Consolidated Entities and Equity Method Investments - Narrative (Details) $ in Millions		6 Months Ended
	May 29, 2019 USD ($)	Jun. 30, 2019 USD ($) investor
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage		67.00%
Global Atlantic
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage		33.00%
Variable Interest Entity, Not Primary Beneficiary | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments		$ 144
SP Solar Holdings I, LP | Variable Interest Entity, Primary Beneficiary | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets		6,500
Liabilities		374
Noncontrolling interests related to other partners' interests		$ 1,100
SP Wind | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage		60.00%
Number of financial investors | investor		3
SP Wind | Financial Investors
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage		40.00%
SP Wind | Variable Interest Entity, Primary Beneficiary | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets		$ 2,500
Liabilities		136
Noncontrolling interests related to other partners' interests		46
DSGP | Variable Interest Entity, Not Primary Beneficiary | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments		$ 116
Triton | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Pre tax loss on disposition of investment	$ 6
Income tax benefit on disposition of investment	13
After-tax gain on disposition of investment	$ 7