Restructuring and Impairments - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014 NA Truck [Member]	Jan. 31, 2013 NA Truck [Member] Discontinuation Engineering Program [Member]	Apr. 30, 2013 NA Truck [Member] Garland Assembly Plant [Member] Garland plant closure [Member]	Jan. 31, 2013 NA Truck [Member] Garland Assembly Plant [Member] Garland plant closure [Member]	Jan. 31, 2014 NA Truck [Member] Huntsville Engine Plant [Member] Employee Severance [Member]	Jan. 31, 2014 NA Truck [Member] Huntsville Engine Plant [Member] Engine Plant Consolidation [Member]	Oct. 31, 2013 Voluntary Separation Program [Member] Employee Severance [Member]	Jan. 31, 2014 Minimum [Member] NA Truck [Member] Chatham [Member]	Jan. 31, 2014 Maximum [Member] NA Truck [Member] Chatham [Member]	Jul. 31, 2013 Discontinuation Engineering Program [Member] NA Truck [Member]
Restructuring Cost and Reserve [Line Items]
Asset impairment charges	$ 18	$ 0	$ 18									$ 17
Restructuring charges	3	2		13	8	12	1	2	11
Restructuring and Related Cost, Expected Cost										$ 20	$ 70