Reverse Repurchase and Repurchase Agreements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Securities Financing Transaction [Line Items]
U.S. and non-U.S. government and agency securities, asset-backed securities and corporate debt	$ 247.4
Securities repledged, delivered or used to settle Securities Sold, Not Yet Purchased	226.4
Pledged securities with carrying value to collateralize its repurchase agreements	$ 141.9