Commitments and Contingent Liabilities- Significant Industry Concentrations Related to Credit Exposure (Detail) (USD $) In Billions, unless otherwise specified	Mar. 31, 2013
Financial institutions
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	$ 13.8
Unfunded commitments	15.5
Total exposure	29.3
Financial institutions | Banks
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	8.6
Unfunded commitments	1.9
Total exposure	10.5
Financial institutions | Securities Industry
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	3.6
Unfunded commitments	1.9
Total exposure	5.5
Financial institutions | Asset Managers
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	1.3
Unfunded commitments	3.5
Total exposure	4.8
Financial institutions | Insurance
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.2
Unfunded commitments	4.1
Total exposure	4.3
Financial institutions | Government
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans
Unfunded commitments	3.0
Total exposure	3.0
Financial institutions | Other
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.1
Unfunded commitments	1.1
Total exposure	1.2
Commercial
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	1.5
Unfunded commitments	18.7
Total exposure	20.2
Commercial | Services and Other
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.5
Unfunded commitments	5.9
Total exposure	6.4
Commercial | Energy and Utilities
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.6
Unfunded commitments	5.8
Total exposure	6.4
Commercial | Manufacturing
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	0.3
Unfunded commitments	5.5
Total exposure	5.8
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