Financial Instruments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Contingent consideration - other accrued liabilities and other long-term liabilities	$ 69,600,000	$ 73,900,000
Waste Management Contract, Sonoma County
Derivative [Line Items]
Contingent consideration - other accrued liabilities and other long-term liabilities	66,700,000
Potential undiscounted future contingent liability payments, minimum	79,000,000
Potential undiscounted future contingent liability payments, maximum	168,000,000
Change in contingent consideration, liability	$ 0
Waste Management Contract, Sonoma County | Landfill
Derivative [Line Items]
Expected useful life	30 years
Landfill Acquisitions
Derivative [Line Items]
Contingent consideration - other accrued liabilities and other long-term liabilities	$ 4,300,000
Change in contingent consideration, liability	0
Carrying Amount
Derivative [Line Items]
Long-term debt	8,400,000,000	8,300,000,000
Contingent consideration - other accrued liabilities and other long-term liabilities	71,000,000.0	71,400,000
Estimate of Fair Value Measurement
Derivative [Line Items]
Long-term debt	$ 8,900,000,000	$ 8,700,000,000