Solar Energy Systems, Leased and To Be Leased - Net - Components of Solar Energy Systems, Leased and to Be Leased (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Capital Leased Assets [Line Items]
Capital leased assets	$ 688.3	$ 112.6
Accumulated depreciation and amortization on capital leased assets	100.6	40.2
Solar Energy Systems [Member]
Capital Leased Assets [Line Items]
Capital leased assets	36.0	36.0
Accumulated depreciation and amortization on capital leased assets	$ 1.9	$ 0.2