Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss), Before Taxes	$ (78)	$ (432)	$ (78)	$ (432)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), before Tax, beginning balance	(301)	310	(442)	506
Unrealized net gain on securities	276	(605)	447	(718)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, before Tax	1	0	2	(2)
Unrealized net gain on derivatives	44	(45)	67	(45)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax	(101)	(100)	(203)	(214)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	3	8	51	41
Accumulated Other Comprehensive Income (Loss), before Tax, ending balance	(78)	(432)	(78)	(432)
Accumulated Other Comprehensive Income Loss Tax [Abstract]
AOCI, beginning balance	101	(125)	153	(197)
Unrealized net gain on securities	(101)	223	(164)	264
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(1)	0	(1)	1
Unrealized net gain on derivatives	(16)	18	(25)	17
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Tax	37	36	75	79
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax	(1)	(3)	(19)	(15)
AOCI, ending balance	19	149	19	149
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI, beginning balance	(200)	185	(289)	309
Unrealized net gain on securities	175	(382)	283	(454)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	0	0	1	(1)
Unrealized net gain on derivatives	28	(27)	42	(28)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	(64)	(64)	(128)	(135)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	2	5	32	26
AOCI, ending balance	$ (59)	$ (283)	$ (59)	$ (283)