Investments in Operating Joint Ventures (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investment in operating joint ventures	$ 1,309	$ 1,329	$ 1,483
Asset management fee income
Schedule of Equity Method Investments [Line Items]
Investment in operating joint ventures	$ 29	$ 32	$ 36

Amount of investment in equity method investee and investment in and advance to affiliate.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant