Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective income tax reconciliation, amount
Income Tax Expense at U.S. Statutory Rate	$ (74.2)	$ (73.1)	$ (88.5)
U.S. State and Local Tax Expense	(0.9)	(1.5)	(8.7)
Permanent Items	(1.0)	(8.1)	(2.7)
Income Taxed at Corporate Partners	65.4	71.3	0.0
U.S. Tax Reform	0.0	0.0	158.5
Change in Valuation Allowance due to Tax Reform	0.0	0.0	(2.0)
Change in Valuation Allowance	(5.6)	2.9	(3.5)
Change in Valuation Allowance due to Tax Status	0.0	0.0	20.3
International Tax Rate Differences	(1.6)	(1.9)	3.2
Foreign Withholding Tax	(0.7)	(0.5)	(0.4)
Change in Tax Rates	(0.7)	(0.5)	(3.0)
US Federal and State Tax Credits	0.0	0.0	10.2
Uncertain Tax Positions	(0.1)	0.0	(0.3)
Change in Tax Status	0.0	0.0	235.4
Other	(1.0)	(0.4)	3.2
Income Tax (Expense) Benefit	$ (20.4)	$ (11.8)	$ 321.7
Effective income tax reconciliation, percent
Income Tax Expense at U.S. Statutory Rate	21.00%	21.00%	35.00%
U.S. State and Local Tax Expense	0.20%	0.50%	3.40%
Permanent Items	0.30%	2.30%	1.00%
Income Taxed at Corporate Partners	(18.50%)	(20.50%)	0.00%
U.S. Tax Reform	0.00%	0.00%	(62.70%)
Change in Valuation Allowance due to Tax Reform	0.00%	0.00%	0.80%
Change in Valuation Allowance	1.50%	(0.80%)	1.40%
Change in Valuation Allowance due to Tax Status	0.00%	0.00%	(8.00%)
International Tax Rate Differences	0.50%	0.50%	(1.30%)
Foreign Withholding Tax	0.20%	0.20%	0.20%
Change in Tax Rates	0.20%	0.10%	1.20%
US Federal and State Tax Credits	0.00%	0.00%	(4.00%)
Uncertain Tax Positions	0.10%	0.00%	0.10%
Change in Tax Status	0.00%	0.00%	(93.00%)
Other	0.30%	0.10%	(1.30%)
Income Tax Benefit (Expense), percent	5.80%	3.40%	(127.20%)