Fair Value Measurements - Fair Value of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Nov. 08, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Public bonds	$ 2,913.5	$ 2,924.9	$ 2,300.0
Public bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Public bonds	2,847.2	3,031.1
Private placement note | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value (excluding premium)	162.6	177.5
Reported Value Measurement | Public bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Public bonds	2,760.0	2,760.0
Reported Value Measurement | Private placement note | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value (excluding premium)	$ 153.5	$ 164.9