Securities (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Securities
Total securities	$ 8,830,000,000		$ 8,830,000,000		$ 9,280,000,000
Trading securities, at fair value	86,097,000		86,097,000		82,357,000
Securities available-for-sale:
Amortized Cost	5,324,611,000		5,324,611,000		6,267,691,000
Gross Unrealized Gains	49,054,000		49,054,000		56,067,000
Gross Unrealized Losses	(45,173,000)		(45,173,000)		(82,641,000)
Fair Value	5,328,492,000		5,328,492,000		6,241,117,000
Proceeds from sales of securities	15,000,000	200,000	626,055,000	1,251,056,000
Securities held-to-maturity:
Total of debt securities held-to-maturity, amortized cost	3,418,353,000		3,418,353,000		2,957,843,000
Gross Unrealized Gains	50,032,000		50,032,000		3,398,000
Gross Unrealized Losses	(26,401,000)		(26,401,000)		(77,306,000)
Fair Value	3,441,984,000		3,441,984,000		2,883,935,000
Realized gains and losses
Gross realized gains	5,368,000	5,790,000	7,970,000	6,836,000
Gross realized losses	(1,000)		(481,000)
Net realized gains	5,367,000	5,790,000	7,489,000	6,836,000
Interest and dividend income on securities (including trading securities)
Taxable interest income	37,500,000	36,700,000	73,500,000	76,600,000
Nontaxable interest income	6,000,000	4,400,000	11,500,000	8,800,000
Dividend income	16,000	100,000	25,000	100,000
Total debt securities
Securities available-for-sale:
Amortized Cost	5,323,990,000		5,323,990,000		6,267,354,000
Gross Unrealized Gains	43,988,000		43,988,000		47,961,000
Gross Unrealized Losses	(45,173,000)		(45,173,000)		(82,641,000)
Fair Value	5,322,805,000		5,322,805,000		6,232,674,000
Securities held-to-maturity:
Total of debt securities held-to-maturity, amortized cost	3,418,353,000		3,418,353,000
U.S. Treasury
Securities available-for-sale:
Amortized Cost	36,213,000		36,213,000		35,312,000
Gross Unrealized Gains	45,000		45,000		23,000
Fair Value	36,258,000		36,258,000		35,335,000
Federal agency - Debt
Securities available-for-sale:
Amortized Cost	1,027,192,000		1,027,192,000		1,417,509,000
Gross Unrealized Gains	815,000		815,000		938,000
Gross Unrealized Losses	(1,491,000)		(1,491,000)		(7,911,000)
Fair Value	1,026,516,000		1,026,516,000		1,410,536,000
Securities held-to-maturity:
Total of debt securities held-to-maturity, amortized cost	302,918,000		302,918,000		178,413,000
Gross Unrealized Gains	4,319,000		4,319,000		133,000
Gross Unrealized Losses	(856,000)		(856,000)		(5,122,000)
Fair Value	306,381,000		306,381,000		173,424,000
Federal agency - MBS
Securities available-for-sale:
Amortized Cost	121,501,000		121,501,000		156,399,000
Gross Unrealized Gains	3,305,000		3,305,000		3,615,000
Gross Unrealized Losses	(1,577,000)		(1,577,000)		(2,788,000)
Fair Value	123,229,000		123,229,000		157,226,000
Securities held-to-maturity:
Total of debt securities held-to-maturity, amortized cost	554,421,000		554,421,000		445,360,000
Gross Unrealized Gains	9,328,000		9,328,000		1,005,000
Gross Unrealized Losses	(4,058,000)		(4,058,000)		(11,930,000)
Fair Value	559,691,000		559,691,000		434,435,000
CMOs - Federal agency
Securities available-for-sale:
Amortized Cost	3,552,834,000		3,552,834,000		4,037,348,000
Gross Unrealized Gains	28,089,000		28,089,000		30,721,000
Gross Unrealized Losses	(41,604,000)		(41,604,000)		(70,771,000)
Fair Value	3,539,319,000		3,539,319,000		3,997,298,000
Securities held-to-maturity:
Total of debt securities held-to-maturity, amortized cost	1,883,461,000		1,883,461,000		1,781,219,000
Gross Unrealized Gains	23,027,000		23,027,000		1,839,000
Gross Unrealized Losses	(16,534,000)		(16,534,000)		(40,621,000)
Fair Value	1,889,954,000		1,889,954,000		1,742,437,000
CMOs - Non-agency
Securities available-for-sale:
Amortized Cost	27,168,000		27,168,000		38,383,000
Gross Unrealized Gains	135,000		135,000		127,000
Gross Unrealized Losses	(400,000)		(400,000)		(1,048,000)
Fair Value	26,903,000		26,903,000		37,462,000
State and municipal
Securities available-for-sale:
Amortized Cost	384,359,000		384,359,000		407,312,000
Gross Unrealized Gains	8,335,000		8,335,000		8,806,000
Gross Unrealized Losses	(101,000)		(101,000)		(123,000)
Fair Value	392,593,000		392,593,000		415,995,000
Securities held-to-maturity:
Total of debt securities held-to-maturity, amortized cost	579,473,000		579,473,000		454,155,000
Gross Unrealized Gains	13,067,000		13,067,000		421,000
Gross Unrealized Losses	(4,949,000)		(4,949,000)		(19,014,000)
Fair Value	587,591,000		587,591,000		435,562,000
Other debt securities
Securities available-for-sale:
Amortized Cost	174,723,000		174,723,000		175,091,000
Gross Unrealized Gains	3,264,000		3,264,000		3,731,000
Fair Value	177,987,000		177,987,000		178,822,000
Securities held-to-maturity:
Total of debt securities held-to-maturity, amortized cost	98,080,000		98,080,000		98,696,000
Gross Unrealized Gains	291,000		291,000
Gross Unrealized Losses	(4,000)		(4,000)		(619,000)
Fair Value	98,367,000		98,367,000		98,077,000
Equity securities and mutual funds
Securities available-for-sale:
Amortized Cost	621,000		621,000		337,000
Gross Unrealized Gains	5,066,000		5,066,000		8,106,000
Fair Value	$ 5,687,000		$ 5,687,000		$ 8,443,000