Acquisitions and Dispositions - Held For Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations $ in Millions	Dec. 31, 2018 USD ($)
Assets Held for Sale:
Current assets	$ 393
Total property, plant, and equipment	4,623
Other non-current assets	727
Total Assets Held for Sale	5,743
Liabilities Held for Sale:
Current liabilities	425
Long-term debt	1,286
Accumulated deferred income taxes	618
Other non-current liabilities	932
Total Liabilities Held for Sale	3,261
Southern Power
Assets Held for Sale:
Current assets	8
Total property, plant, and equipment	576
Other non-current assets	0
Total Assets Held for Sale	584
Liabilities Held for Sale:
Current liabilities	15
Long-term debt	0
Accumulated deferred income taxes	0
Other non-current liabilities	0
Total Liabilities Held for Sale	$ 15