Securities Available for Sale and Securities Held to Maturity (Securities with Unrealized Losses, Aggregated by Category and Period of Continuous Unrealized Loss) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Securities Available for Sale and Securities Held to Maturity [Abstract]
Securities available for sale Less than 12 months Fair Value	$ 14,204		$ 16,962
Securities available for sale Less than 12 months Unrealized Losses	132		200
Securities available for sale 12 months or longer Fair Value	1,795		1,856
Securities available for sale 12 months or longer Unrealized Losses	34		41
Total Securities available for sale with unrealized losses Total Fair Value	15,999		18,818
Total Securities available for sale with unrealized losses Total Unrealized Losses	166		241
Securities held to maturity Less than 12 months Fair Value	15,591		19,805
Securities held to maturity Less than 12 months Unrealized Losses	461		741
Securities held to maturity 12 months or longer Fair Value	2,929		2,605
Securities held to maturity 12 months or longer Unrealized Losses	213		248
Total Securities held to maturity with unrealized losses Total Fair Value	18,520		22,410
Total Securities held to maturity with unrealized losses Total Unrealized Losses	674		989
Securities Less than 12 months Fair Value	29,795	[1]	36,767	[2]
Securities Less than 12 months Unrealized Losses	593	[1]	941	[2]
Securities 12 months or longer Fair Value	4,724	[1]	4,461	[2]
Securities 12 months or longer Unrealized Losses	247	[1]	289	[2]
Total securities with unrealized losses Total Fair Value	34,519	[1]	41,228	[2]
Total securities with unrealized losses Total Unrealized Losses	$ 840	[1]	$ 1,230	[2]

[1] The number of investment positions with unrealized losses totaled 264 for securities available for sale and 154 for securities held to maturity.

[2] The number of investment positions with unrealized losses totaled 273 for securities available for sale and 193 for securities held to maturity.