PROPERTY AND EQUIPMENT

Property and equipment as of December 31, 2017 and 2016 consisted of the following (in millions):



	2017		2016
Drilling rigs and equipment	$	12,272.4	$	11,067.4
Other	183.4		180.8
Work in progress	2,876.3		1,744.3
	$	15,332.1	$	12,992.5

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 ENSCO 140 and ENSCO 141 premium jackup rigs 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 have been delivered by the respective shipyards but have not yet been placed into service as of December 31, 2017.

Work in progress as of December 31, 2016 primarily consisted of $1.1 billion related to the construction of ultra-deepwater drillships ENSCO DS-9 and ENSCO DS-10, $415.4 million related to the construction of ENSCO 140 and ENSCO 141 premium jackup rigs and $85.2 million related to the construction of ENSCO 123, an ultra-premium harsh environment jackup rig.

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 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.

During 2015, we recognized a pre-tax, non-cash loss on impairment of $2.6 billion, of which $2.5 billion was included in income (loss) from continuing operations and $148.6 million was included in income (loss) from discontinued operations, net, in our consolidated statement of operations. The impairments recognized during 2015 resulted from adverse changes in our business climate that led to the conclusion that triggering events had occurred across our fleet.

For rigs whose carrying values were determined not to be recoverable during 2017 and 2015, we recorded an impairment for the difference between their fair values and carrying values. We estimated the fair values of these rigs by applying either an income approach, using projected discounted cash flows, or a market approach. 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.

In instances where we applied an income approach, forecasted day rates and utilization took into account market conditions and our anticipated business outlook. In instances where we applied a market approach, the fair value was based on unobservable third-party estimated prices that would be received in exchange for the assets in an orderly transaction between market participants. We validated all third-party estimated prices using our forecasts of economic returns for the respective rigs or other market data.

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.