Securities Available for Sale and Securities Held to Maturity (Maturities of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, After 1 year through 5 years	$ 2,380
Securities held to maturity, After 5 years through 10 years	20,914
Securities held to maturity, After 10 years	26,794
Securities held to maturity, Fair Value	50,088	$ 34,743
Securities held to maturity, After 1 year through 5 years amortized cost	2,311
Securities held to maturity, After 5 years through 10 years amortized cost	20,878
Securities held to maturity, After 10 years amortized cost	26,818
Securities held to maturity, Amortized Cost	50,007	34,389
U.S. agency mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, After 1 year through 5 years	2,380
Securities held to maturity, After 5 years through 10 years	20,337
Securities held to maturity, After 10 years	26,166
Securities held to maturity, Fair Value	48,883	33,745
Securities held to maturity, Amortized Cost	48,785	33,388
U.S. Treasury securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, After 5 years through 10 years	220
Securities held to maturity, After 10 years	220
Securities held to maturity, Fair Value	220
Securities held to maturity, Amortized Cost	223
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	357
Securities held to maturity, After 10 years	628
Securities held to maturity, Fair Value	985	998
Securities held to maturity, Amortized Cost	$ 999	$ 1,001