Acquisitions - Schedule of Construction Projects (Details) - Jun. 30, 2015 - Southern Power [Member] $ in Millions		USD ($) MW
Business Acquisition [Line Items]
Nameplate Capacity (in mw) | MW		146
PPA Contract Period		25 years
Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost		$ 260
Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost		$ 280
Decatur Parkway Solar Project, LLC [Member]
Business Acquisition [Line Items]
Nameplate Capacity (in mw) | MW		84
PPA Contract Period		25 years
Decatur Parkway Solar Project, LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 170
Decatur Parkway Solar Project, LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 173
Decatur County Solar Project, LLC [Member]
Business Acquisition [Line Items]
Nameplate Capacity (in mw) | MW		20
PPA Contract Period		20 years
Decatur County Solar Project, LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 45
Decatur County Solar Project, LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 47
Butler Solar LLC [Member]
Business Acquisition [Line Items]
Nameplate Capacity (in mw) | MW		103
PPA Contract Period		30 years
Butler Solar LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 220
Butler Solar LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 230
LS Pawpaw, LLC [Member]
Business Acquisition [Line Items]
Nameplate Capacity (in mw) | MW		30
PPA Contract Period		30 years
LS Pawpaw, LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 70
LS Pawpaw, LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 80
Butler Solar Farm, LLC [Member]
Business Acquisition [Line Items]
Nameplate Capacity (in mw) | MW		20
PPA Contract Period		20 years
Butler Solar Farm, LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 42
Butler Solar Farm, LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	[1]	$ 48

[1] Includes the acquisition price of all outstanding membership interests.