Employee Benefits - Net Actuarial Loss (Gain) and Prior Service Cost Included in Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 396	$ 989
Prior service cost	16	18
Total net actuarial loss and prior service cost included in accumulated other comprehensive income	412	1,007
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	(13)	108
Prior service cost	1
Total net actuarial loss and prior service cost included in accumulated other comprehensive income	$ (12)	$ 108