Securities Available for Sale and Securities Held to Maturity (Maturities of Securities Held to Maturity) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity Within 1 year	$ 100
Securities held to maturity After 1 year through 5 years	609
Securities held to maturity After 5 years through 10 years	13,380
Securities held to maturity After 10 years	17,580
Securities held to maturity, fair value	31,669		29,490
Securities held to maturity Within 1 year amortized cost	100
Securities held to maturity After 1 year through 5 years amortized cost	601
Securities held to maturity After 5 years through 10 years amortized cost	13,717
Securities held to maturity After 10 years amortized cost	17,705
Securities held to maturity	32,123		30,318
U.S. agency mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity Within 1 year		[1]
Securities held to maturity After 1 year through 5 years	609	[1]
Securities held to maturity After 5 years through 10 years	13,036	[1]
Securities held to maturity After 10 years	17,013	[1]
Securities held to maturity, fair value	30,658	[1]	28,500
Securities held to maturity	31,066		29,260
Non-agency commercial mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity After 5 years through 10 years	344	[1]
Securities held to maturity After 10 years	567	[1]
Securities held to maturity, fair value	911	[1]	890
Securities held to maturity	957		958
Other securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity Within 1 year	100
Securities held to maturity, fair value	100		100
Securities held to maturity	$ 100		$ 100

[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.