Pension and Other Postretirement Benefits - Schedule of Amounts Expected to be Recognized in Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	$ 489	$ 384	$ 247
Prior service cost (benefit) recognition	19	19	19
Pension Benefits [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	384
Prior service cost (benefit) recognition	15
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	35	25	26
Prior service cost (benefit) recognition	(18)	(16)	(17)
Other Postretirement Benefits [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	19
Prior service cost (benefit) recognition	$ (18)