CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash Flows from Operating Activities
Net income (loss)	$ (279)	$ 48
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation	259	242
Amortization	137	117
Defined benefit plans - expense	35	34
Deferred income taxes and investment tax credits	(30)	(150)
Impairment of assets	592	20
Unrealized (gains) losses on derivatives, and other hedging activities	(80)	216
Other	76	19
Change in current assets and current liabilities
Accounts receivable	64	(1)
Accounts payable	(148)	(45)
Unbilled revenues	93	41
Fuel, materials and supplies	58	(67)
Prepayments	23	5
Counterparty collateral	76	(18)
Price risk management assets and liabilities	(9)	(34)
Taxes payable	(23)	70
Other	(32)	(14)
Other operating activities
Defined benefit plans - funding	(74)	(32)
Other assets	1	(2)
Other liabilities	(8)	16
Net cash provided by operating activities	731	465
Cash Flows from Investing Activities
Expenditures for property, plant and equipment	(252)	(276)
Expenditures for intangible assets	(35)	(38)
Purchases of nuclear plant decommissioning trust investments	(154)	(124)
Proceeds from the sale of nuclear plant decommissioning trust investments	143	112
Proceeds from the receipt of grants	0	164
Net (increase) decrease in restricted cash and cash equivalents	110	(199)
Other investing activities	15	17
Net cash provided by (used in) investing activities	(173)	(344)
Cash Flows from Financing Activities
Issuance of long-term debt	600	0
Retirement of long-term debt	(33)	(308)
Contributions from member	82	730
Distributions to member	(214)	(1,178)
Net increase (decrease) in short-term debt	(667)	590
Other financing activities	(30)	0
Net cash provided by (used in) financing activities	(262)	(166)
Net Increase (Decrease) in Cash and Cash Equivalents	296	(45)
Cash and Cash Equivalents at Beginning of Period	352	239
Cash and Cash Equivalents at End of Period	648	194
Talen Energy Supply
Cash Flows from Operating Activities
Net income (loss)	(279)	48
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation	259	242
Amortization	137	117
Defined benefit plans - expense	35	34
Deferred income taxes and investment tax credits	(30)	(150)
Impairment of assets	592	20
Unrealized (gains) losses on derivatives, and other hedging activities	(80)	216
Other	76	19
Change in current assets and current liabilities
Accounts receivable	64	(1)
Accounts payable	(148)	(45)
Unbilled revenues	93	41
Fuel, materials and supplies	58	(67)
Prepayments	23	5
Counterparty collateral	76	(18)
Price risk management assets and liabilities	(9)	(34)
Taxes payable	(23)	70
Other	(32)	(14)
Other operating activities
Defined benefit plans - funding	(74)	(32)
Other assets	1	(2)
Other liabilities	(8)	16
Net cash provided by operating activities	731	465
Cash Flows from Investing Activities
Expenditures for property, plant and equipment	(252)	(276)
Expenditures for intangible assets	(35)	(38)
Purchases of nuclear plant decommissioning trust investments	(154)	(124)
Proceeds from the sale of nuclear plant decommissioning trust investments	143	112
Proceeds from the receipt of grants	0	164
Net (increase) decrease in restricted cash and cash equivalents	110	(199)
Other investing activities	15	17
Net cash provided by (used in) investing activities	(173)	(344)
Cash Flows from Financing Activities
Issuance of long-term debt	600	0
Retirement of long-term debt	(33)	(308)
Contributions from member	82	730
Distributions to member	(215)	(1,178)
Net increase (decrease) in short-term debt	(667)	590
Other financing activities	(29)	0
Net cash provided by (used in) financing activities	(262)	(166)
Net Increase (Decrease) in Cash and Cash Equivalents	296	(45)
Cash and Cash Equivalents at Beginning of Period	352	239
Cash and Cash Equivalents at End of Period	$ 648	$ 194