Securities (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Pledged securities carrying value	$ 12,900,000,000	$ 15,500,000,000
Unrealized losses on temporarily impaired available for sale securities, 12 months or more	112,000,000	197,000,000
Fair value hedge basis adjustments	88,000,000
Fannie Mae Investment [Member]
Securities, amortized cost	10,600,000,000
Securities, fair value	10,800,000,000
Freddie Mac Investment [Member]
Securities, amortized cost	8,300,000,000
Securities, fair value	8,300,000,000
Non-Agency Residential Mortgage-Backed Securities [Member]
Unrealized losses on temporarily impaired available for sale securities, 12 months or more	11,000,000	55,000,000
States and Political Subdivisions [Member]
Unrealized losses on temporarily impaired available for sale securities, 12 months or more	100,000,000	142,000,000
Covered Securities [Member]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	4,000,000
Covered Securities [Member] | Non-Agency Residential Mortgage-Backed Securities [Member]
Securities, fair value	1,300,000,000	1,300,000,000
Covered Securities [Member] | States and Political Subdivisions [Member]
Securities, fair value	$ 328,000,000	$ 326,000,000