Employee Benefits - Components of Net Pension and Other Postretirement Benefit Costs Reflected in Net Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]
Components of net pension and other postretirement benefit costs reflected in net income
Service cost	$ 95	$ 88	$ 79
Interest cost	125	124	120
Expected return on plan assets	(165)	(155)	(140)
Amortization of net actuarial loss and prior service cost and other	90	80	68
Total benefit costs reflected in net income	145	137	127
Other Postretirement Benefits [Member]
Components of net pension and other postretirement benefit costs reflected in net income
Service cost	13	12	11
Interest cost	19	20	22
Expected return on plan assets	(7)	(6)	(5)
Amortization of net actuarial loss and prior service cost and other	3	3	3
Total benefit costs reflected in net income	$ 28	$ 29	$ 31