Securities Available for Sale and Securities Held to Maturity (Held To Maturity Securities with Unrealized Losses, Aggregated by Category and Period of Continuous Unrealized Loss) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014 security	Dec. 31, 2013 security
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity Less than 12 months Fair Value	$ 415	$ 19,805
Securities held to maturity Less than 12 months Unrealized Losses	1	741
Securities held to maturity 12 months or longer Fair Value	12,805	2,605
Securities held to maturity 12 months or longer Unrealized Losses	308	248
Total Securities held to maturity with unrealized losses Total Fair Value	13,220	22,410
Total Securities held to maturity with unrealized losses Total Unrealized Losses	309	989
Number of held to maturity securities in unrealized loss positions	115	193
U.S. agency mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity Less than 12 months Fair Value	415	19,175
Securities held to maturity Less than 12 months Unrealized Losses	1	698
Securities held to maturity 12 months or longer Fair Value	12,125	2,345
Securities held to maturity 12 months or longer Unrealized Losses	283	223
Total Securities held to maturity with unrealized losses Total Fair Value	12,540	21,520
Total Securities held to maturity with unrealized losses Total Unrealized Losses	284	921
Non-agency commercial mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity Less than 12 months Fair Value		630
Securities held to maturity Less than 12 months Unrealized Losses		43
Securities held to maturity 12 months or longer Fair Value	680	260
Securities held to maturity 12 months or longer Unrealized Losses	25	25
Total Securities held to maturity with unrealized losses Total Fair Value	680	890
Total Securities held to maturity with unrealized losses Total Unrealized Losses	$ 25	$ 68