Book and Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2011	Dec. 31, 2010
Assets
Cash and Due from Banks	$ 4,280.3		$ 4,315.3		$ 3,592.8	$ 2,818.0
Federal Funds Sold and Resell Agreements	290.9		121.3
Interest-Bearing Deposits with Banks	18,871.3		16,696.4
Federal Reserve Deposits and Other Interest-Bearing	2,228.0		13,448.6
Securities
Available for Sale	30,906.8		30,192.5
Held to Maturity	709.7		799.2
Trading Account	9.3		8.0
Loans (excluding Leases)
Client Security Settlement Receivables	985.3		778.3
Deposits
Savings Certificates and Other Time	3,093.8		3,058.3
Non U. S. Offices Interest-Bearing	36,575.4		35,868.0
Federal Funds Purchased	1,973.7		815.3
Securities Sold under Agreements to Repurchase	284.0		1,198.8
Other Borrowings	1,103.0		931.5
Senior Notes	2,122.6		2,126.7
Other Liabilities
Contingent Consideration	58.6		56.8
Carrying (Reported) Amount, Fair Value Disclosure
Assets
Cash and Due from Banks	4,280.3		4,315.3
Federal Funds Sold and Resell Agreements	290.9		121.3
Interest-Bearing Deposits with Banks	18,871.3		16,696.4
Federal Reserve Deposits and Other Interest-Bearing	2,228.0		13,448.6
Securities
Available for Sale	30,906.8	[1]	30,192.5	[2]
Held to Maturity	709.7		799.2
Trading Account	9.3		8.0
Loans (excluding Leases)
Held for Investment	27,845.6		27,782.7
Held for Sale	0.1		9.3
Client Security Settlement Receivables	985.3		778.3
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	172.9		172.9
Affordable Housing Investments	280.50		290.80
Deposits
Demand, Noninterest-Bearing, Savings and Money Market	34,263.8		43,751.2
Savings Certificates and Other Time	3,093.8		3,058.3
Non U. S. Offices Interest-Bearing	36,575.4		35,868.0
Federal Funds Purchased	1,973.7		815.3
Securities Sold under Agreements to Repurchase	284.0		1,198.8
Other Borrowings	1,103.0		931.5
Senior Notes	2,122.6		2,126.7
Long Term Debt (excluding Leases)
Subordinated Debt	1,036.6		1,033.4
Federal Home Loan Bank Borrowings	705.0		1,055.0
Floating Rate Capital Debt	277.0		276.9
Other Liabilities
Standby Letters of Credit	50.1		43.8
Contingent Consideration	58.6		56.8
Loan Commitments	28.9		28.9
Carrying (Reported) Amount, Fair Value Disclosure | Rabbi Trust
Other Assets
Rabbi Trust Investments	122.6		106.3
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Foreign Exchange Contracts
Other Liabilities
Assets	14.6		25.2
Liabilities	45.6		31.8
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Interest Rate Swap Contracts
Other Liabilities
Assets	141.8		149.6
Liabilities	45.9		47.3
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Credit Default Swap Contracts
Other Liabilities
Assets			0.7
Liabilities	0.2		0.1
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Foreign Exchange Contracts
Other Liabilities
Assets	3,127.8		3,062.1
Liabilities	3,063.6		2,959.8
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Interest Rate Swap Contracts
Other Liabilities
Assets	182.1		188.7
Liabilities	177.0		184.6
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Interest Rate Option Contracts
Other Liabilities
Assets	0.1
Liabilities	0.1
Estimate of Fair Value, Fair Value Disclosure
Assets
Cash and Due from Banks	4,280.3		4,315.3
Federal Funds Sold and Resell Agreements	290.9		121.3
Interest-Bearing Deposits with Banks	18,871.3		16,696.4
Federal Reserve Deposits and Other Interest-Bearing	2,228.0		13,448.6
Securities
Available for Sale	30,906.8	[1]	30,192.5	[2]
Held to Maturity	727.2		817.1
Trading Account	9.3		8.0
Loans (excluding Leases)
Held for Investment	27,957.9		27,913.7
Held for Sale	0.1		9.3
Client Security Settlement Receivables	985.3		778.3
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	172.9		172.9
Affordable Housing Investments	306.60		319.90
Deposits
Demand, Noninterest-Bearing, Savings and Money Market	34,263.8		43,751.2
Savings Certificates and Other Time	3,101.3		3,065.5
Non U. S. Offices Interest-Bearing	36,575.4		35,868.0
Federal Funds Purchased	1,973.7		815.3
Securities Sold under Agreements to Repurchase	284.0		1,198.8
Other Borrowings	1,103.0		931.5
Senior Notes	2,192.2		2,197.3
Long Term Debt (excluding Leases)
