PROPERTY, PLANT, AND EQUIPMENT

The following is a summary of Property, plant, and equipment by classification as of December 31:



	2017			2016
Property, plant, and equipment	(In millions)
DTE Electric
Generation	$	12,166		$	11,990
Distribution	8,637			8,134
Other	2,169			1,970
Total DTE Electric	22,972			22,094
DTE Gas
Distribution	3,523			3,382
Storage	533			503
Transmission and other	1,118			925
Total DTE Gas	5,174			4,810
Non-utility and other	3,278			3,125
Total DTE Energy	31,424			30,029
Accumulated depreciation and amortization
DTE Electric
Generation	(4,403		)	(4,364		)
Distribution	(2,914		)	(2,769		)
Other	(667		)	(588		)
Total DTE Electric	(7,984		)	(7,721		)
DTE Gas
Distribution	(1,238		)	(1,198		)
Storage	(159		)	(152		)
Transmission and other	(384		)	(370		)
Total DTE Gas	(1,781		)	(1,720		)
Non-utility and other	(938		)	(858		)
Total DTE Energy	(10,703		)	(10,299		)
Net DTE Energy Property, plant, and equipment	$	20,721		$	19,730
Net DTE Electric Property, plant, and equipment	$	14,988		$	14,373

The following is a summary of the Registrants' AFUDC and interest capitalized for the years ended December 31:



	DTE Energy				DTE Electric
	2017		2016		2017		2016
	(In millions)
Allowance for debt funds used during construction and interest capitalized	$	13	$	10	$	8	$	8
Allowance for equity funds used during construction	23		21		18		18
Total	$	36	$	31	$	26	$	26

The composite depreciation rate for DTE Electric was approximately 3.6% in 2017 and 3.5% in 2016 and 2015. The composite depreciation rate for DTE Gas was 2.7%, 2.4%, and 2.6% in 2017, 2016, and 2015, respectively. The average estimated useful life for each major class of utility Property, plant, and equipment as of December 31, 2017 follows:

The estimated useful lives for DTE Electric's Other utility assets range from 4 to 62 years, while the estimated useful lives for DTE Gas' Transmission and other utility assets range from 5 to 70 years. The estimated useful lives for major classes of DTE Energy's non-utility assets and facilities range from 3 to 83 years.

The following is a summary of Depreciation and amortization expense for DTE Energy:



	2017		2016		2015
	(In millions)
Property, plant, and equipment	$	865	$	783	$	740
Regulatory assets and liabilities	165		193		150
Securitized regulatory assets^(a)	—		—		(38		)
	$	1,030	$	976	$	852

_______________________________________


(a)	Securitization surcharges ended in December 2014 with remaining over recovery refunded to customers in 2015. Securitization bonds were paid and Securitization regulatory assets amortization was completed in 2015. The $38 million credit represents the final adjustments to close out the Securitization program.

The following is a summary of Depreciation and amortization expense for DTE Electric:



	2017		2016		2015
	(In millions)
Property, plant, and equipment	$	620	$	582	$	545
Regulatory assets and liabilities	133		168		126
Securitized regulatory assets^(a)	—		—		(38		)
	$	753	$	750	$	633

_______________________________________


(a)	Securitization surcharges ended in December 2014 with remaining over recovery refunded to customers in 2015. Securitization bonds were paid and Securitization regulatory assets amortization was completed in 2015. The $38 million credit represents the final adjustments to close out the Securitization program.

Capitalized software costs are classified as Property, plant, and equipment and the related amortization is included in accumulated depreciation and amortization on the Registrants' Consolidated Financial Statements. The Registrants capitalize the costs associated with computer software developed or obtained for use in their businesses. The Registrants amortize capitalized software costs on a straight-line basis over the expected period of benefit, ranging from 3 to 15 years for DTE Energy and 4 to 15 years for DTE Electric.

The following balances for capitalized software relate to DTE Energy:



	Year Ended December 31,
	2017		2016		2015
	(In millions)
Amortization expense of capitalized software	$	101	$	89	$	98
Gross carrying value of capitalized software	$	890	$	715
Accumulated amortization of capitalized software	$	500	$	435

The following balances for capitalized software relate to DTE Electric:



	Year Ended December 31,
	2017		2016		2015
	(In millions)
Amortization expense of capitalized software	$	93	$	83	$	80
Gross carrying value of capitalized software	$	774	$	610
Accumulated amortization of capitalized software	$	423	$	365

Property under capital leases for the Registrants is as follows:



	DTE Energy				DTE Electric
	2017		2016		2017		2016
	(In millions)
Gross property under capital leases	$	44	$	44	$	18	$	18
Accumulated amortization of property under capital leases	$	38	$	32	$	12	$	6

Estimated Useful Lives in Years

Generation

Distribution

DTE Electric