Business Acquisition - Additional Information (Detail) (OptionsXpress Holdings, Inc., USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 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	49		101
Net income, acquiree	6		8
Amortization of purchase accounting adjustments related to intangible assets, net of tax		$ 5		$ 10