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Recent Accounting Pronouncements (Details) - USD ($)
$ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2020
Dec. 31, 2019
Jun. 30, 2020
Jan. 01, 2020
Sep. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]              
Accounting Standards Update [Extensible List] us-gaap:AccountingStandardsUpdate201613Member us-gaap:AccountingStandardsUpdate201613Member          
Cumulative-effect decrease to beginning retained earnings $ (32,429) $ (34,595) $ (33,028)   $ (33,760) $ (2,546) $ (2,293)
Cumulative Effect, Period of Adoption, Adjustment              
New Accounting Pronouncements or Change in Accounting Principle [Line Items]              
Cumulative-effect decrease to beginning retained earnings   45          
Retained Earnings              
New Accounting Pronouncements or Change in Accounting Principle [Line Items]              
Cumulative-effect decrease to beginning retained earnings $ (13,141) (12,528) $ (12,877)   $ (12,281) $ (12,083) $ (11,635)
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment              
New Accounting Pronouncements or Change in Accounting Principle [Line Items]              
Cumulative-effect decrease to beginning retained earnings   $ 45   $ 45