.5
Debt Securities
Available-for-sale	36,864.0	42,022.0
Held to Maturity	21,579.6	17,797.4
Loans (excluding Leases)
Client Security Settlement Receivables	2,011.6	1,160.2
Deposits
Savings Certificates and Other Time	877.7	937.1
Non U.S. Offices Interest-Bearing	71,705.4	71,198.4
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	529.1	39.8
Other Borrowings	5,140.6	4,011.5
Senior Notes	3,036.0	3,122.4
Long-Term Debt
Floating Rate Capital Debt	277.8	277.8
Derivative Instruments
Assets	2,004.0	4,097.2
Liabilities	2,277.2	3,738.0
LEVEL 2
Debt Securities
Available-for-sale	34,300.0	39,200.0
BOOK VALUE
ASSETS
Cash and Due from Banks	4,799.3	4,389.5
Federal Reserve and Other Central Bank Deposits	54,232.9	55,503.6
Interest-Bearing Deposits with Banks	3,848.4	4,372.6
Federal Funds Sold	0.1
Securities Purchased under Agreements to Resell	947.8	1,596.5
Debt Securities
Available-for-sale	36,864.0	42,022.0
Held to Maturity	21,655.3	17,791.1
Trading Account	0.5	0.5
Loans (excluding Leases)
Held for Investment	37,116.1	33,558.0
Held for sale	131.2
Client Security Settlement Receivables	2,011.6	1,160.2
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	230.0	275.0
Community Development Investments	903.8	919.6
Employee Benefit and Deferred Compensation	224.5	215.8
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	73,627.1	71,742.5
Savings Certificates and Other Time	877.7	937.1
Non U.S. Offices Interest-Bearing	71,705.4	71,198.4
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	529.1	39.8
Other Borrowings	5,140.6	4,011.5
Senior Notes	3,036.0	3,122.4
Long-Term Debt
Subordinated Debt	1,165.3	1,189.3
Floating Rate Capital Debt	277.8	277.8
Other Liabilities
Standby Letters of Credit	17.9	22.4
Loan Commitments	67.0	77.0
BOOK VALUE \| Asset/Liability Management \| Foreign Exchange Contracts
Derivative Instruments
Assets	147.3	15.6
Liabilities	28.2	311.8
BOOK VALUE \| Asset/Liability Management \| Interest Rate Contracts
Derivative Instruments
Assets	8.9	8.3
Liabilities	7.2	10.2
BOOK VALUE \| Asset/Liability Management \| Other Financial Derivatives
Derivative Instruments
Liabilities	38.4	35.3
BOOK VALUE \| Client-Related and Trading \| Foreign Exchange Contracts
Derivative Instruments
Assets	2,461.6	4,245.1
Liabilities	2,378.1	4,410.7
BOOK VALUE \| Client-Related and Trading \| Interest Rate Contracts
Derivative Instruments
Assets	198.5	289.2
Liabilities	99.0	114.8
TOTAL FAIR VALUE
ASSETS
Cash and Due from Banks	4,799.3	4,389.5
Federal Reserve and Other Central Bank Deposits	54,232.9	55,503.6
Interest-Bearing Deposits with Banks	3,848.4	4,372.6
Federal Funds Sold	0.1
Securities Purchased under Agreements to Resell	947.8	1,596.5
Debt Securities
Available-for-sale	36,864.0	42,022.0
Held to Maturity	21,579.6	17,797.4
Trading Account	0.5	0.5
Loans (excluding Leases)
Held for Investment	37,152.9	34,017.5
Held for sale	150.3
Client Security Settlement Receivables	2,011.6	1,160.2
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	230.0	275.0
Community Development Investments	903.8	919.6
Employee Benefit and Deferred Compensation	227.1	228.9
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	73,627.1	71,742.5
Savings Certificates and Other Time	879.7	943.0
Non U.S. Offices Interest-Bearing	71,705.4	71,198.4
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	529.1	39.8
Other Borrowings	5,141.1	4,012.7
Senior Notes	3,137.0	3,222.6
Long-Term Debt
Subordinated Debt	1,226.3	1,250.1
Floating Rate Capital Debt	271.9	264.6
Other Liabilities
Standby Letters of Credit	17.9	22.4
Loan Commitments	67.0	77.0
TOTAL FAIR VALUE \| Asset/Liability Management \| Foreign Exchange Contracts
Derivative Instruments
Assets	147.3	15.6
Liabilities	28.2	311.8
TOTAL FAIR VALUE \| Asset/Liability Management \| Interest Rate Contracts
Derivative Instruments
Assets	8.9	8.3
Liabilities	7.2	10.2
TOTAL FAIR VALUE \| Asset/Liability Management \| Other Financial Derivatives
Derivative Instruments
Liabilities	38.4	35.3
TOTAL FAIR VALUE \| Client-Related and Trading \| Foreign Exchange Contracts
Derivative Instruments
Assets	2,461.6	4,245.1
Liabilities	2,378.1	4,410.7
TOTAL FAIR VALUE \| Client-Related and Trading \| Interest Rate Contracts
Derivative Instruments
Assets	198.5	289.2
Liabilities	99.0	114.8
TOTAL FAIR VALUE \| LEVEL 1
ASSETS
Cash and Due from Banks	4,799.3	4,389.5
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
Available-for-sale	2,559.0	2,799.9
Held to Maturity	99.0	90.0
Trading Account	0.0	0.0
Loans (excluding Leases)
Held for Investment	0.0	0.0
Held for sale	0.0
