Notes Payable - Borrowings (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Due within one year:
Current portion of medium-term notes	$ 6,569,449	$ 6,986,799
Weighted - average rate (as a percent)	0.60%	0.45%
Medium-term notes due in:
Two years	$ 4,183,016
Three years	3,077,629
Four years	2,513,545
Five years	2,769,456
Thereafter	4,206,063
Total due after one year	16,749,709
Total principal net of discounts	23,319,158
Hedging adjustments	(279,191)	$ (42,377)
Total	$ 23,039,967	22,716,156
Weighted - average rate (as a percent)	1.17%
Total weighted - average rate (as a percent)	1.01%
Two years
Medium-term notes due in:
Weighted - average rate (as a percent)	0.89%
Three years
Medium-term notes due in:
Weighted - average rate (as a percent)	0.97%
Four years
Medium-term notes due in:
Weighted - average rate (as a percent)	0.84%
Five years
Medium-term notes due in:
Weighted - average rate (as a percent)	1.30%
Thereafter
Medium-term notes due in:
Weighted - average rate (as a percent)	1.70%
Discount notes
Due within one year:
Current portion of medium-term notes	$ 1,892,025	$ 2,167,979
Weighted - average rate (as a percent)	0.35%	0.05%
Short-term debt, average outstanding during the quarter	$ 1,950,334	$ 1,822,714
Weighted - average rate, average outstanding during the quarter (as a percent)	0.16%	0.08%
Medium-term notes
Due within one year:
Current portion of medium-term notes	$ 992,942	$ 837,580
Weighted - average rate (as a percent)	0.29%	0.09%
Short-term debt, average outstanding during the quarter	$ 898,484	$ 1,956,870
Weighted - average rate, average outstanding during the quarter (as a percent)	0.16%	0.12%
Medium-term notes due in:
Two years		$ 4,179,985
Three years		2,554,906
Four years		2,119,805
Five years		2,810,894
Thereafter		4,106,144
Total due after one year		15,771,734
Total principal net of discounts		$ 22,758,533
Weighted - average rate (as a percent)		1.10%
Total weighted - average rate (as a percent)		0.90%
Medium-term notes | Two years
Medium-term notes due in:
Weighted - average rate (as a percent)		0.81%
Medium-term notes | Three years
Medium-term notes due in:
Weighted - average rate (as a percent)		0.87%
Medium-term notes | Four years
Medium-term notes due in:
Weighted - average rate (as a percent)		0.85%
Medium-term notes | Five years
Medium-term notes due in:
Weighted - average rate (as a percent)		1.07%
Medium-term notes | Thereafter
Medium-term notes due in:
Weighted - average rate (as a percent)		1.69%
Current portion of medium-term notes
Due within one year:
Current portion of medium-term notes	$ 3,684,482	$ 3,981,240
Weighted - average rate (as a percent)	0.81%	0.75%