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Investments (Real Estate and Real Estate Joint Ventures) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Real Estate [Line Items]
Leased real estate investments, Carrying Value	$ 5,182		$ 5,182		$ 4,893
Other real estate investments, Carrying Value	417		417		420
Real estate joint ventures, Carrying Value	5,925		5,925		5,428
Real Estate Investments, Net	11,524		11,524		$ 10,741
Income (Loss) from Equity Method Investments	(688)	$ 241	(365)	$ 330
Real Estate and Real Estate Joint Ventures
Real Estate [Line Items]
Gross Investment Income, Operating	102	179	267	309
Leased real estate investments
Real Estate [Line Items]
Operating Lease, Lease Income	101	90	207	182
Other real estate investments
Real Estate [Line Items]
Operating Lease, Lease Income	24	56	59	90
Real estate joint ventures
Real Estate [Line Items]
Income (Loss) from Equity Method Investments	$ (23)	$ 33	$ 1	$ 37