Accumulated Other Comprehensive Income (Loss) (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2016 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	$ 15,457
Other comprehensive income (loss), before reclassifications	(120)
Reclassifications to Consolidated Statement of Income	16
Balance	14,600
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	3
Balance	(39)
Pension and Other Postretirement Plans [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(341)
Other comprehensive income (loss), before reclassifications	(120)
Reclassifications to Consolidated Statement of Income	13
Balance	(448)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(383)
Balance	$ (487)