PROPERTY, PLANT AND EQUIPMENT

The following table summarizes the components of the electric generation and distribution assets and other property, plant and equipment (in millions) with their estimated useful lives (in years). The amounts are stated net of all prior asset impairment losses recognized.



		December 31,
	Estimated Useful Life	2016			2015
Electric generation and distribution facilities	4 - 68	$	25,773		$	24,740
Other buildings	3 - 63	2,034			1,856
Furniture, fixtures and equipment	3 - 31	309			288
Other	2 - 50	423			398
Total electric generation and distribution assets and other		28,539			27,282
Accumulated depreciation		(9,528		)	(8,939		)
Net electric generation and distribution assets and other		$	19,011		$	18,343

The following table summarizes depreciation expense (including the amortization of assets recorded under capital leases and the amortization of asset retirement obligations) and interest capitalized during development and construction on qualifying assets for the periods indicated (in millions):



Years Ended December 31,	2016		2015		2014
Depreciation expense	$	1,105	$	1,064	$	1,154
Interest capitalized during development and construction	125		89		118

Property, plant and equipment, net of accumulated depreciation, of $10 billion and $11 billion was mortgaged, pledged or subject to liens as of December 31, 2016 and 2015, respectively.

The following table summarizes regulated and non-regulated generation and distribution property, plant and equipment and accumulated depreciation as of the dates indicated (in millions):



December 31,	2016			2015
Regulated generation, distribution assets and other, gross	$	11,021		$	10,789
Regulated accumulated depreciation	(4,194		)	(3,984		)
Regulated generation, distribution assets and other, net	6,827			6,805
Non-regulated generation, distribution assets and other, gross	17,518			16,493
Non-regulated accumulated depreciation	(5,334		)	(4,955		)
Non-regulated generation, distribution assets and other, net	12,184			11,538
Net electric generation, distribution assets and other	$	19,011		$	18,343

The following table presents amounts recognized related to asset retirement obligations for the periods indicated (in millions):



	2016			2015
Balance at January 1	$	247		$	209
Additional liabilities incurred	12			43
Liabilities settled	(4		)	(6		)
Accretion expense	15			13
Change in estimated cash flows	86			(7		)
Other	1			(5		)
Balance at December 31	$	357		$	247

The Company's asset retirement obligations primarily include active ash landfills, water treatment basins and the removal or dismantlement of certain plants and equipment. The $86 million increase in estimated cash flows for 2016 is primarily relates to revised estimated closure expenditures and earlier plant closure dates than previously forecast at DPL. There were $1 million of legally restricted assets for the year ended December 31, 2016 and $2 million for the year ended December 31, 2015 for purposes of settling asset retirement obligations.

Ownership of Certain Coal-Fired Facilities — DP&L has undivided ownership interests in five coal-fired generation facilities jointly owned with other utilities. DP&L's share of the operating costs of the facilities is included in Cost of Sales in the Consolidated Statements of Operations and its share of investment in the facilities is included in Property, Plant and Equipment in the Consolidated Balance Sheets. DP&L's undivided ownership interest in the facilities as of December 31, 2016 is as follows ($ in millions):



	DP&L Share	DP&L Investment
Production units:	Ownership	Gross Plant In Service		Accumulated Depreciation		Construction Work In Process
Conesville Unit 4	17%	$	—	$	—	$	—
Killen Station	67%	34		—		2
Miami Fort Units 7 and 8	36%	27		—		7
Stuart Station	35%	24		—		23
Zimmer Station	28%	7		—		9
Transmission	Various	99		66		—
Total		$	191	$	66	$	41