Acquisitions and Dispositions - Assets Held for Sale (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Assets Held for Sale:
Current assets	$ 17	$ 393
Liabilities Held for Sale:
Current liabilities	6	425
Other non-current liabilities	20	2,836
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets Held for Sale:
Current assets	17	393
Total property, plant, and equipment	551	4,583
Goodwill and other intangible assets	40	40
Other non-current assets	40	727
Total Assets Held for Sale	648	5,743
Liabilities Held for Sale:
Current liabilities	6	425
Other non-current liabilities	20	932
Long-term debt		1,286
Accumulated deferred income taxes		618
Total Liabilities Held for Sale	26	3,261
Disposal Group, Held-for-sale, Not Discontinued Operations | SOUTHERN POWER CO
Assets Held for Sale:
Current assets	12	8
Total property, plant, and equipment	546	536
Goodwill and other intangible assets	40	40
Other non-current assets	14	0
Total Assets Held for Sale	612	584
Liabilities Held for Sale:
Current liabilities	3	15
Other non-current liabilities	0	0
Long-term debt		0
Accumulated deferred income taxes		0
Total Liabilities Held for Sale	$ 3	$ 15