Contingencies - SPC Litigation (Details) - Southern Power $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Construction contract payment withheld	$ 26
RE Roserock, LLC
Loss Contingencies [Line Items]
Noncontrolling ownership percentage held by parent	51.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration