Loans - Additional Information (Details)		3 Months Ended		6 Months Ended		12 Months Ended
		Nov. 30, 2019 USD ($) associate power_supply_system distribution_system borrower member	Nov. 30, 2018 USD ($)	Nov. 30, 2019 USD ($) associate power_supply_system distribution_system borrower member	Nov. 30, 2018 USD ($)	May 31, 2019 USD ($) associate power_supply_system distribution_system borrower
Accounts, Notes, Loans and Financing Receivable [Line Items]
Line of Credit Commitments as percentage of unadvanced loan commitment		59.00%		59.00%
Long-term Loan commitments as percentage of unadvanced loan commitment		41.00%		41.00%
Loans Receivable Cost of Loans Sold				$ 60,000,000	$ 0
Number of Borrowers | member		898		898
Number of States in which Electric and Telecommunications Borrowers are Located				49
Loans Outstanding		$ 26,426,879,000	$ 25,282,953,000	$ 26,426,879,000	25,282,953,000	$ 25,905,664,000
Number of Borrowers With TDR Loans		1		1		1
Financing Receivable, Troubled Debt Restructuring, Subsequent Default		$ 0	0	$ 0	0
Accounts Receivable, Allowance for Credit Loss, Writeoff		0	0	0	0
Nonperforming TDR loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment		0		0		$ 0
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans		0	$ 0	0	$ 0
Performing line of credit for Troubled Debt Restructuring Borrower [Member] | Line of Credit to Provide Bridge Funding
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments		2,000,000		2,000,000		2,000,000
Loans Outstanding		2,000,000		2,000,000		1,000,000
Performing line of credit for Troubled Debt Restructuring Borrower [Member] | Line of Credit Restricted for Fuel Purchases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments		6,000,000		6,000,000		6,000,000
Loans Outstanding		2,000,000		2,000,000		3,000,000
Nonperforming Financial Instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment		0		0		0
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		173,473,000		173,473,000		176,423,000
CFC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		25,368,276,000		25,368,276,000		24,817,676,000
CFC | Distribution
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		20,682,596,000		20,682,596,000		20,155,266,000
CFC | Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		4,601,783,000		4,601,783,000		4,578,841,000
CFC | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		168,131,000		168,131,000		170,831,000
CFC | Substandard | Distribution
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		120,459,000		120,459,000		122,698,000
CFC | Substandard | Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		47,672,000		47,672,000		48,133,000
Unadvanced commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments	[1]	13,326,179,000		13,326,179,000		13,237,558,000
Unadvanced commitments | CFC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments	[1]	12,473,766,000		12,473,766,000		12,405,385,000
Unadvanced commitments | CFC | Distribution
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments	[1]	8,764,486,000		8,764,486,000		8,773,018,000
Unadvanced commitments | CFC | Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments	[1]	3,531,558,000		3,531,558,000		3,466,680,000
Commitments to Extend Credit Subject to Material Adverse Change Clause
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments		10,256,000,000		10,256,000,000		10,294,000,000
Unadvanced commitments not subject to material adverse change clauses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments		3,070,365,000		3,070,365,000		2,944,000,000
Long-term variable-rate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		930,949,000		930,949,000		1,066,880,000
Long-term variable-rate loans | Unadvanced commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced commitments	[1]	$ 5,410,294,000		$ 5,410,294,000		$ 5,448,636,000
Loans Receivable Commercial and Industrial | Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration Risk, Percentage				2.00%		2.00%
Concentration Risk Number of Borrowers | borrower		20		20		20
Loans Receivable Commercial and Industrial | Credit Concentration Risk | Distribution
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration Risk Number of Borrowers | distribution_system		11		11		10
Loans Receivable Commercial and Industrial | Credit Concentration Risk | Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration Risk Number of Borrowers | power_supply_system		8		8		9
Loans Receivable Commercial and Industrial | Credit Concentration Risk | Associates
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration Risk Number of Borrowers | associate		1		1		1
Loans Receivable Commercial and Industrial | Customer Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration Risk, Percentage				22.00%		22.00%
Loans Receivable Commercial and Industrial | Geographic Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration Risk, Percentage				15.00%		15.00%
Loans Receivable Commercial and Industrial | Product Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration Risk, Percentage				99.00%		99.00%
Loans Guaranteed by Farmer Mac
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		$ 593,000,000		$ 593,000,000		$ 619,000,000
Loans Guaranteed by Rural Utilities Service
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding		$ 150,000,000		$ 150,000,000		$ 154,000,000

[1] The interest rate on unadvanced loan commitments is not set until an advance is made; therefore, all long-term unadvanced loan commitments are reported as variable-rate. However, the borrower may select either a fixed or a variable rate when an advance on a commitment is made.