Reclassifications from Accumulated Other Comprehensive Loss (Detail) $ in Millions	9 Months Ended
	Oct. 31, 2015 USD ($)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic benefit cost	$ 9
Income tax benefit	(3)
Net of tax	6
Pension Benefits
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic benefit cost	10
Postretirement Benefits
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic benefit cost	$ (1)