Employee Incentive Plans - Amounts Recognized in Consolidated Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Allocation
Compensation expense	$ 8.4	$ 12.1	$ 24.6	$ 31.2
Amount of related income tax benefit recognized in net income (loss)	2.0	2.8	5.8	7.2
Restricted units
Allocation
Amount of related income tax benefit recognized in net income (loss)	(1.6)	(1.3)	(6.0)	(1.3)
Cost of unit-based compensation charged to operating expense
Allocation
Compensation expense	2.0	2.1	6.2	4.5
Cost of unit-based compensation charged to general and administrative expense
Allocation
Compensation expense	6.4	10.0	18.4	26.7
Non-controlling interest in unit-based compensation
Allocation
Compensation expense	$ 0.0	$ 0.0	$ 0.0	$ 0.5