Utility & Nonutility Plant (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Cost of Utility 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

Nonutility Plant, Net of Depreciation and Amortization

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