Organization and Basis of Presentation - Schedule of Commercial Office Properties (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) ft² building shares
Real estate properties
Number of Buildings | building	65
Approximate Square Feet unaudited (sqft) | ft²	29,134,784
Weighted Average Occupancy unaudited (as a percent)	92.20%
Debt and preferred equity investments including investments held by unconsolidated joint ventures | $	$ 1,100
Debt and preferred equity investments and other financing receivables included in other balance sheet items | $	$ 100
Number of shares to be received on redemption of one unit of limited partnership interests (shares) | shares	1
Commercial properties
Real estate properties
Number of Buildings | building	56
Approximate Square Feet unaudited (sqft) | ft²	27,388,760
Weighted Average Occupancy unaudited (as a percent)	93.00%
Managed office properties
Real estate properties
Number of Buildings | building	2
Approximate Square Feet unaudited (sqft) | ft²	2,100,000
Consolidated properties
Real estate properties
Number of Buildings | building	36
Approximate Square Feet unaudited (sqft) | ft²	13,372,049
Consolidated properties | Commercial properties
Real estate properties
Number of Buildings | building	35
Approximate Square Feet unaudited (sqft) | ft²	13,289,799
Unconsolidated properties
Real estate properties
Number of Buildings | building	29
Approximate Square Feet unaudited (sqft) | ft²	15,762,735
Unconsolidated properties | Commercial properties
Real estate properties
Number of Buildings | building	21
Approximate Square Feet unaudited (sqft) | ft²	14,098,961
Manhattan
Real estate properties
Number of Buildings | building	49
Approximate Square Feet unaudited (sqft) | ft²	26,525,960
Weighted Average Occupancy unaudited (as a percent)	93.50%
Manhattan | Office
Real estate properties
Number of Buildings | building	27
Approximate Square Feet unaudited (sqft) | ft²	21,395,528
Weighted Average Occupancy unaudited (as a percent)	93.40%
Manhattan | Retail
Real estate properties
Number of Buildings | building	10
Approximate Square Feet unaudited (sqft) | ft²	312,036
Weighted Average Occupancy unaudited (as a percent)	94.60%
Manhattan | Development/Redevelopment
Real estate properties
Number of Buildings | building	12
Approximate Square Feet unaudited (sqft) | ft²	4,818,396
Manhattan | Residential
Real estate properties
Number of Buildings | building	9
Approximate Square Feet unaudited (sqft) | ft²	1,746,024
Weighted Average Occupancy unaudited (as a percent)	79.10%
Manhattan | Consolidated properties
Real estate properties
Number of Buildings | building	28
Approximate Square Feet unaudited (sqft) | ft²	12,426,999
Manhattan | Consolidated properties | Office
Real estate properties
Number of Buildings | building	18
Approximate Square Feet unaudited (sqft) | ft²	10,526,345
Manhattan | Consolidated properties | Retail
Real estate properties
Number of Buildings | building	1
Approximate Square Feet unaudited (sqft) | ft²	10,040
Manhattan | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Buildings | building	9
Approximate Square Feet unaudited (sqft) | ft²	1,890,614
Manhattan | Consolidated properties | Residential
Real estate properties
Number of Buildings | building	1
Approximate Square Feet unaudited (sqft) | ft²	82,250
Manhattan | Unconsolidated properties
Real estate properties
Number of Buildings | building	21
Approximate Square Feet unaudited (sqft) | ft²	14,098,961
Manhattan | Unconsolidated properties | Office
Real estate properties
Number of Buildings | building	9
Approximate Square Feet unaudited (sqft) | ft²	10,869,183
Manhattan | Unconsolidated properties | Retail
Real estate properties
Number of Buildings | building	9
Approximate Square Feet unaudited (sqft) | ft²	301,996
Manhattan | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Buildings | building	3
Approximate Square Feet unaudited (sqft) | ft²	2,927,782
Manhattan | Unconsolidated properties | Residential
Real estate properties
Number of Buildings | building	8
Approximate Square Feet unaudited (sqft) | ft²	1,663,774
Suburban | Office
Real estate properties
Number of Buildings | building	7
Approximate Square Feet unaudited (sqft) | ft²	862,800
Weighted Average Occupancy unaudited (as a percent)	81.60%
Suburban | Consolidated properties | Office
Real estate properties
Number of Buildings | building	7
Approximate Square Feet unaudited (sqft) | ft²	862,800
Suburban | Unconsolidated properties | Office
Real estate properties
Number of Buildings | building	0
Approximate Square Feet unaudited (sqft) | ft²	0