Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 24	$ 33
Interest cost	51	47
Expected return on plan assets	(45)	(40)
Amortization of unrecognized (gain) loss and prior service cost (credit)	3	18
Total	33	58
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	14
Interest cost	22	28
Expected return on plan assets	(1)	(1)
Amortization of unrecognized (gain) loss and prior service cost (credit)	(19)	3
Total	$ 7	$ 44