Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Gain (Loss) on Investments [Line Items]
Amortized cost	$ 87,021		$ 80,945
Gross unrealized Gains	2,128		2,063
Gross unrealized Losses	926		1,001
Fair value	88,223		82,007
Available-for-sale
Gain (Loss) on Investments [Line Items]
Amortized cost	82,202		77,424
Gross unrealized Gains	1,982		1,917
Gross unrealized Losses	810		874
Fair value	83,374		78,467
Available-for-sale | U.S. Treasury
Gain (Loss) on Investments [Line Items]
Amortized cost	14,058		16,814
Gross unrealized Gains	294		514
Gross unrealized Losses	101		2
Fair value	14,251		17,326
Available-for-sale | U.S. Government Agencies
Gain (Loss) on Investments [Line Items]
Amortized cost	1,079		932
Gross unrealized Gains	29		26
Fair value	1,108		958
Available-for-sale | State And Political Subdivisions
Gain (Loss) on Investments [Line Items]
Amortized cost	3,964		2,724
Gross unrealized Gains	58		62
Gross unrealized Losses	49		47
Fair value	3,973		2,739
Available-for-sale | Agency RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	31,882		26,232
Gross unrealized Gains	643		575
Gross unrealized Losses	28		11
Fair value	32,497		26,796
Available-for-sale | Alt-A RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	289		306
Gross unrealized Gains	19		9
Gross unrealized Losses	24		42
Fair value	284		273
Available-for-sale | Prime RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	865		916
Gross unrealized Gains	3		1
Gross unrealized Losses	57		102
Fair value	811		815
Available-for-sale | Subprime RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	593		606
Gross unrealized Gains	3		2
Gross unrealized Losses	175		190
Fair value	421		418
Available-for-sale | Other RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	1,559		1,133
Gross unrealized Gains	2
Gross unrealized Losses	214		230
Fair value	1,347		903
Available-for-sale | Commercial MBS
Gain (Loss) on Investments [Line Items]
Amortized cost	3,435		3,327
Gross unrealized Gains	123		89
Gross unrealized Losses	76		77
Fair value	3,482		3,339
Available-for-sale | Asset-Backed CLOs
Gain (Loss) on Investments [Line Items]
Amortized cost	1,357		1,480
Gross unrealized Gains	2		1
Gross unrealized Losses	21		37
Fair value	1,338		1,444
Available-for-sale | Other Asset-Backed Securities
Gain (Loss) on Investments [Line Items]
Amortized cost	576		527
Gross unrealized Gains	9		8
Gross unrealized Losses	3		3
Fair value	582		532
Available-for-sale | Foreign Covered Bonds
Gain (Loss) on Investments [Line Items]
Amortized cost	3,171		2,410
Gross unrealized Gains	38		18
Gross unrealized Losses	2		3
Fair value	3,207		2,425
Available-for-sale | Corporate Bonds
Gain (Loss) on Investments [Line Items]
Amortized cost	1,642		1,696
Gross unrealized Gains	57		47
Gross unrealized Losses	3		5
Fair value	1,696		1,738
Available-for-sale | Other Debt Securities
Gain (Loss) on Investments [Line Items]
Amortized cost	13,878		14,320
Gross unrealized Gains	300		292
Gross unrealized Losses	24		33
Fair value	14,154	[1]	14,579	[2]
Available-for-sale | Equity Securities
Gain (Loss) on Investments [Line Items]
Amortized cost	28		26
Gross unrealized Gains	6		4
Fair value	34		30
Available-for-sale | Money Market Funds
Gain (Loss) on Investments [Line Items]
Amortized cost	957		973
Fair value	957		973
Available-for-sale | Grantor Trust Alt-A RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	1,734	[3]	1,790	[3]
Gross unrealized Gains	252	[3]	157	[3]
Gross unrealized Losses	24	[3]	68	[3]
Fair value	1,962	[3]	1,879	[3]
Available-for-sale | Grantor Trust Prime RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	1,024	[3]	1,090	[3]
Gross unrealized Gains	136	[3]	106	[3]
Gross unrealized Losses	7	[3]	21	[3]
Fair value	1,153	[3]	1,175	[3]
Available-for-sale | Grantor Trust Sub Prime RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	111	[3]	122	[3]
Gross unrealized Gains	8	[3]	6	[3]
Gross unrealized Losses	2	[3]	3	[3]
Fair value	117	[3]	125	[3]
Held-to-maturity
Gain (Loss) on Investments [Line Items]
Amortized cost	4,819		3,521
Gross unrealized Gains	146		146
Gross unrealized Losses	116		127
Fair value	4,849		3,540
Held-to-maturity | U.S. Treasury
Gain (Loss) on Investments [Line Items]
Amortized cost	862		813
Gross unrealized Gains	43		53
Fair value	905		866
Held-to-maturity | State And Political Subdivisions
Gain (Loss) on Investments [Line Items]
Amortized cost	91		100
Gross unrealized Gains	3		3
Fair value	94		103
Held-to-maturity | Agency RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	2,000		658
Gross unrealized Gains	41		39
Fair value	2,041		697
Held-to-maturity | Alt-A RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	143		153
Gross unrealized Gains	6		4
Gross unrealized Losses	14		19
Fair value	135		138
Held-to-maturity | Prime RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	117		121
Gross unrealized Gains	1
Gross unrealized Losses	7		10
Fair value	111		111
Held-to-maturity | Subprime RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	28		28
Gross unrealized Losses	3		3
Fair value	25		25
Held-to-maturity | Other RMBS
Gain (Loss) on Investments [Line Items]
Amortized cost	1,546		1,617
Gross unrealized Gains	52		47
Gross unrealized Losses	89		93
Fair value	1,509		1,571
Held-to-maturity | Commercial MBS
Gain (Loss) on Investments [Line Items]
Amortized cost	29		28
Gross unrealized Losses	3		2
Fair value	26		26
Held-to-maturity | Other Securities
Gain (Loss) on Investments [Line Items]
Amortized cost	3		3
Fair value	$ 3		$ 3

[1] Includes $12.4 billion, at fair value, of government-sponsored and guaranteed entities, and sovereign debt.

[2] Includes $13.1 billion, at fair value, of government-sponsored and guaranteed entities, and sovereign debt.

[3] Previously included in the Grantor Trust. The Grantor Trust was dissolved in the first quarter of 2011.