Securities Available for Sale and Securities Held to Maturity (Maturities of Securities Held to Maturity) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity Within 1 year
Securities held to maturity After 1 year through 5 years	853
Securities held to maturity After 5 years through 10 years	14,742
Securities held to maturity After 10 years	18,344
Securities held to maturity, fair value	33,939		29,490
Securities held to maturity Within 1 year amortized cost
Securities held to maturity After 1 year through 5 years amortized cost	854
Securities held to maturity After 5 years through 10 years amortized cost	14,827
Securities held to maturity After 10 years amortized cost	18,326
Securities held to maturity, Amortized Cost	34,007		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	853	[1]
Securities held to maturity After 5 years through 10 years	14,390	[1]
Securities held to maturity After 10 years	17,721	[1]
Securities held to maturity, fair value	32,964	[1]	28,500
Securities held to maturity, Amortized Cost	33,005		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	352	[1]
Securities held to maturity After 10 years	623	[1]
Securities held to maturity, fair value	975	[1]	890
Securities held to maturity, Amortized Cost	$ 1,002		$ 958

[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.