

	Regulatory Basis
(Millions of Dollars)	2019			2018
Estimated decommissioning cost obligation from most recently approved study (in 2014 dollars)	$	3,012		$	3,012
Effect of escalating costs	688			539
Estimated decommissioning cost obligation (in current dollars)	3,700			3,551
Effect of escalating costs to payment date	7,505			7,654
Estimated future decommissioning costs (undiscounted)	11,205			11,205
Effect of discounting obligation (using average risk-free interest rate of 2.39% and 3.33% for 2019 and 2018, respectively)	(5,562		)	(6,911		)
Discounted decommissioning cost obligation	$	5,643		$	4,294
Assets held in external decommissioning trust	$	2,440		$	2,055
Underfunding of external decommissioning fund compared to the discounted decommissioning obligation	3,203			2,239

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