Investment Securities (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010
Investment Securities
Non-marketable FHLB and FRB stock held for debt and regulatory purposes	$ 45,300,000	$ 45,200,000
Non-marketable private equity investments held	66,400,000	58,200,000
U.S. Treasury inflation-protected securities held	352,000,000
Auction rate securities held at fair value	139,700,000
Common stock classified as equity securities held by the holding company	29,200,000
Percentage decrease requiring a review for impairment	20.00%
Fair value of securities on other-than-temporary impairment watch list	241,400,000
Aggregate fair value of non-agency mortgage backed securities with other than temporary impairment	134,700,000
Credit-related portion of impairments included in earnings	9,300,000
Noncredit-related portion of impairments recognized in other comprehensive income	7,600,000
Number of individual securities held in the available for sale portfolio	1,500
Number of individual securities in a loss position held in the available for sale portfolio	199
Portfolio securities aggregate fair value loss position	1,300,000,000
Fair value of securities with temporary impairment in a loss position for 12 months or longer	111,700,000
Fair value of securities identified as other-than-temporarily impaired which have been in a loss position for 12 months or longer, as a percentage of the total available for sale portfolio value	1.20%
Unrealized losses on temporarily impaired securities, 12 months or more	205,500,000
Percent of securities with temporary impairment loss position for 12 months or longer	2.20%
Gross unrealized losses included in state and municipal obligation holdings	11,900,000
Unrealized losses included in auction rate securities held	11,100,000
Unrealized losses included in other state and municipal obligations held	802,000
Aggregate fair value of state and municipal obligations excluding auction rate securities	1,100,000,000
State and municipal obligation portfolio, excluding auction rate securities, as a percentage of total available for sale securities	12.10%
Securities pledged as collateral	3,900,000,000
Securities pledged as collateral and may be sold or re-pledged	420,300,000
Number of investments in a single issuer that exceed 10% of stockholder's equity	$ 0
No investment in a single issuer exceeds this percentage of stockholder's equity	10.00%