Securities Available for Sale and Securities Held to Maturity (Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value 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, Amortized Cost	$ 32,123		$ 30,318
Securities held to maturity Gross Unrealized Gains	220		161
Securities held to maturity Gross Unrealized Losses	674		989
Securities held to maturity, fair value	31,669		29,490
U.S. agency mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, Amortized Cost	31,066		29,260
Securities held to maturity Gross Unrealized Gains	219		161
Securities held to maturity Gross Unrealized Losses	627		921
Securities held to maturity, fair value	30,658	[1]	28,500
Non-agency commercial mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, Amortized Cost	957		958
Securities held to maturity Gross Unrealized Gains	1
Securities held to maturity Gross Unrealized Losses	47		68
Securities held to maturity, fair value	911	[1]	890
Other securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, Amortized Cost	100		100
Securities held to maturity, fair value	$ 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.