Investment Securities (Contractual maturities) (Details) $ in Millions	Sep. 30, 2015 USD ($)
Amortized Cost
Within one year	$ 2,162
After one year through five years	4,656
After five years through ten years	4,854
After ten years	17,921
Estimated Fair Value
Within one year	2,171
After one year through five years	4,868
After five years through ten years	5,217
After ten years	$ 20,983