Securities-Aggregate Fair Value of Investments with Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	$ 44,435		$ 5,758
Less than 12 months Unrealized losses	1,387		63
12 months or more Fair value	2,778		2,798
12 months or more Unrealized losses	176		300
Total Fair value	47,213		8,556
Total Unrealized losses	1,563		363
Available-for-sale
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	27,659		5,073
Less than 12 months Unrealized losses	1,192		62
12 months or more Fair value	1,761		2,296
12 months or more Unrealized losses	125		239
Total Fair value	29,420		7,369
Total Unrealized losses	1,317		301
Available-for-sale | U.S. Treasury
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	4,849		956
Less than 12 months Unrealized losses	434		3
12 months or more Fair value	0		0
12 months or more Unrealized losses	0		0
Total Fair value	4,849		956
Total Unrealized losses	434		3
Available-for-sale | U.S. Government agencies
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	97
Less than 12 months Unrealized losses	4
12 months or more Fair value	0
12 months or more Unrealized losses	0
Total Fair value	97
Total Unrealized losses	4		0
Available-for-sale | State and political subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	2,883		1,139
Less than 12 months Unrealized losses	81		7
12 months or more Fair value	139		173
12 months or more Unrealized losses	6		22
Total Fair value	3,022		1,312
Total Unrealized losses	87		29
Available-for-sale | Agency RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	11,898		1,336
Less than 12 months Unrealized losses	475		8
12 months or more Fair value	84		96
12 months or more Unrealized losses	5		0
Total Fair value	11,982		1,432
Total Unrealized losses	480		8
Available-for-sale | Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	16		31
Less than 12 months Unrealized losses	9		13
12 months or more Fair value	34		39
12 months or more Unrealized losses	1		3
Total Fair value	50		70
Total Unrealized losses	10		16
Available-for-sale | Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	113		110
Less than 12 months Unrealized losses	3		2
12 months or more Fair value	180		253
12 months or more Unrealized losses	9		7
Total Fair value	293		363
Total Unrealized losses	12		9
Available-for-sale | Subprime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	0		13
Less than 12 months Unrealized losses	0		3
12 months or more Fair value	384		397
12 months or more Unrealized losses	39		59
Total Fair value	384		410
Total Unrealized losses	39		62
Available-for-sale | Other RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	102		64
Less than 12 months Unrealized losses	28		19
12 months or more Fair value	630		670
12 months or more Unrealized losses	51		90
Total Fair value	732		734
Total Unrealized losses	79		109
Available-for-sale | Commercial MBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	512		131
Less than 12 months Unrealized losses	21		1
12 months or more Fair value	167		310
12 months or more Unrealized losses	10		44
Total Fair value	679		441
Total Unrealized losses	31		45
Available-for-sale | Agency commercial MBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,096
Less than 12 months Unrealized losses	21
12 months or more Fair value	0
12 months or more Unrealized losses	0
Total Fair value	1,096
Total Unrealized losses	21
Available-for-sale | Asset-backed CLOs
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	488		314
Less than 12 months Unrealized losses	1		1
12 months or more Fair value	109		321
12 months or more Unrealized losses	2		9
Total Fair value	597		635
Total Unrealized losses	3		10
Available-for-sale | Other asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,579		779
Less than 12 months Unrealized losses	9		2
12 months or more Fair value	6		7
12 months or more Unrealized losses	1		1
Total Fair value	1,585		786
Total Unrealized losses	10		3
Available-for-sale | Foreign covered bonds
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,164
Less than 12 months Unrealized losses	76
12 months or more Fair value	0
12 months or more Unrealized losses	0
Total Fair value	1,164
Total Unrealized losses	76		0
Available-for-sale | Corporate bonds
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	285		178
Less than 12 months Unrealized losses	17		3
12 months or more Fair value	0		0
12 months or more Unrealized losses	0		0
Total Fair value	285		178
Total Unrealized losses	17		3
Available-for-sale | Other debt securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	2,514
Less than 12 months Unrealized losses	11
12 months or more Fair value	0
12 months or more Unrealized losses	0
Total Fair value	2,514
Total Unrealized losses	11		0
Available-for-sale | Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	33	[1]	22	[1]
Less than 12 months Unrealized losses	1	[1]	0	[1]
12 months or more Fair value	22	[1]	30	[1]
12 months or more Unrealized losses	1	[1]	4	[1]
Total Fair value	55	[1]	52	[1]
Total Unrealized losses	2	[1]	4	[1]
Available-for-sale | Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	30
Less than 12 months Unrealized losses	1
12 months or more Fair value	6
12 months or more Unrealized losses	0
Total Fair value	36
Total Unrealized losses	1	[1]	0	[1]
Held-to-maturity
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	16,776		685
Less than 12 months Unrealized losses	195		1
12 months or more Fair value	1,017		502
12 months or more Unrealized losses	51		61
Total Fair value	17,793		1,187
Total Unrealized losses	246		62
Held-to-maturity | U.S. Treasury
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,920
Less than 12 months Unrealized losses	45
12 months or more Fair value	490
12 months or more Unrealized losses	7
Total Fair value	2,410
Total Unrealized losses	52		0
Held-to-maturity | U.S. Government agencies
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	408
Less than 12 months Unrealized losses	10
12 months or more Fair value	0
12 months or more Unrealized losses	0
Total Fair value	408
Total Unrealized losses	10
Held-to-maturity | State and political subdivisions
Investments, Unrealized Loss Position [Line Items]
Total Unrealized losses	0		0
Held-to-maturity | Agency RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	13,653		234
Less than 12 months Unrealized losses	137		1
12 months or more Fair value	0		0
12 months or more Unrealized losses	0		0
Total Fair value	13,653		234
Total Unrealized losses	137		1
Held-to-maturity | Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	17		38
Less than 12 months Unrealized losses	0		0
12 months or more Fair value	21		24
12 months or more Unrealized losses	3		6
Total Fair value	38		62
Total Unrealized losses	3		6
Held-to-maturity | Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	0		0
Less than 12 months Unrealized losses	0		0
12 months or more Fair value	47		56
12 months or more Unrealized losses	1		1
Total Fair value	47		56
Total Unrealized losses	1		1
Held-to-maturity | Subprime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value			0
Less than 12 months Unrealized losses			0
12 months or more Fair value			24
12 months or more Unrealized losses			1
Total Fair value			24
Total Unrealized losses	0		1
Held-to-maturity | Other RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	145		413
Less than 12 months Unrealized losses	0		0
12 months or more Fair value	439		373
12 months or more Unrealized losses	39		52
Total Fair value	584		786
Total Unrealized losses	39		52
Held-to-maturity | Commercial MBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	0		0
Less than 12 months Unrealized losses	0		0
12 months or more Fair value	20		25
12 months or more Unrealized losses	1		1
Total Fair value	20		25
Total Unrealized losses	1		1
Held-to-maturity | Other debt securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	633
Less than 12 months Unrealized losses	3
12 months or more Fair value	0
12 months or more Unrealized losses	0
Total Fair value	633
Total Unrealized losses	$ 3

[1] Previously included in the Grantor Trust. The Grantor Trust was dissolved in 2011.