Accumulated Other Comprehensive Income (Loss) (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2015 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	$ 22,318
Balance	19,359
Interest-rate Derivatives Previously Subject to Hedge Accounting [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(48)
Reclassifications to Consolidated Statement of Income	3
Balance	(45)
Pension and Other Postretirement Plans [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(469)
Reclassifications to Consolidated Statement of Income	18
Balance	(451)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(517)
Reclassifications to Consolidated Statement of Income	21
Balance	$ (496)