Securities (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Securities
Total securities	$ 8,600,000,000		$ 8,600,000,000		$ 10,720,000,000
Trading securities, at fair value	51,451,000		51,451,000		115,059,000
Securities available-for-sale:
Amortized Cost	6,912,931,000		6,912,931,000		9,057,238,000
Gross Unrealized Gains	70,608,000		70,608,000		163,295,000
Gross Unrealized Losses	(88,409,000)		(88,409,000)		(14,544,000)
Fair Value	6,895,130,000		6,895,130,000		9,205,989,000
Proceeds from sales of securities	584,700,000	1,000,000	1,835,775,000	6,216,000
Securities held-to-maturity:
Amortized Cost	1,649,520,000		1,649,520,000		1,398,403,000
Gross Unrealized Gains	5,596,000		5,596,000		49,617,000
Gross Unrealized Losses	(47,042,000)		(47,042,000)		(1,421,000)
Fair Value	1,608,074,000		1,608,074,000		1,446,599,000
Proceeds from held-to-maturity	0	0	0	0
Realized gains and losses
Gross realized gains	17,533,000	1,315,000	24,369,000	1,851,000
Gross realized losses	(11,745,000)	(459,000)	(11,745,000)	(825,000)
Net realized gains	5,788,000	856,000	12,624,000	1,026,000
Interest and dividend income on securities (including trading securities)
Taxable interest income	35,500,000	40,000,000	112,100,000	120,800,000
Nontaxable interest income	4,500,000	4,100,000	13,300,000	12,000,000
Dividend income	19,000	100,000	100,000	300,000
Total debt securities
Securities available-for-sale:
Amortized Cost	6,912,594,000		6,912,594,000		9,056,902,000
Gross Unrealized Gains	64,898,000		64,898,000		161,930,000
Gross Unrealized Losses	(88,409,000)		(88,409,000)		(14,544,000)
Fair Value	6,889,083,000		6,889,083,000		9,204,288,000
U.S. Treasury
Securities available-for-sale:
Amortized Cost	35,400,000		35,400,000		20,393,000
Gross Unrealized Gains	25,000		25,000		7,000
Gross Unrealized Losses					(3,000)
Fair Value	35,425,000		35,425,000		20,397,000
Federal agency - Debt
Securities available-for-sale:
Amortized Cost	1,007,019,000		1,007,019,000		2,344,374,000
Gross Unrealized Gains	1,078,000		1,078,000		5,031,000
Gross Unrealized Losses	(5,650,000)		(5,650,000)		(203,000)
Fair Value	1,002,447,000		1,002,447,000		2,349,202,000
Securities held-to-maturity:
Amortized Cost	140,020,000		140,020,000		97,183,000
Gross Unrealized Gains	182,000		182,000		4,032,000
Gross Unrealized Losses	(4,305,000)		(4,305,000)
Fair Value	135,897,000		135,897,000		101,215,000
Federal agency - MBS
Securities available-for-sale:
Amortized Cost	192,345,000		192,345,000		653,428,000
Gross Unrealized Gains	7,054,000		7,054,000		39,673,000
Gross Unrealized Losses	(2,226,000)		(2,226,000)		(69,000)
Fair Value	197,173,000		197,173,000		693,032,000
Securities held-to-maturity:
Amortized Cost	359,952,000		359,952,000		303,642,000
Gross Unrealized Gains	1,187,000		1,187,000		11,490,000
Gross Unrealized Losses	(9,753,000)		(9,753,000)		(182,000)
Fair Value	351,386,000		351,386,000		314,950,000
CMOs - Federal agency
Securities available-for-sale:
Amortized Cost	4,773,336,000		4,773,336,000		5,233,126,000
Gross Unrealized Gains	40,818,000		40,818,000		91,165,000
Gross Unrealized Losses	(71,570,000)		(71,570,000)		(6,038,000)
Fair Value	4,742,584,000		4,742,584,000		5,318,253,000
Securities held-to-maturity:
Amortized Cost	849,600,000		849,600,000		745,980,000
Gross Unrealized Gains	3,567,000		3,567,000		28,973,000
Gross Unrealized Losses	(18,158,000)		(18,158,000)		(382,000)
Fair Value	835,009,000		835,009,000		774,571,000
CMOs - Non-agency
Securities available-for-sale:
Amortized Cost	44,484,000		44,484,000		62,975,000
Gross Unrealized Gains	213,000		213,000		662,000
Gross Unrealized Losses	(1,385,000)		(1,385,000)		(2,124,000)
Fair Value	43,312,000		43,312,000		61,513,000
State and municipal
Securities available-for-sale:
Amortized Cost	466,633,000		466,633,000		437,266,000
Gross Unrealized Gains	10,490,000		10,490,000		17,447,000
Gross Unrealized Losses	(1,337,000)		(1,337,000)		(239,000)
Fair Value	475,786,000		475,786,000		454,474,000
Securities held-to-maturity:
Amortized Cost	299,948,000		299,948,000		251,598,000
Gross Unrealized Gains	660,000		660,000		5,122,000
Gross Unrealized Losses	(14,826,000)		(14,826,000)		(857,000)
Fair Value	285,782,000		285,782,000		255,863,000
Other debt securities
Securities available-for-sale:
Amortized Cost	393,377,000		393,377,000		305,340,000
Gross Unrealized Gains	5,220,000		5,220,000		7,945,000
Gross Unrealized Losses	(6,241,000)		(6,241,000)		(5,868,000)
Fair Value	392,356,000		392,356,000		307,417,000
Equity securities and mutual funds
Securities available-for-sale:
Amortized Cost	337,000		337,000		336,000
Gross Unrealized Gains	5,710,000		5,710,000		1,365,000
Fair Value	$ 6,047,000		$ 6,047,000		$ 1,701,000