Real Estate and Accumulated Depreciation (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)
Real Estate And Accumulated Depreciation [Line Items]
Cost of real estate for federal income tax purposes	$ 9,658
Upper Limit
Real Estate And Accumulated Depreciation [Line Items]
Other properties, percentage	5.00%

Cost basis of real estate investments for federal income tax purposes for entities with a substantial portion of business acquiring and holding investment real estate.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Footnote 6
-Subsection 28

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 970
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-28(Footnote 6))
-URI http://asc.fasb.org/extlink&oid=120402810&loc=d3e638233-123024

Name:	srt_RealEstateFederalIncomeTaxBasis
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant