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Loans to Banking Clients and Related Allowance for Loan Losses - Additional Information (Detail) (USD $)
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3 Months Ended | |||
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Mar. 31, 2013
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Dec. 31, 2012
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Mar. 31, 2013
First Mortgage
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Mar. 31, 2012
First Mortgage
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| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||
| Commitments to extend credit related to unused home equity lines of credit, personal loans secured by securities, and other lines of credit | $ 5,400,000,000 | $ 5,400,000,000 | ||
| Total nonaccrual loans | 42,000,000 | 48,000,000 | ||
| Loans accruing interest contractually 90 days or more past due | 0 | 0 | ||
| Nonperforming assets, including nonaccrual loans and other real estate owned | 46,000,000 | 54,000,000 | ||
| Purchased First Mortgages | $ 1,300,000,000 | $ 71,000,000 | ||
| Minimum fair value percentage of collateral to principal amount of loan | 100.00% | 100.00% | ||