Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (294)	$ (59)	$ (294)	$ (59)	$ (65)	$ (122)	$ (200)	$ (289)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	(192)	175	(106)	283
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	5	28	83	42
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Total Unrealized Gain (Loss) Arising During Period, Net of Tax	(187)	203	(23)	325
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(9)	0	(9)	1
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(39)	(64)	(73)	(128)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	6	2	(67)	32
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(42)	(62)	(149)	(95)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(201)	175	(115)	284
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(34)	(36)	10	(86)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	6	2	(67)	32
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(229)	141	(172)	230
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	183	207	183	207	384	298	32	(77)
Derivative [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	107	193	107	193	141	97	229	279
Pension and Other Postretirement Plans Costs [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (584)	$ (459)	$ (584)	$ (459)	$ (590)	$ (517)	$ (461)	$ (491)