Commitments, Off-Balance Sheet Arrangements, Legal Proceedings and Regulatory Matters (Details Textuals) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Off-Balance Sheet, Credit Loss, Liability	$ 41,276,000			$ 41,276,000		$ 47,776,000	$ 21,907,000
Provision for credit losses				(6,500,000)		7,000,000
Expense Related to Qualified Affordable Housing Projects	8,000,000		$ 6,000,000	24,000,000	$ 18,000,000
Remaining Investment in Qualified Affordable Housing Projects	270,000,000			270,000,000		268,000,000
Variable Interest Entity Reporting Entity Involvement Unfunded Obligation Amount	101,000,000			101,000,000		118,000,000
Qualified Affordable Housing Investments, Impairment Loss				0		0
Loans Repurchased Under Make Whole Requests	6,000,000			$ 6,000,000		10,000,000
Loans Sold To Outside Investors Loss ReimbursementSettlement Paid		no		114
Loans Sold To Outside Investors Original Amount	15,700,000,000			$ 15,700,000,000
Loans Sold To Outside Investors Remaining Outstanding Amount	6,500,000,000			6,500,000,000
Mortgage Repurchase Reserve	1,000,000			1,000,000		2,000,000
Residential Mortgage Loans Sold With Recourse Risk	27,000,000			27,000,000		36,000,000
Residential Mortgage Loans Sold With Credit Recourse Risk	26,000,000			26,000,000		33,000,000
UnconsolidatedProjectsLowIncomeHousing [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Other Investments	277,000,000			277,000,000		272,000,000
PrincipalInvestmentCommitment [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Other Investments	$ 24,000,000			$ 24,000,000		$ 25,000,000