Securities (Narrative) (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
FNMA Investment [Member]
Securities, amortized cost	$ 12,400,000,000
Securities, fair value	12,100,000,000
FHLMC Investment [Member]
Securities, amortized cost	5,800,000,000
Securities, fair value	5,600,000,000
States and Political Subdivisions [Member]
Fair value hedge basis adjustments	48,000,000
Covered [Member] | Non-Agency MBS [Member]
Securities, fair value	1,000,000,000	1,100,000,000
Covered [Member] | States and Political Subdivisions [Member]
Securities, fair value	$ 316,000,000	$ 314,000,000