Associated Banc-Corp (ASB) 10-K 6 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2016
Document And Entity Information [Abstract]
Trading Symbol	ASB
Entity Registrant Name	ASSOCIATED BANC-CORP
Entity Central Index Key	7,789
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 3,831,497,000
Entity Common Stock, Shares Outstanding		151,688,740

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 483,666	$ 446,558
Interest-bearing deposits in other financial institutions	199,702	149,175
Federal funds sold and securities purchased under agreements to resell	32,650	46,500
Investment securities held to maturity, at amortized cost	2,282,853	1,273,536
Investment securities available for sale, at fair value	4,043,446	4,680,226
Federal Home Loan Bank and Federal Reserve Bank stocks, at cost	165,331	140,001
Residential loans held for sale (a)	85,544	108,010
Commercial loans held for sale	0	12,474
Loans	20,784,991	20,054,716
Allowance for loan losses	(265,880)	(278,335)
Loans, net	20,519,111	19,776,381
Bank and corporate owned life insurance	591,057	585,290
Tax credit investments	147,099	67,860
Trading assets	69,675	52,398
Premises and equipment, net	330,963	330,315
Goodwill	976,239	971,951
Mortgage servicing rights, net	58,384	61,476
Other intangible assets, net	15,580	15,377
Other assets	482,294	421,787
Total assets	30,483,594	29,139,315
Liabilities and stockholders' equity
Noninterest-bearing demand deposits	5,478,416	5,392,208
Interest-bearing deposits	17,307,546	16,496,240
Total deposits	22,785,962	21,888,448
Federal funds purchased and securities sold under agreements to repurchase	324,815	508,347
Other short-term funding	351,467	583,688
Long-term funding	3,397,450	2,761,795
Trading liabilities	67,660	51,103
Accrued expenses and other liabilities	318,797	254,622
Total liabilities	27,246,151	26,048,003
Stockholders’ equity
Preferred equity	159,929	159,929
Common stock	1,618	1,630
Surplus	1,454,188	1,459,498
Retained earnings	1,819,230	1,695,764
Accumulated other comprehensive income (loss)	(62,758)	(54,679)
Treasury stock, at cost	(134,764)	(170,830)
Total common equity	3,077,514	2,931,383
Total stockholders’ equity	3,237,443	3,091,312
Total liabilities and stockholders’ equity	$ 30,483,594	$ 29,139,315
Preferred shares issued	165,000	165,000
Preferred shares authorized (par value $1.00 per share)	750,000	750,000
Common shares issued	161,751,975	163,030,209
Common shares authorized (par value $0.01 per share)	250,000,000	250,000,000
Treasury shares of common stock	8,908,448	10,909,362

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Stockholders’ equity
Preferred shares, par value	$ 1	$ 1
Common shares, par value	$ 0.01	$ 0.01

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income
Interest and fees on loans	$ 749,000	$ 659,538	$ 615,627
Interest and dividends on investment securities
Taxable	96,909	95,152	100,292
Tax-exempt	32,977	32,049	31,152
Other interest	7,719	4,829	6,591
Total interest income	886,605	791,568	753,662
Interest expense
Interest on deposits	94,025	50,335	33,125
Interest on Federal funds purchased and securities sold under agreements to repurchase	2,527	1,314	943
Interest on other short-term funding	5,677	2,114	465
Interest on long-term funding	43,156	30,532	42,851
Total interest expense	145,385	84,295	77,384
Net interest income	741,220	707,273	676,278
Provision for credit losses	26,000	70,000	37,500
Net interest income after provision for credit losses	715,220	637,273	638,778
Noninterest income
Insurance commissions and fees	81,474	80,795	75,363
Service charges and deposit account fees	64,427	66,609	65,471
Card-based and loan fees	52,688	50,077	47,912
Trust and asset management fees	50,191	46,867	48,840
Brokerage commissions and fees	19,935	16,235	15,378
Mortgage banking, net	19,360	38,121	32,263
Capital markets, net	19,642	22,059	14,558
Bank and corporate owned life insurance	16,250	14,371	9,796
Asset gains (losses), net	(1,244)	(86)	2,540
Investment securities gains (losses), net	434	9,316	8,133
Other	9,523	8,519	9,103
Total noninterest income	332,680	352,883	329,357
Noninterest expense
Personnel	419,778	414,837	404,741
Occupancy	53,842	56,069	60,896
Technology	63,004	57,300	60,613
Equipment	21,201	21,489	23,209
Business development and advertising	28,946	26,351	25,772
Legal and professional	22,509	19,869	17,052
Card issuance and loan costs	11,760	13,641	14,102
Foreclosure / OREO expense, net	4,878	4,844	5,442
FDIC assessment	31,300	34,750	26,000
Other intangible amortization	1,959	2,093	3,094
Other	49,956	51,317	57,426
Total noninterest expense	709,133	702,560	698,347
Income before income taxes	338,767	287,596	269,788
Income tax expense	109,503	87,322	81,487
Net income	229,264	200,274	188,301
Preferred stock dividends	9,347	8,903	7,155
Net income available to common equity	$ 219,917	$ 191,371	$ 181,146
Earnings per common share
Basic	$ 1.45	$ 1.27	$ 1.20
Diluted	$ 1.42	$ 1.26	$ 1.19
Average common shares outstanding
Basic	150,877	148,769	149,350
Diluted	153,647	149,961	150,603

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 229,264	$ 200,274	$ 188,301
Investment securities available for sale
Net unrealized gains (losses)	(12,302)	(17,900)	(37,873)
Net unrealized gain (loss) on available for sale securities transferred to held to maturity securities	(14,738)	0	17,434
Amortization of net unrealized gain (loss) on available for sale securities transferred to held to maturity securities	(2,665)	(5,887)	(555)
Reclassification adjustment for net gain (loss) realized in net income	0	(9,316)	(8,133)
Income tax (expense) benefit	11,331	12,565	11,074
Other comprehensive income (loss) on investment securities available for sale	(18,374)	(20,538)	(18,053)
Defined benefit pension and postretirement obligations
Amortization of prior service cost	(148)	(73)	50
Plan amendments	0	1,759	0
Amortization of actuarial loss (gains)	16,555	(4,026)	(15,636)
Income tax (expense) benefit	(6,112)	815	5,873
Other comprehensive income (loss) on pension and postretirement obligations	10,295	(1,525)	(9,713)
Total other comprehensive income (loss)	(8,079)	(22,063)	(27,766)
Comprehensive income	$ 221,185	$ 178,211	$ 160,535

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Equity	Common Stock	Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2014	$ 2,800,251	$ 59,727	$ 1,665	$ 1,484,933	$ 1,497,818	$ (4,850)	$ (239,042)
Preferred stock shares outstanding, beginning balance (in shares) at Dec. 31, 2014		62
Common stock shares outstanding, beginning balance (in shares) at Dec. 31, 2014			166,544
Comprehensive income
Net income	188,301	$ 0	$ 0	0	188,301	0	0
Other comprehensive income (loss)	(27,766)	0	0	0	0	(27,766)	0
Comprehensive income	160,535
Common stock issued
Stock-based compensation plans, net	20,054	$ 0	$ 0	3,316	(22,538)	0	39,276
Stock Issued During Period, Shares, Acquisitions		0	2,621
Stock Issued During Period, Value, Acquisitions	43,530	$ 0	$ 26	43,504	0	0	0
Purchase of common stock returned to authorized but unissued		0	(4,965)
Purchase of common stock returned to authorized but unissued	(93,000)	$ 0	$ (49)	(92,951)	0	0	0
Purchase of treasury stock	(5,154)	0	0	0	0	0	(5,154)
Cash dividends
Common stock dividends	(62,400)	0	0	0	(62,400)	0	0
Preferred stock dividends	(7,155)	$ 0	$ 0	0	(7,155)	0	0
Issuance of preferred stock		65	0
Issuance of preferred stock	62,966	$ 62,966	$ 0	0	0	0	0
Purchase of preferred stock		(2)	0
Purchase of preferred stock	(1,335)	$ (1,209)	$ 0	0	(126)	0	0
Other	(766)	$ (105)	$ 0	0	(661)	0	0
Stockholders' Equity, Other Shares		0	0
Stock-based compensation expense, net	18,202	$ 0	$ 0	18,202	0	0	0
Tax impact of stock-based compensation	1,518	0	0	1,518	0	0	0
Ending balance at Dec. 31, 2015	2,937,246	$ 121,379	$ 1,642	1,458,522	1,593,239	(32,616)	(204,920)
Common stock shares outstanding, ending balance (in shares) at Dec. 31, 2015			164,200
Preferred stock shares outstanding, ending balance (in shares) at Dec. 31, 2015		125
Comprehensive income
Net income	200,274	$ 0	$ 0	0	200,274	0	0
Other comprehensive income (loss)	(22,063)	0	0	0	0	(22,063)	0
Comprehensive income	178,211
Common stock issued
Stock-based compensation plans, net	21,748	$ 0	$ 0	1,940	(19,356)	0	39,164
Purchase of common stock returned to authorized but unissued		0	(1,170)
Purchase of common stock returned to authorized but unissued	(20,007)	$ 0	$ (12)	(19,995)	0	0	0
Purchase of treasury stock	(5,074)	0	0	0	0	0	(5,074)
Cash dividends
Common stock dividends	(67,855)	0	0	0	(67,855)	0	0
Preferred stock dividends	(8,903)	$ 0	$ 0	0	(8,903)	0	0
Issuance of preferred stock		100	0
Issuance of preferred stock	97,066	$ 97,066	$ 0	0	0	0	0
Redemption of preferred stock	(58,903)	$ (57,338)	$ 0	0	(1,565)	0	0
Redemption of preferred stock		(60)	0
Purchase of preferred stock		0	0
Purchase of preferred stock	(1,248)	$ (1,178)	$ 0	0	(70)	0	0
Stock-based compensation expense, net	21,971	0	0	21,971	0	0	0
Tax impact of stock-based compensation	(2,940)	0	0	(2,940)	0	0	0
Ending balance at Dec. 31, 2016	3,091,312	$ 159,929	$ 1,630	1,459,498	1,695,764	(54,679)	(170,830)
Common stock shares outstanding, ending balance (in shares) at Dec. 31, 2016			163,030
Preferred stock shares outstanding, ending balance (in shares) at Dec. 31, 2016		165
Comprehensive income
Net income	229,264	$ 0	$ 0	0	229,264	0	0
Other comprehensive income (loss)	(8,079)	0	0	0	0	(8,079)	0
Comprehensive income	221,185
Common stock issued
Stock-based compensation plans, net	27,619	$ 0	$ 0	2,297	(20,034)	0	45,356
Stock Issued During Period, Shares, Acquisitions		0	291
Stock Issued During Period, Value, Acquisitions	7,151	$ 0	$ 3	7,148	0	0	0
Purchase of common stock returned to authorized but unissued		0	(1,569)
Purchase of common stock returned to authorized but unissued	(37,031)	$ 0	$ (15)	(37,016)	0	0	0
Purchase of treasury stock	(9,290)	0	0	0	0	0	(9,290)
Cash dividends
Common stock dividends	(76,417)	0	0	0	(76,417)	0	0
Preferred stock dividends	(9,347)	0	0	0	(9,347)	0	0
Stock-based compensation expense, net	21,227	0	0	21,227	0	0	0
Tax impact of stock-based compensation	1,034	0	0	1,034	0	0	0
Ending balance at Dec. 31, 2017	$ 3,237,443	$ 159,929	$ 1,618	$ 1,454,188	$ 1,819,230	$ (62,758)	$ (134,764)
Common stock shares outstanding, ending balance (in shares) at Dec. 31, 2017			161,752
Preferred stock shares outstanding, ending balance (in shares) at Dec. 31, 2017		165

