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Property, Plant And Equipment
 12 Months Ended
Dec. 31, 2018
Property, Plant and Equipment [Abstract]  
Property, Plant And Equipment
Property, Plant and Equipment
Our property, plant and equipment on the Consolidated Balance Sheets are classified as follows: 
At December 31, (in millions)
2018
 
2017
Property, Plant and Equipment
 
 
 
Gas Distribution Utility(1)
$
13,776.0

 
$
12,531.0

Electric Utility(1)
8,374.2

 
7,403.8

Corporate
155.8

 
141.3

Construction Work in Process
474.8

 
950.5

Non-Utility and Other(2)
38.7

 
623.3

Total Property, Plant and Equipment
$
22,819.5

 
$
21,649.9

Accumulated Depreciation and Amortization
 
 
 
Gas Distribution Utility(1)
$
(3,373.8
)
 
$
(3,227.8
)
Electric Utility(1)
(3,809.5
)
 
(3,673.2
)
Corporate
(74.6
)
 
(52.6
)
Non-Utility and Other(2)
(19.1
)
 
(336.8
)
Total Accumulated Depreciation and Amortization
$
(7,277.0
)
 
$
(7,290.4
)
Net Property, Plant and Equipment
$
15,542.5

 
$
14,359.5


(1)NIPSCO’s common utility plant and associated accumulated depreciation and amortization are allocated between Gas Distribution Utility and Electric Utility Property, Plant and Equipment.
(2)Non-Utility and Other as of December 31, 2017 includes net book value of $247.8 million related to Bailly Generating Station (Units 7 and 8) which was reclassified from Electric Utility in the fourth quarter of 2016. In May 2018, Units 7 and 8 were retired from service and the remaining balance was reclassified to "Regulatory assets (noncurrent)" on the Consolidated Balance Sheets. See Note 18-E, "Other Matters," and Note 8, "Regulatory Matters," for additional information.
The weighted average depreciation provisions for utility plant, as a percentage of the original cost, for the periods ended December 31, 2018, 2017 and 2016 were as follows:
 
 
2018
 
2017
 
2016
Electric Operations(1)
2.9
%
 
3.4
%
 
3.3
%
Gas Distribution Operations
2.2
%
 
2.1
%
 
2.1
%

(1)Lower depreciation rate in 2018 due to reduced EERM-related depreciation expense and higher depreciable base from transmission assets being placed into service in 2018.
We recognized depreciation expense of $503.4 million, $501.5 million and $475.1 million for the years ended 2018, 2017 and 2016, respectively.
Amortization of Software Costs. We amortized $54.1 million in 2018, $44.0 million in 2017 and $41.4 million in 2016 related to software costs. Our unamortized software balance was $159.5 million and $189.0 million at December 31, 2018 and 2017, respectively.