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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 |  |

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