Consolidated Statements of Cha7

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock
Cash dividends
Common Stock, per share	$ 0.50	$ 0.45	$ 0.41

Consolidated Statements of Cash

Consolidated Statements 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	$ 229,264	$ 200,274	$ 188,301
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	26,000	70,000	37,500
Depreciation and amortization	46,967	45,434	47,168
Addition to (recovery of) valuation allowance on mortgage servicing rights, net	175	(200)	(425)
Amortization of mortgage servicing rights	10,084	12,327	11,601
Amortization of other intangible assets	1,959	2,093	3,094
Amortization and accretion on earning assets, funding, and other, net	37,476	46,615	39,806
Net amortization of tax credit investments	19,834	5,272	3,100
Deferred income taxes	21,402	10,656	(3,522)
Gain on sales of investment securities, net	(434)	(9,316)	(8,133)
Asset (gains) losses, net	1,244	86	(2,540)
Gain on mortgage banking activities, net	(3,516)	(27,060)	(20,258)
Mortgage loans originated and acquired for sale	(715,357)	(1,271,124)	(1,228,106)
Proceeds from sales of mortgage loans held for sale	819,950	1,542,660	1,241,012
Pension contributions	(6,242)	0	0
(Increase) decrease in interest receivable	(9,476)	(7,836)	395
Increase (decrease) in interest payable	6,535	(4,642)	3,898
Net change in other assets and other liabilities	(27,497)	26,144	(11,685)
Net cash provided by operating activities	458,368	641,383	301,206
Cash Flows from Investing Activities
Net increase in loans	(861,934)	(1,682,579)	(1,136,793)
Purchases of
Available for sale securities	(1,137,191)	(1,304,921)	(2,859,793)
Held to maturity securities	(234,379)	(195,442)	(250,767)
Federal Home Loan Bank and Federal Reserve Bank stocks	(262,986)	(92,761)	(35,647)
Premises, equipment, and software, net of disposals	(47,369)	(103,881)	(54,636)
Proceeds from
Sales of available for sale securities	18,467	549,555	1,601,947
Sale of Federal Home Loan Bank and Federal Reserve Bank stocks	237,656	100,000	77,514
Prepayments, calls, and maturities of available for sale securities	713,486	997,701	1,099,625
Prepayments, calls, and maturities of held to maturity securities	210,753	75,796	17,013
Prepayments, calls and maturities of other assets	20,070	27,692	21,236
Net change in tax credit investments	(53,770)	(23,498)	(14,649)
Net cash (paid) received in acquisition	339	(685)	1,132
Net cash used in investing activities	(1,396,858)	(1,653,023)	(1,533,818)
Cash Flows from Financing Activities
Net increase in deposits	897,514	880,783	2,244,161
Net increase (decrease) in short-term funding	(415,753)	257,619	(233,872)
Repayment of long-term funding	(115,020)	(1,180,038)	(1,500,035)
Proceeds from issuance of long-term funding	750,000	1,265,000	250,000
Proceeds from issuance of common stock for stock-based compensation plans	27,619	21,748	20,054
Proceeds from issuance of preferred stock	0	97,066	62,966
Redemption of preferred stock	0	(58,903)	0
Purchase of preferred stock	0	(1,248)	(1,335)
Purchase of common stock returned to authorized but unissued	(37,031)	(20,007)	(93,000)
Purchase of treasury stock for tax withholding	(9,290)	(5,074)	(5,154)
Cash dividends on common stock	(76,417)	(67,855)	(62,400)
Cash dividends on preferred stock	(9,347)	(8,903)	(7,155)
Net cash provided by financing activities	1,012,275	1,180,188	674,230
Net increase (decrease) in cash and cash equivalents	73,785	168,548	(558,382)
Cash and cash equivalents at beginning of period	642,233	473,685	1,032,067
Cash and cash equivalents at end of period	716,018	642,233	473,685
Supplemental disclosures of cash flow information
Cash paid for interest	138,174	88,269	73,054
Cash paid for income and franchise taxes	81,450	75,558	84,407
Loans and bank premises transferred to other real estate owned	11,505	9,752	10,988
Capitalized mortgage servicing rights	7,167	12,262	12,372
Loans transferred into held for sale from portfolio, net	71,954	256,194	0
Supplemental Cash Flow - Acquisition Information
Fair value of assets acquired, including cash and cash equivalents	647	522	4,590
Fair value ascribed to goodwill and intangible assets	6,450	4,119	51,791
Fair value of liabilities assumed	54	1,423	12,851
Common stock issued in acquisition	$ 7,151	$ 0	$ 43,530

