Schedule III Real Estate and Accumulated Depreciation (Parenthetical) (Detail) (USD $) In Billions, unless otherwise specified	12 Months Ended
Dec. 31, 2011
Real Estate and Accumulated Depreciation [Line Items]
Salvage value	40.00%
Aggregate cost for Federal income tax	$ 3.9
Depreciable Property
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful life	30
Building Improvements
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful life	10
Building Improvements \| Minimum
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful lives, minimum	10
Building Improvements \| Maximum
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful lives, maximum	15
Furniture and Fixtures
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful life	5
In-place leases
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful life	1
New rental units
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful life	20

The component of total income tax expense for the period comprised of the increase (decrease) during the period in the entity's domestic deferred tax assets and liabilities attributable to continuing operations as determined by applying the provisions of the federally enacted tax law.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section I

-Subsection 7

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 109

-Paragraph 45

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph h

-Article 4

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 109

-Paragraph 8, 16, 17, 289

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Deferred Tax Expense (or Benefit)

-URI http://asc.fasb.org/extlink&oid=6510177

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I.7)

-URI http://asc.fasb.org/extlink&oid=6889476&loc=d3e330036-122817

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319

+ Details