Financial Instruments (Fair Value Measurements) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Apr. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt	$ 8,300.0	$ 8,200.0
Contingent consideration and acquisition holdbacks	73.9	71.3
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of fixed rate senior notes and debentures	8,700.0	8,800.0
Contingent consideration and acquisition holdbacks	70.9	$ 73.3
Waste Management Contract, Sonoma County
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration and acquisition holdbacks	67.0
Undiscounted future contingent payments, range of outcomes, value, low	82.0
Undiscounted future contingent payments, range of outcomes, value, high	171.0
Landfill Acquisitions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration and acquisition holdbacks	$ 4.4
Landfill equipment | Waste Management Contract, Sonoma County
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated useful life	30 years
Measurement Input, Discount Rate | Waste Management Contract, Sonoma County
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Business combination, contingent consideration, liability, measurement input			0.040
Measurement Input, Discount Rate | Landfill Acquisitions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Business combination, contingent consideration, liability, measurement input	0.043