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The accounting and reporting policies of the Corporation conform to U.S. generally accepted accounting principles and to general practice within the financial services industry. The following is a description of the more significant of those policies. Business Associated Banc-Corp (individually referred to herein as the "Parent Company" and together with all of its subsidiaries and affiliates, collectively referred to herein as the "Corporation") is a bank holding company headquartered in Wisconsin. The Corporation provides a full range of banking and related financial services to consumer and commercial customers through its network of bank and nonbank subsidiaries. The Corporation is subject to competition from other financial and non-financial institutions that offer similar or competing products and services. The Corporation is regulated by federal and state agencies and is subject to periodic examinations by those agencies. Basis of Financial Statement Presentation The consolidated financial statements include the accounts of the Parent Company and its wholly-owned subsidiaries. Investments in unconsolidated entities (none of which are considered to be variable interest entities in which the Corporation is the primary beneficiary) are accounted for using the cost method of accounting when the Corporation has determined that the cost method is appropriate. Investments not meeting the criteria for cost method accounting are accounted for using the equity method of accounting. Investments in unconsolidated entities are included in other assets, and the Corporation’s share of income or loss is recorded in other noninterest income, while distributions in excess of the investment are recorded in gain on assets. All significant intercompany balances and transactions have been eliminated in consolidation. In preparing the consolidated financial statements, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and revenues and expenses for the period. Actual results could differ significantly from those estimates. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, goodwill impairment assessment, mortgage servicing rights valuation, and income taxes. Management has evaluated subsequent events for potential recognition or disclosure. Investment Securities Securities are classified as held to maturity or available for sale at the time of purchase. Investment securities classified as held to maturity, which management has the positive intent and ability to hold to maturity, are reported at amortized cost. Investment securities classified as available for sale, which management has the intent and ability to hold for an indefinite period of time, but not necessarily to maturity, are carried at fair value, with unrealized gains and losses, net of related deferred income taxes, included in stockholders’ equity as a separate component of other comprehensive income. Any decision to sell investment securities available for sale would be based on various factors, including, but not limited to, asset / liability management strategies, changes in interest rates or prepayment risks, liquidity needs, or regulatory capital considerations. Realized gains or losses on investment security sales (using specific identification method) are included in investment securities gains (losses), net, in the consolidated statements of income. Premiums and discounts are amortized or accreted into interest income over the estimated life (earlier of call date, maturity, or estimated life) of the related security, using a prospective method that approximates level yield. In certain situations, management may elect to transfer certain investment securities from the available for sale classification to the held to maturity classification. In such cases, the investment securities are reclassified at fair value at the time of transfer. Any unrealized gain or loss included in accumulated other comprehensive income (loss) at the time of transfer is retained therein and amortized over the remaining life of the investment security as an adjustment to yield. Declines in the fair value of investment securities (with certain exceptions for debt securities noted below) that are deemed to be other-than-temporary are charged to earnings as a realized loss, and a new cost basis for the investment security is established. In evaluating other-than-temporary impairment, management considers the length of time and extent to which the security has been in an unrealized loss position, changes in security ratings, the financial condition and near-term prospects of the issuer, as well as security and industry specific economic conditions. In addition, the Corporation considers the intent and ability to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value in the near term. Declines in the fair value of debt securities below amortized cost are deemed to be other-than-temporary in circumstances where: (1) the Corporation has the intent to sell a security; (2) it is more likely than not that the Corporation will be required to sell the security before recovery of its amortized cost basis; or (3) the Corporation does not expect to recover the entire amortized cost basis of the security. If the Corporation intends to sell a security or if it is more likely than not that the Corporation will be required to sell the security before recovery, an other-than-temporary impairment write-down is recognized in earnings equal to the difference between the security’s amortized cost basis and its fair value. If an entity does not intend to sell the security or it is more likely than not that it will not be required to sell the security before recovery, the other-than-temporary impairment write-down is separated into an amount representing credit loss, which is recognized in earnings, and an amount related to all other factors, which is recognized in other comprehensive income. Declines in value determined to be other-than-temporary are included in investment securities gains (losses), net, in the consolidated statements of income. See Note 3 for additional information on investment securities. Federal Home Loan Bank (“FHLB”) and Federal Reserve Bank Stocks The Corporation is required to maintain Federal Reserve stock and FHLB stock as a member of both the Federal Reserve System and the FHLB, and in amounts as required by these institutions. These equity securities are “restricted” in that they can only be sold back to the respective institutions or another member institution at par. Therefore, they are less liquid than other marketable equity securities and their fair value is equal to amortized cost. See Note 3 for additional information on the FHLB and Federal Reserve Bank Stocks. Loans Held for Sale Residential Loans Held for Sale: Loans held for sale, which consist generally of current production of certain fixed-rate, first-lien residential mortgage loans, are now carried at estimated fair value. Effective January 1, 2017, management elected the fair value option to account for all newly originated mortgage loans held for sale which results in the financial impact of changing market conditions being reflected currently in earnings as opposed to being dependent upon the timing of sales. The estimated fair value was based on what secondary markets are currently offering for portfolios with similar characteristics, which the Corporation classifies as a Level 2 fair value measurement. Commercial Loans Held for Sale: Loans held for sale are carried at the lower of cost or estimated fair value. The estimated fair value is based on a discounted cash flow analysis, which the Corporation classifies as a Level 2 nonrecurring fair value measurement. Loans Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off are reported at their outstanding principal balances, net of any deferred fees and costs on originated loans. Origination fee income received on loans and amounts representing the estimated direct costs of origination are deferred and amortized to interest income over the life of the loan using the effective interest method. An allowance for loan losses is established for estimated credit losses in the loan portfolio. See Allowance for Loan Losses below for further policy discussion. Nonaccrual Loans: Management considers a loan to be impaired when it is probable that the Corporation will be unable to collect all amounts due according to the original contractual terms of the note agreement, including both principal and interest. This determination is based on management's review of current information and other events regarding the borrowers’ ability to repay their obligations. Management has determined that commercial and consumer loan relationships that have nonaccrual status or have had their terms restructured in a troubled debt restructuring meet this impaired loan definition. Interest income on loans is based on the principal balance outstanding computed using the effective interest method. The accrual of interest income for commercial loans is discontinued when there is a clear indication that the borrower’s cash flow may not be sufficient to meet payments as they become due, while the accrual of interest income for consumer loans is discontinued when loans reach specific delinquency levels. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Loans are generally placed on nonaccrual status when contractually past due 90 days or more as to interest or principal payments, unless the loan is well secured and in the process of collection. Additionally, whenever management becomes aware of facts or circumstances that may adversely impact the collectability of principal or interest on loans, it is management’s practice to place such loans on a nonaccrual status immediately, rather than delaying such action until the loans become 90 days past due. When a loan is placed on nonaccrual status, previously accrued and uncollected interest is reversed, amortization of related deferred loan fees or costs is suspended, and income is recorded only to the extent that interest payments are subsequently received in cash and a determination has been made that the principal and interest of the loan is collectible. If collectability of the principal and interest is in doubt, payments received are applied to loan principal. While a loan is in nonaccrual status, some or all of the cash interest payments received may be treated as interest income on a cash basis as long as the remaining recorded investment in the loan (i.e., after charge off of identified losses, if any) is deemed to be fully collectible. The determination as to the ultimate collectability of the loan's remaining recorded investment must be supported by a current, well documented credit evaluation of the borrower’s financial condition and prospects for repayment, including consideration of the borrower’s sustained historical repayment performance and other relevant factors. A nonaccrual loan is returned to accrual status when all delinquent principal and interest payments become current in accordance with the terms of the loan agreement, the borrower has demonstrated a period of sustained repayment performance, and the ultimate collectability of the total contractual principal and interest is no longer in doubt. A sustained period of repayment performance generally would be a minimum of six months. See Note 4 for additional information on loans. Troubled Debt Restructurings (“Restructured Loans”): Loans are considered restructured loans if concessions have been granted to borrowers that are experiencing financial difficulty. The concessions granted generally involve the modification of terms of the loan, such as changes in payment schedule or interest rate, which generally would not otherwise be considered. Restructured loans can involve loans remaining on nonaccrual, moving to nonaccrual, or continuing on accrual status, depending on the individual facts and circumstances of the borrower. Nonaccrual restructured loans are included and treated with all other nonaccrual loans. In addition, all accruing restructured loans are reported as troubled debt restructurings, which are considered and accounted for as impaired loans. Generally, restructured loans remain on nonaccrual until the customer has attained a sustained period of repayment performance under the modified loan terms (generally a minimum of six months). However, performance prior to the restructuring, or significant events that coincide with the restructuring, are considered in assessing whether the borrower can meet the new terms and whether the loan should be returned to or maintained on accrual status. If the borrower’s ability to meet the revised payment schedule is not reasonably assured, the loan remains on nonaccrual status. See Note 4 for additional information on restructured loans. Allowance for Loan Losses: The allowance for loan losses is a reserve for estimated credit losses on individually evaluated loans determined to be impaired as well as estimated credit losses inherent in the loan portfolio, and is based on quarterly evaluations of the collectability and historical loss experience of loans. Actual credit losses, net of recoveries, are deducted from the allowance for loan losses. A provision for loan losses, which is a charge against earnings, is recorded to bring the allowance for loan losses to a level that, in management’s judgment, is appropriate to absorb probable losses in the loan portfolio. The methodology applied by the Corporation, designed to assess the appropriateness of the allowance for loan losses, is based upon management’s ongoing review and grading of the loan portfolio into criticized loan categories (defined as specific loans warranting either specific allocation, or a criticized status of special mention, substandard, doubtful, or loss). The methodology also focuses on evaluation of several factors, including but not limited to: evaluation of facts and issues related to specific loans, management’s ongoing review and grading of the loan portfolio, consideration of historical loan loss and delinquency experience on each portfolio category, trends in past due and nonaccrual loans, the level of potential problem loans, the risk characteristics of the various classifications of loans, changes in the size and character of the loan portfolio, concentrations of loans to specific borrowers or industries, existing economic conditions, the fair value of underlying collateral, and other qualitative and quantitative factors which could affect potential credit losses. Because each of the criteria used is subject to change, the analysis of the allowance for loan losses is not necessarily indicative of the trend of future loan losses in any particular loan category. The total allowance for loan losses is available to absorb losses from any segment of the loan portfolio. When an individual loan is determined to be impaired, the allowance for loan losses attributable to the loan is allocated based on management’s estimate of the borrower’s ability to repay the loan given the availability of collateral, other sources of cash flows, as well as evaluation of legal options available to the Corporation. The amount of impairment is measured based upon the present value of expected future cash flows discounted at the loan’s effective interest rate, the fair value of the underlying collateral less applicable selling costs, or the observable market price of the loan. If foreclosure is probable or the loan is collateral dependent, impairment is measured using the fair value of the loan’s collateral, less costs to sell. Large groups of homogeneous loans, such as residential mortgage, home equity, and other consumer, are collectively evaluated for impairment. Management believes that the level of the allowance for loan losses is appropriate. While