Debt - Components of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 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	(27.8)	(25.7)
Long-term debt carrying amount	$ 3,930.9	$ 3,997.0
3.125% notes payable, due 2023
Long-Term Debt
Interest rate (as a percent)		3.125%
Long-term debt principal		$ 300.0
Net unamortized discount, premium and debt issuance costs		(0.1)
Long-term debt carrying amount		$ 299.9
3.4% notes payable, due 2025
Long-Term Debt
Interest rate (as a percent)	3.40%	3.40%
Long-term debt principal	$ 400.0	$ 400.0
Net unamortized discount, premium and debt issuance costs	(0.7)	(1.2)
Long-term debt carrying amount	$ 399.3	$ 398.8
3.1% notes payable, due 2026
Long-Term Debt
Interest rate (as a percent)	3.10%	3.10%
Long-term debt principal	$ 350.0	$ 350.0
Net unamortized discount, premium and debt issuance costs	(1.1)	(1.4)
Long-term debt carrying amount	$ 348.9	$ 348.6
3.7% notes payable, due 2029
Long-Term Debt
Interest rate (as a percent)	3.70%	3.70%
Long-term debt principal	$ 500.0	$ 500.0
Net unamortized discount, premium and debt issuance costs	(3.8)	(4.3)
Long-term debt carrying amount	$ 496.2	$ 495.7
2.125% notes payable, due 2030
Long-Term Debt
Interest rate (as a percent)	2.125%	2.125%
Long-term debt principal	$ 600.0	$ 600.0
Net unamortized discount, premium and debt issuance costs	(3.2)	(3.6)
Long-term debt carrying amount	$ 596.8	$ 596.4
5.375% notes payable, due 2033
Long-Term Debt
Interest rate (as a percent)	5.375%
Long-term debt principal	$ 400.0
Net unamortized discount, premium and debt issuance costs	(3.8)
Long-term debt carrying amount	$ 396.2
6.05% notes payable, due 2036
Long-Term Debt
Interest rate (as a percent)	6.05%	6.05%
Long-term debt principal	$ 505.6	$ 505.6
Net unamortized discount, premium and debt issuance costs	(2.1)	(2.3)
Long-term debt carrying amount	$ 503.5	$ 503.3
4.625% notes payable, due 2042
Long-Term Debt
Interest rate (as a percent)	4.625%	4.625%
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
4.35% notes payable, due 2043
Long-Term Debt
Interest rate (as a percent)	4.35%	4.35%
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
4.3% notes payable, due 2046
Long-Term Debt
Interest rate (as a percent)	4.30%	4.30%
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
5.5% notes payable, due 2053
Long-Term Debt
Interest rate (as a percent)	5.50%
Long-term debt principal	$ 300.0
Net unamortized discount, premium and debt issuance costs	(4.3)
Long-term debt carrying amount	295.7
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