Recent Accounting Developments - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Allowance for credit losses	$ 1,736,387		$ 1,051,071	$ 1,019,444	$ 1,017,198
Cumulative effect adjustment to retained earnings	$ 13,444,428		$ 12,820,916
ASU 2016-13 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Allowance for credit losses		$ 132,000
ASU 2016-13 [Member] | Cumulative Effect Period of Adoption Adjustment [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative effect adjustment to retained earnings		$ 132,000