Employee Share-Based Incentive Compensation Plans - Restricted Shares (Details) - Restricted Stock - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Restricted Shares
Beginning of period (in shares)	32,885	35,525	35,390	37,595
Vested (in shares)	0	0	(13,150)	(13,475)
Issued (in shares)	25	0	10,670	11,405
Forfeited (in shares)	0	(135)	0	(135)
End of period (in shares)	32,910	35,390	32,910	35,390
Unamortized Issue Date Fair Value
Beginning of period	$ 30.7	$ 28.8	$ 19.9	$ 16.2
Vested	0.0	0.0	0.0	0.0
Issued	0.1	0.0	19.6	20.0
Forfeited	0.0	0.0	0.0	0.0
Expense recognized	(4.9)	(4.5)	(13.6)	(11.9)
End of period	$ 25.9	$ 24.3	$ 25.9	$ 24.3