Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss), Before Taxes	$ (264)	$ (484)	$ (264)	$ (484)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), before Tax, beginning balance	(78)	(432)	(442)	506
Unrealized net gain on securities	(67)	(18)	379	(736)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, before Tax	9	0	11	(2)
Unrealized net gain on derivatives	(31)	60	36	15
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax	(99)	(101)	(302)	(315)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	2	7	54	48
Accumulated Other Comprehensive Income (Loss), before Tax, ending balance	(264)	(484)	(264)	(484)
Accumulated Other Comprehensive Income Loss Tax [Abstract]
AOCI, beginning balance	19	149	153	(197)
Unrealized net gain on securities	24	7	(140)	271
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(3)	0	(4)	1
Unrealized net gain on derivatives	12	(22)	(13)	(5)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Tax	36	37	111	116
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax	(1)	(3)	(20)	(18)
AOCI, ending balance	87	168	87	168
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI, beginning balance	(59)	(283)	(289)	309
Unrealized net gain on securities	(43)	(11)	239	(465)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	6	0	7	(1)
Unrealized net gain on derivatives	(19)	38	23	10
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	63	64	191	199
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(1)	(4)	(34)	(30)
AOCI, ending balance	$ (177)	$ (316)	$ (177)	$ (316)