Acquisitions (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			3 Months Ended			3 Months Ended	6 Months Ended	1 Months Ended	12 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2014	Jun. 30, 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]	Jun. 30, 2014 Portugal [Member]	Mar. 31, 2013 Zipcar [Member]	Dec. 31, 2013 Zipcar [Member]	Jun. 30, 2014 Apex [Member]	Dec. 31, 2012 Apex [Member]	Aug. 31, 2013 Brazil [Member]	Jun. 30, 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				$ 10	$ 473
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability											7
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		707	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
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High												26
Business Combination, Contingent Consideration, Liability											$ 19