Pension and Other Benefit Plans - Defined Benefit Plan, Amounts That Will be Amortized from Accumulated Other Comprehensive Income (loss) in Next Fiscal Year (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Pension Plans
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Net actuarial losses	$ 274
Prior service cost (credit)	133
Postretirement medical plan
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Net actuarial losses	17
Prior service cost (credit)	$ (32)