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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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Borrowings - Additional Information (Details)	1 Months Ended		12 Months Ended
Borrowings - Additional Information (Details)	Aug. 31, 2020 USD ($)	Jul. 31, 2020 USD ($) ApartmentUnit	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage			3.60%
Commercial Paper Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Payment Terms			397
Debt Instrument, Face Amount			$ 172,000,000.0
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			Dec. 31, 2042
Debt Instrument, Interest Rate, Effective Percentage			4.60%
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate			$ 488,700,000
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage			3.50%
Unsecured Debt [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date			Jan. 27, 2027
Debt Instrument, Face Amount			$ 3,922,000,000	$ 3,472,000,000
Debt Instrument, Interest Rate, Effective Percentage			3.60%
Unsecured Debt [Member] \| Years to Maturity [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Term			6 years 1 month 6 days
Unsecured Debt [Member] \| Minimum [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Term			10 years
Unsecured Debt [Member] \| Maximum [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Term			12 years
Unsecured Debt [Member] \| $1 Billion Unsecured Revolving Credit Faciltiy [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity			$ 1,000,000,000.0
Line of Credit Facility, Maximum Borrowing Capacity			$ 1,500,000,000
Debt Instrument, Maturity Date			May 31, 2023
Line of Credit Facility, Amount Outstanding			$ 0
Letters of Credit Outstanding, Amount			$ 3,400,000
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			$ 3,700,000,000
Unsecured Debt [Member] \| Private Placement [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount			222,000,000.0
Unsecured Debt [Member] \| Private Placement [Member] \| Fixed Rate Debt Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 222,000,000.0
Unsecured Debt [Member] \| 1.700% Notes Due 2031 [Member]
Debt Instrument [Line Items]
Debt Instrument, Payment Terms	Interest on the 2031 Notes is payable on February 15 and August 15 of each year, beginning on February 15, 2021.
Debt Instrument, Face Amount	$ 450,000,000.0
Debt Instrument, Interest Rate, Stated Percentage	1.70%
Debt Instrument, Interest Rate, Effective Percentage	1.76%
Debt Instrument, Redemption Price, Percentage	99.465%
Debt Issuance Costs, Gross	$ 5,300,000
Proceeds from Debt, Net of Issuance Costs	444,700,000
Unsecured Debt [Member] \| Wells Fargo Term Loan [Member]
Debt Instrument [Line Items]
Repayments of Unsecured Debt	$ 300,000,000.0
Maturing July 2020, Three Property Mortgage [Member] \| Secured Debt [Member]
Debt Instrument [Line Items]
Repayments of Secured Debt		$ 63,600,000
Number of Apartment Communities \| ApartmentUnit		3
Maturing July 2020, Four Property Mortgage [Member] \| Secured Debt [Member]
Debt Instrument [Line Items]
Repayments of Secured Debt		$ 72,200,000
Number of Apartment Communities \| ApartmentUnit		4