Securities (Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Securities
AFS securities, debt securities due in one year or less, amortized cost	$ 612
AFS securities, debt securities due in one year or less, fair value	612
AFS securities, debt securities due after one year through five years, amortized cost	828
AFS securities, debt securities due after one year through five years, fair value	839
AFS securities, debt securities due after five years through ten years, amortized cost	583
AFS securities, debt securities due after five years through ten years, fair value	611
AFS securities, debt securities due after ten years, amortized cost	18,637
AFS securities, debt securities due after ten years, fair value	18,845
Total AFS debt securities, amortized cost	20,660
Total AFS debt securities, fair value	20,907
HTM securities, debt securities due after one year through five years, amortized cost	750
HTM securities, debt securities due after one year through five years, fair value	734
HTM securities, debt securities due after five years through ten years, amortized cost	6,007
HTM securities, debt securities due after five years through ten years, fair value	5,960
HTM securities, debt securities due after ten years, amortized cost	13,483
HTM securities, debt securities due after ten years, fair value	13,619
Total HTM securities, amortized cost	20,240	18,101
Total HTM securities, fair value	$ 20,313	$ 17,530