Acquisitions Acquisitions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Aug. 01, 2016	Jun. 01, 2016
Business Acquisition [Line Items]
Business Acquisition Cash Paid			$ 28	$ 298
Goodwill	$ 240	$ 240
Amortization of Intangible Assets	10	6
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		$ 193
Automotive Finance Operations [Member]
Business Acquisition [Line Items]
Goodwill	$ 20	$ 20	$ 20