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Variable Interest Entities (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Variable Interest Entity [Line Items]      
Gains (losses) for consolidated variable interest entities $ 0   $ 0
Carrying amount of other investments 4,765   2,994
Maximum [Member]      
Variable Interest Entity [Line Items]      
Income Tax Credits And Other Tax Benefits From Qualified Affordable Housing Projects 1 $ 1  
Limited Partnerships and Limited Liability Companies [Member]      
Variable Interest Entity [Line Items]      
Carrying amount of other investments 2,000   1,900
Carrying Amount Of Investments In Qualified Affordable Housing Projects $ 11   $ 13