Securities (Narrative) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
FNMA Investment [Member]
Securities, amortized cost	$ 12,500,000,000
Securities, fair value	12,300,000,000
FHLMC Investment [Member]
Securities, amortized cost	5,500,000,000
Securities, fair value	5,500,000,000
States and Political Subdivisions [Member]
Fair value hedge basis adjustments	55,000,000
Securities Acquired from FDIC [Member] | Non-Agency MBS [Member]
Securities, fair value	931,000,000	1,100,000,000
Contractually specified indemnification amount, AFS securities	626,000,000
Securities Acquired from FDIC [Member] | States and Political Subdivisions [Member]
Securities, fair value	$ 312,000,000	$ 314,000,000