Employee Share-Based Incentive Compensation Plans - Performance Shares (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		9 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Target Performance Shares Outstanding
Beginning of period (in shares)			34,992	37,031	37,031	39,449
Shares paid (in shares)			0	0	(13,475)	(13,350)
New grants (in shares)			0	0	11,405	10,895
Forfeitures and cancellations (in shares)			(133)	0	(102)	37
End of period (in shares)			34,859	37,031	34,859	37,031
Accrued Expense
Beginning of period			$ 52.0	$ 44.6	$ 69.4	$ 67.5
Shares paid			0.0	0.0	(44.9)	(40.8)
New grants			0.0	0.0	0.0	0.0
Forfeitures and cancellations			0.0	0.0	0.3	0.2
Expense recognized			3.7	10.5	30.9	28.2
End of period			$ 55.7	$ 55.1	$ 55.7	$ 55.1
Performance Share
Accrued Expense
Percentage of target payout - minimum actual	188.00%	200.00%