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

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- Definition

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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- Definition

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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- Definition

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 requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Senior Unsecured Notes and Secured Debt - Annual Principal Payments Due on Debt Obligations (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2019 GBP (£)	Mar. 31, 2019 CAD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Totals
2019	$ 384,466,000
2020	373,020,000
2021	826,808,000
2022	883,452,000
2023	2,115,637,000
Thereafter	7,827,112,000
Totals	12,410,495,000
Senior Unsecured Notes
Totals
2019	0
2020	232,051,000
2021	450,000,000
2022	600,000,000
2023	1,787,126,000
Thereafter	6,668,360,000
Totals	$ 9,737,537,000			$ 9,699,984,000	$ 8,006,989,000	$ 8,417,447,000
Senior Unsecured Notes \| Minimum
Totals
Interest rate	2.88%	2.88%	2.88%
Senior Unsecured Notes \| Maximum
Totals
Interest rate	6.50%	6.50%	6.50%
Senior Unsecured Notes \| Canadian-denominated 3.35% senior unsecured notes due 2020
Totals
Interest rate	3.35%	3.35%	3.35%
Face amount	$ 224,551,000		$ 300,000,000
Senior Unsecured Notes \| Canadian-denominated unsecured term credit facility
Totals
Face amount	$ 187,126,000		$ 250,000,000
Senior Unsecured Notes \| Canadian-denominated unsecured term credit facility \| Canadian Dealer Offered Rate
Totals
Debt instrument, basis spread on variable rate	0.90%
Interest rate at period end	2.88%	2.88%	2.88%
Senior Unsecured Notes \| Unsecured term credit facility
Totals
Face amount	$ 500,000,000
Senior Unsecured Notes \| Unsecured term credit facility \| LIBOR
Totals
Debt instrument, basis spread on variable rate	0.90%
Interest rate at period end	3.38%	3.38%	3.38%
Senior Unsecured Notes \| Senior unsecured notes due 2028
Totals
Interest rate	4.80%	4.80%	4.80%
Face amount	$ 716,760,000	£ 550,000,000
Senior Unsecured Notes \| Senior unsecured notes due 2034
Totals
Interest rate	4.50%	4.50%	4.50%
Face amount	$ 651,600,000	£ 500,000,000
Secured debt
Totals
2019	384,466,000
2020	140,969,000
2021	376,808,000
2022	283,452,000
2023	328,511,000
Thereafter	1,158,752,000
Totals	2,672,958,000			$ 2,485,711,000	$ 2,498,395,000	$ 2,618,408,000
Carrying values of properties securing the debt	$ 5,892,563,000
Secured debt \| Minimum
Totals
Interest rate	1.69%	1.69%	1.69%
Secured debt \| Maximum
Totals
Interest rate	12.00%	12.00%	12.00%