Fair Value Measurements - Quantitative Information about Non Recurring Fair Value Measurement of Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Level 3 [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Significant Unobservable Inputs	Loss severity rates		Loss severity rates
Level 3 [Member] | Residential Mortgage [Member] | Third Party Appraisal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation Technique(s)	Valuation of third party appraisal on underlying collateral		Valuation of third party appraisal on underlying collateral
Level 3 [Member] | Residential Mortgage [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Range of Inputs	0.00%		0.00%
Level 3 [Member] | Residential Mortgage [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Range of Inputs	100.00%		100.00%
Level 3 [Member] | Impaired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Significant Unobservable Inputs			Loss severity rates
Level 3 [Member] | Impaired loans [Member] | Third Party Appraisal On Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation Technique(s)	Valuation of third party appraisal on underlying collateral		Valuation of third party appraisal on underlying collateral
Level 3 [Member] | Impaired loans [Member] | Loss Severity Rates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Significant Unobservable Inputs	Loss severity rates
Level 3 [Member] | Impaired loans [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Range of Inputs	0.30%		0.60%
Level 3 [Member] | Impaired loans [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Range of Inputs	80.60%		78.90%
Fair Value, Measurements, Nonrecurring [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	227		256
Fair Value, Measurements, Nonrecurring [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	74		77
Fair Value, Measurements, Nonrecurring [Member] | Impaired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	125		155
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	191		222
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	66		67
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Impaired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	125		155
Recurring [Member] | Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Significant Unobservable Inputs	Equity / Equity Index volatility	[1],[2]

[1] Structured deposits and structured notes contain embedded derivative features whose fair value measurements contain significant Level 3 inputs.

[2] We are the client-facing entity and we enter into identical but opposite derivatives to transfer the resultant risks to our affiliates. With the exception of counterparty credit risks, we are market neutral. The corresponding intra-group derivatives are presented as equity derivatives and foreign currency derivatives in the table.