Investment Securities (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 State And Municipal Obligations [Member]	Dec. 31, 2011 State And Municipal Obligations [Member]	Dec. 31, 2008 State And Municipal Obligations [Member]
Investment [Line Items]
Non-marketable FHLB and FRB stock held for debt and regulatory purposes	$ 45,300,000	$ 45,300,000
Non-marketable private equity investments held	75,400,000	70,500,000
U.S. Treasury inflation-protected securities held	360,500,000
Auction rate securities held at fair value					129,900,000
Common stock classified as equity securities held by the holding company	27,500,000
Percentage decrease requiring a review for impairment	20.00%
Fair value of securities on other-than-temporary impairment watch list	211,500,000
Aggregate fair value of non-agency mortgage backed securities with other-than-temporary impairment	118,300,000
Credit-related portion of impairments included in earnings	10,400,000
Noncredit-related portion of impairments recognized in other comprehensive income	1,500,000
Number of individual securities held in the available for sale portfolio	1,550
Number of individual securities in a loss position held in the available for sale portfolio	181
Portfolio securities aggregate fair value loss position	1,259,323,000	1,715,182,000	235,388,000	176,769,000
Fair value of securities with an other-than-temporary impairment, which have been in a loss position for 12 months or longer	60,700,000
Fair value of securities with temporary impairment with loss position for twelve months or longer	195,000,000
The 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.	0.70%
Fair value of securities with temporary impairment in a loss position for 12 months or longer, as a percentage of total available for sale portfolio	2.10%
Gross unrealized losses included in state and municipal obligation holdings	17,900,000
Unrealized losses included in auction rate securities held	16,500,000
Unrealized losses included in other state and municipal obligations held	1,300,000
Aggregate fair value of state and municipal obligations excluding auction rate securities	1,200,000,000
State and municipal obligation portfolio, excluding auction rate securities, as a percentage of total available for sale securities	13.10%
Securities pledged as collateral	4,200,000,000
Securities pledged as collateral and may be sold or re-pledged	$ 420,100,000
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%