AMORTIZATION OF WASTE, SERVICE AND ENERGY CONTRACTS

Waste, Service and Energy Contracts

Our waste, service and energy contracts are intangible assets and liabilities relating to long-term operating contracts at acquired facilities and are recorded upon acquisition at their estimated fair market values based upon discounted cash flows. Intangible assets and liabilities are amortized using the straight line method over their useful lives. Waste and service contract liabilities, net are included as a component of "Other liabilities" on our consolidated balance sheet. Waste, service and energy contracts consisted of the following (in millions):



		As of December 31, 2017									As of December 31, 2016
	Remaining Weighted Average Useful Life	Gross Carrying Amount			Accumulated Amortization			Net			Gross Carrying Amount			Accumulated Amortization			Net
Waste, service and energy contracts (asset)	21 years	$	494		$	243		$	251		$	526		$	263		$	263
Waste and service contracts (liability)	3 years	$	(66	)	$	(62	)	$	(4	)	$	(131	)	$	(124	)	$	(7	)

The following table details the amount of the actual/estimated amortization expense and contra-expense associated with these intangible assets and liabilities as of December 31, 2017 included or expected to be included in our consolidated statements of operations for each of the years indicated (in millions):



	Waste, Service and Energy Contracts (Amortization Expense)		Waste and Service Contracts (Contra-Expense)
Year Ended December 31, 2015	$	25	$	(6	)
Year Ended December 31, 2016	$	21	$	(6	)
Year Ended December 31, 2017	$	14	$	(2	)
2018	$	13	$	(2	)
2019	13		(2		)
2020	13		—
2021	13		—
2022	13		—
Thereafter	186		—
Total	$	251	$	(4	)

The weighted average number of years prior to the next renewal period for contracts that we have an intangible recorded is 5 years.