management uses currently available information to recognize losses on loans, future adjustments to the allowance for loan losses may be necessary based on newly received appraisals, updated commercial customer financial statements, rapidly deteriorating cash flow, and changes in economic conditions that affect our customers. In addition, various regulatory agencies, as an integral part of their examination process, periodically review the Corporation’s allowance for loan losses. Such agencies may require additions to the allowance for loan losses or may require that certain loan balances be charged off or downgraded into criticized loan categories when their credit evaluations differ from those of management based on their judgments about information available to them at the time of their examinations. See Loans and Troubled Debt Restructurings above for further policy discussion and see Note 4 for additional information on the allowance for loan losses. Other Real Estate Owned Other real estate owned is included in other assets in the consolidated balance sheets and is comprised of property acquired through a foreclosure proceeding or acceptance of a deed-in-lieu of foreclosure, and loans classified as in-substance foreclosure. Other real estate owned is recorded at the fair value of the underlying property collateral, less estimated selling costs. This fair value becomes the new cost basis for the foreclosed asset. The initial write-down, if any, will be recorded as a charge off against the allowance for loan losses. Any subsequent write-downs to reflect current fair value, as well as gains and losses on disposition and revenues and expenses incurred in maintaining such properties, are expensed as incurred. Other real estate owned also includes bank premises formerly but no longer used for banking as well as property originally acquired for future expansion but no longer intended to be used for that purpose. Banking premises are transferred at the lower of carrying value or fair value, less estimated selling costs and any write-down is expensed as incurred. Allowance for Unfunded Commitments The allowance for unfunded commitments is maintained at a level believed by management to be sufficient to absorb estimated probable losses related to unfunded credit facilities (including unfunded loan commitments and letters of credit) and is included in accrued expenses and other liabilities in the consolidated balance sheets. The determination of the appropriate level of the allowance for unfunded commitments is based upon an evaluation of the unfunded credit facilities, including an assessment of historical commitment utilization experience and credit risk grading of the loan. Net adjustments to the allowance for unfunded commitments are included in the provision for credit losses in the consolidated statements of income. See Note 4 and Note 16 for additional information on the allowance for unfunded commitments. Mortgage Repurchase Reserve The Corporation sells residential mortgage loans to investors in the normal course of business. Residential mortgage loans sold to investors are predominantly conventional residential first lien mortgages originated under the usual underwriting procedures, and are most often sold on a nonrecourse basis, primarily to the Government Sponsored Enterprises ("GSE"). The Corporation’s agreements to sell residential mortgage loans usually require certain representations and warranties on the underlying loans sold, related to credit information, loan documentation, collateral, and insurability, which if subsequently untrue or breached, could require the Corporation to indemnify or repurchase certain loans affected. To a much lesser degree, the Corporation may sell residential mortgage loans with limited recourse (limited in that the recourse period ends prior to the loan’s maturity, usually after certain time and / or loan paydown criteria have been met), whereby indemnification or repurchase could be required if the loan had defined delinquency issues during the limited recourse periods. The balance in the repurchase reserve at the balance sheet date reflects the estimated amount of potential loss the Corporation could incur from repurchasing a loan (“put back” requests), as well as loss reimbursements, indemnification, and other settlement resolutions (“make whole” payments). See Note 16 for additional information on the mortgage repurchase reserve. Premises and Equipment and Software Premises and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization are computed on the straight-line method over the estimated useful lives of the related assets or the lease term. Maintenance and repairs are charged to expense as incurred, while additions or major improvements are capitalized and depreciated over the estimated useful lives. Leasehold improvements are amortized on a straight-line basis over the lesser of the lease terms or the estimated useful lives of the improvements. Software, included in other assets in the consolidated balance sheets, is amortized on a straight-line basis over the lesser of the contract terms or the estimated useful life of the software. See Note 6 for additional information on premises and equipment. Goodwill and Intangible Assets Goodwill and Other Intangible Assets: The excess of the cost of an acquisition over the fair value of the net assets acquired consists primarily of goodwill, core deposit intangibles, and other identifiable intangibles (primarily related to customer relationships acquired). Core deposit intangibles have estimated finite lives and are amortized on an accelerated basis to expense over a 10 -year period. The other intangibles have estimated finite lives and are amortized on an accelerated basis to expense over their weighted average life (a weighted average life of 11 years for 2017 and 12 years for 2016 ). The Corporation reviews long-lived assets and certain identifiable intangibles for impairment at least annually, or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, in which case an impairment charge would be recorded. Goodwill is not amortized but, instead, is subject to impairment tests on at least an annual basis, and more frequently if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. The impairment testing process is conducted by assigning net assets and goodwill to each reporting unit. An initial qualitative evaluation is made to assess the likelihood of impairment and determine whether further quantitative testing to calculate the fair value is necessary. When the qualitative evaluation indicates that impairment is more likely than not, quantitative testing is required whereby the fair value of each reporting unit is calculated and compared to the recorded book value, “step one.” If the calculated fair value of the reporting unit exceeds its carrying value, goodwill is not considered impaired and “step two” is not considered necessary. If the carrying value of a reporting unit exceeds its calculated fair value, the impairment test continues (“step two”) by comparing the carrying value of the reporting unit’s goodwill to the implied fair value of goodwill. The implied fair value is computed by adjusting all assets and liabilities of the reporting unit to current fair value with the offset adjustment to goodwill. The adjusted goodwill balance is the implied fair value of the goodwill. An impairment charge is recognized if the carrying value of goodwill exceeds the implied fair value of goodwill. See Note 5 for additional information on goodwill and other intangible assets. Mortgage Servicing Rights: The Corporation sells residential mortgage loans in the secondary market and typically retains the right to service the loans sold. Upon sale, a mortgage servicing rights asset is capitalized, which represents the then current fair value of future net cash flows expected to be realized for performing servicing activities. Mortgage servicing rights, when purchased, are initially recorded at fair value. As the Corporation has not elected to subsequently measure any class of servicing assets under the fair value measurement method, the Corporation follows the amortization method. Mortgage servicing rights are amortized in proportion to and over the period of estimated net servicing income, and assessed for impairment at each reporting date. Mortgage servicing rights are carried at the lower of the initial capitalized amount, net of accumulated amortization, or estimated fair value, in the consolidated balance sheets. The Corporation periodically evaluates its mortgage servicing rights asset for impairment. Impairment is assessed based on fair value at each reporting date using estimated prepayment speeds of the underlying mortgage loans serviced and stratifications based on the risk characteristics of the underlying loans (predominantly loan type and note interest rate). As mortgage interest rates fall, prepayment speeds are usually faster and the value of the mortgage servicing rights asset generally decreases, requiring additional valuation reserve. Conversely, as mortgage interest rates rise, prepayment speeds are usually slower and the value of the mortgage servicing rights asset generally increases, requiring less valuation reserve. A valuation allowance is established, through a charge to earnings, to the extent the amortized cost of the mortgage servicing rights exceeds the estimated fair value by stratification. If it is later determined that all or a portion of the temporary impairment no longer exists for a stratification, the valuation is reduced through a recovery to earnings. An other-than-temporary impairment (i.e., recoverability is considered remote when considering interest rates and loan pay off activity) is recognized as a write-down of the mortgage servicing rights asset and the related valuation allowance (to the extent a valuation allowance is available) and then against earnings. A direct write-down permanently reduces the carrying value of the mortgage servicing rights asset and valuation allowance, precluding subsequent recoveries. See Note 5 for additional information on mortgage servicing rights. Income Taxes Amounts provided for income tax expense are based on income reported for financial statement purposes and do not necessarily represent amounts currently payable under tax laws. Deferred income taxes, which arise principally from temporary differences between the amounts reported in the financial statements and the tax bases of assets and liabilities, are included in the amounts provided for income taxes. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income and tax planning strategies which will create taxable income during the periods in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities, the amount of taxes paid in available carryback years, projected future taxable income, and, if necessary, tax planning strategies in making this assessment. The Corporation files a consolidated federal income tax return and separate or combined state income tax returns. Accordingly, amounts equal to tax benefits of those subsidiaries having taxable federal or state losses or credits are offset by other subsidiaries that incur federal or state tax liabilities. It is the Corporation’s policy to provide for uncertainty in income taxes as a part of income tax expense based upon management’s assessment of whether a tax benefit is more likely than not to be sustained upon examination by tax authorities. At December 31, 2017 and 2016 , the Corporation believes it has appropriately accounted for any unrecognized tax benefits. To the extent the Corporation prevails in matters for which a liability for an unrecognized tax benefit was established or is required to pay amounts in excess of the liability established, the Corporation’s effective tax rate in a given financial statement period may be impacted. See Note 13 for additional information on income taxes. Derivative and Hedging Activities Derivative instruments, including derivative instruments embedded in other contracts, are carried at fair value on the consolidated balance sheets with changes in the fair value recorded to earnings or accumulated other comprehensive income, as appropriate. On the date the derivative contract is entered into, the Corporation designates the derivative as a fair value hedge (i.e., a hedge of the fair value of a recognized asset or liability), a cash flow hedge (i.e., a hedge of the variability of cash flows to be received or paid related to a recognized asset or liability), or a free-standing derivative instrument. For a derivative designated as a fair value hedge, the changes in the fair value of the derivative instrument and the changes in the fair value of the hedged asset or liability are recognized in current period earnings as an increase or decrease to the carrying value of the hedged item on the balance sheet and in the related income statement account. For a derivative designated as a cash flow hedge, the effective portions of changes in the fair value of a derivative instrument are recorded in other comprehensive income and the ineffective portions of changes in the fair value of a derivative instrument are recognized in current period earnings as an adjustment to the related income statement account. Amounts within accumulated other comprehensive income are reclassified into earnings in the period the hedged item affects earnings. For a derivative designated as a free-standing derivative instrument, changes in fair value are reported in current period earnings. At December 31, 2017 and 2016 , the Corporation only had free-standing derivative instruments to facilitate customer borrowing activity. These free-standing derivative instruments included: interest rate risk management, commodity hedging, and foreign currency exchange solutions. See Note 14 for additional information on derivative and hedging activities. Retirement Plans The funded status of the retirement plans are recognized as an asset or liability in the consolidated balance sheets, and changes in that funded status are recognized in the year in which the changes occur through other comprehensive income. Plan assets and benefit obligations are measured as of fiscal year end. The measurement of the projected benefit obligation and pension expense involve actuarial valuation methods and the use of various actuarial and economic assumptions. The Corporation monitors the assumptions and updates them periodically. Due to the long-term nature of the pension plan obligation, actual results may differ significantly from estimations. Such differences are adjusted over time as the assumptions are replaced by facts and values are recalculated. See Note 12 for additional information on the Corporation’s retirement plans. Stock-Based Compensation The fair value of stock options granted is estimated on the date of grant using a Black-Scholes option pricing model, while the fair value of restricted common stock awards is their fair market value on the date of grant. The fair values of stock options and restricted stock awards are amortized as compensation expense on a straight-line basis over the vesting period of the grants. Expenses related to stock options and restricted stock awards are fully recognized on the date the colleague meets the definition of normal or early retirement. Compensation expense recognized is included in personnel expense in the consolidated statements of income. See Note 11 for additional information on stock-based compensation. Comprehensive Income Comprehensive income includes all changes in stockholders’ equity during a period, except those resulting from transactions with stockholders. In addition to net income, other components of the Corporation’s comprehensive income include the after tax effect of changes in net unrealized gain / loss on securities available for

