Securities (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 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	48,655,000		48,655,000		115,059,000
Securities available-for-sale:
Amortized Cost	7,033,250,000		7,033,250,000		9,057,238,000
Gross Unrealized Gains	89,728,000		89,728,000		163,295,000
Gross Unrealized Losses	(78,407,000)		(78,407,000)		(14,544,000)
Fair Value	7,044,571,000		7,044,571,000		9,205,989,000
Proceeds from sales of securities	200,000	5,200,000	1,251,056,000	5,189,000
Securities held-to-maturity:
Amortized Cost	1,503,973,000		1,503,973,000		1,398,403,000
Gross Unrealized Gains	4,527,000		4,527,000		49,617,000
Gross Unrealized Losses	(41,943,000)		(41,943,000)		(1,421,000)
Fair Value	1,466,557,000		1,466,557,000		1,446,599,000
Proceeds from held-to-maturity	0	0	0	0
Realized gains and losses
Gross realized gains	5,790,000	40,000	6,836,000	536,000
Gross realized losses		(319,000)		(366,000)
Net realized gains (losses)	5,790,000	(279,000)	6,836,000	170,000
Interest and dividend income on securities (including trading securities)
Taxable interest income	36,700,000	39,300,000	76,600,000	80,900,000
Nontaxable interest income	4,400,000	4,000,000	8,800,000	7,800,000
Dividend income	100,000	200,000	100,000	200,000
Total debt securities
Securities available-for-sale:
Amortized Cost	7,032,913,000		7,032,913,000		9,056,902,000
Gross Unrealized Gains	84,930,000		84,930,000		161,930,000
Gross Unrealized Losses	(78,407,000)		(78,407,000)		(14,544,000)
Fair Value	7,039,436,000		7,039,436,000		9,204,288,000
U.S. Treasury
Securities available-for-sale:
Amortized Cost	30,293,000		30,293,000		20,393,000
Gross Unrealized Gains	8,000		8,000		7,000
Gross Unrealized Losses	(16,000)		(16,000)		(3,000)
Fair Value	30,285,000		30,285,000		20,397,000
Federal agency - Debt
Securities available-for-sale:
Amortized Cost	987,467,000		987,467,000		2,344,374,000
Gross Unrealized Gains	1,491,000		1,491,000		5,031,000
Gross Unrealized Losses	(8,933,000)		(8,933,000)		(203,000)
Fair Value	980,025,000		980,025,000		2,349,202,000
Securities held-to-maturity:
Amortized Cost	109,562,000		109,562,000		97,183,000
Gross Unrealized Gains	27,000		27,000		4,032,000
Gross Unrealized Losses	(1,556,000)		(1,556,000)
Fair Value	108,033,000		108,033,000		101,215,000
Federal agency - MBS
Securities available-for-sale:
Amortized Cost	422,699,000		422,699,000		653,428,000
Gross Unrealized Gains	19,695,000		19,695,000		39,673,000
Gross Unrealized Losses	(4,212,000)		(4,212,000)		(69,000)
Fair Value	438,182,000		438,182,000		693,032,000
Securities held-to-maturity:
Amortized Cost	315,529,000		315,529,000		303,642,000
Gross Unrealized Gains	1,037,000		1,037,000		11,490,000
Gross Unrealized Losses	(8,555,000)		(8,555,000)		(182,000)
Fair Value	308,011,000		308,011,000		314,950,000
CMOs - Federal agency
Securities available-for-sale:
Amortized Cost	4,736,335,000		4,736,335,000		5,233,126,000
Gross Unrealized Gains	47,991,000		47,991,000		91,165,000
Gross Unrealized Losses	(55,713,000)		(55,713,000)		(6,038,000)
Fair Value	4,728,613,000		4,728,613,000		5,318,253,000
Securities held-to-maturity:
Amortized Cost	797,715,000		797,715,000		745,980,000
Gross Unrealized Gains	3,036,000		3,036,000		28,973,000
Gross Unrealized Losses	(16,997,000)		(16,997,000)		(382,000)
Fair Value	783,754,000		783,754,000		774,571,000
CMOs - Non-agency
Securities available-for-sale:
Amortized Cost	47,079,000		47,079,000		62,975,000
Gross Unrealized Gains	142,000		142,000		662,000
Gross Unrealized Losses	(1,894,000)		(1,894,000)		(2,124,000)
Fair Value	45,327,000		45,327,000		61,513,000
State and municipal
Securities available-for-sale:
Amortized Cost	457,869,000		457,869,000		437,266,000
Gross Unrealized Gains	10,939,000		10,939,000		17,447,000
Gross Unrealized Losses	(2,048,000)		(2,048,000)		(239,000)
Fair Value	466,760,000		466,760,000		454,474,000
Securities held-to-maturity:
Amortized Cost	281,167,000		281,167,000		251,598,000
Gross Unrealized Gains	427,000		427,000		5,122,000
Gross Unrealized Losses	(14,835,000)		(14,835,000)		(857,000)
Fair Value	266,759,000		266,759,000		255,863,000
Other debt securities
Securities available-for-sale:
Amortized Cost	351,171,000		351,171,000		305,340,000
Gross Unrealized Gains	4,664,000		4,664,000		7,945,000
Gross Unrealized Losses	(5,591,000)		(5,591,000)		(5,868,000)
Fair Value	350,244,000		350,244,000		307,417,000
Equity securities and mutual funds
Securities available-for-sale:
Amortized Cost	337,000		337,000		336,000
Gross Unrealized Gains	4,798,000		4,798,000		1,365,000
Fair Value	$ 5,135,000		$ 5,135,000		$ 1,701,000