Securities (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Securities
Total securities	$ 9,280,000,000	$ 10,720,000,000
Trading securities, at fair value	82,357,000	115,059,000
Transfer from available-for-sale category to the held-to-maturity	994,329,000
Net unrealized loss of available-for-sale securities in AOCI on the date of transfer	6,000
Securities available-for-sale:
Amortized Cost	6,267,691,000	9,057,238,000
Gross Unrealized Gains	56,067,000	163,295,000
Gross Unrealized Losses	(82,641,000)	(14,544,000)
Fair Value	6,241,117,000	9,205,989,000
Proceeds from sales of securities	2,371,399,000	52,085,000	101,089,000
Securities held-to-maturity:
Amortized Cost	2,957,843,000	1,398,403,000
Gross Unrealized Gains	3,398,000	49,617,000
Gross Unrealized Losses	(77,306,000)	(1,421,000)
Fair Value	2,883,935,000	1,446,599,000
Realized gains and losses
Gross realized gains	27,396,000	2,259,000	6,747,000
Gross realized losses	(19,421,000)	(1,146,000)	(1,681,000)
Net realized gains	7,975,000	1,113,000	5,066,000
Interest and dividend income on securities (including trading securities)
Taxable interest income	149,500,000	160,000,000	146,100,000
Nontaxable interest income	18,100,000	16,300,000	12,400,000
Dividend income	200,000	300,000	800,000
Total debt securities
Securities available-for-sale:
Amortized Cost	6,267,354,000	9,056,902,000
Gross Unrealized Gains	47,961,000	161,930,000
Gross Unrealized Losses	(82,641,000)	(14,544,000)
Fair Value	6,232,674,000	9,204,288,000
Securities held-to-maturity:
Amortized Cost	2,957,843,000
U.S. Treasury
Securities available-for-sale:
Amortized Cost	35,312,000	20,393,000
Gross Unrealized Gains	23,000	7,000
Gross Unrealized Losses		(3,000)
Fair Value	35,335,000	20,397,000
Federal agency - Debt
Securities available-for-sale:
Amortized Cost	1,417,509,000	2,344,374,000
Gross Unrealized Gains	938,000	5,031,000
Gross Unrealized Losses	(7,911,000)	(203,000)
Fair Value	1,410,536,000	2,349,202,000
Securities held-to-maturity:
Amortized Cost	178,413,000	97,183,000
Gross Unrealized Gains	133,000	4,032,000
Gross Unrealized Losses	(5,122,000)
Fair Value	173,424,000	101,215,000
Federal agency - MBS
Securities available-for-sale:
Amortized Cost	156,399,000	653,428,000
Gross Unrealized Gains	3,615,000	39,673,000
Gross Unrealized Losses	(2,788,000)	(69,000)
Fair Value	157,226,000	693,032,000
Securities held-to-maturity:
Amortized Cost	445,360,000	303,642,000
Gross Unrealized Gains	1,005,000	11,490,000
Gross Unrealized Losses	(11,930,000)	(182,000)
Fair Value	434,435,000	314,950,000
CMOs - Federal agency
Securities available-for-sale:
Amortized Cost	4,037,348,000	5,233,126,000
Gross Unrealized Gains	30,721,000	91,165,000
Gross Unrealized Losses	(70,771,000)	(6,038,000)
Fair Value	3,997,298,000	5,318,253,000
Securities held-to-maturity:
Amortized Cost	1,781,219,000	745,980,000
Gross Unrealized Gains	1,839,000	28,973,000
Gross Unrealized Losses	(40,621,000)	(382,000)
Fair Value	1,742,437,000	774,571,000
CMOs - Non-agency
Securities available-for-sale:
Amortized Cost	38,383,000	62,975,000
Gross Unrealized Gains	127,000	662,000
Gross Unrealized Losses	(1,048,000)	(2,124,000)
Fair Value	37,462,000	61,513,000
State and municipal
Securities available-for-sale:
Amortized Cost	407,312,000	437,266,000
Gross Unrealized Gains	8,806,000	17,447,000
Gross Unrealized Losses	(123,000)	(239,000)
Fair Value	415,995,000	454,474,000
Securities held-to-maturity:
Amortized Cost	454,155,000	251,598,000
Gross Unrealized Gains	421,000	5,122,000
Gross Unrealized Losses	(19,014,000)	(857,000)
Fair Value	435,562,000	255,863,000
Other debt securities
Securities available-for-sale:
Amortized Cost	175,091,000	305,340,000
Gross Unrealized Gains	3,731,000	7,945,000
Gross Unrealized Losses		(5,868,000)
Fair Value	178,822,000	307,417,000
Securities held-to-maturity:
Amortized Cost	98,696,000
Gross Unrealized Losses	(619,000)
Fair Value	98,077,000
Equity securities and mutual funds
Securities available-for-sale:
Amortized Cost	337,000	336,000
Gross Unrealized Gains	8,106,000	1,365,000
Fair Value	$ 8,443,000	$ 1,701,000