Segment and Related Information - Financial Data for Business Segments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) state	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) state	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of States in which Entity Operates | state	4		4
Operating revenues	$ 4,459	$ 4,337	$ 8,451	$ 8,520
Segment net income (loss)	612	629	1,097	1,138
Total assets	90,873		90,873		$ 78,318
Kemper IGCC [Member]
Segment Reporting Information [Line Items]
Pre-Tax Charge To Income	81	23	134	32
After Tax Charge To Income	50	14	83	20
Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,379	4,324	8,360	8,496
Segment net income (loss)	684	607	1,198	1,117
Total assets	81,363		81,363		77,560
Intersegment Eliminations [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	(109)	(90)	(212)	(213)
Segment net income (loss)	0	0	0	0
Total assets	(425)		(425)		(397)
Consolidation Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(45)	(30)	(81)	(59)
Segment net income (loss)	(4)	4	(7)	0
Total assets	(995)		(995)		(1,061)
Traditional Operating Companies [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,115	4,077	7,884	8,025
Segment net income (loss)	595	561	1,059	1,038
Total assets	70,706		70,706		69,052
Southern Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	107	85	204	199
Southern Power [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	373	337	688	684
Segment net income (loss)	89	46	139	79
Total assets	11,082		11,082		8,905
All Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	125	43	172	83
Segment net income (loss)	(68)	$ 18	(94)	$ 21
Total assets	$ 10,505		$ 10,505		$ 1,819