Fair Value of Assets and Liabilities (Fair Value Assets Measured on Non-Recurring Basis) (Details) - Partnership Interest [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value Assets Carrying Value Prior To Impairment	[1]	$ 20	$ 18
Fair Value Assets Gains Losses	[1]	$ (17)	$ (11)

[1] Impairments on these investments were recognized at estimated fair value determined using the net asset values of the Company’s ownership interest as provided in the financial statements of the investees. Real estate joint ventures were recognized at estimated fair value determined using historical and forecasted information for specific properties, including net operating income, occupancy, and sales levels. The market for these investments has limited activity and price transparency