Summary of secured and unsecured debt (Details) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)
Debt Instrument
Long-term Debt	$ 8,513,609	$ 8,513,609
Long-term Debt, Percentage Bearing Variable Interest, Amount, Net	749,978	749,978
Total Consolidated	$ 9,263,587	$ 9,263,587
Percentage of Total	100.00%	100.00%
Interest Rate	3.27%	3.27%
Weighted Average Remaining Terms (in years)		11 years 10 months 24 days
Percentage of fixed rate/hedged total debt	92.00%	92.00%
Percentage of unhedged floating rate total debt	8.00%	8.00%
Commercial Paper
Debt Instrument
Percentage of Total	8.10%	8.10%
Weighted Average Remaining Terms (in years)		9 days
Short-term debt, Percentage Bearing Fixed Interest, Amount, Net	$ 0	$ 0
Short-term Debt, Percentage Bearing Variable Interest, Amount, Net	749,978	749,978
Commercial Paper Program	$ 749,978	$ 749,978
Weighted-average yield to maturity, commercial paper	0.21%
Commercial Paper \| Maximum
Debt Instrument
Number of maturity days from date of issuance		397
Secured notes payable
Debt Instrument
Long-term Debt	$ 198,758	$ 198,758
Long-term Debt, Percentage Bearing Variable Interest, Amount, Net	0	0
Total Consolidated	$ 198,758	$ 198,758
Percentage of Total	2.10%	2.10%
Interest Rate	3.41%	3.41%
Weighted Average Remaining Terms (in years)		2 years 4 months 24 days
Unsecured senior notes payable
Debt Instrument
Long-term Debt	$ 8,314,851	$ 8,314,851
Long-term Debt, Percentage Bearing Variable Interest, Amount, Net	0	0
Total Consolidated	$ 8,314,851	$ 8,314,851
Percentage of Total	89.80%	89.80%
Interest Rate	3.54%	3.54%
Weighted Average Remaining Terms (in years)		12 years 9 months 18 days
Unsecured senior lines of credit
Debt Instrument
Long-term Debt	$ 0	$ 0
Long-term Debt, Percentage Bearing Variable Interest, Amount, Net	0	0
Total Consolidated	$ 0	$ 0
Percentage of Total	0.00%	0.00%
Weighted Average Remaining Terms (in years)		4 years 3 months 18 days
Unsecured senior lines of credit \| London Interbank Offered Rate (LIBOR)
Debt Instrument
Applicable margin (as a percent)		0.815%

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Short-term debt, Percentage Bearing Fixed Interest, Amount, Net

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Represents the outstanding balance of variable interest rate debt as a percentage of aggregate debt outstanding.

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Weighted-average yield to maturity, commercial paper

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Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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

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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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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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