Investment Securities (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 Investments_In_Single_Issuer Securities	Dec. 31, 2013 Securities	Dec. 31, 2012	Dec. 31, 2011
Investment [Line Items]
Non-marketable FHLB and FRB stock held for debt and regulatory purposes	$ 46,600,000	$ 46,500,000
Non-marketable private equity investments held	60,200,000	60,700,000
U.S. Treasury inflation-protected securities held	501,300,000
Percentage decrease requiring a review for impairment	20.00%
Fair value of securities on other-than-temporary impairment watch list	123,900,000	188,800,000
Cumulative, credit-related portion of impairment on these securities, recorded in earnings	13,734,000	12,499,000	11,306,000	9,931,000
Number of individual securities held in the available for sale portfolio	1,900
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	363	507
Portfolio securities aggregate fair value loss position	3,262,858,000	3,433,325,000
Available for sale securities in loss position at period end, change in unrealized loss	(82,800,000)
Fair value of securities in loss position for twelve months or longer	1,137,135,000	421,202,000
Fair value of securities in a loss position for 12 months or longer, as a percentage of total available for sale portfolio	11.90%
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	35,384,000	118,178,000
Securities pledged as collateral	4,700,000,000	3,900,000,000
Securities pledged as collateral and may be sold or re-pledged	467,100,000
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%
State and municipal obligations [Member]
Investment [Line Items]
Auction rate securities held at fair value	95,100,000
Portfolio securities aggregate fair value loss position	388,682,000	656,968,000
Fair value of securities in loss position for twelve months or longer	215,702,000	178,150,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	8,354,000	33,345,000
Unrealized losses included in auction rate securities held	5,600,000
Unrealized losses included in other state and municipal obligations held	2,700,000
Aggregate fair value of state and municipal obligations excluding auction rate securities	1,700,000,000
State and municipal obligation portfolio, excluding auction rate securities, as a percentage of total available for sale securities	18.00%
Equity securities [Member]
Investment [Line Items]
Common stock classified as equity securities held by the holding company	37,400,000
Non-agency mortgage-backed securities [Member]
Investment [Line Items]
Fair value of securities on other-than-temporary impairment watch list	54,600,000
Cumulative, credit-related portion of impairment on these securities, recorded in earnings	13,700,000
Portfolio securities aggregate fair value loss position	185,314,000	75,743,000
Fair value of securities in loss position for twelve months or longer	43,659,000	22,289,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 1,228,000	$ 1,620,000