Business Combinations, Dispositions and Related Transactions - Schedule of Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Current assets	$ 11.2	$ 17.2
Other noncurrent assets	40.8	211.4
LIABILITIES
Total current liabilities	47.3	46.1
Total noncurrent liabilities	52.9	94.2
Waste Management
ASSETS
Current assets	11.2	17.2
Restricted cash	27.2	21.6
Property and equipment, net	6.0	138.5
Other noncurrent assets	7.6	8.4
Total noncurrent assets	40.8	211.4
Total assets	52.0	228.6
LIABILITIES
Current portion of long-term debt	3.0	3.3
Other current liabilities	8.2	11.4
Total current liabilities	47.3	46.1
Long-term debt	65.0	67.9
Accrued noncurrent closure and post closure costs	31.7	29.4
Total noncurrent liabilities	52.9	94.2
Total liabilities	100.2	140.3
Deferred income taxes	(43.8)	(3.1)
Waste Management | Capitalized Operating Permits
ASSETS
Waste disposal site operating permits, net		42.9
Waste Management | Contran | Trade Accounts Payables
LIABILITIES
Payable to affiliates	$ 36.1	$ 31.4