Debt (Narrative) (Details) (USD $)	12 Months Ended		12 Months Ended						12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2012 Maximum [Member]	Dec. 31, 2012 2010 Credit Agreement [Member] item	Dec. 31, 2012 Second Amended And Restated Indenture Of Trust [Member] item	Dec. 31, 2012 CoBank Master Loan Agreement [member] item	Dec. 31, 2012 2010 Amended And Extended Credit Agreement [Member] Maximum [Member]	Dec. 31, 2012 Unsecured Credit Agreement [Member] Initial Credit Agreement [Member]	Nov. 17, 2010 Unsecured Credit Agreement [Member] Initial Credit Agreement [Member]	Dec. 31, 2012 Unsecured Credit Agreement [Member] Amended Credit Agreement [Member]	May 04, 2012 Unsecured Credit Agreement [Member] Amended Credit Agreement [Member]	Dec. 31, 2012 Unsecured Credit Agreement [Member] Amended And Extended Credit Agreement [Member]	Jun. 29, 2012 Unsecured Credit Agreement [Member] Amended And Extended Credit Agreement [Member]	Dec. 31, 2012 2002 Series A Bond Of 6.2% Maturing 2012 [Member]	Dec. 31, 2012 2011 Series A Bond Of 4.2% Maturing 2031 [Member]	Jan. 21, 2011 2011 Series A Bond Of 4.2% Maturing 2031 [Member]	Dec. 31, 2012 2011 Series A Bond Of 4.75% Maturing 2041 [Member]	Jan. 21, 2011 2011 Series A Bond Of 4.75% Maturing 2041 [Member]	Dec. 31, 2012 2012 Series A Bond Of 4.01% Maturing 2032 [Member]	Jan. 11, 2012 2012 Series A Bond Of 4.01% Maturing 2032 [Member]	Dec. 31, 2012 2012 Series A Bond Of 4.41% Maturing 2042 [Member]	Jan. 11, 2012 2012 Series A Bond Of 4.41% Maturing 2042 [Member]	Dec. 31, 2012 2012 Series A Bond Of 4.78% Maturing 2042 [Member]	Jan. 11, 2012 2012 Series A Bond Of 4.78% Maturing 2042 [Member]	Dec. 31, 2012 Term Loan Facility [Member]
Debt Instrument [Line Items]
Yield margins for interest multiplier to total interest expense					1.1	1.1	1.1
Distribution percentage of patronage capital	5.00%
Distribution percentage of assignable margins	50.00%
Percentage of aggregate equities and margins to total liabilities, equities and margins	30.00%
Line of credit, maximum borrowing capacity	$ 50,000,000							$ 100,000,000		$ 300,000,000		$ 100,000,000
Line of credit, borrowing rate description	The borrowing rate is calculated using the total rate per annum and may be fixed by NRUCFC.												one month London Interbank Offered Rate (LIBOR) plus 107.5 basis points, along with a 17.5 basis points facility fee (based on an A-/A3 unsecured debt rating).
Line of credit, basis spread on variable rate														1.075%
Line of credit facility, basis points facility fee														0.175%
Line of credit, borrowing rate	2.90%	3.20%
Period of time the line of credit needs to be paid down for five consecutive days	12 months
Number of consecutive days debt needs to be paid down to $0 during a twelve month period	5 days
Line of credit, initiation date									Nov. 17, 2010
Line of credit, amendment date											May 4, 2012		June 29, 2012
Line of credit, expiration date	Oct. 12, 2017												Nov. 17, 2016
Commercial paper	11,500,000	175,000,000
Commercial paper repricing term			1 day	270 days
Debt face amount																	$ 90.0		$ 185.0		$ 75.0		$ 125.0		$ 50.0
Maturity date																Mar. 15, 2031		Mar. 15, 2041		Mar. 15, 2032		Mar. 15, 2042		Mar. 15, 2042
Bonds, interest rate															6.20%		4.20%		4.75%		4.01%		4.41%		4.78%
Frequency of payment															interest payable semi-annually February 1 and August 1	interest payable semi-annually March 15 and September 15 and principal due annually beginning in 2012		interest payable semi-annually March 15 and September 15 and principal due annually beginning in 2012		interest payable semi-annually March 15 and September 15 and principal due annually beginning in 2013		interest payable semi-annually March 15 and September 15 and principal due annually between 2013 and 2020 and between 2032 and 2042		interest payable semi-annually March 15 and September 15 and principal due annually beginning in 2023
Average life of bond																	10 years		15 years 6 months		10 years 8 months 12 days		15 years 8 months 12 days		20 years 8 months 12 days
Debt, issuance date																										Jan. 19, 2011