Investment Securities (Contractual maturities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Amortized cost
Within one year	$ 2,478
After one year through five years	3,521
After five years through ten years	5,285
After ten years	18,782
Estimated fair value
Within one year	2,492
After one year through five years	3,768
After five years through ten years	5,686
After ten years	$ 22,888