Reconciliation of Carrying Amounts of Real Estate Investments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Beginning Balance	$ 15,408us-gaap_RealEstateGrossAtCarryingValue	$ 15,661us-gaap_RealEstateGrossAtCarryingValue	$ 15,020us-gaap_RealEstateGrossAtCarryingValue
Additions:
Acquisitions	137us-gaap_RealEstateOtherAcquisitions	184us-gaap_RealEstateOtherAcquisitions	427us-gaap_RealEstateOtherAcquisitions
Capital expenditures and transfers from construction-in-progress	288us-gaap_RealEstateImprovements	353us-gaap_RealEstateImprovements	443us-gaap_RealEstateImprovements
Deductions:
Dispositions and other	(501)us-gaap_RealEstateCostOfRealEstateSold	(789)us-gaap_RealEstateCostOfRealEstateSold	(172)us-gaap_RealEstateCostOfRealEstateSold
Impairments	(6)	(1)	(57)
Ending Balance	$ 15,326us-gaap_RealEstateGrossAtCarryingValue	$ 15,408us-gaap_RealEstateGrossAtCarryingValue	$ 15,661us-gaap_RealEstateGrossAtCarryingValue

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- Details

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- Definition

Amount of real estate investments sold for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule III)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 970

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-28.4)

-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Amount, before accumulated depreciation, of real estate investments for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

+ Details

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- Definition

Amount of increase in real estate investments related to improvements for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of increase in real estate investments from acquisitions other than through foreclosure for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Amount of write-down or reserve recognized in the income statement on real estate investments for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule III)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 970

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-28.FN5)

-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

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