XML 24 R11.htm IDEA: XBRL DOCUMENT v3.8.0.1
Utility & Nonutility Plant
 12 Months Ended
Dec. 31, 2017
Property, Plant and Equipment [Abstract]  
Utility & Nonutility Plant
Utility & Nonutility Plant

The original cost of Utility Plant, together with depreciation rates expressed as a percentage of original cost, follows:
 
 
At December 31,
(In millions)
 
2017
 
2016
 
 
Original Cost
 
Depreciation
Rates as a
Percent of 
Original Cost
 
Original Cost
 
Depreciation
Rates as a
Percent of 
Original Cost
Gas utility plant
 
$
3,969.6

 
3.4
%
 
$
3,587.5

 
3.4
%
Electric utility plant
 
2,833.5

 
3.3
%
 
2,752.0

 
3.3
%
Common utility plant
 
59.0

 
3.2
%
 
56.3

 
3.2
%
Construction work in progress
 
70.7

 
—

 
63.0

 
—

Asset retirement obligations
 
82.6

 
—

 
86.6

 
—

Total original cost
 
$
7,015.4

 
 

 
$
6,545.4

 
 


 
SIGECO and Alcoa Generating Corporation (AGC), a subsidiary of Alcoa, Inc. (Alcoa), own a 300 MW unit at the Warrick Power Plant (Warrick Unit 4) as tenants in common.  SIGECO's share of the cost of this unit at December 31, 2017, is $191.0 million with accumulated depreciation totaling $119.7 million.  AGC and SIGECO share equally in the cost of operation and output of the unit.  SIGECO's share of operating costs is included in Other operating expenses in the Consolidated Statements of Income.

Nonutility Plant, net of accumulated depreciation and amortization follows:
 
 
At December 31,
(In millions)
 
2017
 
2016
Vehicles & equipment

 
$
220.2

 
$
207.4

Computer hardware & software

 
156.5

 
121.8

Land & buildings
 
77.1

 
77.9

All other
 
10.3

 
16.8

Nonutility plant - net
 
$
464.1

 
$
423.9


 
Nonutility Plant is presented net of accumulated depreciation and amortization of $506.9 million and $460.8 million as of December 31, 2017 and 2016, respectively.  For the years ended December 31, 2017, 2016, and 2015, the Company capitalized interest totaling $1.2 million, $1.0 million, and $0.4 million, respectively, on nonutility plant construction projects.

In 2016, the estimated depreciable lives for certain pieces of equipment at Minnesota Limited, LLC were reevaluated and extended due to a change in service life of the equipment. As a result of this evaluation, the Company extended the estimated useful life of certain pieces of equipment effective January 1, 2016. The effect of this change in estimate was a reduction of annual depreciation expense of approximately $9.6 million.