Acquisitions - Schedule of Construction Projects (Details) - Southern Power [Member] $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) MW
Business Acquisition [Line Items]
Approx. Nameplate Capacity, Solar (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]
Approx. Nameplate Capacity, Solar (MW) | MW	84
PPA Contract Period	25 years
Decatur Parkway Solar Project, LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 170
Decatur Parkway Solar Project, LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 173
Decatur County Solar Project, LLC [Member]
Business Acquisition [Line Items]
Approx. Nameplate Capacity, Solar (MW) | MW	20
PPA Contract Period	20 years
Decatur County Solar Project, LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 45
Decatur County Solar Project, LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 47
Butler Solar LLC [Member]
Business Acquisition [Line Items]
Approx. Nameplate Capacity, Solar (MW) | MW	103
PPA Contract Period	30 years
Butler Solar LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 220
Butler Solar LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 230
LS Pawpaw, LLC [Member]
Business Acquisition [Line Items]
Approx. Nameplate Capacity, Solar (MW) | MW	30
PPA Contract Period	30 years
LS Pawpaw, LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 70
LS Pawpaw, LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 80
Butler Solar Farm, LLC [Member]
Business Acquisition [Line Items]
Approx. Nameplate Capacity, Solar (MW) | MW	20
PPA Contract Period	20 years
Butler Solar Farm, LLC [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 42
Butler Solar Farm, LLC [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated Construction Cost	$ 48