Acquisitions (Details) (Southern Power [Member], USD $) In Millions, unless otherwise specified	Sep. 28, 2012 Apex Nevada Solar LLC [Member]	Jun. 29, 2012 Apex Nevada Solar LLC [Member] MW	Oct. 16, 2012 Spectrum Nevada Solar Llc [Member]	Sep. 30, 2012 Spectrum Nevada Solar Llc [Member]	Sep. 28, 2012 Spectrum Nevada Solar Llc [Member] MW	Oct. 16, 2012 Granville Solar Llc [Member] MW
Acquisitions (Textual) [Abstract]
Percent of interest owned indirectly by Southern Power		90.00%	90.00%		90.00%
Power of solar polycrystalline silicon facility		20			30	2.5
Beginning year of output of constructed plant		2012			2013	2012
Cash Consideration for acquisition of the interests in Apex		$ 102.0			$ 17.6	$ 10.4
Cash Consideration paid at closing		86.5			99.9	7.8
Business Acquisition Cash Paid Upon Completion Of Milestone	9.5
Cash Consideration will be paid under MIPA	6.0					2.6
Business Acquisition, Purchase Price Allocation, Current Assets, Work-in-Progress				$ 17.6