Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash Flows From Operating Activities: [Abstract]
Net income	$ 40,988	$ 75,094
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Provision for credit losses	35,000	0
Change in fair value of mortgage servicing rights	27,988	8,522
Unrealized losses (gains) from derivative contracts	(13,788)	641
Tax effect from equity compensation, net	(1,816)	(215)
Change in bank-owned life insurance	(2,170)	(2,198)
Share-based compensation	2,030	1,865
Depreciation and amortization	18,907	16,800
Net amortization of securities discounts and premiums	11,213	14,511
Net realized gains on financial instruments and other net gains	(4,035)	(5,956)
Net gain on mortgage loans held for sale	(10,779)	(20,702)
Mortgage loans originated for sale	(1,244,015)	(1,565,016)
Proceeds from sale of mortgage loans held for sale	1,239,391	1,382,042
Capitalized mortgage servicing rights	(13,582)	(19,150)
Change in trading and fair value option securities	(132,436)	(52,479)
Change in receivables	(3,264)	(16,008)
Change in other assets	3,145	(6,293)
Change in accrued interest, taxes and expense	(13,132)	5,521
Change in other liabilities	65,593	8,173
Net cash provided by (used in) operating activities	5,238	(174,848)
Cash Flows From Investing Activities: [Abstract]
Proceeds from maturities or redemptions of investment securities	32,308	19,378
Proceeds from maturities or redemptions of available for sale securities	335,565	513,939
Purchases of investment securities	(12,189)	(3,363)
Purchases of available for sale securities	(536,078)	(980,768)
Proceeds from sales of available for sale securities	469,382	334,825
Change in amount receivable on unsettled securities transactions	34,553	64,661
Loans originated, net of principal collected	(92,648)	(458,118)
Net payments on derivative asset contracts	(155,263)	(83,354)
Acquisitions, net of cash acquired	(7,700)	0
Proceeds from disposition of assets	38,903	66,111
Purchases of assets	(75,893)	(108,579)
Net cash provided by (used in) investing activities	30,940	(635,268)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	(605,148)	(30,574)
Net change in time deposits	(64,690)	43,062
Net change in other borrowed funds	246,609	1,283,330
Net proceeds on derivative liability contracts	154,506	70,377
Net change in derivative margin accounts	(75,876)	(101,290)
Change in amount due on unsettled security transactions	2,611	(264,605)
Issuance of common and treasury stock, net	1,451	2,640
Tax effect from equity compensation, net	1,816	215
Repurchase of common stock	0	(29,484)
Dividends paid	(28,384)	(28,727)
Net cash provided by (used in) financing activities	(367,105)	944,944
Net increase (decrease) in cash and cash equivalents	(330,927)	134,828
Cash and cash equivalents at beginning of period	2,643,599	2,475,842
Cash and cash equivalents at end of period	2,312,672	2,610,670
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	19,934	15,380
Cash paid for taxes	6,004	3,232
Net loans and bank premises transferred to repossessed real estate and other assets	2,211	2,768
Residential mortgage loans guaranteed by U.S. government agencies that became eligible for repurchase during the period	28,594	29,409
Conveyance of other real estate owned guaranteed by U.S. government agencies	$ 15,147	$ 66,912