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Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Parenthetical) (Detail) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Derivative [Line Items]    
Notional Amount $ 33,850,000,000 $ 51,050,000,000
Forward-Starting Interest Rate Swap Agreements [Member]    
Derivative [Line Items]    
Notional Amount 14,900,000,000 32,100,000,000
Fair Value Hedges [Member]    
Derivative [Line Items]    
Reduction of estimated fair value losses on hedging instruments 68,900,000 101,500,000
Cash Flow Hedges [Member]    
Derivative [Line Items]    
Reduction of estimated fair value losses on hedging instruments $ 217,800,000 $ 372,200,000