Summary of Significant Accounting Policies - Business Acquisitions (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended		3 Months Ended		12 Months Ended		0 Months Ended
	Nov. 26, 2014	Nov. 06, 2014	Dec. 31, 2014 MW		Dec. 31, 2014 MW		May 22, 2014	Apr. 17, 2014	Apr. 23, 2013
Business Acquisition [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share			100.00%		100.00%
Southern Power [Member] | Turner Renewable Energy [Member]
Business Acquisition [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share			10.00%		10.00%
Southern Power [Member] | Solar Gen 2 Imperial Valley, LLC [Member]
Business Acquisition [Line Items]
MW Capacity		150	150	[1],[2]	150	[1],[2]
Jointly Owned Utility Plant, Proportionate Ownership Share			51.00%	[1],[2]	51.00%	[1],[2]
Year of Operation	2014				2014	[1],[2]
PPA Contract Period		25 years			25 years	[1],[2]
Payments to Acquire Businesses, Gross			$ 504.7		$ 504.7	[1],[2]
Southern Power [Member] | Macho Springs, LLC [Member]
Business Acquisition [Line Items]
MW Capacity			50	[3],[4]	50	[3],[4]	50
Jointly Owned Utility Plant, Proportionate Ownership Share			90.00%	[3],[4]	90.00%	[3],[4]
Year of Operation					2014	[3],[4]
PPA Contract Period					20 years	[3],[4]	20 years
Payments to Acquire Businesses, Gross					130.0	[3],[4]	130.0
Southern Power [Member] | Adobe Solar LLC [Member]
Business Acquisition [Line Items]
MW Capacity			20	[3],[4]	20	[3],[4]		20
Jointly Owned Utility Plant, Proportionate Ownership Share			90.00%	[3],[4]	90.00%	[3],[4]		90.00%
Year of Operation					2014	[3],[4]		2014
PPA Contract Period					20 years	[3],[4]		20 years
Payments to Acquire Businesses, Gross					96.2	[3],[4]		96.2
Southern Power [Member] | Campo Verde Solar LLC [Member]
Business Acquisition [Line Items]
MW Capacity			139	[3],[4],[5]	139	[3],[4],[5]			139
Jointly Owned Utility Plant, Proportionate Ownership Share			90.00%	[3],[4],[5]	90.00%	[3],[4],[5]
Year of Operation					2013	[3],[4],[5]			2013
PPA Contract Period					20 years	[3],[4],[5]			20 years
Payments to Acquire Businesses, Gross					136.6	[3],[4],[5]			136.6
Business Acquisition Cost of Acquired Entity Purchase Consideration Cash Will Be Paid									$ 355.5

[1] Reflects Southern Power's portion of the purchase price.

[2] This acquisition was made by Southern Power through its subsidiaries Southern Renewable Partnerships, LLC and SG2 Holdings, LLC. SG2 Holdings, LLC is jointly-owned by Southern Power and First Solar, Inc.

[3] Reflects 100% of the purchase price, including Turner Renewable Energy, LLC's 10% equity contribution.

[4] This acquisition was made by Southern Power and Turner Renewable Energy, LLC through Southern Turner Renewable Energy, LLC.

[5] Under an engineering, procurement, and construction agreement, an additional $355.5 million was paid to a subsidiary of First Solar, Inc. to complete the construction of the solar facility.