Client Security Settlement Receivables	0.0	0.0
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	0.0	0.0
Community Development Investments	0.0	0.0
Employee Benefit and Deferred Compensation	123.7	138.6
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	73,627.1	71,742.5
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
Subordinated Debt	0.0	0.0
Floating Rate Capital Debt	0.0	0.0
Other Liabilities
Standby Letters of Credit	0.0	0.0
Loan Commitments	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 1 \| Asset/Liability Management \| Foreign Exchange Contracts
Derivative Instruments
Assets	0.0	0.0
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 1 \| Asset/Liability Management \| Interest Rate Contracts
Derivative Instruments
Assets	0.0	0.0
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 1 \| Asset/Liability Management \| Other Financial Derivatives
Derivative Instruments
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 1 \| Client-Related and Trading \| Foreign Exchange Contracts
Derivative Instruments
Assets	0.0	0.0
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 1 \| Client-Related and Trading \| Interest Rate Contracts
Derivative Instruments
Assets	0.0	0.0
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 2
ASSETS
Cash and Due from Banks	0.0	0.0
Federal Reserve and Other Central Bank Deposits	54,232.9	55,503.6
Interest-Bearing Deposits with Banks	3,848.4	4,372.6
Federal Funds Sold	0.1
Securities Purchased under Agreements to Resell	947.8	1,596.5
Debt Securities
Available-for-sale	34,305.0	39,222.1
Held to Maturity	21,480.6	17,707.4
Trading Account	0.5	0.5
Loans (excluding Leases)
Held for Investment	0.0	0.0
Held for sale	150.3
Client Security Settlement Receivables	2,011.6	1,160.2
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	230.0	275.0
Community Development Investments	903.8	919.6
Employee Benefit and Deferred Compensation	103.4	90.3
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0.0	0.0
Savings Certificates and Other Time	879.7	943.0
Non U.S. Offices Interest-Bearing	71,705.4	71,198.4
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	529.1	39.8
Other Borrowings	5,141.1	4,012.7
Senior Notes	3,137.0	3,222.6
Long-Term Debt
Subordinated Debt	1,226.3	1,250.1
Floating Rate Capital Debt	271.9	264.6
Other Liabilities
Standby Letters of Credit	0.0	0.0
Loan Commitments	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 2 \| Asset/Liability Management \| Foreign Exchange Contracts
Derivative Instruments
Assets	147.3	15.6
Liabilities	28.2	311.8
TOTAL FAIR VALUE \| LEVEL 2 \| Asset/Liability Management \| Interest Rate Contracts
Derivative Instruments
Assets	8.9	8.3
Liabilities	7.2	10.2
TOTAL FAIR VALUE \| LEVEL 2 \| Asset/Liability Management \| Other Financial Derivatives
Derivative Instruments
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 2 \| Client-Related and Trading \| Foreign Exchange Contracts
Derivative Instruments
Assets	2,461.6	4,245.1
Liabilities	2,378.1	4,410.7
TOTAL FAIR VALUE \| LEVEL 2 \| Client-Related and Trading \| Interest Rate Contracts
Derivative Instruments
Assets	198.5	289.2
Liabilities	99.0	114.8
TOTAL 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
Available-for-sale	0.0	0.0
Held to Maturity	0.0	0.0
Trading Account	0.0	0.0
Loans (excluding Leases)
Held for Investment	37,152.9	34,017.5
Held for sale	0.0
Client Security Settlement Receivables	0.0	0.0
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	0.0	0.0
Community Development Investments	0.0	0.0
Employee Benefit and Deferred Compensation	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
Subordinated Debt	0.0	0.0
Floating Rate Capital Debt	0.0	0.0
Other Liabilities
Standby Letters of Credit	17.9	22.4
Loan Commitments	67.0	77.0
TOTAL FAIR VALUE \| LEVEL 3 \| Asset/Liability Management \| Foreign Exchange Contracts
Derivative Instruments
Assets	0.0	0.0
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 3 \| Asset/Liability Management \| Interest Rate Contracts
Derivative Instruments
Assets	0.0	0.0
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 3 \| Asset/Liability Management \| Other Financial Derivatives
Derivative Instruments
Liabilities	38.4	35.3
TOTAL FAIR VALUE \| LEVEL 3 \| Client-Related and Trading \| Foreign Exchange Contracts
Derivative Instruments
Assets	0.0	0.0
Liabilities	0.0	0.0
TOTAL FAIR VALUE \| LEVEL 3 \| Client-Related and Trading \| Interest Rate Contracts
Derivative Instruments
Assets	0.0	0.0
Liabilities	$ 0.0	$ 0.0

Affordable Housing Investments.

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