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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Changes in Accounting Policies (Details) - USD ($)
$ in Millions
Sep. 30, 2021
Jun. 30, 2021
Sep. 30, 2020
Jun. 30, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Cumulative adjustment, increase to opening balance of retained earnings $ 6,115 $ 6,091 $ 4,481  
Retained Earnings        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Cumulative adjustment, increase to opening balance of retained earnings $ 12,864 12,244 $ 10,480 $ 10,134
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Cumulative adjustment, increase to opening balance of retained earnings   121   $ (3)
Accounting Standards Update 2019-12 | Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Cumulative adjustment, increase to opening balance of retained earnings   $ 121