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisition	Acquisitions On October 2, 2017, the Corporation completed its previously announced acquisition of Whitnell & Co., a wealth management family office services firm based in Oak Brook, IL. The Corporation recorded goodwill of $4 million and other intangibles of $2 million related to the Whitnell & Co. acquisition. During the first quarter of 2017, the Corporation completed a small insurance acquisition to complement its existing insurance and benefits related products and services provided by Associated Benefits and Risk Consulting. The Corporation recorded goodwill of $55,000 and other intangibles of $162,000 related to the insurance acquisition. See Note 5 for additional information on goodwill and other intangible assets On February 1, 2018, the Corporation acquired Bank Mutual Corporation ("Bank Mutual") pursuant to an Agreement and Plan of Merger, dated as of July 20, 2017 (the "Merger Agreement") under which Bank Mutual merged with and into the Corporation. Under the terms of the Merger Agreement, Bank Mutual’s shareholders received 0.422 shares of the Corporation's common stock for each share of Bank Mutual’s common stock. The Corporation expects to issue approximately 19.6 million shares for a total deal value of approximately $485 million based on the closing sale price of a share of Associated common stock on January 31, 2018. We expect to merge Bank Mutual's banking subsidiary into Associated Bank in late June or July 2018. See Note 23

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities Investment securities are generally classified as available for sale or held to maturity at the time of purchase. See Note 1 for the Corporation’s accounting policy for investment securities. The majority of the Corporation's investment securities are mortgage-related securities issued by the Government National Mortgage Association (“GNMA”) or GSEs such as the Federal National Mortgage Association (“FNMA”) and the Federal Home Loan Mortgage Corporation (“FHLMC”). December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value ($ in Thousands) Investment securities available for sale U.S. Treasury securities $ 1,003 $ — $ (7 ) $ 996 Residential mortgage-related securities FNMA / FHLMC 457,680 9,722 (2,634 ) 464,768 GNMA 1,944,453 275 (31,378 ) 1,913,350 Private-label 1,067 — (8 ) 1,059 GNMA commercial mortgage-related securities 1,547,173 5 (33,901 ) 1,513,277 FFELP asset backed securities 144,322 867 (13 ) 145,176 Other securities (debt and equity) 4,719 127 (26 ) 4,820 Total investment securities available for sale $ 4,100,417 $ 10,996 $ (67,967 ) $ 4,043,446 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) $ 1,281,320 $ 13,899 $ (3,177 ) $ 1,292,042 Residential mortgage-related securities FNMA / FHLMC 40,995 398 (489 ) 40,904 GNMA 414,440 2,700 (6,400 ) 410,740 GNMA commercial mortgage-related securities 546,098 9,546 (15,756 ) 539,888 Total investment securities held to maturity $ 2,282,853 $ 26,543 $ (25,822 ) $ 2,283,574 December 31, 2016 Amortized Gross Gross Fair Value ($ in Thousands) Investment securities available for sale U.S. Treasury securities $ 1,000 $ — $ — $ 1,000 Residential mortgage-related securities: FNMA / FHLMC 625,234 17,298 (2,602 ) 639,930 GNMA 2,028,301 1,372 (25,198 ) 2,004,475 Private-label 1,134 1 (14 ) 1,121 GNMA commercial mortgage-related securities 2,064,508 356 (35,966 ) 2,028,898 Other securities (debt and equity) 4,718 105 (21 ) 4,802 Total investment securities available for sale $ 4,724,895 $ 19,132 $ (63,801 ) $ 4,680,226 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) $ 1,145,843 $ 3,868 $ (12,036 ) $ 1,137,675 Residential mortgage-related securities FNMA / FHLMC 37,697 439 (693 ) 37,443 GNMA 89,996 216 (656 ) 89,556 Total investment securities held to maturity $ 1,273,536 $ 4,523 $ (13,385 ) $ 1,264,674 The expected maturities of investment securities available for sale and held to maturity at December 31, 2017 , are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Available for Sale Held to Maturity Amortized Cost Fair Value Amortized Cost Fair Value ($ in Thousands) Due in one year or less $ 1,001 $ 1,001 $ 50,089 $ 44,781 Due after one year through five years 4,703 4,669 226,053 229,939 Due after five years through ten years — — 322,413 324,380 Due after ten years — — 682,765 692,942 Total debt securities 5,704 5,670 1,281,320 1,292,042 Residential mortgage-related securities FNMA / FHLMC 457,680 464,768 40,995 40,904 GNMA 1,944,453 1,913,350 414,440 410,740 Private-label 1,067 1,059 — — GNMA commercial mortgage-related securities 1,547,173 1,513,277 546,098 539,888 FFELP asset backed securities 144,322 145,176 — — Equity securities 18 146 — — Total investment securities $ 4,100,417 $ 4,043,446 $ 2,282,853 $ 2,283,574 Ratio of Fair Value to Amortized Cost 98.6 % 100.0 % During the year ended December 31, 2017 , the Corporation reclassified GNMA residential mortgage-related securities and GNMA commercial mortgage-related securities from available for sale to held to maturity with an amortized cost of approximately $1 billion . The GNMA residential and commercial mortgage-related securities are principally securities with a CRA component in the underlying collateral. The reclassification of these investment securities was accounted for at fair value. Management elected to transfer these investment securities as the Corporation has the positive intent and ability to hold these investment securities to maturity. Total proceeds and gross realized gains and losses from sales of investment securities for each of the three years ended December 31 were as follows. There were no other-than-temporary impairment write-downs on investment securities for 2017 , 2016 , or 2015 . 2017 2016 2015 ($ in Thousands) Gross gains on available for sale securities $ — $ 9,485 $ 12,270 Gross gains on held to maturity securities 439 33 — Total gains 439 9,518 12,270 Gross losses on available for sale securities — (202 ) (4,137 ) Gross losses on held to maturity securities (5 ) — — Total losses (5 ) (202 ) (4,137 ) Investment securities gains, net $ 434 $ 9,316 $ 8,133 Proceeds from sales of investment securities $ 18,467 $ 549,555 $ 1,601,947 During 2017, the Corporation sold approximately $18 million of municipal securities classified as held to maturity due to significant credit concerns and negative actions taken by credit rating agencies, primarily as a result of budgetary pressures in the State of Illinois and State of Connecticut. These sales resulted in a net gain of approximately $434,000 . During 2016 and 2015, the Corporation restructured its investment securities portfolio from FNMA and FHLMC mortgage-related securities and reinvested into GNMA mortgage-related securities. The Corporation sold approximately $550 million of FNMA and FHLMC mortgage-related securities in 2016 and sold approximately $1.6 billion in 2015, generating net gains on sales of $9 million and $8 million , respectively. The sales of FNMA and FHLMC mortgage-related securities and the subsequent purchase of GNMA mortgage-related securities lowered risk weighted assets and related capital requirements. Securities with a carrying value of approximately $3.1 billion and $1.8 billion at December 31, 2017 , and December 31, 2016 , respectively, were pledged to secure certain deposits or for other purposes as required or permitted by law. The following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time individual securities have been in a continuous unrealized loss position, at December 31, 2017 . Less than 12 months 12 months or more Total December 31, 2017 Number of Securities Unrealized Losses Fair Value Number of Securities Unrealized Losses Fair Value Unrealized Losses Fair Value ($ in Thousands) Investment securities available for sale U.S. Treasury securities 1 $ (7 ) $ 996 — $ — $ — $ (7 ) $ 996 Residential mortgage-related securities FNMA / FHLMC 9 (572 ) 69,939 9 (2,062 ) 142,093 (2,634 ) 212,032 GNMA 44 (8,927 ) 1,028,221 25 (22,451 ) 737,198 (31,378 ) 1,765,419 Private-label — — — 1 (8 ) 1,059 (8 ) 1,059 GNMA commercial mortgage-related securities 33 (5,554 ) 480,514 70 (28,347 ) 1,026,642 (33,901 ) 1,507,156 FFELP asset backed securities 1 (13 ) 12,158 — — — (13 ) 12,158 Other securities (debt and equity) 4 (26 ) 1,675 — — — (26 ) 1,675 Total 92 $ (15,099 ) $ 1,593,503 105 $ (52,868 ) $ 1,906,992 $ (67,967 ) $ 3,500,495 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) 157 $ (746 ) $ 122,761 132 $ (2,431 ) $ 127,043 $ (3,177 ) $ 249,804 Residential mortgage-related securities FNMA / FHLMC 8 (73 ) 13,143 10 (417 ) 16,262 (490 ) 29,405 GNMA 35 (3,373 ) 268,388 18 (3,026 ) 120,892 (6,399 ) 389,280 GNMA commercial mortgage-related securities 2 (299 ) 52,997 23 (15,457 ) 486,891 (15,756 ) 539,888 Total 202 $ (4,491 ) $ 457,289 183 $ (21,331 ) $ 751,088 $ (25,822 ) $ 1,208,377 For comparative purposes, the following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2016 . Less than 12 months 12 months or more Total December 31, 2016 Number Unrealized Fair Number Unrealized Fair Unrealized Fair ($ in Thousands) Investment securities available for sale Residential mortgage-related securities FNMA / FHLMC 14 $ (2,602 ) $ 244,252 — $ — $ — $ (2,602 ) $ 244,252 GNMA 54 (25,198 ) 1,723,523 — — — (25,198 ) 1,723,523 Private-label — — — 1 (14 ) 1,119 (14 ) 1,119 GNMA commercial mortgage-related securities 74 (16,445 ) 1,427,889 21 (19,521 ) 429,258 (35,966 ) 1,857,147 Other securities (debt and equity) 3 (21 ) 1,479 — — — (21 ) 1,479 Total 145 $ (44,266 ) $ 3,397,143 22 $ (19,535 ) $ 430,377 $ (63,801 ) $ 3,827,520 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) 700 $ (11,937 ) $ 414,186 4 $ (99 ) $ 1,752 $ (12,036 ) $ 415,938 Residential mortgage-related securities FNMA / FHLMC 14 (441 ) 17,477 1 (252 ) 6,031 (693 ) 23,508 GNMA 39 (656 ) 64,633 — — — (656 ) 64,633 Total 753 $ (13,034 ) $ 496,296 5 $ (351 ) $ 7,783 $ (13,385 ) $ 504,079 The Corporation reviews the investment securities portfolio on a quarterly basis to monitor its exposure to other-than-temporary impairment. A determination as to whether a security’s decline in fair value is other-than-temporary takes into consideration numerous factors and the relative significance of any single factor can vary by security. Some factors the Corporation may consider in the other-than-temporary impairment analysis include, the length of time and extent to which the security has been in an unrealized loss position, changes in security ratings, financial condition and near-term prospects of the issuer, as well as security and industry specific economic conditions. Based on the Corporation’s evaluation, management does not believe any unrealized loss at December 31, 2017 , represents an other-than-temporary impairment as these unrealized losses are primarily attributable to changes in interest rates and the current market conditions, and not credit deterioration. The unrealized losses reported for municipal securities relate to various state and local political subdivisions and school districts. The unrealized losses at December 31, 2017 for mortgage-related securities is due to the increase in overall interest rates. The U.S. Treasury 3-year and 5-year rates increased by 51 bp and 27 bp, respectively, from December 31, 2016. The Corporation currently does not intend to sell nor does it believe that it will be required to sell the securities contained in the above unrealized losses table before recovery of their amortized cost basis. FHLB and Federal Reserve Bank Stocks: The Corporation is required to maintain Federal Reserve stock and FHLB stock as a member of both the Federal Reserve System and the FHLB, and in amounts as required by these institutions. These equity securities are “restricted” in that they can only be sold back to the respective institutions or another member institution at par. Therefore, they are less liquid than other marketable equity securities and their fair value is equal to amortized cost. At December 31, 2017 , and 2016 , the Corporation had FHLB stock of $89 million and $65 million , respectively. The Corporation had Federal Reserve Bank stock of $76 million and $75 million at December 31, 2017 and 2016

