Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 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)	6/30/14		12/31/13		6/30/14			12/31/13		6/30/14		12/31/13		6/30/14			12/31/13
Cash equivalents	$	138	$	549	$	21		$	24	$	—	$	—	$	159		$	573
Marketable securities:
Corporate debt securities	—		—		92			87		—		—		92			87
U.S. government and agency debt securities	—		—		4			12		—		—		4			12
Asset-backed debt securities	—		—		17			20		—		—		17			20
Certificates of deposit	—		—		19			17		—		—		19			17
Municipal debt securities	—		—		6			6		—		—		6			6
Derivative assets	—		—		6			5		—		—		6			5
Derivative liabilities	—		—		(5		)	—		—		—		(5		)	—