PROPERTY AND EQUIPMENT

Property and equipment as of December 31, 2018 and 2017 consisted of the following (in millions):



	2018		2017
Drilling rigs and equipment	$	14,542.5	$	12,272.4
Work-in-progress	779.2		2,876.3
Other	195.3		183.4
	$	15,517.0	$	15,332.1

Work-in-progress as of December 31, 2018 primarily consisted of $416.8 million related to the construction of ultra-deepwater drillships ENSCO DS-13 and ENSCO DS-14 and $352.4 million related to the construction of ENSCO 123, an ultra-premium harsh environment jackup rig.

Work-in-progress as of December 31, 2017 primarily consisted of $2.0 billion related to the construction of ultra-deepwater drillships ENSCO DS-9, ENSCO DS-10, ENSCO DS-13 and ENSCO DS-14, $423.6 million related to the construction of premium jackup rigs ENSCO 140 and ENSCO 141 and $321.6 million related to the construction of ENSCO 123, an ultra-premium harsh environment jackup rig.

ENSCO DS-9, ENSCO DS-10, ENSCO 140 and ENSCO 141 were placed into service and reclassified from work-in-progress to drilling rigs and equipment during the year ended December 31, 2018.

Impairment of Long-Lived Assets

On a quarterly basis, we evaluate the carrying value of our property and equipment to identify events or changes in circumstances ("triggering events") that indicate the carrying value may not be recoverable.

During 2018, we recorded a pre-tax, non-cash loss on impairment of $40.3 million related to one older non-core jackup rig. During the fourth quarter, we concluded that a triggering event occurred due to the expiration of a legacy higher day rate contract resulting in the performance of a recoverability test. We determined that the estimated undiscounted cash flows over the remaining useful life of the rig were not sufficient to recover the rig’s carrying value and concluded the rig was impaired as of December 31, 2018.

During 2017, we recognized a pre-tax, non-cash loss on impairment of $182.9 million related to older, less capable, non-core assets in our fleet. During the fourth quarter, we determined that the remaining useful life of certain non-core rigs would not extend substantially beyond their current contracts, resulting in triggering events and the performance of recoverability tests. Our estimates of undiscounted cash flows over the revised estimated remaining useful lives were not sufficient to recover each asset’s carrying value. Accordingly, we concluded that two semisubmersibles and one jackup were impaired as of December 31, 2017.

For rigs whose carrying values were determined not to be recoverable during 2018 and 2017, we recorded an impairment for the difference between their fair values and carrying values. We estimated the fair values of these rigs by applying an income approach, using projected discounted cash flows. These valuations were based on unobservable inputs that require significant judgments for which there is limited information, including assumptions regarding future day rates, utilization, operating costs and capital requirements. Forecasted day rates and utilization took into account market conditions and our anticipated business outlook.

If the global economy, our overall business outlook and/or our expectations regarding the marketability of one or more of our drilling rigs deteriorate further, we may conclude that a triggering event has occurred and perform a recoverability test that could lead to a material impairment charge in future periods.