Acquisitions - Construction Projects (Details) - Southern Power [Member] $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) MW
Business Acquisition [Line Items]
Power of Solar Polycrystalline Silicon Facility | MW	146
Life Output Of Plant	25 years
Decatur Parkway Solar Project, LLC [Member]
Business Acquisition [Line Items]
Power of Solar Polycrystalline Silicon Facility | MW	84
Life Output Of Plant	25 years
Estimated Cost	$ 169
Decatur County Solar Project, LLC [Member]
Business Acquisition [Line Items]
Power of Solar Polycrystalline Silicon Facility | MW	20
Life Output Of Plant	20 years
Estimated Cost	$ 46
Butler Solar LLC [Member]
Business Acquisition [Line Items]
Power of Solar Polycrystalline Silicon Facility | MW	103
Life Output Of Plant	30 years
LS Pawpaw, LLC [Member]
Business Acquisition [Line Items]
Power of Solar Polycrystalline Silicon Facility | MW	30
Life Output Of Plant	30 years
Butler Solar Farm, LLC [Member]
Business Acquisition [Line Items]
Power of Solar Polycrystalline Silicon Facility | MW	22
Life Output Of Plant	20 years
Estimated Cost	$ 45
Maximum [Member]
Business Acquisition [Line Items]
Estimated Cost	280
Maximum [Member] | Butler Solar LLC [Member]
Business Acquisition [Line Items]
Estimated Cost	230
Maximum [Member] | LS Pawpaw, LLC [Member]
Business Acquisition [Line Items]
Estimated Cost	80
Minimum [Member]
Business Acquisition [Line Items]
Estimated Cost	260
Minimum [Member] | Butler Solar LLC [Member]
Business Acquisition [Line Items]
Estimated Cost	220
Minimum [Member] | LS Pawpaw, LLC [Member]
Business Acquisition [Line Items]
Estimated Cost	$ 70