Real Estate Real Estate Values (Details) (USD $)	3 Months Ended		39 Months Ended											3 Months Ended			39 Months Ended			3 Months Ended		3 Months Ended			3 Months Ended	9 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Projects under development [Member]	Dec. 31, 2012 Projects under development [Member]	Mar. 31, 2013 Land held for development [Member]	Dec. 31, 2012 Land held for development [Member]	Mar. 31, 2013 2014 [Member]	Mar. 31, 2013 2015 [Member]	Mar. 31, 2013 2016 [Member]	Mar. 31, 2013 2017 [Member]	Mar. 31, 2013 2018 [Member]	Mar. 31, 2013 Investment Banking and Legal/Accounting Fees [Member]	Mar. 31, 2013 Archstone [Member]	Mar. 31, 2012 Archstone [Member]	Mar. 31, 2013 Archstone [Member]	Mar. 31, 2013 Building and Building Improvements [Member]	Mar. 31, 2013 Furniture and Fixtures [Member]	Mar. 31, 2013 Archstone Transaction [Member]	May 09, 2013 Archstone Transaction [Member]	Mar. 31, 2013 OPERATING PARTNERSHIP	Mar. 31, 2012 OPERATING PARTNERSHIP	Dec. 31, 2012 OPERATING PARTNERSHIP	Mar. 31, 2013 Archstone Transaction [Member]	Sep. 30, 2012 Land Parcel [Member]
Land	$ 6,319,353,000		$ 6,319,353,000	$ 4,554,912,000																		$ 6,319,353,000		$ 4,554,912,000
Property, Plant and Equipment, Gross [Abstract]
Investment Building and Building Improvements	18,222,448,000		18,222,448,000	14,135,740,000
Fixtures and Equipment, Gross	1,234,836,000		1,234,836,000	1,343,765,000
Finite-Lived Intangible Assets, Gross	508,951,000		508,951,000	232,439,000
Land Under Development					224,562,000	210,632,000
Projects under development	500,829,000		500,829,000	387,750,000	276,267,000	177,118,000	49,941,000	58,955,000														500,829,000		387,750,000
Land held for development	577,676,000		577,676,000	353,823,000			527,735,000	294,868,000														577,676,000		353,823,000
Investment in real estate	27,364,093,000		27,364,093,000	21,008,429,000																		27,364,093,000		21,008,429,000
Real Estate Investment Property, Accumulated Depreciation	(4,434,775,000)		(4,434,775,000)	(4,912,221,000)																		(4,434,775,000)		(4,912,221,000)
Real Estate Investment Property, Net	22,929,318,000		22,929,318,000	16,096,208,000																		22,929,318,000		16,096,208,000
Business Acquisition, Percentage of Voting Interests Acquired																				60.00%	60.00%
Joint Venture Partner Ownership Percentage	80.00%		80.00%																	40.00%
Properties acquired																				71
Property Units Acquired																				20,160
Partially Owned Properties Acquired Properties																				1
Partially Owned Units Acquired Units																				432
Partially Owned Unconsolidated Properties Acquired																				1
Partially Owned Unconsolidated Units Acquired																				336
Master Leased Properties Acquired	3		3																	3
Master Leased Units Acquired																				853
Uncompleted Development Properties Acquired																				4
Uncompleted Development Units Acquired																				964
Land parcels acquired																				14						12
Business Acquisition, Purchase Price Allocation, Assets Acquired																				8,986,443,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual																				52,627,340
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual																				36,200,000
Number of Properties Subject to Ground Leases	9		9
Business Acquisition, Purchase Price Allocation, Land															2,239,000,000		2,239,000,000
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment																		5,833,258,000	61,470,000
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets															304,830,000		304,830,000
Business Combination Purchase Price Allocation Projects Under Development															36,583,000		36,583,000
Business Combination Purchase Price Allocation Land Held for Development															236,918,000		236,918,000
