Note 7. Property, Plant and Equipment

The historical costs of our property, plant and equipment and related accumulated depreciation balances were as follows at the dates indicated:

	Estimated Useful Life in Years	June 30, 2015			December 31, 2014
Plants, pipelines and facilities (1)	3-45 (6)	$	31,449.8		$	30,834.9
Underground and other storage facilities (2)	5-40 (7)		2,726.6			2,584.2
Platforms and facilities (3)	20-31		659.7			659.7
Transportation equipment (4)	3-10		159.0			154.2
Marine vessels (5)	15-30		826.1			796.4
Land			261.2			262.6
Construction in progress			3,588.2			2,754.7
Total historical cost of property, plant and equipment			39,670.6			38,046.7
Less accumulated depreciation			8,750.9			8,165.1
Subtotal property, plant and equipment, net			30,919.7			29,881.6
Carrying values reclassified to assets held for sale (8)			(1,135.9	)		--
Total property, plant and equipment, net		$	29,783.8		$	29,881.6

(1) Plants, pipelines and facilities include processing plants; NGL, natural gas, crude oil and petrochemical and refined products pipelines; terminal loading and unloading facilities; office furniture and equipment; buildings; laboratory and shop equipment and related assets.
(2) Underground and other storage facilities include underground product storage caverns; above ground storage tanks; water wells and related assets.
(3) Platforms and facilities included offshore platforms and related facilities and other associated assets located in the Gulf of Mexico (see Note 6).
(4) Transportation equipment includes tractor-trailer tank trucks and other vehicles and similar assets used in our operations.
(5) Marine vessels include tow boats, barges and related equipment used in our marine transportation business.
(6) In general, the estimated useful lives of major assets within this category are: processing plants, 20-35 years; pipelines and related equipment, 5-45 years; terminal facilities, 10-35 years; office furniture and equipment, 3-20 years; buildings, 20-40 years; and laboratory and shop equipment, 5-35 years.
(7) In general, the estimated useful lives of assets within this category are: underground storage facilities, 5-35 years; storage tanks, 10-40 years; and water wells, 5-35 years.
(8) See Note 6 regarding the reclassification of $1.84 billion of offshore Gulf of Mexico property, plant and equipment values, net of $706.8 million of accumulated depreciation, to assets held for sale at June 30, 2015.

The following table summarizes our depreciation expense and capitalized interest amounts for the periods indicated:

	For the Three Months Ended June 30,				For the Six Months Ended June 30,
	2015		2014		2015		2014
Depreciation expense (1)	$	292.6	$	271.0	$	583.9	$	538.9
Capitalized interest (2)		35.7		17.7		65.3		36.2

(1) Depreciation expense is a component of “Costs and expenses” as presented on our Unaudited Condensed Statements of Consolidated Operations.
(2) We capitalize interest costs incurred on funds used to construct property, plant and equipment while the asset is in its construction phase. The capitalized interest is recorded as part of the asset to which it relates and is amortized over the asset’s estimated useful life as a component of depreciation expense. When capitalized interest is recorded, it reduces interest expense from what it would be otherwise.

At June 30, 2015, the net carrying values of property, plant and equipment attributable to our Offshore Business were reclassified to “Assets held for sale” as discussed in Note 6. Since these assets are classified as held for sale, we will no longer depreciate the underlying historical costs after June 30, 2015. For the three and six months ended June 30, 2015, we recognized $19.7 million and $40.1 million, respectively, of depreciation expense associated with these held for sale assets. Likewise, for the three and six months ended June 30, 2014, we recognized $20.4 million and $40.8 million, respectively, of depreciation expense associated with these assets.

Asset Retirement Obligations

We record asset retirement obligations (“AROs”) in connection with legal requirements to perform specified retirement activities under contractual arrangements and/or governmental regulations. Our contractual AROs primarily result from right-of-way agreements associated with our pipeline operations and real estate leases associated with our plant sites. In addition, we record AROs in connection with governmental regulations associated with the abandonment or retirement of (i) above-ground brine storage pits, (ii) offshore Gulf of Mexico platform and pipeline assets and (iii) certain marine vessels. We also record AROs in connection with regulatory requirements associated with the renovation or demolition of certain assets containing hazardous substances such as asbestos. We typically fund our AROs using cash flow from operations.

Property, plant and equipment at June 30, 2015 and December 31, 2014 includes $16.9 million and $31.3 million, respectively, of asset retirement costs capitalized as an increase in the associated long-lived asset.

The following table presents information regarding our AROs since December 31, 2014:

ARO liability balance, December 31, 2014	$	98.3
Liabilities incurred		0.1
Liabilities settled		(5.5	)
Revisions in estimated cash flows		49.0
Accretion expense		3.1
Reclassification of Offshore Business AROs to “Liabilities related to assets held for sale”		(90.9	)
ARO liability balance, June 30, 2015	$	54.1

Our AROs related to the Matagorda Gathering System, which is located in Texas state waters in the Matagorda Island area, increased $39.5 million in the second quarter of 2015 due to a change in management estimate associated with pending and future pipeline abandonment activities. In June 2015, we were notified by the U.S. Army Corps of Engineers (the “CoE”) to fully remove two pipeline segments included in this system that we had originally requested to abandon in-place. As a result, we adjusted the ARO liabilities for those pipeline segments under CoE jurisdiction to account for the estimated cost of removal. All ARO liabilities related to our Offshore Business (including those of the Matagorda Gathering System) were reclassified to “Liabilities related to assets held for sale” as presented on our Unaudited Condensed Consolidated Balance Sheet at June 30, 2015. The total amount reclassified was $90.9 million.

With respect to our AROs, the following table presents our forecast of accretion expense for the periods indicated (excluding those classified as held for sale at June 30, 2015):

Remainder of 2015				2016				2017				2018				2019
$	1.8			$	3.5			$	3.8			$	4.1			$	4.4

Certain of our unconsolidated affiliates have AROs recorded at June 30, 2015 and December 31, 2014 relating to contractual agreements and regulatory requirements. These amounts are immaterial to our consolidated financial statements.