Acquisitions - Acquisitions Table (Details) $ in Millions																3 Months Ended	9 Months Ended	12 Months Ended
	Feb. 11, 2016 USD ($) MW	Dec. 17, 2015 USD ($) MW	Dec. 11, 2015 USD ($) MW	Nov. 23, 2015 USD ($) MW	Oct. 22, 2015 USD ($) MW	Sep. 04, 2015 USD ($) MW	Aug. 31, 2015 USD ($) MW	Aug. 28, 2015 USD ($) MW	Apr. 30, 2015 USD ($) MW	Apr. 15, 2015 USD ($) MW	Feb. 24, 2015 USD ($)	Nov. 26, 2014 USD ($)	Nov. 06, 2014 USD ($) MW	May. 22, 2014 USD ($) MW	Apr. 17, 2014 USD ($) MW	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($) MW	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Business Acquisition [Line Items]
Capital contributions from noncontrolling interests																		$ 567.0	$ 221.0
Construction in Progress, Gross																$ 9,082.0		9,082.0	7,792.0
Other Assets, Noncurrent																737.0		737.0	922.0
Southern Power [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, after Year Five																239.0		239.0
Life Output Of Plant																	25 years
Amortization of Intangible Assets																		3.0	3.0	$ 3.0
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months																10.0		10.0
Power of Solar Polycrystalline Silicon Facility | MW																	146
Capital contributions from noncontrolling interests																		567.0	221.0
Business Combination, Contingent Consideration, Liability																36.0		36.0	8.0
Total Cost Of Construction																		1,800.0
Construction in Progress, Gross																1,137.0		1,137.0	11.0
Other Assets, Noncurrent																139.0		139.0	$ 100.0
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months																17.0		17.0
Finite-Lived Intangible Assets, Amortization Expense, Year Two																17.0		17.0
Finite-Lived Intangible Assets, Amortization Expense, Year Three																17.0		17.0
Finite-Lived Intangible Assets, Amortization Expense, Year Four																17.0		17.0
Southern Power [Member] | Lost Hills Blackwell, North Star, Tranquillity, Desert Stateline, Roserock, Garland and Garland A [Member]
Business Acquisition [Line Items]
Capital contributions from noncontrolling interests																		227.0
Southern Power [Member] | RE Garland Holdings, LLC [Member]
Business Acquisition [Line Items]
Life Output Of Plant		20 years
Southern Power [Member] | Adobe Solar LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent															90.00%
Life Output Of Plant															20 years
Payments to Acquire Businesses, Gross														$ 97.0	$ 86.0
Power of Solar Polycrystalline Silicon Facility | MW															20
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment															$ 84.0
Reimbursable Transmission Costs Receivable															15.0
Purchased Power Agreement Intangible															6.0
Business Combination, Bargain Purchase, Gain Recognized, Amount															5.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent															$ 3.0
Southern Power [Member] | Kay Wind, LLC [Member]
Business Acquisition [Line Items]
Energy From Wind-Powered Generating Facilities | MW			299
Noncontrolling Interest, Ownership Percentage by Parent			100.00%
Life Output Of Plant			20 years
Payments to Acquire Businesses, Gross			$ 481.0								$ 481.0
Business Combination, Contingent Consideration, Liability			$ 35.0
Reimbursable Transmission Costs Receivable																8.0		8.0
Construction in Progress, Gross																481.0		481.0
Construction Payable																8.0		8.0
Southern Power [Member] | Grant Wind, LLC [Member]
Business Acquisition [Line Items]
Energy From Wind-Powered Generating Facilities | MW						151
Noncontrolling Interest, Ownership Percentage by Parent						100.00%
Life Output Of Plant						20 years
Payments to Acquire Businesses, Gross						$ 258.0
Business Combination, Contingent Consideration, Liability						$ 24.0
Period Of Operation For Performance Testing And Production						10 years
Southern Power [Member] | Lost Hills Blackwell Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent										51.00%
Life Output Of Plant										29 years
Payments to Acquire Businesses, Gross										$ 73.0
Power of Solar Polycrystalline Silicon Facility | MW										33
Business Combination, Contingent Consideration, Liability										$ 3.0
Business Combination, Consideration Transferred										107.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment																105.0		105.0
Reimbursable Transmission Costs Receivable																3.0		3.0
Construction Payable																4.0		4.0
Southern Power [Member] | NS Solar Holdings, LLC (North Star) [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, after Year Five																18.0		18.0
Noncontrolling Interest, Ownership Percentage by Parent									51.00%
Life Output Of Plant									20 years
Amortization of Intangible Assets																		1.0
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months																1.2		1.2
Payments to Acquire Businesses, Gross									$ 208.0
Power of Solar Polycrystalline Silicon Facility | MW									61
Business Combination, Contingent Consideration, Liability									$ 233.0
Business Combination, Consideration Transferred									307.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment																266.0		266.0
Reimbursable Transmission Costs Receivable																21.0		21.0
