Investment Securities (Narrative) (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Investment Securities Disclosure [Abstract]
Gross unrealized loss on debt securities held to maturity	$ 2,000,000	$ 6,000,000
Gross unrealized loss on debt securities held to maturity in a continuous loss position for less than 12 months - fair value	200,000,000	500,000,000
Gain on derivatives used to hedge purchase of investment securities	91,000,000
Gross unrealized loss on debt securities held to maturity in a continuous loss position greater than 12 months - fair value	$ 100,000,000