v3.5.0.2
Discontinued operations (Details)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended
Jun. 26, 2015
USD ($)
item
MW
Sep. 30, 2015
USD ($)
$ / shares
Sep. 30, 2016
USD ($)
Sep. 30, 2015
USD ($)
$ / shares
Discontinued operations        
Gain on the disposal       $ (47.2)
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]        
Income (loss) from operations of discontinued businesses, net of tax   $ (0.5)   20.6
Income (loss) from operations of discontinued businesses, net of noncontrolling interests   (0.5)   $ 31.6
Basic and diluted earnings per share related to income (loss) from discontinued operations (in dollars per share) | $ / shares       $ 0.26
Wind Projects | Discontinued Operations, Held-for-sale or Disposed of by Sale        
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]        
Revenue       $ 34.8
Operations and maintenance       10.8
Depreciation and amortization       10.3
Total Project expenses       21.1
Change in fair value of derivatives       (0.7)
Equity in earnings of unconsolidated affiliates       (0.3)
Interest expense, net       (6.7)
Gain (loss) on sale of asset   (0.2)   47.2
Total Project other income (expense)   (0.2)   39.5
Income (loss) from operations of discontinued businesses   (0.2)   53.2
Income tax expense   0.3   32.6
Income (loss) from operations of discontinued businesses, net of tax   (0.5)   20.6
Net loss attributable to noncontrolling interests of discontinued businesses       (11.0)
Income (loss) from operations of discontinued businesses, net of noncontrolling interests   $ (0.5)   $ 31.6
Basic and diluted earnings per share related to income (loss) from discontinued operations (in dollars per share) | $ / shares   $ 0.00   $ 0.26
Wind Projects | APT | Discontinued Operations, Disposed of by Sale        
Discontinued operations        
Consideration received on disposal interests $ 335.0      
Wind Projects | Wind (Discontinued Operations) | Discontinued Operations, Held-for-sale or Disposed of by Sale        
Net Cash Provided by (Used in) Discontinued Operations [Abstract]        
Cash provided by operating activities       $ 21.9
Cash used in investing activities       $ (12.8)
Wind Projects | Wind (Discontinued Operations) | APT | Discontinued Operations, Disposed of by Sale        
Discontinued operations        
Ownership interest sold (as a percent) 100.00%      
Number of operating wind projects sold | item 5      
Wind power project capacity of disposed projects (in MW) | MW 521      
Project debt deconsolidated $ 249.0      
Project debt deconsolidated, including adjustment for entities with proportional ownership interest 274.0      
Non-controlling interests deconsolidated $ 224.0      
Goshen North | Wind (Discontinued Operations) | APT | Discontinued Operations, Disposed of by Sale        
Discontinued operations        
Ownership interest sold (as a percent) 12.50%      
Idaho Wind | Wind (Discontinued Operations) | APT | Discontinued Operations, Disposed of by Sale        
Discontinued operations        
Ownership interest sold (as a percent) 27.60%      
Meadow Creek | Wind (Discontinued Operations) | APT | Discontinued Operations, Disposed of by Sale        
Discontinued operations        
Ownership interest sold (as a percent) 100.00%      
Rockland Wind Farm | Wind (Discontinued Operations) | APT | Discontinued Operations, Disposed of by Sale        
Discontinued operations        
Ownership interest sold (as a percent) 50.00%      
Consolidated ownership interest sold (as a percent) 100.00%      
Canadian Hills | Wind (Discontinued Operations) | APT | Discontinued Operations, Disposed of by Sale        
Discontinued operations        
Consolidated ownership interest sold (as a percent) 99.00%      
Income from Discontinued Operations [Member] | Wind Projects | Wind (Discontinued Operations) | APT | Discontinued Operations, Disposed of by Sale        
Discontinued operations        
Gain on the disposal     $ 47.2