Subordinated Debt	1,055.5		1,040.0
Federal Home Loan Bank Borrowings	723.7		1,082.1
Floating Rate Capital Debt	232.3		211.6
Other Liabilities
Standby Letters of Credit	50.1		43.8
Contingent Consideration	58.6		56.8
Loan Commitments	28.9		28.9
Estimate of Fair Value, Fair Value Disclosure | Rabbi Trust
Other Assets
Rabbi Trust Investments	122.6		106.3
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Foreign Exchange Contracts
Other Liabilities
Assets	14.6		25.2
Liabilities	45.6		31.8
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Interest Rate Swap Contracts
Other Liabilities
Assets	141.8		149.6
Liabilities	45.9		47.3
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Credit Default Swap Contracts
Other Liabilities
Assets			0.7
Liabilities	0.2		0.1
Estimate of Fair Value, Fair Value Disclosure | Client Related and Trading | Foreign Exchange Contracts
Other Liabilities
Assets	3,127.8		3,062.1
Liabilities	3,063.6		2,959.8
Estimate of Fair Value, Fair Value Disclosure | Client Related and Trading | Interest Rate Swap Contracts
Other Liabilities
Assets	182.1		188.7
Liabilities	177.0		184.6
Estimate of Fair Value, Fair Value Disclosure | Client Related and Trading | Interest Rate Option Contracts
Other Liabilities
Assets	0.1
Liabilities	0.1
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1
Assets
Cash and Due from Banks	4,280.3		4,315.3
Securities
Available for Sale	2,766.5	[1]	4,029.4	[2]
Deposits
Demand, Noninterest-Bearing, Savings and Money Market	34,263.8		43,751.2
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1 | Rabbi Trust
Other Assets
Rabbi Trust Investments	83.6		71.4
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2
Assets
Federal Funds Sold and Resell Agreements	290.9		121.3
Interest-Bearing Deposits with Banks	18,871.3		16,696.4
Federal Reserve Deposits and Other Interest-Bearing	2,228.0		13,448.6
Securities
Available for Sale	27,964.0	[1]	25,984.8	[2]
Held to Maturity	727.2		817.1
Trading Account	9.3		8.0
Loans (excluding Leases)
Client Security Settlement Receivables	985.3		778.3
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	172.9		172.9
Affordable Housing Investments	306.60		319.90
Deposits
Savings Certificates and Other Time	3,101.3		3,065.5
Non U. S. Offices Interest-Bearing	36,575.4		35,868.0
Federal Funds Purchased	1,973.7		815.3
Securities Sold under Agreements to Repurchase	284.0		1,198.8
Other Borrowings	1,103.0		931.5
Senior Notes	2,192.2		2,197.3
Long Term Debt (excluding Leases)
Subordinated Debt	1,055.5		1,040.0
Federal Home Loan Bank Borrowings	723.7		1,082.1
Floating Rate Capital Debt	232.3		211.6
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Rabbi Trust
Other Assets
Rabbi Trust Investments	39.0		34.9
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Foreign Exchange Contracts
Other Liabilities
Assets	14.6		25.2
Liabilities	45.6		31.8
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Interest Rate Swap Contracts
Other Liabilities
Assets	141.8		149.6
Liabilities	45.9		47.3
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Credit Default Swap Contracts
Other Liabilities
Assets			0.7
Liabilities	0.2		0.1
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Foreign Exchange Contracts
Other Liabilities
Assets	3,127.8		3,062.1
Liabilities	3,063.6		2,959.8
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Interest Rate Swap Contracts
Other Liabilities
Assets	182.1		188.7
Liabilities	177.0		184.6
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Interest Rate Option Contracts
Other Liabilities
Assets	0.1
Liabilities	0.1
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3
Securities
Available for Sale	176.3	[1]	178.3	[2]
Loans (excluding Leases)
Held for Investment	27,957.9		27,913.7
Held for Sale	0.1		9.3
Other Liabilities
Standby Letters of Credit	50.1		43.8
Contingent Consideration	58.6		56.8
Loan Commitments	$ 28.9		$ 28.9

[1] Refer to the table located on page 31 for the disaggregation of available-for-sale-securities.

[2] Refer to the table located on page 32 for the disaggregation of available-for-sale-securities.