Acquisitions and Dispositions - Held for Sale (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets Held for Sale:
Current assets	$ 2,704	$ 12
Liabilities Held for Sale:
Current liabilities	706	0
Other non-current liabilities	2,833	0
SOUTHERN POWER CO
Assets Held for Sale:
Current assets	17	1
Liabilities Held for Sale:
Current liabilities	2	0
SOUTHERN Co GAS
Assets Held for Sale:
Current assets	2,298	0
Liabilities Held for Sale:
Current liabilities	412	$ 0
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets Held for Sale:
Current assets	487
Total property, plant, and equipment	5,462
Goodwill and other intangible assets	668
Other non-current assets	705
Total Assets Held for Sale	7,322
Liabilities Held for Sale:
Current liabilities	354
Long-term debt	1,285
Accumulated deferred income taxes	566
Other non-current liabilities	1,334
Total Liabilities Held for Sale	3,539
Disposal Group, Held-for-sale, Not Discontinued Operations | SOUTHERN POWER CO
Assets Held for Sale:
Current assets	17
Total property, plant, and equipment	168
Goodwill and other intangible assets	0
Other non-current assets	15
Total Assets Held for Sale	200
Liabilities Held for Sale:
Current liabilities	2
Long-term debt	0
Accumulated deferred income taxes	0
Other non-current liabilities	0
Total Liabilities Held for Sale	2
Disposal Group, Held-for-sale, Not Discontinued Operations | SOUTHERN Co GAS
Assets Held for Sale:
Current assets	81
Total property, plant, and equipment	1,408
Goodwill and other intangible assets	668
Other non-current assets	141
Total Assets Held for Sale	2,298
Liabilities Held for Sale:
Current liabilities	61
Long-term debt	0
Accumulated deferred income taxes	26
Other non-current liabilities	325
Total Liabilities Held for Sale	$ 412