Common Equity - Restricted Shares (Details) - Restricted stock - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Restricted Stock Activity
Outstanding, shares, beginning of period	89,885	99,061
Granted, shares		72,211
Released, shares		(76,109)
Forfeited, shares		(5,278)
Outstanding, shares, end of period		89,885	99,061
Restricted Stock Weighted-Average Grant Date Fair Value
Outstanding, weighted-average grant date fair value, beginning of period	$ 94.73	$ 88.89
Granted, weighted-average grant date fair value		96.04
Released, weighted-average grant date fair value		88.51
Forfeited, weighted-average grant date fair value		92.80
Outstanding, weighted-average grant date fair value, end of period		$ 94.73	$ 88.89
Restricted Stock - Additional Disclosures
Intrinsic value of released restricted shares		$ 7.5	$ 6.5	$ 11.1
Tax benefit from released restricted shares		2.1	$ 1.8	$ 3.1
Compensation cost not yet recognized		$ 2.8
Weighted-average period over which unrecognized compensation cost is expected to be recognized		1 year 8 months 12 days
Subsequent event
Restricted Stock Activity
Granted, shares	75,453
Restricted Stock Weighted-Average Grant Date Fair Value
Granted, weighted-average grant date fair value	$ 93.69