Business Acquisition - Additional Information (Detail) (OptionsXpress Holdings, Inc., USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 01, 2011
OptionsXpress Holdings, Inc.
Business Acquisition [Line Items]
Business acquisition, consideration paid					$ 714
Common shares issued per each share of acquiree					1.02
Business acquisition, common stock issued share					59,000,000
Fair value of common stock issued					710
Business acquisition, other noncash consideration					4
Business acquisition purchase price allocation, goodwill					511
Business acquisition purchase price allocation, intangible assets					285
Net revenue, acquiree	42		143
Net income, acquiree			7
Acquisition related costs, after tax, incurred by the Company and excluded from proforma net income		10		12
Acquisition related costs, before tax, incurred by optionsXpress Holdings, Inc., prior to the acquisition date and excluded from proforma net income			15
Amortization of purchase accounting adjustments related to intangible assets, net of tax		$ 6		$ 17