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 deferral 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, 2011		At September 30, 2011
Current regulatory assets
Unrealized losses on commodity derivatives	$	371	$	225
Deferred nuclear generating units	236		236
Environmental agreements	87		—
Environmental cleanup costs – Kingston ash spill	73		73
Deferred capital leases	2		2
Fuel cost adjustment receivable	—		7
Total current regulatory assets	769		543
Non-current regulatory assets
Deferred pension costs and other post-retirement benefits costs	5,718		5,807
Unrealized losses on swaps and swaptions	1,220		1,164
Nuclear decommissioning costs	964		1,012
Environmental cleanup costs - Kingston ash spill	856		874
Deferred nuclear generating units	650		709
Construction costs	619		619
Non-nuclear decommissioning costs	526		519
Unrealized losses on commodity derivatives	347		221
Environmental agreements	253		346
Other non-current regulatory assets	231		234
Total non-current regulatory assets	11,384		11,505
Total regulatory assets	$	12,153	$	12,048

Current regulatory liabilities
Fuel cost adjustment tax equivalents	$	137	$	127
Unrealized gains on commodity derivatives	81		153
Fuel cost adjustment liability	79		—
Total current regulatory liabilities	297		280
Non-current regulatory liabilities
Unrealized gains on commodity derivatives	205		285
Total regulatory liabilities	$	502	$	565