Financing - Schedule Of Credit Arrangements With Project Credit Facilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Aug. 31, 2015
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 8,443
Line of Credit Facility, Remaining Borrowing Capacity	8,273
Southern Power [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600		$ 600
Line of Credit Facility, Remaining Borrowing Capacity	522	$ 566
Southern Power [Member] | RE Roserock Holdings, LLC [Member] | Construction Loan Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	63
Southern Power [Member] | RE Roserock Holdings, LLC [Member] | Bridge Loan [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	180
Southern Power [Member] | RE Roserock Holdings, LLC [Member] | Construction Loan And Bridge Loan [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	243
Line of Credit Facility, Remaining Borrowing Capacity	34
Southern Power [Member] | RE Roserock Holdings, LLC [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	23
Line of Credit Facility, Remaining Borrowing Capacity	$ 16