Certain Regulatory Requirements and Capital Ratios - Additional Information (Detail) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Average deposited in a special reserve account for the exclusive benefit of customers pursuant to SEC Regulations	$ 744,000,000	$ 547,000,000
Trust Preferred Securities [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier I capital (to risk-weighted assets)	$ 2,200,000,000