Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Expense) Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amounts recognized in other comprehensive income (expense)
Net actuarial gain (loss)	$ (405)	$ 416	$ (155)
Amortization of net actuarial (gain) loss	27	132	93
Amortization of net prior service cost (credit)	0	1	2
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	99	85	76
Interest cost	99	78	85
Expected return on plan assets	(106)	(91)	(91)
Amortization of net actuarial loss (gain)	34	118	93
Amortization of net prior service cost (credit)	0	0	0
Settlement loss	0	14	0
Net periodic benefit cost	126	204	163
Amounts recognized in other comprehensive income (expense)
Net actuarial gain (loss)	(333)	342	(156)
Amortization of net actuarial (gain) loss	34	118	93
Amortization of net prior service cost (credit)	0	0	0
Settlement loss	0	14	0
Total amounts recognized in other comprehensive income (expense)	(299)	474	(63)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	7	9	9
Interest cost	15	14	16
Expected return on plan assets	0	0	0
Amortization of net actuarial loss (gain)	(7)	0	0
Amortization of net prior service cost (credit)	0	1	2
Settlement loss	0	0	0
Net periodic benefit cost	15	24	27
Amounts recognized in other comprehensive income (expense)
Net actuarial gain (loss)	(72)	74	1
Amortization of net actuarial (gain) loss	(7)	0	0
Amortization of net prior service cost (credit)	0	1	2
Settlement loss	0	0	0
Total amounts recognized in other comprehensive income (expense)	$ (79)	$ 75	$ 3