Book and Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011	Dec. 31, 2010
Assets
Cash and Due from Banks	$ 3,396.7		$ 4,315.3		$ 4,336.6	$ 2,818.0
Federal Funds Sold and Resell Agreements	573.4		121.3
Interest-Bearing Deposits with Banks	19,347.8		16,696.4
Federal Reserve Deposits and Other Interest-Bearing	6,230.5		13,448.6
Securities
Available for Sale	28,136.1		30,192.5
Held to Maturity	1,048.0		799.2
Trading Account	5.2		8.0
Client Security Settlement Receivables	1,078.2		778.3
Deposits
Savings Certificates and Other Time	3,011.0		3,058.3
Non U. S. Offices Interest-Bearing	39,076.1		35,868.0
Federal Funds Purchased	573.7		815.3
Securities Sold under Agreements to Repurchase	382.6		1,198.8
Other Borrowings	442.7		931.5
Senior Notes	2,610.3		2,126.7
Other Liabilities
Contingent Consideration	48.9		56.8
Carrying (Reported) Amount, Fair Value Disclosure
Assets
Cash and Due from Banks	3,396.7		4,315.3
Federal Funds Sold and Resell Agreements	573.4		121.3
Interest-Bearing Deposits with Banks	19,347.8		16,696.4
Federal Reserve Deposits and Other Interest-Bearing	6,230.5		13,448.6
Securities
Available for Sale	28,136.1	[1]	30,192.5	[2]
Held to Maturity	1,048.0		799.2
Trading Account	5.2		8.0
Loans Held for Investment (excluding Leases)	28,235.9		27,782.7
Held for Sale			9.3
Client Security Settlement Receivables	1,078.2		778.3
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	197.6		172.9
Affordable Housing Investments	295.3		290.8
Employee Benefit and Deferred Compensation	121.4		106.3
Deposits
Demand, Noninterest-Bearing, Savings and Money Market	34,844.5		43,751.2
Savings Certificates and Other Time	3,011.0		3,058.3
Non U. S. Offices Interest-Bearing	39,076.1		35,868.0
Federal Funds Purchased	573.7		815.3
Securities Sold under Agreements to Repurchase	382.6		1,198.8
Other Borrowings	442.7		931.5
Senior Notes	2,610.3		2,126.7
Long Term Debt (excluding Leases)
Subordinated Debt	1,051.2		1,033.4
Federal Home Loan Bank Borrowings	335.0		1,055.0
Floating Rate Capital Debt	277.0		276.9
Other Liabilities
Standby Letters of Credit	65.8		61.3
Contingent Consideration	48.9		56.8
Loan Commitments	39.0		45.5
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Foreign Exchange Contracts
Derivative Instruments
Assets	36.0		25.2
Liabilities	39.2		31.8
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Interest Rate Swap Contracts
Derivative Instruments
Assets	139.3		149.6
Liabilities	77.2		47.3
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Credit Default Swap Contracts
Derivative Instruments
Assets			0.7
Liabilities	1.1		0.1
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Assets	2,085.2		3,062.1
Liabilities	2,037.9		2,959.8
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Interest Rate Swap Contracts
Derivative Instruments
Assets	196.3		188.7
Liabilities	190.1		184.6
Estimate of Fair Value, Fair Value Disclosure
Assets
Cash and Due from Banks	3,396.7		4,315.3
Federal Funds Sold and Resell Agreements	573.4		121.3
Interest-Bearing Deposits with Banks	19,347.8		16,696.4
Federal Reserve Deposits and Other Interest-Bearing	6,230.5		13,448.6
Securities
Available for Sale	28,136.1	[1]	30,192.5	[2]
Held to Maturity	1,064.2		817.1
Trading Account	5.2		8.0
Loans Held for Investment (excluding Leases)	28,347.4		27,913.7
Held for Sale			9.3
Client Security Settlement Receivables	1,078.2		778.3
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	197.6		172.9
Affordable Housing Investments	322.5		319.9
Employee Benefit and Deferred Compensation	127.0		117.3
Deposits
Demand, Noninterest-Bearing, Savings and Money Market	34,844.5		43,751.2
Savings Certificates and Other Time	3,024.8		3,065.5
Non U. S. Offices Interest-Bearing	39,076.1		35,868.0
