Real Estate (Details) (USD $)	3 Months Ended		9 Months Ended		45 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Dec. 31, 2012
Land	$ 6,201,333,000		$ 6,201,333,000		$ 6,201,333,000	$ 4,554,912,000
Property, Plant and Equipment, Gross [Abstract]
Investment Building and Building Improvements	17,555,388,000		17,555,388,000		17,555,388,000	14,135,740,000
Fixtures and Equipment, Gross	1,196,410,000		1,196,410,000		1,196,410,000	1,343,765,000
Finite-Lived Intangible Assets, Gross	503,159,000		503,159,000		503,159,000	232,439,000
Projects under development	779,053,000		779,053,000		779,053,000	387,750,000
Land held for development	505,494,000		505,494,000		505,494,000	353,823,000
Real Estate Investment Property, at Cost	26,740,837,000		26,740,837,000		26,740,837,000	21,008,429,000
Real Estate Investment Property, Accumulated Depreciation	(4,654,594,000)		(4,654,594,000)		(4,654,594,000)	(4,912,221,000)
Investment in real estate, net	22,086,243,000		22,086,243,000		22,086,243,000	16,096,208,000
Ground Lease Intangibles Below Market	178,251,000		178,251,000		178,251,000
Retail Lease Intangibles Above Market	2,310,000		2,310,000		2,310,000
Lease Intangible Assets	180,561,000		180,561,000		180,561,000
Lease Intangible Assets, Net	177,340,000		177,340,000		177,340,000
Ground Lease Intangibles Above Market	2,400,000		2,400,000		2,400,000
Retail Lease Intangibles Below Market	7,790,000		7,790,000		7,790,000
Lease Intangible Liabilities	10,190,000		10,190,000		10,190,000
Amortization Of Intangible Liabilities	(993,000)		(993,000)		(993,000)
Lease Intangible Liabilities, net	9,197,000		9,197,000		9,197,000
Ground Lease Amortization	1,100,000		2,500,000
Retail Lease Amortization	100,000		300,000
Weighted Average Ground Lease Amortization Period	49.8		49.8		49.8
Weighted Average Retail Lease Amortization Period	5.3		5.3		5.3
Properties acquired			1
Property Units Acquired			322
Master Leased Properties Acquired	3		3		3
Payments to Acquire Businesses, Net of Cash Acquired			4,000,875,000	0
Mortgage notes payable	6,230,675,000		6,230,675,000		6,230,675,000	3,898,369,000
Issuance of Common Shares			34,468,085
Noncash or Part Noncash Acquisition, Debt Assumed			34,100,000
Mark-to-Market Debt Premiums			127,900,000
Number of Properties Subject to Ground Leases	9		9		9
Business Combination, Acquisition Related Costs			200,000	6,900,000	95,400,000
Payments of Financing Costs			(18,254,000)	(4,599,000)
Merger Expenses	182,000	87,000	19,741,000	1,921,000	81,900,000
(Loss) from investments in unconsolidated entities due to merger expenses	(1,771,000)	0	(54,781,000)	0
Business Acquisition, Pro Forma Revenue	629,446,000	596,734,000	1,854,509,000	1,726,304,000
Business Acquisition, Proforma Income Loss From Continuing Operations	84,978,000	107,024,000	132,592,000	(179,574,000)
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax	403,181,000	145,145,000	2,024,346,000	434,253,000
Business Acquisition, Pro Forma Net Income (Loss)	488,159,000	252,169,000	2,156,938,000	254,679,000
Business Acquisition, Proforma Net Income Available to Common Shares	468,959,000	234,471,000	2,070,153,000	232,053,000
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 1.30	$ 0.66	$ 5.76	$ 0.65
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 1.30	$ 0.66	$ 5.74	$ 0.65
Business Acquisition, Proforma Weighted Average Common Shares Basic	359,811,000	357,654,000	359,611,000	356,434,000
Business Acquisition, Proforma Weighted Average Number Of Shares Diluted	375,883,000	375,091,000	375,808,000	356,434,000
Consolidated Properties [Member]
Property, Plant and Equipment, Gross [Abstract]
Uncompleted Development Properties Acquired	2		2		2
Archstone [Member]
Property, Plant and Equipment, Gross [Abstract]
Amortization of Intangible Assets	(3,221,000)		(3,221,000)		(3,221,000)
Payments to Acquire Businesses, Net of Cash Acquired			4,000,000,000
Mortgage notes payable	2,000,000,000		2,000,000,000		2,000,000,000
Noncash or Part Noncash Acquisition, Debt Assumed			3,100,000,000
Business Acquisition, Purchase Price Allocation, Land	2,239,000,000		2,239,000,000		2,239,000,000
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets	304,830,000		304,830,000		304,830,000
Business Combination Purchase Price Allocation Projects Under Development	36,583,000		36,583,000		36,583,000
Business Combination Purchase Price Allocation Land Held for Development	239,898,000		239,898,000		239,898,000
Business Combination Purchase Price Allocation Investments in Unconsolidated Entities	188,139,000		188,139,000		188,139,000
Business Acquisition, Purchase Price Allocation, Other Assets	196,310,000		196,310,000		196,310,000
Business Acquisition, Purchase Price Allocation, Other Liabilities	(112,369,000)		(112,369,000)		(112,369,000)
Payments of Financing Costs			2,500,000		13,500,000
Merger Expenses				1,921,000
Severance Costs			53,600,000
2013 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	1,080,000		1,080,000		1,080,000
Retail Lease Intangibles Amortization	(218,000)		(218,000)		(218,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	862,000		862,000		862,000
2014 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(1,144,000)		(1,144,000)		(1,144,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	3,177,000		3,177,000		3,177,000
2015 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(1,150,000)		(1,150,000)		(1,150,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	3,171,000		3,171,000		3,171,000
