Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2023	Mar. 08, 2023	Dec. 31, 2022
Long-Term Debt
Long-term debt principal	$ 3,958.7		$ 4,022.7
Net unamortized discount, premium and debt issuance costs	(28.5)		(25.7)
Long-term debt carrying amount	$ 3,930.2		3,997.0
Senior notes
Long-Term Debt
Long-term debt issued		$ 700.0
3.125% notes payable, due 2023
Long-Term Debt
Long-term debt principal			300.0
Net unamortized discount, premium and debt issuance costs			(0.1)
Long-term debt carrying amount			$ 299.9
Interest rate (as a percent)	3.125%		3.125%
3.4% notes payable, due 2025
Long-Term Debt
Long-term debt principal	$ 400.0		$ 400.0
Net unamortized discount, premium and debt issuance costs	(0.8)		(1.2)
Long-term debt carrying amount	$ 399.2		$ 398.8
Interest rate (as a percent)	3.40%		3.40%
3.1% notes payable, due 2026
Long-Term Debt
Long-term debt principal	$ 350.0		$ 350.0
Net unamortized discount, premium and debt issuance costs	(1.2)		(1.4)
Long-term debt carrying amount	$ 348.8		$ 348.6
Interest rate (as a percent)	3.10%		3.10%
3.7% notes payable, due 2029
Long-Term Debt
Long-term debt principal	$ 500.0		$ 500.0
Net unamortized discount, premium and debt issuance costs	(4.0)		(4.3)
Long-term debt carrying amount	$ 496.0		$ 495.7
Interest rate (as a percent)	3.70%		3.70%
2.125% notes payable, due 2030
Long-Term Debt
Long-term debt principal	$ 600.0		$ 600.0
Net unamortized discount, premium and debt issuance costs	(3.3)		(3.6)
Long-term debt carrying amount	$ 596.7		$ 596.4
Interest rate (as a percent)	2.125%		2.125%
5.375% notes payable, due 2033
Long-Term Debt
Long-term debt principal	$ 400.0
Net unamortized discount, premium and debt issuance costs	(3.9)
Long-term debt carrying amount	$ 396.1
Interest rate (as a percent)	5.375%
5.375% notes payable, due 2033 | Senior notes
Long-Term Debt
Long-term debt issued		$ 400.0
Interest rate (as a percent)		5.375%
6.05% notes payable, due 2036
Long-Term Debt
Long-term debt principal	$ 505.6		$ 505.6
Net unamortized discount, premium and debt issuance costs	(2.2)		(2.3)
Long-term debt carrying amount	$ 503.4		$ 503.3
Interest rate (as a percent)	6.05%		6.05%
4.625% notes payable, due 2042
Long-Term Debt
Long-term debt principal	$ 300.0		$ 300.0
Net unamortized discount, premium and debt issuance costs	(2.8)		(2.9)
Long-term debt carrying amount	$ 297.2		$ 297.1
Interest rate (as a percent)	4.625%		4.625%
4.35% notes payable, due 2043
Long-Term Debt
Long-term debt principal	$ 300.0		$ 300.0
Net unamortized discount, premium and debt issuance costs	(2.9)		(3.0)
Long-term debt carrying amount	$ 297.1		$ 297.0
Interest rate (as a percent)	4.35%		4.35%
4.3% notes payable, due 2046
Long-Term Debt
Long-term debt principal	$ 300.0		$ 300.0
Net unamortized discount, premium and debt issuance costs	(3.0)		(3.1)
Long-term debt carrying amount	$ 297.0		$ 296.9
Interest rate (as a percent)	4.30%		4.30%
5.5% notes payable, due 2053
Long-Term Debt
Long-term debt principal	$ 300.0
Net unamortized discount, premium and debt issuance costs	(4.3)
Long-term debt carrying amount	$ 295.7
Interest rate (as a percent)	5.50%
5.5% notes payable, due 2053 | Senior notes
Long-Term Debt
Long-term debt issued		$ 300.0
Interest rate (as a percent)		5.50%
Floating rate notes payable, due 2055
Long-Term Debt
Long-term debt principal			$ 400.0
Net unamortized discount, premium and debt issuance costs			(4.5)
Long-term debt carrying amount			395.5
Mortgages and notes payable | Non-recourse
Long-Term Debt
Long-term debt principal	$ 3.1		67.1
Net unamortized discount, premium and debt issuance costs	(0.1)		0.7
Long-term debt carrying amount	$ 3.0		$ 67.8