Employee Share-Based Incentive Compensation Plans - Restricted Shares (Details) - Restricted Stock - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Restricted Shares
Beginning of period (in shares)	37,850	43,105	43,395
Issued (in shares)	13,225	13,475	14,055
Vested (in shares)	(12,725)	(17,936)	(14,345)
Forfeited (in shares)	0	(794)	0
Expense recognized (in shares)	0	0	0
End of period (in shares)	38,350	37,850	43,105
Unamortized Issue Date Fair Value
Beginning of period	$ 15.9	$ 15.2	$ 16.7
Issued	13.8	16.1	15.1
Vested	0.0	0.0	0.0
Forfeited	0.0	(0.8)	0.0
Expense recognized	(14.2)	(14.6)	(16.6)
End of period	$ 15.5	$ 15.9	$ 15.2