Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
AOCI, beginning balance	$ 310	$ 2,624	$ 506	$ 2,744
Unrealized net gain on securities	(605)	236	(718)	331
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, before Tax	0	(14)	(2)	(32)
Unrealized net gain on derivatives	(45)	14	(45)	6
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax	(100)	(121)	(214)	(272)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	8	(6)	41	(44)
AOCI, ending balance	(432)	2,733	(432)	2,733
Accumulated Other Comprehensive Income Loss Tax [Abstract]
AOCI, beginning balance	(125)	(950)	(197)	(995)
Unrealized net gain on securities	223	(85)	264	(119)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	0	5	1	12
Unrealized net gain on derivatives	18	(7)	17	(5)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Tax	36	45	79	101
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax	(3)	2	(15)	16
AOCI, ending balance	149	(990)	149	(990)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI, beginning balance	185	1,674	309	1,749
Unrealized net gain on securities	(382)	151	(454)	212
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	0	(9)	(1)	(20)
Unrealized net gain on derivatives	(27)	7	(28)	1
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	(64)	(76)	(135)	(171)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	5	(4)	26	(28)
AOCI, ending balance	$ (283)	$ 1,743	$ (283)	$ 1,743