Acquisition of TradeKing Acquisition of TradeKing (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Aug. 01, 2016	Jun. 01, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Amortization of Intangible Assets	$ 3
Payments to Acquire Businesses, Gross		$ 28	$ 298
Goodwill	240			$ 27
Other Intangible Assets [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill			82
Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents			50
Other Assets [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill			14
Deferred Tax Asset [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill			4
Employee compensation and benefits [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents			40
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities			(41)
Other Liabilities [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities			(4)
Corporate and Other [Member]
Business Acquisition [Line Items]
Goodwill	193		$ 193	0
Automotive Finance Operations [Member]
Business Acquisition [Line Items]
Goodwill	$ 20			$ 0