Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Benefit Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 20	$ 23	$ 43	$ 46
Interest cost	18	18	38	36
Expected return on plan assets	(26)	(26)	(54)	(53)
Amortization – prior service credit	(11)	(11)	(23)	(22)
Amortization – actuarial loss	13	18	26	39
Amortization - settlement loss	(5)	(60)	(69)	(60)
Net periodic benefit cost	19	82	99	106
Other Benefits
Components of net periodic benefit cost:
Service cost	6	6	13	12
Interest cost	9	6	17	13
Expected return on plan assets	0	0	0	0
Amortization – prior service credit	(1)	0	(2)	(2)
Amortization – actuarial loss	0	0	1	1
Amortization - settlement loss	0	0	0	0
Net periodic benefit cost	$ 14	$ 12	$ 29	$ 24