Organization and Basis of Presentation - Merger Purchase Price Allocation (Details) (BRE Properties, Inc. [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Apr. 01, 2014
BRE Properties, Inc. [Member]
Business Acquisition [Line Items]
Cash assumed	$ 140
Rental properties and real estate under development	5,605
Real estate held for sale, net	108
Co-investments	224
Acquired in-place lease value	77
Other assets	16
Mortgage notes payable and unsecured debt	(1,747.0)
Other liabilities	(87)
Redeemable noncontrolling interest	(5)
Total consideration for BRE merger	4,331	4,300
Cash consideration for BRE merger	556.0
Equity consideration for BRE merger	$ 3,775

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Co Investments

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- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Prepaid Expenses

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Assets assumed in the business combination including Rental properties and real estate under development.

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Value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable to acquire the entity.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

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This element represents the fair value of the noncontrolling interest in the acquiree at the acquisition date.

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Amount of assets acquired at the acquisition date.

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Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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Amount of other liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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The amount of property, plant, and equipment recognized as of the acquisition date.

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- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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