Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2016

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)	3/31/16		12/31/15		3/31/16			12/31/15			3/31/16		12/31/15		3/31/16			12/31/15
Cash equivalents	$	112	$	223	$	50		$	25		$	—	$	—	$	162		$	248
Equity mutual funds	4		4		—			—			—		—		4			4
Marketable securities:
Corporate debt securities	—		—		134			134			—		—		134			134
U.S. government and agency debt securities	—		—		52			57			—		—		52			57
Asset-backed debt securities	—		—		13			21			—		—		13			21
Certificates of deposit	—		—		26			15			—		—		26			15
Municipal debt securities	—		—		1			3			—		—		1			3
Derivative assets	—		—		3			9			—		—		3			9
Derivative liabilities	—		—		(24		)	(22		)	—		—		(24		)	(22		)