16. Fair Value Measurements

Assets and Liabilities Accounted for at Fair Value

Fair value is defined as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When measuring assets and liabilities that are required to be recorded at fair value, the Company considers the principal or most advantageous market in which the Company would transact. Fair value is estimated by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement:

Level 1 — Quoted prices in active markets for identical assets or liabilities.

Level 2 — Observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 — Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability.

We use valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. In measuring the fair value of our assets and liabilities, we use market data or assumptions that we believe market participants would use in pricing an asset or liability, including assumptions about risk when appropriate. Our assets and liabilities that are measured at fair value on a recurring basis include the following as of December 31 (in millions):


			Fair Value Measurements Using
			Quoted		Significant
			Prices in		Other		Significant
			Active		Observable		Unobservable
			Markets		Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
2017
Assets:
Money market funds	$	225	$	225	$	—	$	—
Available-for-sale securities		49		—		49		—
Fixed-income securities		47		—		47		—
Redeemable preferred stock		55		—		—		55
Total assets	$	376	$	225	$	96	$	55

2016
Assets:
Money market funds	$	35	$	35	$	—	$	—
Available-for-sale securities		46		—		46		—
Fixed-income securities		39		—		39		—
Redeemable preferred stock		54		—		—		54
Total assets	$	174	$	35	$	85	$	54

Money Market Funds

We invest portions of our restricted trust and escrow account balances in money market funds. We measure the fair value of these investments using quoted prices in active markets for identical assets. The fair value of our money market funds approximates our cost basis in the investments. The increase in money market funds as of December 31, 2017 is primarily related to the premiums paid to a wholly-owned insurance captive.

Available-for-Sale Securities

Available-for-sale securities are primarily related to the restricted trust funds that were created to settle certain of our final capping, closure, post-closure or environmental remediation obligations, which are discussed further in Note 18. These trust funds are invested in U.S. Treasury securities and equity and bond funds. We measure the fair value of these securities using quoted prices for identical or similar assets in inactive markets. Any changes in fair value of these trusts related to unrealized gains and losses have been appropriately reflected as a component of accumulated other comprehensive income (loss).

Fixed-Income Securities

We invest a portion of our restricted trust and escrow account balances in fixed-income securities, including U.S. Treasury securities, U.S. agency securities, municipal securities and mortgage- and asset-backed securities. We measure the fair value of these securities using quoted prices for identical or similar assets in inactive markets. The fair value of our fixed-income securities approximates our cost basis in these investments.

Redeemable Preferred Stock

Redeemable preferred stock is primarily related to a noncontrolling investment in an unconsolidated entity and is included in investments in unconsolidated entities in our Consolidated Balance Sheets. The fair value of our investment has been measured based on third-party investors’ recent or pending transactions in these securities, which are considered the best evidence of fair value. When this evidence is not available, we use other valuation techniques as appropriate and available. These valuation methodologies may include transactions in similar instruments, discounted cash flow techniques, third-party appraisals or industry multiples and public comparables. Redeemable preferred stock also includes stock received in conjunction with the 2014 sale of our Puerto Rico operations.

Fair Value of Debt

As of December 31, 2017 and 2016, the carrying value of our debt was $9.5 billion and $9.3 billion, respectively. The estimated fair value of our debt was approximately $9.9 billion and $9.7 billion as of December 31, 2017 and 2016, respectively. The fair value of our fixed-rate debt is estimated by using a discounted cash flow approach and current market rates for similar types of instruments. The carrying value of our variable-rate debt approximates fair value due to the short-term nature of the interest rates. The increase in the fair value of our debt when comparing December 31, 2017 with December 31, 2016 is primarily related to net borrowings of $172 million during 2017 and fluctuations in current market rates for similar types of instruments.

Although we have determined the estimated fair value amounts using available market information and commonly accepted valuation methodologies, considerable judgment is required in interpreting market data to develop the estimates of fair value. Accordingly, our estimates are not necessarily indicative of the amounts that we, or holders of the instruments, could realize in a current market exchange. The use of different assumptions or estimation methodologies could have a material effect on the estimated fair values. The fair value estimates are based on Level 2 inputs of the fair value hierarchy available as of December 31, 2017 and 2016. These amounts have not been revalued since those dates, and current estimates of fair value could differ significantly from the amounts presented.