Regulatory Assets and Liabilities

Regulatory assets generally represent incurred costs that have been deferred because such costs are probable of future recovery in customer rates. Regulatory liabilities generally represent obligations to make refunds to customers for previous collections for costs that are not likely to be incurred or deferrals of gains that will be credited to customers in future periods. Components of regulatory assets and regulatory liabilities are summarized in the table below:



Regulatory Assets and Liabilities
	At December 31, 2013		At September 30, 2013
Current regulatory assets
Deferred nuclear generating units	$	237	$	237
Unrealized losses on commodity derivatives	154		183
Environmental agreements	81		73
Environmental cleanup costs - Kingston ash spill	64		68
Fuel cost adjustment receivable	26		—
Total current regulatory assets	562		561

Non-current regulatory assets
Deferred pension costs and other post-retirement benefits costs	4,011		4,076
Unrealized losses on interest rate derivatives	669		808
Nuclear decommissioning costs	856		893
Environmental cleanup costs - Kingston ash spill	518		681
Non-nuclear decommissioning costs	570		571
Deferred nuclear generating units	1,411		1,438
Environmental agreements	164		189
Unrealized losses on commodity derivatives	133		139
Other non-current regulatory assets	328		336
Total non-current regulatory assets	8,660		9,131
Total regulatory assets	$	9,222	$	9,692

Current regulatory liabilities
Fuel cost adjustment tax equivalents	$	169	$	176
Fuel cost adjustment liability	—		29
Unrealized gains on commodity derivatives	5		7
Total current regulatory liabilities	174		212

Non-current regulatory liabilities
Unrealized gains on commodity derivatives	1		1
Total non-current regulatory liabilities	1		1
Total regulatory liabilities	$	175	$	213