Investment Securities (Contractual maturities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Amortized Cost [Member]
Investment [Line Items]
Within one year	$ 2,771
After one year through five years	3,480
After five years through ten years	5,032
After ten years	18,056
Estimated Fair Value [Member]
Investment [Line Items]
Within one year	2,786
After one year through five years	3,688
After five years through ten years	5,264
After ten years	$ 20,061