Amounts Recognized in Consolidated Balance Sheet and Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits
Amounts recognized in the consolidated balance sheets consist of:
Noncurrent asset	$ 49	$ 35
Current liability	(2)	(4)
Noncurrent liability	(1,650)	(2,400)
Total liability	(1,603)	(2,369)
Amounts recognized in accumulated other comprehensive income (loss) consist of:
Net actuarial gain (loss)	(162)	(826)
Prior service credit (cost)		2
Total accumulated other comprehensive income (loss)	(162)	(824)
Other Postretirement Benefits
Amounts recognized in the consolidated balance sheets consist of:
Current liability	(59)	(71)
Noncurrent liability	(1,703)	(2,614)
Total liability	(1,762)	(2,685)
Amounts recognized in accumulated other comprehensive income (loss) consist of:
Net actuarial gain (loss)	555	(79)
Prior service credit (cost)	306	(24)
Total accumulated other comprehensive income (loss)	$ 861	$ (103)