Investments (Aggregate Values and Unrealized Gains and Losses) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Investment securities, aggregate fair value, continuous unrealized losses of more than 12 months	$ 832,400,000
Investment securities available for sale
Cost	7,163,574,000	5,404,335,000
Gross Unrealized Gains	20,589,000	28,188,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	12,246,000	44,820,000
Fair Value	7,171,917,000us-gaap_AvailableForSaleSecurities	5,387,703,000us-gaap_AvailableForSaleSecurities
Investment securities held to maturity
Cost	518,000us-gaap_HeldToMaturitySecurities	907,000us-gaap_HeldToMaturitySecurities
Investment securities, aggregate unrealized loss, continuous unrealized losses of more than 12 months	10,000,000
U. S. Treasury
Investment securities available for sale
Cost	2,626,900,000	373,223,000
Gross Unrealized Gains	2,922,000	259,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	152,000	45,000
Fair Value	2,629,670,000	373,437,000
Government Agency
Investment securities available for sale
Cost	908,362,000	2,543,223,000
Gross Unrealized Gains	702,000	1,798,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	247,000	792,000
Fair Value	908,817,000	2,544,229,000
Mortgage Backed Securities, Other [Member]
Investment securities available for sale
Cost	3,628,187,000	2,486,297,000
Gross Unrealized Gains	16,964,000	4,526,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	11,847,000	43,950,000
Fair Value	3,633,304,000	2,446,873,000
Investment securities held to maturity
Cost	518,000	907,000
Held To Maturity Securities Accumulated Unrecognized Holding Gain	26,000	67,000
Held To Maturity Securities Accumulated Unrecognized Holding Loss	0	0
Fair Value	544,000	974,000
Equity Securities
Investment securities available for sale
Cost		543,000
Gross Unrealized Gains		21,604,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments		0
Fair Value		22,147,000
State, County and Municipal
Investment securities available for sale
Cost	125,000	186,000
Gross Unrealized Gains	1,000	1,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	126,000	187,000
Other Debt Obligations
Investment securities available for sale
Cost		863,000
Gross Unrealized Gains		0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments		33,000
Fair Value		$ 830,000

Investment securities, aggregate fair value, continuous unrealized losses of more than 12 months

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Investment securities, aggregate unrealized loss, continuous unrealized losses of more than 12 months

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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