Reclassifications from Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Jan. 31, 2015
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic benefit cost	$ 12
Income tax expense	4
Net of tax	8
Pension Benefits
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic benefit cost	15
Postretirement Benefits
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic benefit cost	$ (3)