Acquisitions (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Other than Temporary Impairment Losses, Investments	$ 33	$ 0	$ 33	$ 0
Business Acquisition, Purchase Price Allocation, Intangible Assets Other than Goodwill	188		188
Customer Relationships	76		76
Equity Method Investments	0		0		0
Zipcar [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Date of acquisition	Mar. 14, 2013
Acquisition purchase price	473		473
Business Acquisition, Purchase Price Allocation, Intangible Assets Other than Goodwill	112		112
Business Acquisition, Purchase Price Allocation, Goodwill Amount	275		275
Other intangibles, useful life, in years			8 years
Brazil [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Date of acquisition	Aug. 12, 2013
Payless [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Date of acquisition	Jul. 15, 2013
Acquisition purchase price	50		50
Business Acquisition, Purchase Price Allocation, Intangible Assets Not Amortizable	23		23
Business Acquisition, Purchase Price Allocation, Goodwill Amount	27		27
Other intangibles, useful life, in years			15 years
License Agreements [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Business Acquisition, Purchase Price Allocation, Intangible Assets Other than Goodwill	7		7
Apex [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Date of acquisition	Oct. 01, 2012
Business Acquisition, Purchase Price Allocation, Intangible Assets Other than Goodwill	21		21
Business Acquisition, Purchase Price Allocation, Goodwill Amount	16		16
Number Of Vehicles	4,000		4,000
Business Acquisition, Cost of Acquired Entity, Cash Paid	63		63
Business Acquisition, Contingent Consideration, Potential Cash Payment	9		9
Business Acquisition, Contingent Consideration, Potential Cash Payment	26		26
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	33		33
BRAZIL
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Business Acquisition, Contingent Consideration, Potential Cash Payment	13		13
Trademarks [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Business Acquisition, Purchase Price Allocation, Intangible Assets Other than Goodwill	16		16
Brazil [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Acquisition purchase price	53		53
Other than Temporary Impairment Losses, Investments	33
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	33
Equity Method Investment, Ownership Percentage	50.00%		50.00%
Equity Method Investments	$ 20		$ 20