Segment and Related Information - Balance Sheet Data (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		$ 12,403	$ 12,809
Operating Segments | East
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		9,979	11,430
Operating Segments | West
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		1,273	1,231
Other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	[1]	1,151	148
Talen Energy Supply
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		12,412	12,809
Talen Energy Supply | Operating Segments | East
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		9,979	11,430
Talen Energy Supply | Operating Segments | West
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		1,273	1,231
Talen Energy Supply | Other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	[1]	$ 1,160	$ 148

[1] Primarily consists of unallocated items, including cash and PP&E.