Commitments, Off-Balance Sheet Arrangements, Legal Proceedings and Regulatory Matters (Details Textuals) - USD ($)	3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Jun. 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	$ 50,776,000			$ 47,776,000	$ 21,907,000
Provision for credit losses	3,000,000			7,000,000
Expense Related to Qualified Affordable Housing Projects	8,000,000	$ 6,000,000
Remaining Investment in Qualified Affordable Housing Projects	277,000,000			268,000,000
Variable Interest Entity Reporting Entity Involvement Unfunded Obligation Amount	119,000,000			118,000,000
Qualified Affordable Housing Investments, Impairment Loss	0		$ 0
Loans Repurchased Under Make Whole Requests	$ 2,000,000			10,000,000
Loans Sold To Outside Investors Loss ReimbursementSettlement Paid	109 thousand		no
Loans Sold To Outside Investors Original Amount	$ 14,700,000,000
Loans Sold To Outside Investors Remaining Outstanding Amount	6,500,000,000
Mortgage Repurchase Reserve	1,000,000			2,000,000
Residential Mortgage Loans Sold With Recourse Risk	27,000,000			36,000,000
Residential Mortgage Loans Sold With Credit Recourse Risk	31,000,000			33,000,000
UnconsolidatedProjectsLowIncomeHousing [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Other Investments	280,000,000			272,000,000
PrincipalInvestmentCommitment [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Other Investments	$ 23,000,000			$ 25,000,000