Investment Securities (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Securities Investments_In_Single_Issuer	Dec. 31, 2011
Investment [Line Items]
Non-marketable FHLB and FRB stock held for debt and regulatory purposes	$ 45,400,000	$ 45,300,000
Non-marketable private equity investments held	73,200,000	70,500,000
U.S. Treasury inflation-protected securities held	438,600,000
Common stock classified as equity securities held by the holding company	30,700,000
Percentage decrease requiring a review for impairment	20.00%
Fair value of securities on other-than-temporary impairment watch list	220,700,000	220,900,000
Aggregate fair value of non-agency mortgage backed securities with other-than-temporary impairment	101,700,000
Credit-related portion of impairments included in earnings	11,600,000
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	144
Portfolio securities aggregate fair value loss position	901,882,000	1,715,182,000
Fair value of securities with temporary impairment with loss position for twelve months or longer	166,300,000
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	1.70%
Fair value of securities with an other-than-temporary impairment, which have been in a loss position for 12 months or longer	5,500,000
Gross unrealized losses included in state and municipal obligation holdings	16,300,000
Unrealized losses included in auction rate securities held	14,200,000
Unrealized losses included in other state and municipal obligations held	2,100,000
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	15.60%
Securities pledged as collateral	4,300,000,000	4,300,000,000
Securities pledged as collateral and may be sold or re-pledged	736,200,000
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%
Collateral swap agreements	300,000,000
Basis points earned on collateral swap agreements	0.86%
State and municipal obligations [Member]
Investment [Line Items]
Auction rate securities held at fair value	126,400,000
Portfolio securities aggregate fair value loss position	254,130,000	176,769,000
Agency mortgage-backed securities [Member]
Investment [Line Items]
Portfolio securities aggregate fair value loss position	5,874,000	72,019,000
Collateral swaps, collateral posted	314,000,000
Investment Grade Asset-backed, Commercial Mortgage-backed, and Corporate Bonds [Member]
Investment [Line Items]
Collateral swaps, collateral accepted	$ 345,500,000