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Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2014
Loss Contingencies [Line Items]  
Minimum estimated range of aggregate loss for legal proceedings $ 0
Maximum estimated range of aggregate loss for legal proceedings 41
Total amount of ARS the firm purchased and hold 91.5
Amount of ARS committed to purchase from clients 5.0
Eligible investor subject to future buyback principal value 5
Eligible investor subject to future buyback potential additional losses related to valuation adjustments 116.8
Period of auction rates security to be purchased from rendering of the award 30 days
Loss contingency charged against earnings 7.7
Scenario, Forecast [Member]
  
Loss Contingencies [Line Items]  
Amount of ARS committed to purchase from clients $ 24.0