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Borrowings - Additional Information (Details) | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
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 |  |

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