Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2014

Fair Value Disclosures [Abstract]

Assets and liabilities measured at fair value on a recurring basis

Our assets and liabilities measured at fair value on a recurring basis were as follows:

	Quoted Prices in Active Markets for Identical Assets (Level 1)				Significant Other Observable Inputs (Level 2)					Significant Unobservable Inputs (Level 3)				Total
(millions)	3/31/14		12/31/13		3/31/14			12/31/13		3/31/14		12/31/13		3/31/14			12/31/13
Cash equivalents	$	72	$	549	$	22		$	24	$	—	$	—	$	94		$	573
Marketable securities:
Corporate debt securities	—		—		93			87		—		—		93			87
U.S. government and agency debt securities	—		—		8			12		—		—		8			12
Asset-backed debt securities	—		—		16			20		—		—		16			20
Certificates of deposit	—		—		16			17		—		—		16			17
Municipal debt securities	—		—		5			6		—		—		5			6
Derivative assets	—		—		9			5		—		—		9			5
Derivative liabilities	—		—		(2		)	—		—		—		(2		)	—