Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Schedule of inventory

Our inventory as of December 31 consisted of:

(in millions)	2019		2018
Materials and supplies	$	148.3	$	146.1
Fossil fuel	51.1		58.7
Natural gas in storage	30.4		36.6
Total	$	229.8	$	241.4

Allowance for funds used during construction

We recorded the following AFUDC for the years ended December 31:

(in millions)	2019		2018		2017
AFUDC – Debt	$	1.5	$	1.5	$	1.2
AFUDC – Equity	3.7		3.9		3.1

Schedule of assumptions used to estimate the fair value of stock options granted

The following table shows the estimated weighted-average fair value per stock option granted to our employees along with the weighted-average assumptions used in the valuation models:

	2019			2018			2017
Stock options granted	59,404			81,730			80,770
Estimated weighted-average fair value per stock option	$	8.60		$	7.26		$	7.12
Assumptions used to value the options:
Risk-free interest rate	2.5% – 2.7%			1.6% – 2.5%			0.7% – 2.5%
Dividend yield	3.6		%	3.5		%	3.5		%
Expected volatility	17.0		%	18.0		%	19.0		%
Expected life (years)	8.5			5.1			6.2