Debt - Non-Recourse Mortgages and Notes Payable (Details) - Non-recourse mortgages and notes payable - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Long-Term Debt
Outstanding principal balances per real estate development, low end of range	$ 3.1	$ 3.7
Outstanding principal balances per real estate development, high end of range	15.1	64.2
Real estate	$ 194.1	$ 238.2
Minimum
Long-Term Debt
Interest rate (as a percent)	3.50%	3.90%
Maximum
Long-Term Debt
Interest rate (as a percent)	4.80%	4.80%