Segment and Related Information - Financial Data for Business Segments and Products and Services (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) entities	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) entities	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information [Line Items]
Number of traditional operating companies | entities	4								4
Revenues	$ 3,568	$ 5,401	$ 4,337	$ 4,183	$ 4,017	$ 5,339	$ 4,467	$ 4,644	$ 17,489	$ 18,467	$ 17,087
Financial data for business segments
Operating revenues	3,568	5,401	4,337	4,183	4,017	5,339	4,467	4,644	17,489	18,467	17,087
Depreciation and amortization									2,034	1,945	1,901
Interest income									23	19	19
Interest expense									840	835	824
Income taxes									1,194	977	849
Segment net income (loss)	271	959	629	508	283	718	$ 611	351	2,367	1,963	1,644
Total assets	78,318				70,233				78,318	70,233	64,264
Gross property additions									6,169	6,522	5,868
Segment and Related Information (Textual) [Abstract]
Unamortized Debt Issuance Expense	241				202				241	202	139
Kemper IGCC [Member]
Segment and Related Information (Textual) [Abstract]
Pre-Tax Charge To Income	183	150	23	9	70	418		380	365	868	1,200
After Tax Charge To Income	113	$ 93	$ 14	$ 6	43	$ 258		$ 235	226	536	729
Electric Utilities [Member]
Segment Reporting Information [Line Items]
Revenues									17,442	18,406	17,035
Financial data for business segments
Operating revenues									17,442	18,406	17,035
Depreciation and amortization									2,020	1,929	1,886
Interest income									22	18	18
Interest expense									774	794	788
Income taxes									1,326	1,053	935
Segment net income (loss)									2,401	1,969	1,652
Total assets	77,560				69,402				77,560	69,402	63,504
Gross property additions									6,129	6,510	5,859
Traditional Operating Companies [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Revenues									16,491	17,354	16,136
Financial data for business segments
Operating revenues									16,491	17,354	16,136
Depreciation and amortization									1,772	1,709	1,711
Interest income									19	17	17
Interest expense									697	705	714
Income taxes									1,305	1,056	889
Segment net income (loss)									2,186	1,797	1,486
Total assets	69,052				64,300				69,052	64,300	59,188
Gross property additions									5,124	5,568	5,226
Southern Power [Member]
Segment Reporting Information [Line Items]
Revenues									417	383	346
Financial data for business segments
Operating revenues									417	383	346
Southern Power [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Revenues									1,390	1,501	1,275
Financial data for business segments
Operating revenues									1,390	1,501	1,275
Depreciation and amortization									248	220	175
Interest income									2	1	1
Interest expense									77	89	74
Income taxes									21	(3)	46
Segment net income (loss)									215	172	166
Total assets	8,905				5,233				8,905	5,233	4,417
Gross property additions									1,005	942	633
All Other [Member]
Segment Reporting Information [Line Items]
Revenues									152	159	139
Financial data for business segments
Operating revenues									152	159	139
Depreciation and amortization									14	16	15
Interest income									6	3	2
Interest expense									69	43	36
Income taxes									(132)	(76)	(85)
Segment net income (loss)									(32)	(3)	(10)
Total assets	1,819				1,143				1,819	1,143	1,064
Gross property additions									40	11	9
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									(105)	(98)	(87)
Financial data for business segments
Operating revenues									(105)	(98)	(87)
Depreciation and amortization									0	0	0
Interest income									(5)	(2)	(1)
Interest expense									(3)	(2)	0
Income taxes									0	0	(1)
Segment net income (loss)									(2)	(3)	2
Total assets	(1,061)				(312)				(1,061)	(312)	(304)
Gross property additions									0	1	0
Intersegment Eliminations [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Revenues									(439)	(449)	(376)
Financial data for business segments
Operating revenues									(439)	(449)	(376)
Depreciation and amortization									0	0	0
Interest income									1	0	0
Interest expense									0	0	0
Income taxes									0	0	0
Segment net income (loss)									0	0	0
Total assets	$ (397)				$ (131)				(397)	(131)	(101)
Gross property additions									$ 0	0	0
Deferred Tax Liability, Noncurrent [Member]
Segment and Related Information (Textual) [Abstract]
Prior Period Reclassification Adjustment										$ 488	$ 143