Debt - Additional Information (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
	Oct. 08, 2021	Sep. 21, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Amortization of financing costs			$ 0.5	$ 0.5	$ 1.5	$ 1.5
Long term debt			$ 3,190.4		3,190.4		$ 2,493.7
Debt instrument interest					$ 55.2	$ 56.9
Senior Notes | 3.05% Senior Notes, due October 2051
Debt Instrument [Line Items]
Debt instrument, face amount		$ 700.0
Stated interest rate		3.05%	3.05%		3.05%
Debt instrument, maturity date		Oct. 31, 2051			Oct. 31, 2051
Long term debt			$ 696.3		$ 696.3		$ 0.0
Payments of debt issuance costs		$ 7.6
Senior Notes | 4.50% Senior Notes, due November 2023
Debt Instrument [Line Items]
Debt instrument, face amount		$ 700.0
Stated interest rate		4.50%	4.50%		4.50%
Debt instrument, maturity date		Nov. 01, 2023
Senior Notes | Fixed-Rate Senior Notes
Debt Instrument [Line Items]
Book value of fixed rate debt			$ 3,190.4		$ 3,190.4
Long-term debt (fixed-rate debt), fair value			3,416.0		$ 3,416.0
Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, maturity date					Aug. 29, 2021
Debt instrument offering date					Jun. 08, 2021
Letter Of Credit
Debt Instrument [Line Items]
Long term debt			23.5		$ 23.5
Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, term					5 years
Long term debt			$ 350.0		$ 350.0
Subsequent Events | Senior Notes | 4.50% Senior Notes, due November 2023
Debt Instrument [Line Items]
Stated interest rate	4.50%
Write off amount of remaining balance of unamortized debt issuance costs	$ 1.4
Debt instrument, repurchase amount	769.8
Redemption premium	56.1
Accrued and unpaid interest	$ 13.7