Acquisitions - Summary of Purchase Price Allocation Initially Recorded on Consolidated Balance Sheet for all Acquisitions (Parenthetical) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Business Acquisition [Line Items]
Goodwill expected to be deductible for tax purposes	$ 5		$ 14
Identifiable definite-lived intangible assets	194	[1]	19	[2]
Weighted average life of identifiable definite-lived intangible assets acquired	7 years 2 months 12 days		8 years
Cash acquired from acquisition	62		3
Assets acquired, accounts receivable	25		2
Liabilities assumed, deferred merchant payables	76		11
Liabilities assumed, accrued expenses	15		1
Liabilities assumed, deferred revenue	5		3
Developed Technology
Business Acquisition [Line Items]
Identifiable definite-lived intangible assets	43
Weighted average life of identifiable definite-lived intangible assets acquired	4 years 10 months 24 days
Trade Names
Business Acquisition [Line Items]
Identifiable definite-lived intangible assets	44		8
Weighted average life of identifiable definite-lived intangible assets acquired	10 years
Customer Lists and Supplier Relationships
Business Acquisition [Line Items]
Identifiable definite-lived intangible assets	82
Weighted average life of identifiable definite-lived intangible assets acquired	7 years 2 months 12 days
Subscriber Relationships
Business Acquisition [Line Items]
Identifiable definite-lived intangible assets	25		8
Weighted average life of identifiable definite-lived intangible assets acquired	6 years
Developed Technology and Other
Business Acquisition [Line Items]
Identifiable definite-lived intangible assets			$ 3

[1] Identifiable definite-lived intangible assets acquired during 2014 were comprised of trade names of $44 million with a weighted average life of 10.0 years, customer lists and supplier relationships of $82 million with a weighted average life of 7.2 years, subscriber relationships of $25 million with a weighted average life of 6.0 years and developed technology and other of $43 million with a weighted average life of 4.9 years. The overall weighted-average life of the identifiable definite-lived intangible assets acquired in the purchase of the companies during 2014 was 7.2 years, and will be amortized on a straight-line basis over their estimated useful lives from acquisition date.

[2] Identifiable definite-lived intangible assets acquired during 2013 were comprised of trade names of $8 million, subscriber relationships of $8 million, and developed technology and other of $3 million. The overall weighted-average life of the identifiable definite-lived intangible assets acquired in the purchase of the companies during 2013 was 8.0 years, which is being amortized on a straight-line basis over their estimated useful lives from acquisition date.