Federal Funds Purchased	573.7		815.3
Securities Sold under Agreements to Repurchase	382.6		1,198.8
Other Borrowings	442.7		931.5
Senior Notes	2,731.4		2,197.3
Long Term Debt (excluding Leases)
Subordinated Debt	1,067.3		1,040.0
Federal Home Loan Bank Borrowings	348.0		1,082.1
Floating Rate Capital Debt	231.7		211.6
Other Liabilities
Standby Letters of Credit	65.8		61.3
Contingent Consideration	48.9		56.8
Loan Commitments	39.0		45.5
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Foreign Exchange Contracts
Derivative Instruments
Assets	36.0		25.2
Liabilities	39.2		31.8
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Interest Rate Swap Contracts
Derivative Instruments
Assets	139.3		149.6
Liabilities	77.2		47.3
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Credit Default Swap Contracts
Derivative Instruments
Assets			0.7
Liabilities	1.1		0.1
Estimate of Fair Value, Fair Value Disclosure | Client Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Assets	2,085.2		3,062.1
Liabilities	2,037.9		2,959.8
Estimate of Fair Value, Fair Value Disclosure | Client Related and Trading | Interest Rate Swap Contracts
Derivative Instruments
Assets	196.3		188.7
Liabilities	190.1		184.6
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1
Assets
Cash and Due from Banks	3,396.7		4,315.3
Securities
Available for Sale	1,787.8	[1]	4,029.4	[2]
Other Assets
Employee Benefit and Deferred Compensation	88.9		82.4
Deposits
Demand, Noninterest-Bearing, Savings and Money Market	34,844.5		43,751.2
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2
Assets
Federal Funds Sold and Resell Agreements	573.4		121.3
Interest-Bearing Deposits with Banks	19,347.8		16,696.4
Federal Reserve Deposits and Other Interest-Bearing	6,230.5		13,448.6
Securities
Available for Sale	26,248.8	[1]	25,984.8	[2]
Held to Maturity	1,064.2		817.1
Trading Account	5.2		8.0
Client Security Settlement Receivables	1,078.2		778.3
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	197.6		172.9
Affordable Housing Investments	322.5		319.9
Employee Benefit and Deferred Compensation	38.1		34.9
Deposits
Savings Certificates and Other Time	3,024.8		3,065.5
Non U. S. Offices Interest-Bearing	39,076.1		35,868.0
Federal Funds Purchased	573.7		815.3
Securities Sold under Agreements to Repurchase	382.6		1,198.8
Other Borrowings	442.7		931.5
Senior Notes	2,731.4		2,197.3
Long Term Debt (excluding Leases)
Subordinated Debt	1,067.3		1,040.0
Federal Home Loan Bank Borrowings	348.0		1,082.1
Floating Rate Capital Debt	231.7		211.6
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Foreign Exchange Contracts
Derivative Instruments
Assets	36.0		25.2
Liabilities	39.2		31.8
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Interest Rate Swap Contracts
Derivative Instruments
Assets	139.3		149.6
Liabilities	77.2		47.3
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Credit Default Swap Contracts
Derivative Instruments
Assets			0.7
Liabilities	1.1		0.1
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Assets	2,085.2		3,062.1
Liabilities	2,037.9		2,959.8
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Interest Rate Swap Contracts
Derivative Instruments
Assets	196.3		188.7
Liabilities	190.1		184.6
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3
Securities
Available for Sale	99.5	[1]	178.3	[2]
Loans Held for Investment (excluding Leases)	28,347.4		27,913.7
Held for Sale			9.3
Other Liabilities
Standby Letters of Credit	65.8		61.3
Contingent Consideration	48.9		56.8
Loan Commitments	$ 39.0		$ 45.5

[1] Refer to the table located on page 35 for the disaggregation of available for sale securities.

[2] Refer to the table located on page 36 for the disaggregation of available for sale securities.