2016 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(1,042,000)		(1,042,000)		(1,042,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	3,279,000		3,279,000		3,279,000
2017 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(674,000)		(674,000)		(674,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	3,647,000		3,647,000		3,647,000
2018 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(205,000)		(205,000)		(205,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	4,116,000		4,116,000		4,116,000
Investment Banking and Legal/Accounting Fees [Member]
Property, Plant and Equipment, Gross [Abstract]
Merger Expenses			19,700,000
Building and Building Improvements [Member]
Property, Plant and Equipment, Gross [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	5,832,554,000		5,832,554,000		5,832,554,000
Furniture and Fixtures [Member]
Property, Plant and Equipment, Gross [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	61,470,000		61,470,000		61,470,000
Archstone Transaction [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Below Market	178,251,000		178,251,000		178,251,000
Retail Lease Intangibles Above Market	2,310,000		2,310,000		2,310,000
Ground Lease Intangibles Above Market	2,400,000		2,400,000		2,400,000
Retail Lease Intangibles Below Market	8,040,000		8,040,000		8,040,000
Business Acquisition, Percentage of Voting Interests Acquired	60.00%		60.00%		60.00%
Properties acquired			71
Partially Owned Properties Acquired Properties	1		1		1
Partially Owned Units Acquired Units	432		432		432
Partially Owned Unconsolidated Properties Acquired	1		1		1
Partially Owned Unconsolidated Units Acquired	336		336		336
Master Leased Properties Acquired	3		3		3
Master Leased Units Acquired	853		853		853
Uncompleted Development Properties Acquired	4		4		4
Uncompleted Development Units Acquired	964		964		964
Land parcels acquired			14
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	8,986,415,000		8,986,415,000		8,986,415,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	153,500,000		358,000,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	104,200,000		244,200,000
Unconsolidated Properties [Member]
Property, Plant and Equipment, Gross [Abstract]
Uncompleted Development Properties Acquired	2		2		2
Projects under development [Member]
Property, Plant and Equipment, Gross [Abstract]
Land Under Development	280,718,000		280,718,000		280,718,000	210,632,000
Projects under development	498,335,000		498,335,000		498,335,000	177,118,000
Land held for development [Member]
Property, Plant and Equipment, Gross [Abstract]
Projects under development	70,267,000		70,267,000		70,267,000	58,955,000
Land held for development	435,227,000		435,227,000		435,227,000	294,868,000
Archstone Transaction [Member]
Property, Plant and Equipment, Gross [Abstract]
Property Units Acquired			20,160
OPERATING PARTNERSHIP
Land	6,201,333,000		6,201,333,000		6,201,333,000	4,554,912,000
Property, Plant and Equipment, Gross [Abstract]
Projects under development	779,053,000		779,053,000		779,053,000	387,750,000
Land held for development	505,494,000		505,494,000		505,494,000	353,823,000
Real Estate Investment Property, at Cost	26,740,837,000		26,740,837,000		26,740,837,000	21,008,429,000
Real Estate Investment Property, Accumulated Depreciation	(4,654,594,000)		(4,654,594,000)		(4,654,594,000)	(4,912,221,000)
Investment in real estate, net	22,086,243,000		22,086,243,000		22,086,243,000	16,096,208,000
Payments to Acquire Businesses, Net of Cash Acquired			4,000,875,000	0
Mortgage notes payable	6,230,675,000		6,230,675,000		6,230,675,000	3,898,369,000
Payments of Financing Costs			(18,254,000)	(4,599,000)
Merger Expenses	182,000	87,000	19,741,000	1,921,000
(Loss) from investments in unconsolidated entities due to merger expenses	(1,771,000)	0	(54,781,000)	0
Business Acquisition, Pro Forma Revenue	629,446,000	596,734,000	1,854,509,000	1,726,304,000
Business Acquisition, Proforma Income Loss From Continuing Operations	84,978,000	107,024,000	132,592,000	(179,574,000)
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax	403,181,000	145,145,000	2,024,346,000	434,253,000
Business Acquisition, Pro Forma Net Income (Loss)	488,159,000	252,169,000	2,156,938,000	254,679,000
Business Acquisition, Proforma Net Income Available to Units	487,433,000	245,725,000	2,155,736,000	242,962,000
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 1.30	$ 0.66	$ 5.76	$ 0.65
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 1.30	$ 0.66	$ 5.74	$ 0.65
Business Acquisition, Proforma Weighted Average Limited Partnership And General Partnership Units Outstanding Basic	373,547,000	371,831,000	373,347,000	370,250,000
Business Acquisition, Proforma Weighted Average Number Of Limited Partnership And General Partnership Unit Outstanding Diluted	375,883,000	375,091,000	375,808,000	370,250,000
Archstone Transaction [Member]
Property, Plant and Equipment, Gross [Abstract]
Issuance of Common Shares			34,468,085
Stock Issued During Period, Value, New Issues			1,900,000,000
Average Price Per Common Share Issued			$ 55.99
DelayedDrawTermLoan [Member]
Property, Plant and Equipment, Gross [Abstract]
Term Loan Principal Amount	$ 750,000,000		$ 750,000,000		$ 750,000,000
Land [Member]
Property, Plant and Equipment, Gross [Abstract]
Property Units Acquired			0
Land parcels acquired			1