Securities (Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Securities
AFS securities, debt securities due in one year or less, amortized cost	$ 522
AFS securities, debt securities due in one year or less, fair value	523
AFS securities, debt securities due after one year through five years, amortized cost	678
AFS securities, debt securities due after one year through five years, fair value	688
AFS securities, debt securities due after five years through ten years, amortized cost	545
AFS securities, debt securities due after five years through ten years, fair value	578
AFS securities, debt securities due after ten years, amortized cost	19,285
AFS securities, debt securities due after ten years, fair value	19,385
Total AFS debt securities, amortized cost	21,030
Total AFS debt securities, fair value	21,174
HTM securities, debt securities due after one year through five years, amortized cost	200
HTM securities, debt securities due after one year through five years, fair value	194
HTM securities, debt securities due after five years through ten years, amortized cost	6,440
HTM securities, debt securities due after five years through ten years, fair cost	6,268
HTM securities, debt securities due after ten years, amortized cost	14,077
HTM securities, debt securities due after ten years, fair value	14,040
HTM securities, amortized cost	20,717	18,101
Held-to-maturity Securities, Fair Value	$ 20,502	$ 17,530