Derivative Financial Instruments - Notional Amount of Interest Rate Swap Agreements Outstanding Maturity (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Total	$ 51,050,000,000	$ 57,550,000,000
Interest Rate Swap Agreements [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
2021	27,700,000,000
2022	16,500,000,000
2023	6,350,000,000
2027	500,000,000
Total	$ 51,050,000,000