The effect of our hedging relationships and derivative instruments on the consolidated statements of income for the three and six months ended June 30, 2024 and 2023 follows (in millions):


	Classification and amount of gain (loss) recognized in income on hedging relationships and derivative instruments
		Three Months Ended June 30,				Six Months Ended June 30,
		2024		2023		2024		2023
		Interest Expense		Interest Expense		Interest Expense		Interest Expense

Total amount of expense line items presented in the consolidated statements of income in which the effects of hedging relationships and derivative instruments are recorded		$	(128.3)	$	(124.4)	$	(267.6)	$	(251.1)

The effects of cash flow hedging relationships in Subtopic 815-20:
(Loss) gain on cash flow hedging relationships:
Interest rate swap locks		$	(0.9)	$	(1.0)	$	(1.7)	$	(2.0)
2022 interest rate swap		$	6.6	$	1.6	$	8.0	$	(0.6)

The effects of derivative instruments not in Subtopic 815-20:
Loss on free-standing derivative instruments:
Interest rate contract:
Net loss on change in fair value of free-standing derivative instruments		$	(0.1)	$	(0.2)	$	(0.1)	$	(1.3)

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, current investments, accounts payable and certain other accrued liabilities, approximates fair value because of their short-term nature. As of June 30, 2024 and December 31, 2023, our assets and liabilities that are measured at fair value on a recurring basis include the following:


	June 30, 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	$	45.1	$	45.1	$	45.1	$	—	$	—
Bonds - restricted cash and marketable securities and other assets	77.1		77.1		—		77.1		—
Derivative and hedging assets - other assets	59.3		59.3		—		59.3		—

Total assets	$	181.5	$	181.5	$	45.1	$	136.4	$	—
Liabilities:


Derivative and hedging liabilities - other accrued liabilities and other long-term liabilities	$	79.9	$	79.9	$	—	$	79.9	$	—

Contingent consideration - other accrued liabilities and other long-term liabilities	63.8		63.8		—		—		63.8
Total liabilities	$	143.7	$	143.7	$	—	$	79.9	$	63.8


	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	$	43.1	$	43.1	$	43.1	$	—	$	—
Bonds - restricted cash and marketable securities and other assets	76.3		76.3		—		76.3		—

Derivative and hedging assets - prepaid and other current assets and other assets	78.3		78.3		—		78.3		—
Total assets	$	197.7	$	197.7	$	43.1	$	154.6	$	—
Liabilities:
Derivative and hedging liabilities - other accrued liabilities and other long-term liabilities	$	79.6	$	79.6	$	—	$	79.6	$	—

Contingent consideration - other accrued liabilities and other long-term liabilities	63.6		63.6		—		—		63.6


Total liabilities	$	143.2	$	143.2	$	—	$	79.6	$	63.6

The carrying value of our total debt was $13.0 billion and $12.8 billion as of June 30, 2024 and December 31, 2023, respectively, and the fair value of our total debt was $12.3 billion and $12.5 billion as of June 30, 2024 and December 31, 2023, 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 were based on Level 2 inputs of the fair value hierarchy as of June 30, 2024 and December 31, 2023. See Note 7, 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 June 30, 2024, the Sonoma contingent consideration represents the fair value of $59.2 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 $81 million and $114 million. During the six months ended June 30, 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.