Business Combination Purchase Price Allocation Investments in Unconsolidated Entities															189,244,000		189,244,000
Business Acquisition, Purchase Price Allocation, Other Assets															196,310,000		196,310,000
Business Acquisition, Purchase Price Allocation, Other Liabilities															(111,170,000)		(111,170,000)
Payments to Acquire Businesses, Net of Cash Acquired	4,000,643,000	0													4,000,000,000							4,000,643,000	0
Secured Debt	6,380,424,000		6,380,424,000	3,898,369,000											2,000,000,000		2,000,000,000					6,380,424,000		3,898,369,000
Issuance of Common Shares	34,468,085																								34,468,085
Stock Issued During Period, Value, New Issues																									1,900,000,000
Average Price Per Common Share Issued																									$ 55.99
Noncash or Part Noncash Acquisition, Debt Assumed	34,100,000														3,100,000,000
Mark-to-Market Debt Premiums	127,900,000
Term Loan Principal Amount	750,000,000		750,000,000
Ground Lease Intangibles Below Market	178,251,000		178,251,000
Retail Lease Intangibles Above Market	2,310,000		2,310,000
Lease Intangible Assets	180,561,000		180,561,000
Amortization of Intangible Assets															(460,000)
Lease Intangible Assets, Net	180,101,000		180,101,000
Ground Lease Intangibles Above Market	2,400,000		2,400,000
Retail Lease Intangibles Below Market	8,040,000		8,040,000
Lease Intangible Liabilities	10,440,000		10,440,000
Amortization Of Intangible Liabilities	(168,000)		(168,000)
Lease Intangible Liabilities, net	10,272,000		10,272,000
Ground Lease Amortization	400,000		400,000
Retail Lease Amortization	100,000		100,000
Weighted Average Ground Lease Amortization Period	49.8		49.8
Weighted Average Retail Lease Amortization Period	5.3		5.3
Ground Lease Intangibles Amortization									4,321	4,321	4,321	4,321	4,321
Retail Lease Intangibles Amortization									(1,230)	(1,236)	(1,050)	(674)	(205)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles									3,091	3,085	3,271	3,647	4,116
Business Combination, Acquisition Related Costs	100,000	500,000	86,000,000
Payments of Financing Costs	(13,869,000)	(4,227,000)													2,500,000		13,500,000					(13,869,000)	(4,227,000)
Merger Expenses	19,092,000	1,149,000	72,500,000											19,092,000		(1,100,000)						(19,092,000)	(1,149,000)
Income Loss From Equity Method Investments Merger Expenses	(46,011,000)	0																				(46,011,000)	0
Business Acquisition, Pro Forma Revenue	638,499,000	586,173,000																				638,499,000	586,173,000
Business Acquisition, Proforma Income Loss From Continuing Operations	(34,473,000)	(149,998,000)																				(34,473,000)	(149,998,000)
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax	1,213,615,000	166,364,000																				1,213,615,000	166,364,000
Business Acquisition, Pro Forma Net Income (Loss)	1,179,142,000	16,366,000																				1,179,142,000	16,366,000
Business Acquisition, Proforma Net Income Available to Common Shares	1,130,671,000	13,068,000
Business Acquisition, Proforma Net Income Available to Units																						1,178,887,000	13,659,000
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 3.15	$ 0.04																				$ 3.15	$ 0.04
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 3.15	$ 0.04																				$ 3.15	$ 0.04
Business Acquisition, Proforma Weighted Average Common Shares Basic	359,362,000	355,123,000
Business Acquisition, Proforma Weighted Average Number Of Shares Diluted	359,362,000	355,123,000
Business Acquisition, Proforma Weighted Average Limited Partnership And General Partnership Units Outstanding Basic																						373,085,000	368,329,000
Business Acquisition, Proforma Weighted Average Number Of Limited Partnership And General Partnership Unit Outstanding Diluted																						373,085,000	368,329,000
Severance Costs															$ 44,800,000