Acquisitions and Dispositions - Assets Held for Sale (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets Held for Sale:
Current assets	$ 55	$ 393
Liabilities Held for Sale:
Current liabilities	38	425
Other non-current liabilities	39	2,836
SOUTHERN POWER CO
Liabilities Held for Sale:
Current liabilities	9	15
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets Held for Sale:
Current assets	55	393
Total property, plant, and equipment	637	4,583
Goodwill and other intangible assets	82	40
Other non-current assets	44	727
Total Assets Held for Sale	818	5,743
Liabilities Held for Sale:
Current liabilities	38	425
Long-term debt		1,286
Accumulated deferred income taxes		618
Other non-current liabilities	39	932
Total Liabilities Held for Sale	77	3,261
Disposal Group, Held-for-sale, Not Discontinued Operations | SOUTHERN POWER CO
Assets Held for Sale:
Current assets	11	8
Total property, plant, and equipment	604	536
Goodwill and other intangible assets	40	40
Other non-current assets	0	0
Total Assets Held for Sale	655	584
Liabilities Held for Sale:
Current liabilities	9	15
Long-term debt		0
Accumulated deferred income taxes		0
Other non-current liabilities	0	0
Total Liabilities Held for Sale	$ 9	$ 15