Accounts Receivable, Net (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Schedule of accounts receivable [Line Items]
Amounts billed or billable	$ 2,825				$ 2,639
Unbilled amounts	349				335
Allowance for doubtful accounts	(109)				(108)
Accounts Receivable, Net	3,065				2,866
Billable contracts receivable to be invoiced in the subsequent month	1,027				1,049
Accounts Receivable Sales Arrangements [Abstract]
Deferred proceeds receivables from sales of accounts receivables	115				116
Remaining account receivable sold and derecognized	768				766
Schedule of accounts receivables sales [Abstract]
Accounts receivable sales	854		875
Deferred proceeds	115		147
Loss on sales of accounts receivable	4		6
Estimated increase (decrease) to operating cash flows	$ 16	[1]	$ (68)	[1]

[1] Represents the difference between current and prior year fourth quarter receivable sales adjusted for the effects of: (i) the deferred proceeds, (ii) collections prior to the end of the quarter and (iii) currency.