Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Benefit Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 24	$ 24	$ 67	$ 70
Interest cost	18	19	56	55
Expected return on plan assets	(27)	(28)	(81)	(81)
Amortization – prior service credit	(12)	(12)	(35)	(34)
Amortization – actuarial loss	12	14	38	53
Amortization - settlement loss	21	23	90	83
Net periodic benefit cost	36	40	135	146
Other Benefits
Components of net periodic benefit cost:
Service cost	7	7	20	19
Interest cost	7	6	24	19
Expected return on plan assets	0	0	0	0
Amortization – prior service credit	(1)	(1)	(3)	(3)
Amortization – actuarial loss	1	1	2	2
Amortization - settlement loss	0	0	0	0
Net periodic benefit cost	$ 14	$ 13	$ 43	$ 37