Acquisitions (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		3 Months Ended			3 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Edmonton [Member]	Mar. 31, 2014 Customer Relationships [Member]	Mar. 31, 2014 License Agreement Terms [Member]	Mar. 31, 2014 Portugal [Member]	Mar. 31, 2013 Zipcar [Member]	Dec. 31, 2013 Zipcar [Member]	Aug. 31, 2013 Brazil [Member]	Mar. 31, 2014 Brazil [Member]	Dec. 31, 2013 Brazil [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Date of acquisition			Feb. 01, 2014			Feb. 01, 2014		Mar. 14, 2013			Aug. 12, 2013
Business Combination, Consideration Transferred			$ 33			$ 9	$ 473
Business Acquisition Purchase Price Allocation Vehicles Net	86
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	17			11	6	2
Goodwill	713	691	9			13
Other intangibles, useful life, in years	12 years 0 months 0 days		4 years 0 months 0 days			2 years 0 months 0 days
Indefinite-Lived License Agreements			3
Business Combination, Consideration Transferred, Other						15
Equity Method Investment, Ownership Percentage										50.00%
Payments to Acquire Equity Method Investments									$ 53	$ 6