Fair Value Measurements

3 Months Ended

Mar. 31, 2012

Fair Value Measurements [Abstract]

Fair Value Measurements

10.     Fair Value Measurements

Certain assets and liabilities are required to be recorded at fair value. There are three levels of inputs that may be used to measure fair value. Level 1 is defined as quoted prices for identical assets and liabilities in active markets. Level 2 is defined as quoted prices for similar assets and liabilities in active markets; quoted prices for identical or similar assets and liabilities in markets that are not active; and model-derived valuations in which all significant inputs and significant value drivers are observable in active markets. Level 3 is defined as valuations derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. Certain assets and liabilities are measured at fair value on a nonrecurring basis rather than on an ongoing basis, such as when there is evidence of impairment or when a new liability is being established that requires fair value measurement.

The cash equivalents shown in the table below primarily consist of money market funds that are valued based on quoted prices in active markets and as a result are classified as Level 1. We use quoted prices, other readily observable market data and internally developed valuation models when valuing our derivatives and marketable securities and have classified them as Level 2. Derivatives are valued using the income approach including discounted-cash-flow models or a Black-Scholes option pricing model and readily observable market data. The inputs for the valuation models are obtained from data providers and include end-of-period spot and forward natural gas prices and foreign currency exchange rates, natural gas price volatility and LIBOR and swap rates for discounting the cash flows implied from the derivative contracts. Marketable securities are valued using income and market value approaches and values are based on quoted prices or other observable market inputs received from data providers. The valuation process may include pricing matrices, or prices based upon yields, credit spreads or prices of securities of comparable quality, coupon, maturity and type. 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)	3/31/12		12/31/11		3/31/12			12/31/11			3/31/12		12/31/11		3/31/12			12/31/11
Cash equivalents		257		128		27			31			-		-		284			159
Marketable securities:
Corporate debt securities		-		-		86			174			-		-		86			174
U.S. government and agency debt securities		-		-		12			32			-		-		12			32
Asset-backed debt securities		-		-		9			18			-		-		9			18
Certificates of deposit		-		-		16			35			-		-		16			35
Municipal debt securities		-		-		15			27			-		-		15			27
Derivative assets		-		-		3			4			-		-		3			4
Derivative liabilities		-		-		(9	)		(8	)		-		-		(9	)		(8	)