Summary of Preliminary Fair Values of Assets Acquired and Liabilities Assumed as of Acquisition Date (Detail) (optionsXpress Holdings, Inc., USD $) In Millions, unless otherwise specified	Sep. 01, 2011
optionsXpress Holdings, Inc.
Assets
Cash and cash equivalents	$ 84
Cash and investments segregated and on deposit for regulatory purposes	1,074
Receivables from brokers, dealers, and clearing organizations	40
Receivables from brokerage clients	185
Other securities owned - at fair value	32
Intangible assets	285
Other assets	24
Total assets acquired	1,724	[1]
Liabilities
Payables to brokerage clients	1,221
Deferred tax liability	95
Long-term debt	110	[2]
Accrued expenses and other liabilities	91
Total liabilities assumed	1,517	[1]
Net assets acquired	$ 207

[1] All assets and liabilities, except for cash and cash equivalents, represent non-cash investing activities.

[2] The Company paid off long-term debt acquired from optionsXpress subsequent to the date of acquisition in September 2011.