Loans

Loans	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Loans	Loans Loans at December 31 are summarized below. 2017 2016 ($ in Thousands) Commercial and industrial $ 6,399,693 $ 6,489,014 Commercial real estate - owner occupied 802,209 897,724 Commercial and business lending 7,201,902 7,386,738 Commercial real estate - investor 3,315,254 3,574,732 Real estate construction 1,451,684 1,432,497 Commercial real estate lending 4,766,938 5,007,229 Total commercial 11,968,840 12,393,967 Residential mortgage 7,546,534 6,332,327 Home equity 883,804 934,443 Other consumer 385,813 393,979 Total consumer 8,816,151 7,660,749 Total loans $ 20,784,991 $ 20,054,716 The Corporation has granted loans to its directors, executive officers, or their related interests. These loans were made on substantially the same terms, including rates and collateral, as those prevailing at the time for comparable transactions with other unrelated customers, and do not involve more than a normal risk of collection. These loans to related parties are summarized below. 2017 2016 ($ in Thousands) Balance at beginning of year $ 27,589 $ 36,597 New loans 5,329 10,677 Repayments (7,632 ) (11,089 ) Change due to status of executive officers and directors (5,026 ) (8,596 ) Balance at end of year $ 20,260 $ 27,589 The following table presents commercial and consumer loans by credit quality indicator at December 31, 2017 . Pass Special Mention Potential Problem Nonaccrual Total ($ in Thousands) Commercial and industrial $ 6,015,884 $ 157,245 $ 113,778 $ 112,786 $ 6,399,693 Commercial real estate - owner occupied 723,291 14,181 41,997 22,740 802,209 Commercial and business lending 6,739,175 171,426 155,775 135,526 7,201,902 Commercial real estate - investor 3,266,389 24,845 19,291 4,729 3,315,254 Real estate construction 1,421,504 29,206 — 974 1,451,684 Commercial real estate lending 4,687,893 54,051 19,291 5,703 4,766,938 Total commercial 11,427,068 225,477 175,066 141,229 11,968,840 Residential mortgage 7,490,860 426 1,616 53,632 7,546,534 Home equity 868,958 1,137 195 13,514 883,804 Other consumer 384,990 652 — 171 385,813 Total consumer 8,744,808 2,215 1,811 67,317 8,816,151 Total loans $ 20,171,876 $ 227,692 $ 176,877 $ 208,546 $ 20,784,991 The following table presents commercial and consumer loans by credit quality indicator at December 31, 2016 . Pass Special Mention Potential Problem Nonaccrual Total ($ in Thousands) Commercial and industrial $ 5,937,119 $ 141,328 $ 227,196 $ 183,371 $ 6,489,014 Commercial real estate - owner occupied 805,871 17,785 64,524 9,544 897,724 Commercial and business lending 6,742,990 159,113 291,720 192,915 7,386,738 Commercial real estate - investor 3,491,217 14,236 51,228 18,051 3,574,732 Real estate construction 1,429,083 105 2,465 844 1,432,497 Commercial real estate lending 4,920,300 14,341 53,693 18,895 5,007,229 Total commercial 11,663,290 173,454 345,413 211,810 12,393,967 Residential mortgage 6,275,162 1,314 5,615 50,236 6,332,327 Home equity 919,740 1,588 114 13,001 934,443 Other consumer 393,161 562 — 256 393,979 Total consumer 7,588,063 3,464 5,729 63,493 7,660,749 Total loans $ 19,251,353 $ 176,918 $ 351,142 $ 275,303 $ 20,054,716 Factors that are important to managing overall credit quality are sound loan underwriting and administration, systematic monitoring of existing loans and commitments, effective loan review on an ongoing basis, early identification of potential problems, an appropriate allowance for loan losses, allowance for unfunded commitments, nonaccrual, and charge off policies. See Note 1 for the Corporation's accounting policy for loans. For commercial loans, management has determined the pass credit quality indicator to include credits that exhibit acceptable financial statements, cash flow, and leverage. If any risk exists, it is mitigated by the loan structure, collateral, monitoring, or control. For consumer loans, performing loans include credits that are performing in accordance with the original contractual terms. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Special mention credits have potential weaknesses that deserve management’s attention. If left uncorrected, these potential weaknesses may result in deterioration of the repayment prospects for the credit. Potential problem loans are considered inadequately protected by the current net worth and paying capacity of the obligor or the collateral pledged. These loans generally have a well-defined weakness, or weaknesses, that may jeopardize liquidation of the debt and are characterized by the distinct possibility that the Corporation will sustain some loss if the deficiencies are not corrected. Lastly, management considers a loan to be impaired when it is probable that the Corporation will be unable to collect all amounts due according to the original contractual terms of the note agreement, including both principal and interest. Management has determined that commercial and consumer loan relationships that have nonaccrual status or have had their terms restructured in a troubled debt restructuring meet this impaired loan definition. Commercial loans classified as special mention, potential problem, and nonaccrual loans are reviewed at a minimum on a quarterly basis, while pass rated credits are reviewed on an annual basis or more frequently if the loan renewal is less than one year or if otherwise warranted. The following table presents loans by past due status at December 31, 2017 . Current 30-59 Days Past Due 60-89 Days Past Due 90 Days or More Past Due (a) Nonaccrual (b) Total ($ in Thousands) Commercial and industrial $ 6,286,369 $ 170 $ 101 $ 267 $ 112,786 $ 6,399,693 Commercial real estate - owner occupied 779,421 48 — — 22,740 802,209 Commercial and business lending 7,065,790 218 101 267 135,526 7,201,902 Commercial real estate - investor 3,310,000 374 — 151 4,729 3,315,254 Real estate construction 1,450,459 168 83 — 974 1,451,684 Commercial real estate lending 4,760,459 542 83 151 5,703 4,766,938 Total commercial 11,826,249 760 184 418 141,229 11,968,840 Residential mortgage 7,483,350 9,186 366 — 53,632 7,546,534 Home equity 863,465 5,688 1,137 — 13,514 883,804 Other consumer 382,186 1,227 780 1,449 171 385,813 Total consumer 8,729,001 16,101 2,283 1,449 67,317 8,816,151 Total loans $ 20,555,250 $ 16,861 $ 2,467 $ 1,867 $ 208,546 $ 20,784,991 (a) The recorded investment in loans past due 90 days or more and still accruing totaled $2 million at December 31, 2017 (the same as the reported balances for the accruing loans noted above). (b) Of the total nonaccrual loans, $135 million or 65% were current with respect to payment at December 31, 2017 . The following table presents loans by past due status at December 31, 2016 . Current 30-59 Days Past Due 60-89 Days Past Due 90 Days or More Past Due (a) Nonaccrual (b) Total ($ in Thousands) Commercial and industrial $ 6,303,994 $ 965 $ 448 $ 236 $ 183,371 $ 6,489,014 Commercial real estate - owner occupied 886,796 968 416 — 9,544 897,724 Commercial and business lending 7,190,790 1,933 864 236 192,915 7,386,738 Commercial real estate - investor 3,555,750 431 500 — 18,051 3,574,732 Real estate construction 1,431,284 264 105 — 844 1,432,497 Commercial real estate lending 4,987,034 695 605 — 18,895 5,007,229 Total commercial 12,177,824 2,628 1,469 236 211,810 12,393,967 Residential mortgage 6,273,949 7,298 844 — 50,236 6,332,327 Home equity 915,593 4,265 1,584 — 13,001 934,443 Other consumer 389,157 2,471 718 1,377 256 393,979 Total consumer 7,578,699 14,034 3,146 1,377 63,493 7,660,749 Total loans $ 19,756,523 $ 16,662 $ 4,615 $ 1,613 $ 275,303 $ 20,054,716 (a) The recorded investment in loans past due 90 days or more and still accruing totaled $2 million at December 31, 2016 (the same as the reported balances for the accruing loans noted above). (b) Of the total nonaccrual loans, $224 million or 81% were current with respect to payment at December 31, 2016 . The following table presents impaired loans individually evaluated under ASC Topic 310 at December 31, 2017 . Recorded Unpaid Related Average Interest ($ in Thousands) Loans with a related allowance Commercial and industrial $ 81,649 $ 83,579 $ 10,838 $ 58,494 $ 2,629 Commercial real estate - owner occupied 23,796 23,937 2,973 12,124 736 Commercial and business lending 105,445 107,516 13,811 70,618 3,365 Commercial real estate - investor 17,823 17,862 1,597 16,924 1,694 Real estate construction 467 578 86 484 29 Commercial real estate lending 18,290 18,440 1,683 17,408 1,723 Total commercial 123,735 125,956 15,494 88,026 5,088 Residential mortgage 40,561 42,922 6,512 40,411 1,614 Home equity 10,250 10,986 3,718 10,521 549 Other consumer 1,135 1,138 122 1,140 3 Total consumer 51,946 55,046 10,352 52,072 2,166 Total loans $ 175,681 $ 181,002 $ 25,846 $ 140,098 $ 7,254 Loans with no related allowance Commercial and industrial $ 60,595 $ 82,839 $ — $ 89,275 $ 492 Commercial real estate - owner occupied 2,438 2,829 — 1,948 36 Commercial and business lending 63,033 85,668 — 91,223 528 Commercial real estate - investor 1,295 1,295 — — 45 Real estate construction — — — — — Commercial real estate lending 1,295 1,295 — — 45 Total commercial 64,328 86,963 — 91,223 573 Residential mortgage 6,925 7,204 — 4,999 217 Home equity 641 645 — 540 7 Other consumer — — — — — Total consumer 7,566 7,849 — 5,539 224 Total loans $ 71,894 $ 94,812 $ — $ 96,762 $ 797 Total Commercial and industrial $ 142,244 $ 166,418 $ 10,838 $ 147,769 $ 3,121 Commercial real estate - owner occupied 26,234 26,766 2,973 14,072 772 Commercial and business lending 168,478 193,184 13,811 161,841 3,893 Commercial real estate - investor 19,118 19,157 1,597 16,924 1,739 Real estate construction 467 578 86 484 29 Commercial real estate lending 19,585 19,735 1,683 17,408 1,768 Total commercial 188,063 212,919 15,494 179,249 5,661 Residential mortgage 47,486 50,126 6,512 45,410 1,831 Home equity 10,891 11,631 3,718 11,061 556 Other consumer 1,135 1,138 122 1,140 3 Total consumer 59,512 62,895 10,352 57,611 2,390 Total loans (a) $ 247,575 $ 275,814 $ 25,846 $ 236,860 $ 8,051 (a) The net recorded investment (defined as recorded investment, net of the related allowance) of the impaired loans represented 80% of the unpaid principal balance at December 31, 2017 . The following table presents impaired loans individually evaluated under ASC Topic 310 at December 31, 2016 . Recorded Investment Unpaid Principal Balance Related Allowance Average Recorded Investment Interest Income Recognized ($ in Thousands) Loans with a related allowance Commercial and industrial $ 99,786 $ 105,175 $ 21,047 $ 104,808 $ 2,345 Commercial real estate - owner occupied 5,544 5,568 23 5,840 263 Commercial and business lending 105,330 110,743 21,070 110,648 2,608 Commercial real estate - investor 26,764 27,031 3,410 30,665 2,120 Real estate construction 509 648 84 529 31 Commercial real estate lending 27,273 27,679 3,494 31,194 2,151 Total commercial 132,603 138,422 24,564 141,842 4,759 Residential mortgage 37,902 39,979 6,438 38,608 1,551 Home equity 11,070 11,909 3,943 11,420 627 Other consumer 1,012 1,023 109 1,021 2 Total consumer 49,984 52,911 10,490 51,049 2,180 Total loans $ 182,587 $ 191,333 $ 35,054 $ 192,891 $ 6,939 Loans with no related allowance Commercial