In measuring fair values of assets and liabilities, we use valuation techniques that maximize the use of observable inputs (Level 1) and minimize the use of unobservable inputs (Level 3). We also use market data or assumptions that we believe market participants would use in pricing an asset or liability, including assumptions about risk when appropriate.

The carrying value for certain of our financial instruments, including cash, accounts receivable, accounts payable and certain other accrued liabilities, approximates fair value because of their short-term nature.

As of December 31, 2024 and 2023, our assets and liabilities that are measured at fair value on a recurring basis include the following:


	December 31, 2024
			Fair Value
	Carrying Amount		Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market mutual funds - restricted cash and marketable securities and other assets	$	62	$	62	$	62	$	—	$	—
Bonds and fixed income - restricted cash and marketable securities and other assets	90		90		—		90		—
Derivative and hedging assets - other assets, prepaid expenses and other current assets	55		55		—		55		—
Total assets	$	207	$	207	$	62	$	145	$	—
Liabilities:
Derivative and hedging liabilities - other accrued liabilities and other long-term liabilities	$	72	$	72	$	—	$	72	$	—

Contingent consideration - other accrued liabilities and other long-term liabilities	65		65		—		—		65
Total liabilities	$	137	$	137	$	—	$	72	$	65


	December 31, 2023
			Fair Value
	Carrying Amount		Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market mutual funds - restricted cash and marketable securities and other assets	$	43	$	43	$	43	$	—	$	—
Bonds - restricted cash and marketable securities and other assets	76		76		—		76		—
Derivative and hedging assets - other assets	78		78		—		78		—
Total assets	$	197	$	197	$	43	$	154	$	—
Liabilities:
Derivative and hedging liabilities - other accrued liabilities and other long-term liabilities	$	80	$	80	$	—	$	80	$	—
Contingent consideration - other accrued liabilities and other long-term liabilities	64		64		—		—		64
Total liabilities	$	144	$	144	$	—	$	80	$	64

As of December 31, 2024 and 2023, the carrying value of our total debt was $12.7 billion and $12.8 billion, respectively, and the fair value of our total debt was $12.2 billion and $12.5 billion, respectively. The estimated fair value of our fixed rate senior notes and debentures is based on quoted market prices. The fair value of our remaining notes payable, tax-exempt financings and borrowings under our credit facilities approximates the carrying value because the interest rates are variable. The fair value estimates are based on Level 2 inputs of the fair value hierarchy as of December 31, 2024 and 2023. See Note 9, Debt, for further information related to our debt.

In 2015, we entered into a waste management contract with the County of Sonoma, California to operate the county's waste management facilities. As of December 31, 2024, the Sonoma contingent consideration represents the fair value of $57 million payable to the County of Sonoma based on the achievement of future annual tonnage targets through the expected remaining capacity of the landfill. The potential undiscounted amount of all future contingent payments that we could be required to make under the waste management contract is estimated to be between approximately $77 million and $105 million. During 2024, the activity in the contingent consideration liability included accretion, which was offset by concession payments made in the ordinary course of business. There were no changes to the estimate of fair value.