Employee Share-Based Incentive Compensation Plans - Performance Shares (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		9 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Target Performance Shares Outstanding
Beginning of period (in shares)			37,031	39,449	39,449	40,828
Shares paid (in shares)			0	0	(13,350)	(14,625)
New grants (in shares)			0	0	10,895	13,225
Forfeitures and cancellations (in shares)			0	0	37	21
End of period (in shares)			37,031	39,449	37,031	39,449
Accrued Expense
Beginning of period			$ 44.6	$ 41.2	$ 67.5	$ 42.2
Shares paid			0.0	0.0	(40.8)	(26.4)
New grants			0.0	0.0	0.0	0.0
Forfeitures and cancellations			0.0	(0.1)	0.2	(0.2)
Expense recognized			10.5	11.9	28.2	37.4
End of period			$ 55.1	$ 53.0	$ 55.1	$ 53.0
Performance Share
Accrued Expense
Percentage of target payout - minimum actual	200.00%	172.00%