Amounts Recognized in Consolidated Balance Sheet and Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Other Postretirement Benefits
Amounts recognized in the consolidated balance sheets consist of:
Current liability	$ (64)	$ (62)
Noncurrent liability	(1,882)	(1,933)
Total liability	(1,946)	(1,995)
Amounts recognized in accumulated other comprehensive income (loss) consist of:
Net actuarial gain (loss)	236	233
Prior service credit (loss)	246	278
Total accumulated other comprehensive income (loss)	482	511
Pension Benefits
Amounts recognized in the consolidated balance sheets consist of:
Noncurrent asset	2	2
Current liability	(12)	(17)
Noncurrent liability	(1,488)	(2,226)
Total liability	(1,498)	(2,241)
Amounts recognized in accumulated other comprehensive income (loss) consist of:
Net actuarial gain (loss)	(844)	(982)
Prior service credit (loss)	(1)	(1)
Total accumulated other comprehensive income (loss)	$ (845)	$ (983)