Asset Retirement Obligations (ARO)

9 Months Ended

Sep. 30, 2018

Asset Retirement Obligation Disclosure [Abstract]

The majority of the ARO recognized by the Company at September 30, 2018 and December 31, 2017 related to the estimated costs to dismantle and abandon certain of its retail gasoline stations. The Company has not recorded an ARO for certain of its marketing assets because sufficient information is presently not available to estimate a range of potential settlement dates for the obligation. These assets are consistently being upgraded and are expected to be operational into the foreseeable future. In these cases, the obligation will be initially recognized in the period in which sufficient information exists to estimate the obligation.

A reconciliation of the beginning and ending aggregate carrying amount of the ARO is shown in the following table.



(Millions of dollars)	September 30, 2018			December 31, 2017
Balance at beginning of period	$	28.2		$	26.2
Accretion expense	1.5			1.8
Settlements of liabilities	(0.3		)	(0.3		)
Liabilities incurred	0.6			0.5
Balance at end of period	$	30.0		$	28.2

The estimation of future ARO is based on a number of assumptions requiring professional judgment. The Company cannot predict the type of revisions to these assumptions that may be required in future periods due to the lack of availability of additional information.