Debt (Tables)

3 Months Ended

Mar. 31, 2012

Debt [Abstract]

Outstanding letters of credit under committed lines of credit

We had outstanding letters of credit under our committed lines of credit as follows (in millions):

				Amounts Outstanding
	Borrowing Capacity		Expiration	March 31, 2012		December 31, 2011
Letter of credit facilities	$	500	June 2012	$	500	$	300
Revolver	$	3,000	December 2016	$	153	$	119
Canadian revolving credit facility	C$	115	December 2012	C$	20	C$	20

Changes in accounts receivable sales facility

Changes in the amounts outstanding under our accounts receivable sales facility were as follows (in millions):

	Three Months Ended March 31,
	2012			2011
Balance as of beginning of period	$	250		$	100
Proceeds from the sale of receivables	—			—
Repayments	(150		)	—
Balance as of end of period	$	100		$	100