Purchased Power Agreement Intangible																25.0		25.0
Construction Payable																238.0		238.0
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months																1.2		1.2
Finite-Lived Intangible Assets, Amortization Expense, Year Two																1.2		1.2
Finite-Lived Intangible Assets, Amortization Expense, Year Three																1.2		1.2
Finite-Lived Intangible Assets, Amortization Expense, Year Four																1.2		1.2
Southern Power [Member] | RE Tranquility Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent								51.00%
Life Output Of Plant								18 years
Payments to Acquire Businesses, Gross								$ 100.0
Power of Solar Polycrystalline Silicon Facility | MW								205
Construction in Progress, Gross								$ 186.0
Other Receivables								24.0
Construction Payable								37.0
Southern Power [Member] | Desert Stateline Holdings, LLC [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, after Year Five																192.8		192.8
Noncontrolling Interest, Ownership Percentage by Parent							51.00%
Life Output Of Plant							20 years
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months																6.2		6.2
Payments to Acquire Businesses, Gross							$ 439.0
Power of Solar Polycrystalline Silicon Facility | MW							299
Purchased Power Agreement Intangible							$ 249.0
Construction in Progress, Gross							413.0
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months																12.5		12.5
Finite-Lived Intangible Assets, Amortization Expense, Year Two																12.5		12.5
Finite-Lived Intangible Assets, Amortization Expense, Year Three																12.5		12.5
Finite-Lived Intangible Assets, Amortization Expense, Year Four																12.5		12.5
Southern Power [Member] | GASNA 31P, LLC (Morelos) [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent					90.00%
Life Output Of Plant					20 years
Payments to Acquire Businesses, Gross					$ 45.0
Power of Solar Polycrystalline Silicon Facility | MW					15
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment																49.0		49.0
Reimbursable Transmission Costs Receivable																1.0		1.0
Southern Power [Member] | RE Roserock Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent				51.00%
Life Output Of Plant				20 years
Payments to Acquire Businesses, Gross				$ 45.0
Power of Solar Polycrystalline Silicon Facility | MW				160
Construction in Progress, Gross																75.0		75.0
Other Receivables																6.0		6.0
Construction Payable																10.0		10.0
Southern Power [Member] | RE Roserock Holdings, LLC [Member]
Business Acquisition [Line Items]
Life Output Of Plant		15 years
Southern Power [Member] | Macho Springs, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent														90.00%
Life Output Of Plant														20 years
Payments to Acquire Businesses, Gross														$ 117.0
Power of Solar Polycrystalline Silicon Facility | MW														50
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment														$ 128.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets														1.0
Reimbursable Transmission Costs Receivable														1.0
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination														$ 130.0
Southern Power [Member] | First Solar [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross													$ 128.0			599.0
Southern Power [Member] | Solar Gen 2 Imperial Valley, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent													51.00%
Life Output Of Plant													25 years
Payments to Acquire Businesses, Gross													$ 505.0			505.0
Power of Solar Polycrystalline Silicon Facility | MW													150
Southern Power [Member] | RE Garland Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		51.00%
Payments to Acquire Businesses, Gross		$ 49.0
Power of Solar Polycrystalline Silicon Facility | MW		205
Construction in Progress, Gross																107.0		107.0
Other Assets, Noncurrent																1.0		1.0
Construction Payable																28.0		28.0
Southern Power [Member] | Decatur Parkway Solar Project, LLC [Member]
Business Acquisition [Line Items]
Life Output Of Plant																	25 years
Power of Solar Polycrystalline Silicon Facility | MW																	84
Estimated Cost																	$ 169.0
Southern Power [Member] | Decatur County Solar Project, LLC [Member]
Business Acquisition [Line Items]
Life Output Of Plant																	20 years
Power of Solar Polycrystalline Silicon Facility | MW																	20
Estimated Cost																	$ 46.0
Southern Power [Member] | Butler Solar Farm, LLC [Member]
Business Acquisition [Line Items]
Life Output Of Plant																	20 years
Power of Solar Polycrystalline Silicon Facility | MW																	22
Estimated Cost																	$ 45.0
SG2 Holdings, LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross												$ 593.0				6.0
SG2 Holdings, LLC [Member] | Solar Gen 2 Imperial Valley, LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment																708.0		708.0
Reimbursable Transmission Costs Receivable																20.0		20.0
Southern Power and Turner Renewable Energy [Member] | GASNA 31P, LLC (Morelos) [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross					$ 50.0
Recurrent Energy [Member] | RE Tranquility Holdings, LLC [Member]
Business Acquisition [Line Items]
