Financing - Securities Due Within One Year (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Line Items]
Senior notes	$ 2,950	$ 2,354
Long-term bank term loans		1,420
Revenue bonds	173	90
First mortgage bonds	50
Capitalized leases	24	31
Other	1	(3)
Total	3,198	3,892
Alabama Power
Debt Disclosure [Line Items]
Senior notes	200
Revenue bonds	0
First mortgage bonds	0
Capitalized leases	1
Other	0
Total	201
Georgia Power
Debt Disclosure [Line Items]
Senior notes	500	750
Long-term bank term loans		100
Revenue bonds	108	0
First mortgage bonds	0
Capitalized leases	13	11
Other	(4)	(4)
Total	617	857
Mississippi Power
Debt Disclosure [Line Items]
Senior notes	0	0
Long-term bank term loans		900
Revenue bonds	40	90
First mortgage bonds	0
Capitalized leases	0	0
Other	0	(1)
Total	40	989
Long-term pollution control bond, current	40	40
Revenue bonds, current	50	50
Southern Power
Debt Disclosure [Line Items]
Senior notes	600	350
Long-term bank term loans		420
Revenue bonds	0	0
First mortgage bonds	0
Capitalized leases	0	0
Other	(1)	0
Total	599	770
Southern Company Gas
Debt Disclosure [Line Items]
Senior notes	300	155
Long-term bank term loans		0
Revenue bonds	0	0
First mortgage bonds	50
Capitalized leases	0	0
Other	7	2
Total	$ 357	$ 157