Investment Securities (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013 Securities	Dec. 31, 2012 Securities
Investment [Line Items]
Non-marketable FHLB and FRB stock held for debt and regulatory purposes	$ 45,400,000	$ 45,400,000
Non-marketable private equity investments held	73,200,000	73,200,000
U.S. Treasury inflation-protected securities held	437,200,000
Common stock classified as equity securities held by the holding company	37,000,000
Percentage decrease requiring a review for impairment	20.00%
Fair value of securities on other-than-temporary impairment watch list	214,800,000	220,700,000
Aggregate fair value of non-agency mortgage backed securities with other-than-temporary impairment	96,400,000
Credit-related portion of impairments included in earnings	12,000,000
Number of individual securities held in the available for sale portfolio	1,700
Number of individual securities held in the available for sale portfolio in a loss position	197	144
Portfolio securities aggregate fair value loss position	1,769,667,000	901,882,000
Increase In Unrealized Loss	4,600,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	24,743,000	20,171,000
Minimum period that OTTI securities have been in a loss position	12 months
Fair value of securities with an other-than-temporary impairment, which have been in a loss position for 12 months or longer	2,400,000
Fair value of securities with temporary impairment with loss position for twelve months or longer	202,200,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Percent of Portfolio	2.10%
Gross unrealized losses included in state and municipal obligation holdings	15,700,000
Securities pledged as collateral	4,800,000,000
Securities pledged as collateral and may be sold or re-pledged	733,500,000
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%
State And Municipal Obligations [Member]
Investment [Line Items]
Auction rate securities held at fair value	128,100,000
Portfolio securities aggregate fair value loss position	248,106,000	254,130,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	15,725,000	16,295,000
Unrealized losses included in auction rate securities held	12,200,000
Unrealized losses included in other state and municipal obligations held	3,500,000
Aggregate fair value of state and municipal obligations excluding auction rate securities	$ 1,500,000,000
State and municipal obligation portfolio, excluding auction rate securities, as a percentage of total available for sale securities	16.00%