Contribution of Assets								173.0
Initial Distribution Received								$ 100.0
Estimated Future Construction Payments																493.0		$ 493.0
Recurrent Energy [Member] | RE Roserock Holdings, LLC [Member]
Business Acquisition [Line Items]
Contribution of Assets				$ 26.0
Recurrent Energy [Member] | RE Garland Holdings, LLC [Member]
Business Acquisition [Line Items]
Contribution of Assets		$ 31.0
First Solar [Member] | Lost Hills Blackwell Holdings, LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross										$ 34.0
First Solar [Member] | NS Solar Holdings, LLC (North Star) [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross									$ 99.0
First Solar [Member] | Desert Stateline Holdings, LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross							$ 223.0
First Solar [Member] | Solar Gen 2 Imperial Valley, LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																$ 223.0
Class A Membership Interest [Member] | Southern Power [Member] | Lost Hills Blackwell, North Star, Tranquillity, Desert Stateline, Roserock, Garland and Garland A [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent																100.00%		100.00%
Percentage Of Entitled Cash Distributions																51.00%		51.00%
Class A Membership Interest [Member] | Southern Power [Member] | Solar Gen 2 Imperial Valley, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent																100.00%		100.00%
Percentage Of Entitled Cash Distributions										51.00%
Class B Membership Interest [Member] | First Solar and Recurrent Energy [Member] | Lost Hills Blackwell, North Star, Tranquillity, Desert Stateline, Roserock, Garland and Garland A [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent																100.00%		100.00%
Class B Membership Interest [Member] | Recurrent Energy [Member] | RE Tranquility Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent								100.00%
Class B Membership Interest [Member] | Recurrent Energy [Member] | RE Roserock Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent				100.00%
Class B Membership Interest [Member] | Recurrent Energy [Member] | RE Garland Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		100.00%
Class B Membership Interest [Member] | First Solar [Member] | Lost Hills Blackwell, North Star, Tranquillity, Desert Stateline, Roserock, Garland and Garland A [Member]
Business Acquisition [Line Items]
Percentage Of Entitled Cash Distributions																49.00%		49.00%
Class B Membership Interest [Member] | First Solar [Member] | Lost Hills Blackwell Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent										100.00%
Class B Membership Interest [Member] | First Solar [Member] | NS Solar Holdings, LLC (North Star) [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent									100.00%
Class B Membership Interest [Member] | First Solar [Member] | Desert Stateline Holdings, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent							100.00%
Class B Membership Interest [Member] | First Solar [Member] | Solar Gen 2 Imperial Valley, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent																100.00%		100.00%
Percentage Of Entitled Cash Distributions										49.00%
Minimum [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Estimated Cost																	260.0
Minimum [Member] | Southern Power [Member] | RE Tranquility Holdings, LLC [Member]
Business Acquisition [Line Items]
Estimated Future Construction Payments																$ 473.0		$ 473.0
Minimum [Member] | Southern Power [Member] | RE Roserock Holdings, LLC [Member]
Business Acquisition [Line Items]
Estimated Future Construction Payments																333.0		333.0
Minimum [Member] | Southern Power [Member] | RE Garland Holdings, LLC [Member]
Business Acquisition [Line Items]
Estimated Future Construction Payments																532.0		532.0
Minimum [Member] | Southern Power and First Solar [Member] | Desert Stateline Holdings, LLC [Member]
Business Acquisition [Line Items]
Estimated Future Construction Payments																1,200.0		1,200.0
Maximum [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Estimated Cost																	$ 280.0
Maximum [Member] | Southern Power [Member] | RE Roserock Holdings, LLC [Member]
Business Acquisition [Line Items]
Estimated Future Construction Payments																353.0		353.0
Maximum [Member] | Southern Power [Member] | RE Garland Holdings, LLC [Member]
Business Acquisition [Line Items]
Estimated Future Construction Payments																552.0		552.0
Maximum [Member] | Southern Power and First Solar [Member] | Desert Stateline Holdings, LLC [Member]
Business Acquisition [Line Items]
Estimated Future Construction Payments																$ 1,300.0		$ 1,300.0
Turner Renewable Energy [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share					10.00%											10.00%		10.00%
Subsequent Event [Member] | Southern Power [Member] | 70SM1 8ME, LCC (Calipatria) [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	90.00%
Life Output Of Plant	20 years
Payments to Acquire Businesses, Gross	$ 52.0
Power of Solar Polycrystalline Silicon Facility | MW	20
Subsequent Event [Member] | Southern Power and Turner Renewable Energy [Member] | 70SM1 8ME, LCC (Calipatria) [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 58.0
Subsequent Event [Member] | Turner Renewable Energy [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	10.00%