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	Dec. 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	$ 11,028		$ 16,962
Securities available for sale Less than 12 months Unrealized Losses	25		200
Securities available for sale 12 months or longer Fair Value	6,807		1,856
Securities available for sale 12 months or longer Unrealized Losses	58		41
Total Securities available for sale with unrealized losses Total Fair Value	17,835		18,818
Total Securities available for sale with unrealized losses Total Unrealized Losses	83		241
Securities held to maturity Less than 12 months Fair Value	264		19,805
Securities held to maturity Less than 12 months Unrealized Losses	1		741
Securities held to maturity 12 months or longer Fair Value	11,075		2,605
Securities held to maturity 12 months or longer Unrealized Losses	187		248
Total Securities held to maturity with unrealized losses Total Fair Value	11,339		22,410
Total Securities held to maturity with unrealized losses Total Unrealized Losses	188		989
Securities Less than 12 months Fair Value	11,292	[1]	36,767	[2]
Securities Less than 12 months Unrealized Losses	26	[1]	941	[2]
Securities 12 months or longer Fair Value	17,882	[1]	4,461	[2]
Securities 12 months or longer Unrealized Losses	245	[1]	289	[2]
Total securities with unrealized losses Total Fair Value	29,174	[1]	41,228	[2]
Total securities with unrealized losses Total Unrealized Losses	$ 271	[1]	$ 1,230	[2]

[1] The number of investment positions with unrealized losses totaled 173 for securities available for sale and 111 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.