Recent Accounting Developments - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Allowance for credit losses	$ 1,758,505	$ 1,638,236		$ 1,051,071	$ 1,038,437	$ 1,029,867	$ 1,019,444
Cumulative effect adjustment to retained earnings	$ 13,132,374			$ 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