Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash Flows From Operating Activities: [Abstract]
Net income	$ 263,320	$ 182,372
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	0	65,000
Change in fair value of mortgage servicing rights due to market changes	5,726	41,944
Change in the fair value of mortgage servicing rights due to loan runoff	24,928	29,385
Net unrealized gains from derivative contracts	(3,937)	(9,755)
Share-based compensation	17,390	7,569
Depreciation and amortization	39,154	35,158
Net amortization of securities discounts and premiums	22,149	31,373
Net realized gains on financial instruments and other net gains	(1,930)	(13,663)
Net gain on mortgage loans held for sale	(35,778)	(61,775)
Mortgage loans originated for sale	(2,446,793)	(4,927,442)
Proceeds from sale of mortgage loans held for sale	2,503,759	4,855,682
Capitalized mortgage servicing rights	(29,439)	(56,345)
Change in trading and fair value option securities	(1,019,906)	(204,030)
Change in receivables	459,480	(483,836)
Change in other assets	(18,991)	(17,931)
Change in accrued interest, taxes and expense	(99)	27,780
Change in other liabilities	43,767	7,262
Net cash provided by (used in) operating activities	(177,200)	(491,252)
Cash Flows From Investing Activities: [Abstract]
Proceeds from maturities or redemptions of investment securities	94,243	65,104
Proceeds from maturities or redemptions of available for sale securities	1,345,575	1,120,917
Purchases of investment securities	(18,802)	(18,599)
Purchases of available for sale securities	(2,001,160)	(1,860,287)
Proceeds from sales of available for sale securities	966,044	1,027,379
Change in amount receivable on unsettled securities transactions	(223,037)	20,551
Loans originated, net of principal collected	(156,404)	(551,351)
Net payments on derivative asset contracts	334,709	(79,512)
Acquisitions, net of cash acquired	0	(7,700)
Proceeds from disposition of assets	162,793	131,761
Purchases of assets	(170,937)	(159,263)
Net cash provided by (used in) investing activities	333,024	(311,000)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	(850,505)	243,779
Net change in time deposits	(49,511)	(236,433)
Net change in other borrowed funds	957,859	1,015,822
Repayment of subordinated debentures	0	226,550
Issuance of subordinated debentures	0	145,331
Net proceeds on derivative liability contracts	(339,566)	76,144
Net change in derivative margin accounts	(8,583)	(129,141)
Change in amount due on unsettled security transactions	154,273	(16,220)
Issuance of common and treasury stock, net	3,175	5,418
Repurchase of common stock	0	17,771
Dividends paid	(86,481)	(84,832)
Net cash provided by (used in) financing activities	(219,339)	775,547
Net increase (decrease) in cash and cash equivalents	(63,515)	(26,705)
Cash and cash equivalents at beginning of period	2,537,497	2,643,599
Cash and cash equivalents at end of period	2,473,982	2,616,894
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	89,901	61,522
Cash paid for taxes	95,967	43,096
Net loans and bank premises transferred to repossessed real estate and other assets	4,649	20,580
Residential mortgage loans guaranteed by U.S. government agencies that became eligible for repurchase during the period	101,299	79,710
Conveyance of other real estate owned guaranteed by U.S. government agencies	$ 32,033	$ 50,855