Revolving Credit Facility and Commercial Paper Program (Details)	3 Months Ended
	Mar. 31, 2022 USD ($) extension currency	Mar. 31, 2021	Dec. 31, 2021 USD ($)
Credit facility
Credit facility origination costs	$ 3,661,000		$ 4,352,000
Maximum aggregate capacity of commercial paper program	1,000,000,000
Commercial paper borrowings outstanding	$ 950,000,000		901,400,000
Weighted average interest rate at the end of the period (as a percent)	0.80%
Revolving credit facility | Unsecured debt
Credit facility
Maximum borrowing capacity	$ 3,000,000,000
Number of extensions | extension	2
Term of extension option	6 months
Number of currencies allowable per facility | currency	14
Credit facility expansion option	$ 1,000,000,000
Credit facility origination costs	3,700,000		4,400,000
Current borrowing capacity	2,430,000,000		2,430,000,000
Outstanding balance	$ 569,600,000		$ 650,000,000
Weighted average borrowing rate during the period (as a percent)	1.10%	0.80%
Weighted average interest rate at the end of the period (as a percent)	1.20%
Revolving credit facility | Unsecured debt | LIBOR
Credit facility
Basis spread on variable rate (as a percent)	0.775%
Commitment fee (as a percent)	0.125%
All-in drawn variable interest rate (as a percent)	0.90%
Commercial paper
Credit facility
Weighted average borrowing rate during the period (as a percent)	0.50%	0.30%