Employee Share-Based Incentive Compensation Plans - Restricted Shares (Details) - Restricted Stock - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Restricted Shares
Beginning of period (in shares)	34,525	37,595	37,595	38,350
Issued (in shares)	1,000	0	11,405	10,895
Vested (in shares)	0	0	(13,475)	(11,650)
Forfeited (in shares)	0	0	0	0
End of period (in shares)	35,525	37,595	35,525	37,595
Unamortized Issue Date Fair Value
Beginning of period	$ 31.3	$ 28.3	$ 16.2	$ 15.5
Issued	1.7	0.0	20.0	16.0
Vested	0.0	0.0	0.0	0.0
Forfeited	0.0	0.0	0.0	0.0
Expense recognized	(4.2)	(4.0)	(7.4)	(7.2)
End of period	$ 28.8	$ 24.3	$ 28.8	$ 24.3