Allowance for Credit Losses - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 01, 2020	May 31, 2021	Mar. 31, 2021	May 31, 2020
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		$ 28,415,107		$ 26,690,854	[1]
Impaired Financing Receivable, Related Allowance				34,833
Deferred origination costs		11,854		11,526	[1]
Impaired Financing Receivable, with Related Allowance, Recorded Investment				172,800
Credit Reserve for Unadvanced Loan Commitments		1,000		1,000
Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease)		32,000
Asset-specific allowance(1)		$ 43,090		$ 34,833
Financing Receivable, Allowance For Credit Losses, Collectively Evaluated For Impairment Ratio		0.15%		0.07%
Cumulative effect from adoption of new accounting standard | Accounting Standards Update 2016-13
Loan Loss Allowance
Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease)	$ 4,000
Non-performing loans
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		$ 237,497		$ 167,708
Doubtful [Member]
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		237,497		167,708
CFC
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		27,287,856		25,607,657	[1]
Impaired Financing Receivable, Related Allowance				33,854
Deferred origination costs		12,000		11,000
Impaired Financing Receivable, with Related Allowance, Recorded Investment				167,708
Asset-specific allowance(1)		$ 39,542		$ 33,854
Financing Receivable, Allowance For Credit Losses, Collectively Evaluated For Impairment Ratio		0.15%		0.05%
CFC | Doubtful [Member]
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		$ 228,312		$ 167,708
CFC | Brazos Electric Power Cooperative
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		85,000
Letters of Credit Outstanding, Amount		1,000	$ 3,000
CFC | Rayburn Country Electric Cooperative
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		379,000
Collective Allowance
Loan Loss Allowance
Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease)		24,000
Asset-Specific Allowance
Loan Loss Allowance
Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease)		8,000
Power Supply Systems [Member] | CFC
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		5,154,312		4,731,506	[1]
Asset-specific allowance(1)		$ 39,542		$ 33,854
Financing Receivable, Allowance For Credit Losses, Collectively Evaluated For Impairment Ratio		0.51%		0.09%
Power Supply Systems [Member] | CFC | Non-performing loans
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		$ 228,312		$ 167,708
Power Supply Systems [Member] | CFC | Doubtful [Member]
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		228,312		$ 167,708
Power Supply Systems [Member] | CFC | Brazos Electric Power Cooperative | Non-performing loans
Loan Loss Allowance
Loans and Leases Receivable, Net of Deferred Income		$ 85,000

[1] The interest rate on unadvanced loan commitments is not set until an advance is made; therefore, all unadvanced long-term loan commitments are reported as variable rate. However, the borrower may select either a fixed or a variable rate when an advance is drawn under a loan commitment.(2) Represents the unpaid principal balance, net of charge-offs and recoveries, of loans as of the end of each period.