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, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	$ 384	$ 247	$ 181
Prior service cost (benefit) recognition	19	19	17
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	25	26	33
Prior service cost (benefit) recognition	$ (16)	$ (17)	$ (15)