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	Sep. 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	$ 4,584	$ 19,805
Securities held to maturity Less than 12 months Unrealized Losses	19	741
Securities held to maturity 12 months or longer Fair Value	12,210	2,605
Securities held to maturity 12 months or longer Unrealized Losses	369	248
Total Securities held to maturity with unrealized losses Total Fair Value	16,794	22,410
Total Securities held to maturity with unrealized losses Total Unrealized Losses	388	989
Number of held to maturity securities in unrealized loss positions	144	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	4,421	19,175
Securities held to maturity Less than 12 months Unrealized Losses	17	698
Securities held to maturity 12 months or longer Fair Value	11,565	2,345
Securities held to maturity 12 months or longer Unrealized Losses	340	223
Total Securities held to maturity with unrealized losses Total Fair Value	15,986	21,520
Total Securities held to maturity with unrealized losses Total Unrealized Losses	357	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	163	630
Securities held to maturity Less than 12 months Unrealized Losses	2	43
Securities held to maturity 12 months or longer Fair Value	645	260
Securities held to maturity 12 months or longer Unrealized Losses	29	25
Total Securities held to maturity with unrealized losses Total Fair Value	808	890
Total Securities held to maturity with unrealized losses Total Unrealized Losses	$ 31	$ 68