Employee Share-Based Incentive Compensation Plans - Restricted Shares (Details) - Restricted Stock - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Restricted Shares
Beginning of period (in shares)	37,595	38,350	37,850
Issued (in shares)	11,405	10,895	13,225
Vested (in shares)	(13,475)	(11,650)	(12,725)
Forfeited (in shares)	(135)	0	0
End of period (in shares)	35,390	37,595	38,350
Accrued Expense
Beginning of period	$ 16.2	$ 15.5	$ 15.9
Issued	20.0	16.0	13.8
Vested	0.0	0.0	0.0
Forfeited	0.0	0.0	0.0
Expense recognized	(16.3)	(15.3)	(14.2)
End of period	$ 19.9	$ 16.2	$ 15.5