and industrial $ 113,485 $ 134,863 $ — $ 117,980 $ 1,519 Commercial real estate - owner occupied 8,439 9,266 — 8,759 138 Commercial and business lending 121,924 144,129 — 126,739 1,657 Commercial real estate - investor 6,144 6,478 — 7,092 — Real estate construction — — — — — Commercial real estate lending 6,144 6,478 — 7,092 — Total commercial 128,068 150,607 — 133,831 1,657 Residential mortgage 5,974 6,998 — 6,610 184 Home equity 106 107 — 107 4 Other consumer — — — — — Total consumer 6,080 7,105 — 6,717 188 Total loans $ 134,148 $ 157,712 $ — $ 140,548 $ 1,845 Total Commercial and industrial $ 213,271 $ 240,038 $ 21,047 $ 222,788 $ 3,864 Commercial real estate - owner occupied 13,983 14,834 23 14,599 401 Commercial and business lending 227,254 254,872 21,070 237,387 4,265 Commercial real estate - investor 32,908 33,509 3,410 37,757 2,120 Real estate construction 509 648 84 529 31 Commercial real estate lending 33,417 34,157 3,494 38,286 2,151 Total commercial 260,671 289,029 24,564 275,673 6,416 Residential mortgage 43,876 46,977 6,438 45,218 1,735 Home equity 11,176 12,016 3,943 11,527 631 Other consumer 1,012 1,023 109 1,021 2 Total consumer 56,064 60,016 10,490 57,766 2,368 Total loans (a) $ 316,735 $ 349,045 $ 35,054 $ 333,439 $ 8,784 (a) The net recorded investment (defined as recorded investment, net of the related allowance) of the impaired loans represented 81% of the unpaid principal balance at December 31, 2016 . Troubled Debt Restructurings (“Restructured Loans”) Loans are considered restructured loans if concessions have been granted to borrowers that are experiencing financial difficulty. See Note 1 for the Corporation's accounting policy for troubled debt restructurings. The Corporation had a recorded investment of approximately $9 million in loans modified in troubled debt restructurings for the year ended December 31, 2017 , of which approximately $6 million were in accrual status and $3 million were in nonaccrual pending a sustained period of repayment. As of December 31, 2017 there was approximately $9 million of commitments to lend additional funds to borrowers with restructured loans. The following table presents nonaccrual and performing restructured loans by loan portfolio. December 31, 2017 December 31, 2016 December 31, 2015 Performing Restructured Loans Nonaccrual Restructured Loans (a) Performing Restructured Loans Nonaccrual Restructured Loans (a) Performing Restructured Loans Nonaccrual Restructured Loans (a) ($ in Thousands) Commercial and industrial $ 30,047 $ 1,776 $ 31,884 $ 1,276 $ 29,293 $ 1,714 Commercial real estate - owner occupied 3,989 — 5,490 2,220 7,877 2,703 Commercial real estate - investor 14,389 — 15,289 924 21,915 3,936 Real estate construction 310 157 359 150 510 177 Residential mortgage 17,068 18,991 18,100 21,906 19,870 24,592 Home equity 7,705 2,537 7,756 2,877 7,069 4,522 Other consumer 1,110 25 979 32 829 40 Total restructured loans $ 74,618 $ 23,486 $ 79,857 $ 29,385 $ 87,363 $ 37,684 (a) Nonaccrual restructured loans have been included within nonaccrual loans. The following table provides the number of loans modified in a troubled debt restructuring by loan portfolio during the years ended December 31, 2017 , 2016 and 2015 , respectively, and the recorded investment and unpaid principal balance as of December 31, 2017 , 2016 and 2015 , respectively. Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Number of Loans Recorded Investment (a) Unpaid Principal Balance (b) Number of Loans Recorded Investment (a) Unpaid Principal Balance (b) Number Recorded (a) Unpaid (b) ($ in Thousands) Commercial and industrial 8 $ 3,991 $ 6,339 8 $ 1,509 $ 1,526 12 $ 2,219 $ 2,900 Commercial real estate - owner occupied 2 690 690 1 116 122 5 3,694 3,901 Commercial real estate - investor — — — — — — 5 21,573 21,640 Real estate construction — — — 1 65 91 4 78 79 Residential mortgage 45 4,238 4,364 63 5,535 5,792 97 10,464 10,996 Home equity 22 507 507 57 2,030 2,084 88 3,103 3,249 Other consumer — — — 1 15 16 — — — Total 77 $ 9,426 $ 11,900 131 $ 9,270 $ 9,631 211 $ 41,131 $ 42,765 (a) Represents post-modification outstanding recorded investment. (b) Represents pre-modification outstanding recorded investment. Restructured loan modifications may include payment schedule modifications, interest rate concessions, maturity date extensions, modification of note structure (A/B Note), non-reaffirmed Chapter 7 bankruptcies, principal reduction, or some combination of these concessions. For the year ended December 31, 2017 , restructured loan modifications of commercial and industrial, commercial real estate, and real estate construction loans primarily included maturity date extensions, interest rate concessions, payment schedule modifications, or a combination of these concessions. Restructured loan modifications of home equity and residential mortgage loans primarily included maturity date extensions, interest rate concessions, non-reaffirmed Chapter 7 bankruptcies, or a combination of these concessions for the year ended December 31, 2017 . The following table provides the number of loans modified in a troubled debt restructuring during the previous twelve months which subsequently defaulted during the year ended December 31, 2017 , 2016 and 2015 , respectively, as well as the recorded investment in these restructured loans as of December 31, 2017 , 2016 and 2015 , respectively. Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Recorded ($ in Thousands) Commercial and industrial 2 $ — — $ — 2 $ 197 Residential mortgage 36 3,137 44 4,102 61 6,815 Home equity 27 735 23 457 28 1,220 Other consumer 1 7 1 15 — — Total 66 $ 3,879 68 $ 4,574 91 $ 8,232 All loans modified in a troubled debt restructuring are evaluated for impairment. The nature and extent of the impairment of restructured loans, including those which have experienced a subsequent payment default, is considered in the determination of an appropriate level of the allowance for loan losses. Allowance for Credit Losses The allowance for credit losses is comprised of the allowance for loan losses and the allowance for unfunded commitments. The level of the allowance for loan losses represents management’s estimate of an amount appropriate to provide for probable credit losses in the loan portfolio at the balance sheet date. See Note 1 for the Corporation's accounting policy on the allowance for loan losses. The allowance for unfunded commitments is maintained at a level believed by management to be sufficient to absorb estimated probable losses related to unfunded credit facilities (including unfunded loan commitments and letters of credit) and is included in accrued expenses and other liabilities on the consolidated balance sheets. See Note 16 for additional information on the allowance for unfunded commitments. A summary of the changes in the allowance for loan losses by portfolio segment for the year ended December 31, 2017 , was as follows. Commercial and industrial Commercial real estate - owner occupied Commercial real estate - investor Real estate construction Residential mortgage Home equity Other consumer Total ($ in Thousands) December 31, 2016 $ 140,126 $ 14,034 $ 45,285 $ 26,932 $ 27,046 $ 20,364 $ 4,548 $ 278,335 Charge offs (44,533 ) (344 ) (991 ) (604 ) (2,611 ) (2,724 ) (4,439 ) (56,246 ) Recoveries 11,465 173 242 74 927 3,194 716 16,791 Net charge offs (33,068 ) (171 ) (749 ) (530 ) (1,684 ) 470 (3,723 ) (39,455 ) Provision for loan losses 16,010 (3,511 ) (3,477 ) 7,968 4,245 1,292 4,473 27,000 December 31, 2017 $ 123,068 $ 10,352 $ 41,059 $ 34,370 $ 29,607 $ 22,126 $ 5,298 $ 265,880 Allowance for loan losses Individually evaluated for impairment $ 10,838 $ 2,973 $ 1,597 $ 86 $ 6,512 $ 3,718 $ 122 $ 25,846 Collectively evaluated for impairment 112,230 7,379 39,462 34,284 23,095 18,408 5,176 240,034 Total allowance for loan losses $ 123,068 $ 10,352 $ 41,059 $ 34,370 $ 29,607 $ 22,126 $ 5,298 $ 265,880 Loans Individually evaluated for impairment $ 142,244 $ 26,234 $ 19,118 $ 467 $ 47,486 $ 10,891 $ 1,135 $ 247,575 Collectively evaluated for impairment 6,257,449 775,975 3,296,136 1,451,217 7,499,048 872,913 384,678 20,537,416 Total loans $ 6,399,693 $ 802,209 $ 3,315,254 $ 1,451,684 $ 7,546,534 $ 883,804 $ 385,813 $ 20,784,991 For comparison purposes, a summary of the changes in the allowance for loan losses by portfolio segment for the year ended December 31, 2016 , was as follows. Commercial and industrial Commercial real estate - owner occupied Commercial real estate - investor Real estate construction Residential mortgage Home equity Other consumer Total ($ in Thousands) December 31, 2015 $ 129,959 $ 18,680 $ 43,018 $ 25,266 $ 28,261 $ 23,555 $ 5,525 $ 274,264 Charge offs (71,016 ) (512 ) (1,504 ) (558 ) (4,332 ) (4,686 ) (3,831 ) (86,439 ) Recoveries 14,543 74 1,624 203 755 3,491 820 21,510 Net charge offs (56,473 ) (438 ) 120 (355 ) (3,577 ) (1,195 ) (3,011 ) (64,929 ) Provision for loan losses 66,640 (4,208 ) 2,147 2,021 2,362 (1,996 ) 2,034 69,000 December 31, 2016 $ 140,126 $ 14,034 $ 45,285 $ 26,932 $ 27,046 $ 20,364 $ 4,548 $ 278,335 Allowance for loan losses Individually evaluated for impairment $ 21,047 $ 23 $ 3,410 $ 84 $ 6,438 $ 3,943 $ 109 $ 35,054 Collectively evaluated for impairment 119,079 14,011 41,875 26,848 20,608 16,421 4,439 243,281 Total allowance for loan losses $ 140,126 $ 14,034 $ 45,285 $ 26,932 $ 27,046 $ 20,364 $ 4,548 $ 278,335 Loans Individually evaluated for impairment $ 213,271 $ 13,983 $ 32,908 $ 509 $ 43,876 $ 11,176 $ 1,012 $ 316,735 Collectively evaluated for impairment 6,275,743 883,741 3,541,824 1,431,988 6,288,451 923,267 392,967 19,737,981 Total loans $ 6,489,014 $ 897,724 $ 3,574,732 $ 1,432,497 $ 6,332,327 $ 934,443 $ 393,979 $ 20,054,716 The allowance related to the oil and gas portfolio was $27 million at December 31, 2017 and represented 4.5% of total oil and gas loans. Year Ended December 31, 2017 Year Ended December 31, 2016 ($ in Millions) Balance at beginning of period $ 38 $ 42 Charge offs (25 ) (59 ) Recoveries — — Net Charge offs (25 ) (59 ) Provision for loan losses 14 55 Balance at end of period $ 27 $ 38 Allowance for loan losses Individually evaluated for impairment $ 5 $ 14 Collectively evaluated for impairment 22 24 Total allowance for loan losses $ 27 $ 38 Loans Individually evaluated for impairment $ 77 $ 147 Collectively evaluated for impairment 523 521 Total loans $ 600 $ 668 The allowance for unfunded commitments is maintained at a level believed by management to be sufficient to absorb estimated probable losses related to unfunded credit facilities (including unfunded loan commitments and letters of credit) and is included in accrued expenses and other liabilities on the consolidated balance sheets. See Note 16 for additional information on the allowance for unfunded commitments and see Note 1 for the Corporation's accounting policy for allowance for unfunded commitments. A summary of the changes in the allowance for unfunded commitments was as follows. Years Ended December 31, 2017 2016 2015 ($ in Thousands) Allowance for Unfunded Commitments Balance at beginning of period $ 25,400 $ 24,400 $ 24,900 Provision for unfunded commitments (1,000 ) 1,000 (500 ) Balance at end of period $ 24,400 $ 25,400 $ 24,400

