Acquisitions and Dispositions - Schedule of Assets Held for Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Assets Held for Sale:
Receivables – energy marketing	$ 486	$ 0
Natural gas for sale	90	0
Other current assets	76	0
Total property, plant, and equipment	11	8
Leveraged leases	45	52
Accumulated deferred income taxes	30	0
Other non-current assets	49	0
Total Assets Held for Sale	787	60
Liabilities Held for Sale:
Energy marketing trade payables	491	0
Other current liabilities	148	0
Other non-current liabilities	38	0
Total Liabilities Held for Sale	677	$ 0
SOUTHERN Co GAS
Assets Held for Sale:
Receivables – energy marketing	486
Natural gas for sale	90
Other current assets	76
Total property, plant, and equipment	5
Leveraged leases	0
Accumulated deferred income taxes	30
Other non-current assets	49
Total Assets Held for Sale	736
Liabilities Held for Sale:
Energy marketing trade payables	491
Other current liabilities	148
Other non-current liabilities	38
Total Liabilities Held for Sale	$ 677