Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount of assets pledged to secure a debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in remainder of current fiscal year.

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Senior Unsecured Notes and Secured Debt - Annual Principal Payments Due on Debt Obligations (Details)	6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2021 CAD ($)	Jun. 30, 2021 GBP (£)	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Annual principal payments due
2021	$ 253,459,000
2022	496,699,000
2023	1,190,934,000
2024	1,535,318,000
2025	1,431,449,000
Thereafter	8,656,254,000
Totals	13,564,113,000
Senior unsecured notes
Annual principal payments due
2021	0
2022	10,000,000
2023	701,525,000
2024	1,350,000,000
2025	1,250,000,000
Thereafter	7,941,460,000
Totals	$ 11,252,985,000			$ 11,509,533,000	$ 11,912,711,000	$ 10,427,562,000
Senior unsecured notes \| Minimum
Annual principal payments due
Interest rate	0.79%	0.79%	0.79%
Senior unsecured notes \| Maximum
Annual principal payments due
Interest rate	6.50%	6.50%	6.50%
Senior unsecured notes \| Canadian-denominated unsecured term credit facility
Annual principal payments due
Face amount	$ 201,525,000	$ 250,000,000
Senior unsecured notes \| Canadian-denominated unsecured term credit facility \| Canadian dealer offered rate
Annual principal payments due
Interest rate margin	0.90%
Effective rate	1.31%	1.31%	1.31%
Senior unsecured notes \| Unsecured term credit facility
Annual principal payments due
Face amount	$ 500,000,000
Senior unsecured notes \| Unsecured term credit facility \| LIBOR
Annual principal payments due
Interest rate margin	0.90%
Effective rate	1.00%	1.00%	1.00%
Senior unsecured notes \| 2.95% Senior unsecured notes due 2023
Annual principal payments due
Interest rate	2.95%	2.95%	2.95%
Face amount	$ 241,830,000	$ 300,000,000
Senior unsecured notes \| Senior unsecured notes due 2028
Annual principal payments due
Interest rate	4.80%	4.80%	4.80%
Face amount	$ 759,330,000		£ 550,000,000
Senior unsecured notes \| 4.50% Senior unsecured notes due 2034
Annual principal payments due
Interest rate	4.50%	4.50%	4.50%
Face amount	$ 690,300,000		£ 500,000,000
Secured debt
Annual principal payments due
2021	253,459,000
2022	486,699,000
2023	489,409,000
2024	185,318,000
2025	181,449,000
Thereafter	714,794,000
Totals	2,311,128,000			$ 2,378,073,000	$ 2,627,989,000	$ 2,993,342,000
Carrying values of properties securing the debt	$ 5,312,000,000
Secured debt \| Minimum
Annual principal payments due
Interest rate	0.03%	0.03%	0.03%
Secured debt \| Maximum
Annual principal payments due
Interest rate	7.93%	7.93%	7.93%