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Fair Value Of Financial Instruments (Narrative) (Detail) - USD ($)
$ in Millions
12 Months Ended
Feb. 10, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Percentage of level 3 assets at fair value in total assets measured at fair value value   20.00% 15.00%    
Percentage of level 3 liabilities at fair value in total liabilities measured at fair value   68.00% 72.00%    
Cumulative changes in instrument-specific credit risk of liabilities elected under the fair value option   $ (115) $ 2 $ 156 $ 19
Loan Repurchase Commitments [Member] | Subsequent Event [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Payments for Litigation Settlements $ 600        
Instrument-specific credit risk of liabilities measured at fair value, net [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Cumulative changes in instrument-specific credit risk of liabilities elected under the fair value option   51 107 110 $ 0
Loss on instrument-specific credit risk recognized in earnings   $ 6 $ 28 $ 97