Solar Energy Systems, Leased and To Be Leased - Net - Components of Solar Energy Systems, Leased and to Be Leased (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Capital Leased Assets [Line Items]
Capital leased assets	$ 1,400.0	$ 688.3
Solar Energy Systems [Member]
Capital Leased Assets [Line Items]
Capital leased assets	36.0	36.0
Accumulated depreciation and amortization on capital leased assets	$ 3.3	$ 1.9