Business Combinations - Acquisition Activity (Details) - USD ($) $ in Millions	1 Months Ended
	Feb. 28, 2019	May 31, 2018	Sep. 30, 2019	Dec. 31, 2018
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill			$ 5,097	$ 5,160
Motors.co.uk
Business Acquisition [Line Items]
Purchase consideration	$ 93
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill	65
Purchased intangible assets	30
Net liabilities	(2)
Total	$ 93
Giosis Pte. Ltd.
Business Acquisition [Line Items]
Purchase consideration		$ 306
Percent of business acquired		100.00%
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill		$ 532
Purchased intangible assets		91
Net liabilities		(50)
Total		$ 573