Accumulated Other Comprehensive Income - Changes in AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (345)	$ (289)	$ (356)	$ (352)
Other comprehensive income before reclassification, net of income taxes	76	(39)	107	40
Amounts reclassified from accumulated other comprehensive income, net of income taxes	(3)	3	(23)	(13)
Total other comprehensive income (loss), net of tax	73	(36)	84	27
Ending balance	(272)	(325)	(272)	(325)
Unrealized Gains (Losses) on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(6)	(4)	(63)
Other comprehensive income before reclassification, net of income taxes	54	(33)	57	24
Amounts reclassified from accumulated other comprehensive income, net of income taxes			1
Total other comprehensive income (loss), net of tax	54	(33)	58	24
Ending balance	54	(39)	54	(39)
Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	7	(7)	(8)	(11)
Other comprehensive income before reclassification, net of income taxes	65	3	107	25
Amounts reclassified from accumulated other comprehensive income, net of income taxes	(17)	(11)	(44)	(29)
Total other comprehensive income (loss), net of tax	48	(8)	63	(4)
Ending balance	55	(15)	55	(15)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	9	39	22	42
Other comprehensive income before reclassification, net of income taxes	(5)	(9)	(19)	(9)
Amounts reclassified from accumulated other comprehensive income, net of income taxes			1	(3)
Total other comprehensive income (loss), net of tax	(5)	(9)	(18)	(12)
Ending balance	4	30	4	30
Net Pension and Postretirement Benefit Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(361)	(315)	(366)	(320)
Other comprehensive income before reclassification, net of income taxes	(38)		(38)
Amounts reclassified from accumulated other comprehensive income, net of income taxes	14	14	19	19
Total other comprehensive income (loss), net of tax	(24)	14	(19)	19
Ending balance	$ (385)	$ (301)	$ (385)	$ (301)