Debt instrument maturity period.

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Debt instrument maturity year.

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Number of apartment communities.

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Number of term loans.

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Settlement of Forward Swaps

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Percentage points added to the reference rate to compute the variable rate on the 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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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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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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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No definition available.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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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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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the 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 inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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Cash inflow associated with loan origination (the process when securing a mortgage for a piece of real property) or lease origination.

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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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The cash outflow to repay long-term debt that is not secured by collateral. Excludes repayments of tax exempt unsecured debt.

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Borrowings - Additional Information (Details)	1 Months Ended					12 Months Ended
Borrowings - Additional Information (Details)	Nov. 30, 2019 USD ($)	Aug. 31, 2019 USD ($)	May 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) Loan ApartmentUnit	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage						3.80%
Commercial Paper Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Payment Terms						397 days
Debt Instrument, Face Amount						$ 70,000,000.0
Debt Instrument, Interest Rate, Effective Percentage						2.05%
Debt Instrument, Term						8 days
Maximum [Member] \| Commercial Paper Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 500,000,000.0
Secured Debt [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date						Apr. 02, 2037
Debt Instrument, Interest Rate, Effective Percentage						4.50%
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate						$ 629,800,000
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage						3.70%
Unsecured Debt [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date						Jul. 19, 2026
Debt Instrument, Face Amount						$ 3,472,000,000	$ 2,642,000,000
Debt Instrument, Interest Rate, Effective Percentage						3.90%
Unsecured Debt [Member] \| Years To Maturity [Member] \| Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Term						6 years 7 months 6 days
Unsecured Debt [Member] \| Minimum [Member] \| Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Term						10 years
Unsecured Debt [Member] \| Maximum [Member] \| Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Term						12 years
Unsecured Debt [Member] \| $1 billion unsecured revolving credit facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity						$ 1,000,000,000.0
Debt Instrument, Basis Spread on Variable Rate						1.45%
Debt Instrument, Maturity Date						May 31, 2023
Line of Credit Facility, Amount Outstanding						$ 0
Letters of Credit Outstanding, Amount						2,700,000
Unsecured Debt [Member] \| $1 billion unsecured revolving credit facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity						$ 1,500,000,000
Unsecured Debt [Member] \| $1 billion unsecured revolving credit facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.75%
Unsecured Debt [Member] \| Public Income Notes [Member] \| Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 3,300,000,000
Unsecured Debt [Member] \| Private Placement [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						222,000,000.0
Debt Instrument, Interest Rate, Stated Percentage	3.61%
Repayments of Unsecured Debt	$ 20,000,000.0
Unsecured Debt [Member] \| Private Placement [Member] \| Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						222,000,000.0
Unsecured Debt [Member] \| 3.95% Initial Notes Due 2029 [Member] \| M A A L P
Debt Instrument [Line Items]
Debt Instrument, Payment Terms				Interest on the Initial 2029 Notes is payable on March 15 and September 15 of each year, beginning on September 15, 2019.
Debt Instrument, Face Amount				$ 300,000,000.0
Debt Instrument, Interest Rate, Effective Percentage				4.24%
Debt Instrument, Term				10 years
Debt Instrument, Interest Rate, Stated Percentage				3.95%
Debt Instrument, Redemption Price, Percentage				99.72%
Debt Issuance Costs, Gross				$ 2,800,000
Proceeds from Debt, Net of Issuance Costs				297,200,000
Settlement of Forward Swaps				$ 300,000,000.0
Unsecured Debt [Member] \| 3.95% Additional Notes due 2029 [Member] \| M A A L P
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 250,000,000.0
Debt Instrument, Interest Rate, Effective Percentage		2.985%
Debt Instrument, Interest Rate, Stated Percentage		3.95%
Debt Instrument, Redemption Price, Percentage		107.827%
Debt Issuance Costs, Gross		$ 22,100,000
Proceeds from Debt, Net of Issuance Costs		272,100,000
Unsecured Debt [Member] \| 2.75% Notes due 2030 [Member]
Debt Instrument [Line Items]
Debt Instrument, Payment Terms	Interest on the 2030 Notes is payable on March 15 and September 15 of each year, beginning on March 15, 2020.
Debt Instrument, Face Amount	$ 300,000,000.0
Debt Instrument, Interest Rate, Effective Percentage	3.065%
Debt Instrument, Term	10 years
Debt Instrument, Interest Rate, Stated Percentage	2.75%
Debt Instrument, Redemption Price, Percentage	99.762%
Debt Issuance Costs, Gross	$ 2,700,000
Proceeds from Debt, Net of Issuance Costs	297,300,000
Settlement of Forward Swaps	150,000,000.0
Unsecured Debt [Member] \| Wells Fargo Term Loan
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 300,000,000.0
Debt Instrument, Interest Rate, Stated Percentage						2.32%
Repayments of Unsecured Debt			$ 300,000,000.0
Number of Term Loans \| Loan						1
Debt Instrument Maturity Year						2022
Debt Instrument Maturity Period						2020-01
Unsecured Debt [Member] \| Wells Fargo Term Loan \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.90%
Unsecured Debt [Member] \| Wells Fargo Term Loan \| Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						1.75%
Unsecured Debt [Member] \| Key Bank Term Loan
Debt Instrument [Line Items]
Repayments of Unsecured Debt	$ 150,000.0
Unsecured Debt [Member] \| U S Bank Term Loan [Member]
Debt Instrument [Line Items]
Repayments of Unsecured Debt		150,000,000.0
Mortgage maturing in February 2049 [Member] \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage						4.43%
Proceeds from Loan Originations						$ 191,300,000
Number of apartment communities \| ApartmentUnit						7
Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage						4.50%
Secured Debt [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date						Apr. 02, 2037
Debt Instrument, Interest Rate, Effective Percentage						4.50%
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate						$ 629,817,000	$ 476,161,000
Secured Debt [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Repayments of Secured Debt		$ 13,200,000			$ 17,200,000