Securities Available for Sale and Securities Held to Maturity (Maturities of Securities Available for Sale and Securities Held to Maturity) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Investment [Line Items]
Securities available for sale fair value Within 1 year	$ 5,422
Securities available for sale fair value After 1 year through 5 years	10,739
Securities available for sale fair value After 5 years through 10 years	6,891
Securities available for sale fair value After 10 years	25,362
Securities available for sale	48,414		46,123
Securities available for sale Within 1 year amortized cost	5,412
Securities available for sale After 1 year through 5 years amortized cost	10,773
Securities available for sale After 5 years through 10 years amortized cost	6,888
Securities available for sale After 10 years amortized cost	25,337
Securities available for sale Amortized Cost	48,410		45,644
Securities held to maturity Within 1 year
Securities held to maturity After 1 year through 5 years	100
Securities held to maturity After 5 years through 10 years	11,792
Securities held to maturity After 10 years	13,396
Securities held to maturity, fair value	25,288		18,732
Securities held to maturity Within 1 year amortized cost
Securities held to maturity After 1 year through 5 years amortized cost	100
Securities held to maturity After 5 years through 10 years amortized cost	12,219
Securities held to maturity After 10 years amortized cost	13,499
Securities held to maturity	25,818		18,194
U.S. agency mortgage-backed securities [Member]
Investment [Line Items]
Securities available for sale fair value After 1 year through 5 years	122	[1]
Securities available for sale fair value After 5 years through 10 years	3,974	[1]
Securities available for sale fair value After 10 years	14,512	[1]
Securities available for sale	18,608	[1]	20,476
Securities available for sale Amortized Cost	18,422		20,080
Securities held to maturity Within 1 year		[1]
Securities held to maturity After 5 years through 10 years	11,458	[1]
Securities held to maturity After 10 years	12,970	[1]
Securities held to maturity, fair value	24,428	[1]	18,289
Securities held to maturity	24,887		17,750
Asset-backed securities [Member]
Investment [Line Items]
Securities available for sale fair value After 1 year through 5 years	856
Securities available for sale fair value After 5 years through 10 years	1,060
Securities available for sale fair value After 10 years	9,923
Securities available for sale	11,839		8,164
Securities available for sale Amortized Cost	11,895		8,104
Corporate debt securities [Member]
Investment [Line Items]
Securities available for sale fair value Within 1 year	2,234
Securities available for sale fair value After 1 year through 5 years	6,085
Securities available for sale	8,319		6,256
Securities available for sale Amortized Cost	8,306		6,197
Certificates of deposit [Member]
Investment [Line Items]
Securities available for sale fair value Within 1 year	3,028
Securities available for sale fair value After 1 year through 5 years	1,893
Securities available for sale	4,921		6,161
Securities available for sale Amortized Cost	4,915		6,150
U.S. agency notes [Member]
Investment [Line Items]
Securities available for sale fair value After 1 year through 5 years	1,781
Securities available for sale fair value After 5 years through 10 years	1,854
Securities available for sale	3,635		3,464
Securities available for sale Amortized Cost	3,740		3,465
Non-agency residential mortgage-backed securities [Member]
Investment [Line Items]
Securities available for sale fair value After 1 year through 5 years	2	[1]
Securities available for sale fair value After 5 years through 10 years	3	[1]
Securities available for sale fair value After 10 years	646	[1]
Securities available for sale	651	[1]	733
Securities available for sale Amortized Cost	700		796
Commercial paper [Member]
Investment [Line Items]
Securities available for sale fair value Within 1 year	160
Securities available for sale	160		574
Securities available for sale Amortized Cost	160		574
Other securities [Member]
Investment [Line Items]
Securities available for sale fair value After 10 years	281
Securities available for sale	281		295
Securities available for sale Amortized Cost	272		278
Securities held to maturity Within 1 year
Securities held to maturity After 1 year through 5 years	100
Securities held to maturity After 5 years through 10 years	334
Securities held to maturity After 10 years	426
Securities held to maturity, fair value	860		443
Securities held to maturity	$ 931		$ 444

[1] Mortgage-backed securities have been allocated to maturity groupings based on final contractual maturities. Actual maturities will differ from final contractual maturities because borrowers on a certain portion of loans underlying these securities have the right to prepay their obligations.