Valuation and Qualifying Accounts (Detail) (Allowance for doubtful accounts of brokerage clients, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Allowance for doubtful accounts of brokerage clients
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 2	[1]	$ 1	[1]	$ 2	[1]
Charged to Expense	4	[1]	6	[1]	3	[1]
Other			3	[1],[2]
Written off	(5)	[1]	(8)	[1]	(4)	[1]
Balance at End of Year	$ 1	[1]	$ 2	[1]	$ 1	[1]

[1] Excludes banking-related valuation and qualifying accounts. See "Item 8 - Financial Statements and Supplementary Data - Notes to Consolidated Financial Statements - 7. Loans to Banking Clients and Related Allowance for Loan Losses."

[2] Includes collections of previously written-off accounts.