Investment Securities (Contractual maturities) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Amortized Cost [Member]
Investment [Line Items]
Within one year	$ 2,675
After one year through five years	3,424
After five years through ten years	5,346
After ten years	17,841
Estimated Fair Value [Member]
Investment [Line Items]
Within one year	2,689
After one year through five years	3,630
After five years through ten years	5,604
After ten years	$ 20,132