Investments in Limited Partnerships - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) Partnership	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Schedule of Investments [Line Items]
Unfunded equity commitments in other liabilities	$ 13,668,873				$ 13,126,191				$ 13,668,873	$ 13,126,191
Tax benefits including low-income housing and historic tax credits	11,703	$ 7,669	$ 42	$ 3,621	7,046	$ 8,334	$ 10,103	$ 8,858	23,035	34,341	$ 31,412
Partnerships losses and impairment									$ 3,300	2,600	2,100
Number of limited partnerships held | Partnership									7
Equity Method Investments [Member]
Schedule of Investments [Line Items]
Tax benefits including low-income housing and historic tax credits									$ 3,200	2,500	2,100
Limited Liability Company [Member]
Schedule of Investments [Line Items]
Amount invested in partnerships	5,800				7,100				5,800	7,100
Limited Liability Company [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Investments [Line Items]
Partnership gains (losses) under equity method									(603)	618	$ 712
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Assets [Member]
Schedule of Investments [Line Items]
Amount invested in partnerships	31,400				25,700				31,400	25,700
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Liabilities [Member]
Schedule of Investments [Line Items]
Unfunded equity commitments in other liabilities	$ 19,900				$ 15,600				$ 19,900	$ 15,600