Employee Share-Based Incentive Compensation Plans - Performance Shares (Details) - Performance Shares - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Target Performance Shares Outstanding
Beginning of period (in shares)	42,458	42,473	40,616
Shares paid or expired (in shares)	(14,336)	(14,070)	(13,715)
New grants (in shares)	13,475	14,055	15,600
Forfeitures and cancellations (in shares)	(769)	0	(28)
Expense recognized (in shares)	0	0	0
End of period (in shares)	40,828	42,458	42,473
Accrued Expense
Beginning of period	$ 56.3	$ 43.7	$ 31.7
Shares paid or expired	(35.2)	(27.7)	(18.1)
New grants	0.0	0.0	0.0
Forfeitures and cancellations	0.4	(0.4)	(0.1)
Expense recognized	20.7	40.7	30.2
End of period	$ 42.2	$ 56.3	$ 43.7
Range Of Performance Cycle From 2018 to 2020 | W T M Incentive and Phantom Plan
Accrued Expense
Payout for maximum growth target percentage	200.00%
Range Of Performance Cycle From 2017 to 2019 | W T M Incentive and Phantom Plan
Accrued Expense
Payout for maximum growth target percentage		180.00%
Payout for minimum growth target percentage		174.00%
Range Of Performance Cycle From 2016-2018 | W T M Incentive and Phantom Plan
Accrued Expense
Payout for maximum growth target percentage			166.00%
Payout for minimum growth target percentage			139.00%