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	Dec. 31, 2013		Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity	$ 30,318		$ 18,194
Securities held to maturity Gross Unrealized Gains	161		558
Securities held to maturity Gross Unrealized Losses	989		20
Securities held to maturity, fair value	29,490		18,732
U.S. agency mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity	29,260		17,750
Securities held to maturity Gross Unrealized Gains	161		558
Securities held to maturity Gross Unrealized Losses	921		19
Securities held to maturity, fair value	28,500	[1]	18,289
Non-agency commercial mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity	958
Securities held to maturity Gross Unrealized Losses	68
Securities held to maturity, fair value	890	[1]
Other securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity	100		444
Securities held to maturity Gross Unrealized Losses			1
Securities held to maturity, fair value	$ 100		$ 443

[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.