Accumulated Other Comprehensive Income (Loss) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	$ 15,457
Other comprehensive income (loss), before reclassifications	(105)
Reclassifications to Consolidated Statement of Income	(3)
Balance	14,701
Interest-rate Derivatives Previously Subject to Hedge Accounting [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(42)
Other comprehensive income (loss), before reclassifications	0
Reclassifications to Consolidated Statement of Income	2
Balance	(40)
Pension and Other Postretirement Plans [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(341)
Other comprehensive income (loss), before reclassifications	(105)
Reclassifications to Consolidated Statement of Income	(5)
Balance	(451)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(383)
Balance	$ (491)