Intangible Assets (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Intangible Assets (Textual) [Abstract]
Accumulated amortization	$ 530	$ 448	$ 360
Average useful life of customer and vendor relationships	13 years
Intangible Assets (Additional Textual) [Abstract]
Amortization Expense relating to intangible asset, Year One	79
Amortization Expense relating to intangible asset, Year Two	76
Amortization Expense relating to intangible asset, Year Three	68
Amortization Expense relating to intangible asset, Year Four	49
Amortization Expense relating to intangible asset, Year Five	42
Customer Relationships [Member]
Intangible Assets (Textual) [Abstract]
Amortization expense	81	88	89
Accumulated amortization	528	447
Vendor Relationships and Other [Member]
Intangible Assets (Textual) [Abstract]
Amortization expense	1	1
Accumulated amortization	2	1
Customer and Vendor Relationship [Member]
Intangible Assets (Textual) [Abstract]
Average useful life of customer and vendor relationships	13 years
Maximum [Member] | Vendor Relationships and Other [Member]
Intangible Assets (Textual) [Abstract]
Amortization expense			$ 1