Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income	$ 1,408,306	$ 1,315,114	$ 1,079,667
Adjustments to reconcile net income to net cash provided by operating activities
Provision for credit losses	168,000	190,000	170,000
Depreciation and amortization of premises and equipment	109,587	106,996	99,019
Amortization of capitalized servicing rights	56,172	50,982	49,906
Amortization of core deposit and other intangible assets	31,366	42,613	26,424
Provision for deferred income taxes	400,790	174,013	396,596
Asset write-downs	15,429	21,036	9,029
Net gain on sales of assets	(53,467)	(63,222)	(67,759)
Net change in accrued interest receivable, payable	(17,896)	(12,282)	(46,338)
Net change in other accrued income and expense	(201,981)	60,263	(289,139)
Net change in loans originated for sale	711,657	(665,649)	323,330
Net change in trading account assets and liabilities	153,972	(36,453)	(8,327)
Net cash provided by operating activities	2,781,935	1,183,411	1,742,408
Cash flows from investing activities
Proceeds from sales of investment securities Available for sale	534,160	63,513	5,654,850
Proceeds from sales of investment securities Other	178,468	94,749	183,892
Proceeds from maturities of investment securities Available for sale	2,131,118	2,309,208	2,392,331
Proceeds from maturities of investment securities Held to maturity	528,585	609,080	662,959
Purchases of investment securities Available for sale	(251,185)	(3,562,711)	(3,614,324)
Purchases of investment securities Held to maturity	(1,425,690)	(214,791)	(29,431)
Purchases of investment securities Other	(132,378)	(1,808)	(99,317)
Net (increase) decrease in loans and leases	1,931,492	(2,952,129)	(2,326,744)
Net (increase) decrease in interest-bearing deposits at banks	(78,265)	2,593,712	6,445,451
Capital expenditures, net	(78,966)	(107,693)	(81,936)
Net decrease in loan servicing advances	37,761	170,141	448,271
Acquisition of bank and bank holding company, net of cash acquired			(1,932,596)
Other, net	19,825	277,961	10,876
Net cash provided (used) by investing activities	3,394,925	(720,768)	7,714,282
Cash flows from financing activities
Net increase (decrease) in deposits	(3,075,322)	3,554,673	504,393
Net increase (decrease) in short-term borrowings	11,657	(1,937,105)	(2,167,405)
Proceeds from long-term borrowings	2,145,950		1,500,000
Payments on long-term borrowings	(3,433,440)	(1,119,898)	(8,912,474)
Purchases of treasury stock	(1,205,905)	(641,334)
Dividends paid — common	(457,402)	(441,891)	(375,017)
Dividends paid — preferred	(72,734)	(81,270)	(81,270)
Redemption of Series D preferred stock		(500,000)
Other, net	10,675	161,691	69,766
Net cash used by financing activities	(6,076,521)	(510,134)	(9,462,007)
Net increase (decrease) in cash and cash equivalents	100,339	(47,491)	(5,317)
Cash and cash equivalents at beginning of year	1,320,549	1,368,040	1,373,357
Cash and cash equivalents at end of year	1,420,888	1,320,549	1,368,040
Supplemental disclosure of cash flow information
Interest received during the year	4,155,723	3,903,374	3,134,311
Interest paid during the year	405,290	498,951	400,329
Income taxes paid during the year	494,205	276,866	378,660
Supplemental schedule of noncash investing and financing activities
Real estate acquired in settlement of loans	121,292	124,033	67,753
Acquisition of bank and bank holding company
Common stock issued			3,110,581
Common stock awards converted			28,243
Fair value of Assets acquired (noncash)			36,567,632
Fair value of Liabilities assumed			31,496,212
Securitization of residential mortgage loans allocated to Available-for-sale investment securities	36,747	24,233	65,023
Securitization of residential mortgage loans allocated to capitalized servicing rights	$ 422	248	$ 646
Series F Preferred Stock [Member]
Cash flows from financing activities
Proceeds from issuance of Series F preferred stock		$ 495,000