Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2012

Fair Value Measurements [Abstract]

Assets and liabilities measured at fair value on a recurring basis

	Quoted Prices in Active Markets for Identical Assets (Level 1)				Significant Other Observable Inputs (Level 2)						Significant Unobservable Inputs (Level 3)				Total
(millions)	6/30/12		12/31/11		6/30/12			12/31/11			6/30/12		12/31/11		6/30/12			12/31/11
Cash equivalents	$	198	$	128	$	31		$	31		$	—	$	—	$	229		$	159
Marketable securities:
Corporate debt securities		—		—		66			174			—		—		66			174
U.S. government and agency debt securities		—		—		13			32			—		—		13			32
Asset-backed debt securities		—		—		13			18			—		—		13			18
Certificates of deposit		—		—		13			35			—		—		13			35
Municipal debt securities		—		—		23			27			—		—		23			27
Derivative assets		—		—		3			4			—		—		3			4
Derivative liabilities		—		—		(5	)		(8	)		—		—		(5	)		(8	)