Investment Securities (Contractual maturities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Amortized cost
Within one year	$ 1,850
After one year through five years	3,807
After five years through ten years	5,294
After ten years	18,642
Estimated fair value
Within one year	1,857
After one year through five years	4,150
After five years through ten years	5,626
After ten years	$ 22,126