Investment Securities (Contractual maturities) (Details) $ in Millions	Jun. 30, 2016 USD ($)
Amortized cost
Within one year	$ 5,218
After one year through five years	3,901
After five years through ten years	4,521
After ten years	17,626
Estimated fair value
Within one year	5,226
After one year through five years	4,167
After five years through ten years	5,070
After ten years	$ 21,968