Off-Balance Sheet Risks Significant Industry Concentrations (Detail) (USD $) In Billions, unless otherwise specified	Mar. 31, 2012
Financial Institutions
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	$ 11.0
Unfunded commitments	14.6
Total exposure	25.6
Financial Institutions | Banks
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	5.6
Unfunded commitments	1.6
Total exposure	7.2
Financial Institutions | Securities Industry
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	4.4
Unfunded commitments	2.2
Total exposure	6.6
Financial Institutions | Insurance
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.1
Unfunded commitments	4.3
Total exposure	4.4
Financial Institutions | Asset Managers
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.8
Unfunded commitments	3.5
Total exposure	4.3
Financial Institutions | Government
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Unfunded commitments	1.5
Total exposure	1.5
Financial Institutions | Other Industry
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.1
Unfunded commitments	1.5
Total exposure	1.6
Commercial
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	1.2
Unfunded commitments	16.6
Total exposure	17.8
Commercial | Manufacturing
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.3
Unfunded commitments	5.8
Total exposure	6.1
Commercial | Energy and Utilities
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.3
Unfunded commitments	4.9
Total exposure	5.2
Commercial | Services and Other
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.5
Unfunded commitments	4.4
Total exposure	4.9
Commercial | Media and Telecom
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.1
Unfunded commitments	1.5
Total exposure	$ 1.6