Fair Value Measurements

12 Months Ended

Dec. 31, 2018

Certain assets and liabilities are required to be recorded at fair value. The fair values of our cash equivalents, equity mutual funds, marketable securities and derivatives were determined using the fair value hierarchy of inputs described in Note 1, Significant Accounting Policies.



	USG Valuation Method
Level 1	Cash equivalents and equity mutual funds consist of money market funds that are valued based on quoted prices in active markets.
Level 2	Marketable securities, including certain cash equivalents, are valued using a "market value" approach. Values are based on quoted prices and other observable market inputs received from data providers.
Level 2	Derivatives are valued using the "income" approach such as discounted-cash-flow models 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, foreign currency exchange rates, natural gas price volatility and LIBOR and swap rates for discounting the cash flows implied from the derivative contracts.
Level 3	No level 3 investments.

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)	12/31/18		12/31/17		12/31/18			12/31/17			12/31/18		12/31/17		12/31/18			12/31/17
Cash equivalents	$	121	$	124	$	36		$	24		$	—	$	—	$	157		$	148
Equity mutual funds	5		6		—			—			—		—		5			6
Marketable securities:
Corporate debt securities	—		—		73			68			—		—		73			68
U.S. government and agency debt securities	—		—		5			6			—		—		5			6
Asset-backed debt securities	—		—		15			11			—		—		15			11
Certificates of deposit	—		—		5			13			—		—		5			13
Municipal debt securities	—		—		—			1			—		—		—			1
Derivative assets	—		—		10			2			—		—		10			2
Derivative liabilities	—		—		(16		)	(17		)	—		—		(16		)	(17		)

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

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