CONSOLIDATED STATEMENTS OF CHANGES IN CAPITAL OF ERP OPERATING LIMITED PARTNERSHIP (Unaudited) - USD ($) $ in Thousands	Total	ERPOP [Member]	PREFERRED SHARES ERPOP [Member]	General Partner [Member] ERPOP [Member]	Limited Partner ERPOP [Member]	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) ERPOP [Member]	DISTRIBUTIONS [Member] ERPOP [Member]	PARTIALLY OWNED PROPERTIES [Member] ERPOP [Member]
Balance, beginning of year at Dec. 31, 2019			$ 37,280	$ 10,355,789	$ 227,837	$ (77,563)
Balance, beginning of year at Dec. 31, 2019								$ 1,183
Conversion of OP Units held by Limited Partners into OP Units held by General Partner				3,913	(3,913)
Exercise of EQR share options				11,426
EQR's Employee Share Purchase Plan (ESPP)				3,556
EQR restricted shares				9,238	12
EQR share options				1,819
EQR ESPP discount				626
Net income available to Units - General Partner		$ 658,462		658,462
OP Units General Partner distributions				(673,019)
Supplemental Executive Retirement Plan (SERP)				(395)
Change in market value of Redeemable Limited Partners				169,825
Adjustment for Limited Partners ownership in Operating Partnership				438	(438)
Equity compensation associated with Units - Limited Partners					9,525
Net income available to Units - Limited Partners		24,624			24,624
Units - Limited Partners distributions					(25,000)
Change in carrying value of Redeemable Limited Partners					(131)
Unrealized holding (losses) arising during the period	$ 14,113	14,113				(1,190)
Losses reclassified into earnings from other comprehensive income	(17,275)	(17,275)				17,275
Distributions declared per Unit outstanding							$ 1.8075
Net income attributable to Noncontrolling Interests	699,517	699,517						14,113
Contributions by Noncontrolling Interests								417
Distributions to Noncontrolling Interests								(11,343)
Balance, end of period at Sep. 30, 2020			37,280	10,541,678	232,516	(61,478)
Balance, end of period at Sep. 30, 2020								4,370
Balance, beginning of year at Jun. 30, 2020			37,280	10,627,748	235,169	(67,355)
Balance, beginning of year at Jun. 30, 2020								4,634
Conversion of OP Units held by Limited Partners into OP Units held by General Partner				57	(57)
Exercise of EQR share options				104
EQR's Employee Share Purchase Plan (ESPP)				1,197
EQR restricted shares				1,984
EQR share options				526
EQR ESPP discount				210
Net income available to Units - General Partner		90,513		90,513
OP Units General Partner distributions				(224,269)
Supplemental Executive Retirement Plan (SERP)				111
Change in market value of Redeemable Limited Partners				41,072
Adjustment for Limited Partners ownership in Operating Partnership				2,425	(2,425)
Equity compensation associated with Units - Limited Partners					2,499
Net income available to Units - Limited Partners		3,376			3,376
Units - Limited Partners distributions					(7,963)
Change in carrying value of Redeemable Limited Partners					1,917
Unrealized holding (losses) arising during the period	703	703
Losses reclassified into earnings from other comprehensive income	(5,877)	(5,877)				5,877
Distributions declared per Unit outstanding							0.6025
Net income attributable to Noncontrolling Interests	95,365	95,365						703
Contributions by Noncontrolling Interests								76
Distributions to Noncontrolling Interests								(1,043)
Balance, end of period at Sep. 30, 2020			37,280	10,541,678	232,516	(61,478)
Balance, end of period at Sep. 30, 2020								4,370
Balance, beginning of year at Dec. 31, 2020			37,280	10,532,037	233,162	(43,666)
Balance, beginning of year at Dec. 31, 2020								4,673
Conversion of OP Units held by Limited Partners into OP Units held by General Partner				68,257	(68,257)
Exercise of EQR share options				68,807
EQR's Employee Share Purchase Plan (ESPP)				3,455
EQR restricted shares				6,572
EQR share options				2,541
EQR ESPP discount				798
Net income available to Units - General Partner		803,558		803,558
OP Units General Partner distributions				(676,158)
Offering costs				(267)
Supplemental Executive Retirement Plan (SERP)				(1,335)
Change in market value of Redeemable Limited Partners				(119,237)
Adjustment for Limited Partners ownership in Operating Partnership				(27,085)	27,085
Equity compensation associated with Units - Limited Partners					14,173
Net income available to Units - Limited Partners		27,903			27,903
Units - Limited Partners distributions					(23,366)
Change in carrying value of Redeemable Limited Partners					(1,745)
Unrealized holding (losses) arising during the period	1,957	1,957
Losses reclassified into earnings from other comprehensive income	(7,000)	(7,000)				7,000
Distributions declared per Unit outstanding							1.8075
Net income attributable to Noncontrolling Interests	835,736	835,736						1,957
Distributions to Noncontrolling Interests								(4,492)
Balance, end of period at Sep. 30, 2021			37,280	10,661,943	208,955	(36,666)
Balance, end of period at Sep. 30, 2021								2,138
Balance, beginning of year at Jun. 30, 2021			37,280	10,435,740	205,691	(39,029)
Balance, beginning of year at Jun. 30, 2021								2,365
Conversion of OP Units held by Limited Partners into OP Units held by General Partner				1,597	(1,597)
Exercise of EQR share options				29,184
EQR's Employee Share Purchase Plan (ESPP)				788
EQR restricted shares				1,758
EQR share options				565
EQR ESPP discount				165
Net income available to Units - General Partner		431,178		431,178
OP Units General Partner distributions				(225,938)
Offering costs				(267)
Supplemental Executive Retirement Plan (SERP)				722
Change in market value of Redeemable Limited Partners				(17,271)
Adjustment for Limited Partners ownership in Operating Partnership				3,722	(3,722)
Equity compensation associated with Units - Limited Partners					3,642
Net income available to Units - Limited Partners		14,847			14,847
Units - Limited Partners distributions					(7,367)
Change in carrying value of Redeemable Limited Partners					(2,539)
Unrealized holding (losses) arising during the period	534	534
Losses reclassified into earnings from other comprehensive income	(2,363)	(2,363)				2,363
Distributions declared per Unit outstanding							$ 0.6025
Net income attributable to Noncontrolling Interests	$ 447,332	$ 447,332						534
Distributions to Noncontrolling Interests								(761)
Balance, end of period at Sep. 30, 2021			$ 37,280	$ 10,661,943	$ 208,955	$ (36,666)
Balance, end of period at Sep. 30, 2021								$ 2,138