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General Adoption of New Accounting Pronouncements (Details) - USD ($)
$ in Millions
Mar. 31, 2021
Dec. 31, 2020
Mar. 31, 2020
Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Cumulative Effect on Retained Earnings, Net of Tax $ (59,076) $ (59,441) $ (52,197)  
Retained Earnings [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Cumulative Effect on Retained Earnings, Net of Tax $ (41,637) (39,337) $ (36,331) $ (36,142)
Retained Earnings [Member] | Cumulative Effect, Period of Adoption, Adjustment        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Cumulative Effect on Retained Earnings, Net of Tax   $ 0   $ 63