CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash Flows from Operating Activities
Net income (loss)	$ 122	$ (53)
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation	164	162
Amortization	93	77
Defined benefit plans - expense	23	32
Deferred income taxes and investment tax credits	(46)	(120)
Impairment of assets	3	18
Unrealized (gains) losses on derivatives, and other hedging activities	(40)	232
Other	41	10
Change in current assets and current liabilities
Accounts receivable	50	25
Accounts payable	(135)	(55)
Unbilled revenues	80	67
Fuel, materials and supplies	33	9
Prepayments	37	(16)
Counterparty collateral	36	(15)
Price risk management assets and liabilities	(1)	(33)
Other	(34)	(29)
Other operating activities
Defined benefit plans - funding	(74)	(32)
Other assets	2	(1)
Other liabilities	1	12
Net cash provided by operating activities	355	290
Cash Flows from Investing Activities
Expenditures for property, plant and equipment	(179)	(176)
Expenditures for intangible assets	(19)	(24)
Purchases of nuclear plant decommissioning trust investments	(108)	(73)
Proceeds from the sale of nuclear plant decommissioning trust investments	100	65
Proceeds from the receipt of grants	0	56
Net (increase) decrease in restricted cash and cash equivalents	67	(258)
Other investing activities	12	7
Net cash provided by (used in) investing activities	(127)	(403)
Cash Flows from Financing Activities
Issuance of long-term debt	600	0
Contributions from member	82	730
Distributions to member	(214)	(914)
Net increase (decrease) in short-term debt	(668)	324
Other financing activities	(28)	(2)
Net cash provided by (used in) financing activities	(228)	138
Net Increase (Decrease) in Cash and Cash Equivalents	0	25
Cash and Cash Equivalents at Beginning of Period	352	239
Cash and Cash Equivalents at End of Period	352	264
Talen Energy Supply
Cash Flows from Operating Activities
Net income (loss)	122	(53)
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation	164	162
Amortization	93	77
Defined benefit plans - expense	23	32
Deferred income taxes and investment tax credits	(46)	(120)
Impairment of assets	3	18
Unrealized (gains) losses on derivatives, and other hedging activities	(40)	232
Other	41	10
Change in current assets and current liabilities
Accounts receivable	50	25
Accounts payable	(135)	(55)
Unbilled revenues	80	67
Fuel, materials and supplies	33	9
Prepayments	37	(16)
Counterparty collateral	36	(15)
Price risk management assets and liabilities	(1)	(33)
Other	(34)	(29)
Other operating activities
Defined benefit plans - funding	(74)	(32)
Other assets	2	(1)
Other liabilities	1	12
Net cash provided by operating activities	355	290
Cash Flows from Investing Activities
Expenditures for property, plant and equipment	(179)	(176)
Expenditures for intangible assets	(19)	(24)
Purchases of nuclear plant decommissioning trust investments	(108)	(73)
Proceeds from the sale of nuclear plant decommissioning trust investments	100	65
Proceeds from the receipt of grants	0	56
Net (increase) decrease in restricted cash and cash equivalents	67	(258)
Other investing activities	12	7
Net cash provided by (used in) investing activities	(127)	(403)
Cash Flows from Financing Activities
Issuance of long-term debt	600	0
Contributions from member	82	730
Distributions to member	(215)	(914)
Net increase (decrease) in short-term debt	(668)	324
Other financing activities	(27)	(2)
Net cash provided by (used in) financing activities	(228)	138
Net Increase (Decrease) in Cash and Cash Equivalents	0	25
Cash and Cash Equivalents at Beginning of Period	352	239
Cash and Cash Equivalents at End of Period	$ 352	$ 264