Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		9 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Variable Interest Entity [Line Items]
Unfunded commitments to fund low-income housing partnerships		$ 39,018
Variable interest entity, nonconsolidated, carrying amount, assets		20,109,489	$ 18,095,496	$ 17,672,140
CARES Act estimated provision for relief measures		2,200,000,000
Accounting Standards Update 2016-13
Variable Interest Entity [Line Items]
Total reserve for credit losses			116,849
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
Variable Interest Entity [Line Items]
Total reserve for credit losses	$ (5,072)
Increase to retained earnings	$ 3,632
Other Liabilities
Variable Interest Entity [Line Items]
Unfunded commitments to fund low-income housing partnerships		39,000	21,300
Other Assets | Variable Interest Entity Nonconsolidated
Variable Interest Entity [Line Items]
Variable interest entity, nonconsolidated, carrying amount, assets		$ 123,600	$ 84,600
Low-income Housing Partnerships
Variable Interest Entity [Line Items]
Period over which Federal tax credits or benefits are generally recognized (in years)		10 years
Period over which State tax credits or benefits are generally recognized (in years)		5 years
Solar Energy Partnerships
Variable Interest Entity [Line Items]
Period over which Federal tax credits or benefits are generally recognized (in years)		6 years