Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Schedule of inventory

Our inventories as of December 31 consisted of:

(in millions)	2023		2022
Natural gas in storage	$	327.8	$	446.3
Materials and supplies	320.0		257.0
Fossil fuel	127.4		103.8
Total	$	775.2	$	807.1

Schedule of annual utility composite depreciation rates

Annual utility composite depreciation rates are shown below:

Annual Utility Composite Depreciation Rates	2023	2022	2021
WE	3.03%	3.06%	3.09%
WPS	2.93%	2.67%	2.66%
WG	2.61%	2.47%	2.44%
PGL	3.13%	3.13%	3.12%
NSG	2.46%	2.43%	2.52%
MERC	2.60%	2.56%	2.58%
MGU	2.73%	2.75%	2.70%
UMERC	2.97%	3.01%	2.94%

Schedule of AFUDC rates and amounts

Average AFUDC rates are shown below:

	2023
	Average AFUDC Retail Rate	Average AFUDC Wholesale Rate
WE	8.45%	6.70%
WPS	7.46%	4.60%
WG	7.94%	N/A
UMERC	6.28%	N/A
WBS	7.46%	N/A

Our regulated utilities and WBS recorded the following AFUDC for the years ended December 31:

(in millions)	2023		2022		2021
AFUDC-Debt
WE	$	13.0	$	6.9	$	2.9
WPS	2.9		2.3		3.5
WG	3.4		1.4		0.2
UMERC	—		0.1		0.1
WBS	0.1		0.1		0.1
Other	0.1		0.2		—
Total AFUDC-Debt	$	19.5	$	11.0	$	6.8
AFUDC-Equity
WE	$	41.0	$	18.8	$	7.9
WPS	7.6		5.8		9.0
WG	9.8		3.9		0.6
UMERC	—		0.1		0.1
WBS	0.4		0.3		0.2
Other	0.3		0.5		0.2
Total AFUDC-Equity	$	59.1	$	29.4	$	18.0

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 along with the weighted-average assumptions used in the valuation models:

	2023			2022			2021
Stock options granted	257,780			437,269			530,612
Estimated weighted-average fair value per stock option	$	19.58		$	14.71		$	13.20
Assumptions used to value the options:
Risk-free interest rate	3.8% – 4.8%			0.2% – 1.6%			0.1% – 0.9%
Dividend yield	3.2		%	3.2		%	2.9		%
Expected volatility	22.0		%	21.0		%	21.0		%
Expected life (years)	8.3			8.7			8.7