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

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Description of the payment terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

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The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

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Borrowings - Additional Information (Details) $ in Thousands	1 Months Ended				3 Months Ended	9 Months Ended
	Sep. 30, 2021 USD ($)	Aug. 31, 2021 USD ($)	Jul. 31, 2021 USD ($)	Feb. 28, 2021 USD ($) ApartmentUnit	Sep. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	3.40%				3.40%	3.40%
Commercial Paper Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Payment Terms						397
Debt Instrument, Face Amount	$ 25,000				$ 25,000	$ 25,000
Debt Instrument, Unused Borrowing Capacity, Amount	161,500				161,500	161,500
Maximum [Member] \| Commercial Paper Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500,000				$ 500,000	$ 500,000
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	3.30%				3.30%	3.30%
Unsecured Debt [Member] \| Other Non-operating (Income) Expense [Member]
Debt Instrument [Line Items]
Prepayment penalties and Write-offs of unamortized costs					$ 13,400
Unsecured Debt [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date						Mar. 04, 2029
Debt Instrument, Face Amount	$ 4,175,000				$ 4,175,000	$ 4,175,000
Debt Instrument, Interest Rate, Effective Percentage	3.30%				3.30%	3.30%
Unsecured Debt [Member] \| Years to Maturity [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Term						7 years 4 months 24 days
Unsecured Debt [Member] \| Minimum [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Term						5 years
Unsecured Debt [Member] \| Maximum [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Term						30 years
Unsecured Debt [Member] \| $1 Billion Unsecured Revolving Credit Faciltiy [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,000,000				$ 1,000,000	$ 1,000,000
Line of Credit Facility, Maximum Borrowing Capacity	1,500,000				1,500,000	$ 1,500,000
Debt Instrument, Maturity Date						May 31, 2023
Line of Credit Facility, Amount Outstanding	0				0	$ 0
Letters of Credit Outstanding, Amount	3,400				3,400	$ 3,400
Unsecured Debt [Member] \| $1 Billion Unsecured Revolving Credit Faciltiy [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.75%
Unsecured Debt [Member] \| $1 Billion Unsecured Revolving Credit Faciltiy [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						1.45%
Unsecured Debt [Member] \| Public Income Notes [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	4,200,000				4,200,000	$ 4,200,000
Unsecured Debt [Member] \| Private Placement [Member]
Debt Instrument [Line Items]
Retirement of tranche of Senior Unsecured Notes			$ 72,800
Unsecured Debt [Member] \| Maturing in September 2026, Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Payment Terms		Interest on the 2026 Notes is payable semi-annually in arrears on March 15 and September 15 of each year beginning March 15, 2022.
Debt Instrument, Interest Rate, Stated Percentage		1.10%
Debt Instrument, Redemption Price, Percentage		99.553%
Proceeds from Debt, Net of Issuance Costs		$ 296,900
Debt Issuance Costs, Gross		$ 3,100
Debt Instrument, Interest Rate, Effective Percentage		1.191%
Unsecured Debt [Member] \| Maturing in September 2026, Senior Notes [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 300,000
Unsecured Debt [Member] \| Maturing in November 2022, Trance of Senior Notes [Member]
Debt Instrument [Line Items]
Retirement of tranche of Senior Unsecured Notes	117,000
Unsecured Debt [Member] \| Maturing in December 2022, Tranche of Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	250,000				$ 250,000	$ 250,000
Retirement of tranche of Senior Unsecured Notes	125,000
Unsecured Debt [Member] \| Maturing in July 2023, Tranche of Senior Notes [Member]
Debt Instrument [Line Items]
Retirement of tranche of Senior Unsecured Notes	12,300
Unsecured Debt [Member] \| Maturing in December 2024, Tranche of Senior Notes [Member]
Debt Instrument [Line Items]
Retirement of tranche of Senior Unsecured Notes	$ 20,000
Unsecured Debt [Member] \| Maturing in September 2051, Six Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Payment Terms		Interest on the 2051 Notes is payable semi-annually in arrears on March 15 and September 15 of each year beginning March 15, 2022.
Debt Instrument, Face Amount		$ 300,000
Debt Instrument, Interest Rate, Stated Percentage		2.875%
Debt Instrument, Redemption Price, Percentage		98.588%
Proceeds from Debt, Net of Issuance Costs		$ 293,100
Debt Issuance Costs, Gross		$ 6,900
Debt Instrument, Interest Rate, Effective Percentage		2.946%
Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	4.40%				4.40%	4.40%
Secured Debt [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date						Dec. 31, 2048
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate	$ 368,900				$ 368,900	$ 368,900
Debt Instrument, Interest Rate, Effective Percentage	4.40%				4.40%	4.40%
Secured Debt [Member] \| Maturing July 2020, Three Property Mortgage [Member]
Debt Instrument [Line Items]
Repayments of Secured Debt				$ 118,600
Number of Apartment Communities \| ApartmentUnit				8