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Derivatives - Additional Information (Detail) - USD ($)
3 Months Ended
Sep. 30, 2020
Jun. 30, 2020
Derivative [Line Items]    
Minimum required liquidity under certain counterparty agreements $ 1,000,000,000.0  
Minimum liquidity for the period as defined by certain counterparty agreements 1,000,000,000.0  
Gross amounts of derivative assets, elected to offset 274,000,000 $ 399,000,000
Gross amounts of derivative liabilities, elected to offset $ 340,000,000 $ 399,000,000
Senior Unsecured Obligations    
Derivative [Line Items]    
Debt instrument credit rating AAA