Unsecured senior notes payable, LOC, and commercial paper (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Jul. 31, 2023	Sep. 22, 2022
Debt Instrument
Principal	$ 13,176,006
Debt Balance at 100%	13,090,834
Commercial Paper
Debt Instrument
Principal	$ 299,900
Commercial paper, maximum issuance				$ 2,500,000
Weighted-average yield to maturity, commercial paper	4.60%
Weighted-average remaining maturity term, commercial paper	13 days
Commercial Paper | Minimum
Debt Instrument
Debt Instrument, Term	30 days
Commercial Paper | Maximum
Debt Instrument
Debt Instrument, Term	397 days
5.50% Unsecured Senior Notes Payable
Debt Instrument
Principal	$ 550,000
Stated interest rate (as a percent)	5.50%
Debt Balance at 100%	$ 543,223
Unsecured senior line of credit
Debt Instrument
Line of Credit Facility, Maximum Borrowing Capacity	$ 5,000,000
Applicable margin (as a percent)	0.855%		0.875%
Annual facility fee (as a percent)	0.145%		0.15%
Interest rate adjustment amount, maximum					0.04%
Facility fee rate adjustment amount, maximum					0.01%
Interest rate adjustment amount, decrease		0.02%
Facility fee rate adjustment amount, decrease		0.005%
Debt Balance at 100%	$ 0
Unsecured senior line of credit | Commercial Paper
Debt Instrument
Principal	300,000
Debt Balance at 100%	$ 299,883