Postretirement Health Care and Life Insurance Benefits (One Percentage Point Change In Assumed Health Care Cost Rates Would Have The Following Effects) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Jan. 31, 2015
Postretirement Medical Plans with Prescription Drug Benefits [Abstract]
Effect on total of service and interest cost, 1 - percentage point increase	$ 0
Effect on total of service and interest cost, 1 - percentage point decrease	0
Effect on accumulated postretirement benefit obligations, 1 - percentage point increase	17
Effect on accumulated postretirement benefit obligations, 1 - percentage point decrease	$ (15)