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Other Intangible Assets Goodwill: Goodwill is not amortized but, instead, is subject to impairment tests on at least an annual basis, and more frequently if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. See Note 1 for the Corporation’s accounting policy for goodwill and other intangible assets. The Corporation conducted its most recent annual impairment testing in May 2017 , utilizing a qualitative assessment. Factors that management considered in this assessment included macroeconomic conditions, industry and market considerations, overall financial performance of the Corporation and each reporting unit (both current and projected), changes in management strategy, and changes in the composition or carrying amount of net assets. In addition, management considered the increases in both the Corporation’s common stock price and in the overall bank common stock index (based on the S&P 400 Regional Bank Sub-Industry Index), as well as the Corporation’s earnings per common share trend over the past year. Based on these assessments, management concluded that the 2017 annual qualitative impairment assessment indicated that it is more likely than not that the estimated fair value exceeded the carrying value (including goodwill) for each reporting unit. Therefore, a step one quantitative analysis was not required. There were no events since the May 2017 impairment testing that have changed the Corporation's impairment assessment conclusion. There were no impairment charges recorded in 2017 , 2016 , or 2015 . At December 31, 2017 , the Corporation had goodwill of $976 million , compared to $972 million at December 31, 2016 including goodwill of $428 million assigned to the Corporate and Commercial Specialty segment and the remaining assigned to the Community, Consumer and Business segment. There was an addition to the carrying amount of goodwill of approximately $55,000 as a result of a small insurance acquisition during the first quarter of 2017, along with an addition of approximately $4 million in fourth quarter 2017 from the Whitnell acquisition. See Note 2 for additional information on the Corporation's acquisitions. Other Intangible Assets: The Corporation has other intangible assets that are amortized, consisting of core deposit intangibles, other intangibles (primarily related to customer relationships acquired in connection with the Corporation’s insurance agency acquisitions), and mortgage servicing rights. During the first and fourth quarter of 2017, the Corporation added approximately $162,000 and $2 million of other intangibles, respectively, relating to customer relationships associated with one small insurance acquisition in first quarter 2017, and the Whitnell acquisition in fourth quarter 2017. See Note 2 for additional information on the Corporation's acquisitions. For core deposit intangibles and other intangibles, changes in the gross carrying amount, accumulated amortization, and net book value were as follows. 2017 2016 2015 ($ in Thousands) Core deposit intangibles Gross carrying amount $ 4,385 $ 4,385 $ 19,545 Accumulated amortization (4,385 ) (4,273 ) (19,152 ) Net book value $ — $ 112 $ 393 Amortization during the year $ 112 $ 281 $ 1,404 Other intangibles Gross carrying amount $ 34,572 $ 32,410 $ 31,398 Accumulated amortization (18,992 ) (17,145 ) (15,333 ) Net book value $ 15,580 $ 15,265 $ 16,065 Additions during the period $ 2,162 $ 1,012 $ 12,115 Amortization during the year $ 1,847 $ 1,812 $ 1,690 Mortgage Servicing Rights: The Corporation sells residential mortgage loans in the secondary market and typically retains the right to service the loans sold. Mortgage servicing rights are amortized in proportion to and over the period of estimated net servicing income, and assessed for impairment at each reporting date. See Note 1 for the Corporation’s accounting policy for mortgage servicing rights. See Note 16 for a discussion of the recourse provisions on sold residential mortgage loans. See Note 18 which further discusses fair value measurement relative to the mortgage servicing rights asset. A summary of changes in the balance of the mortgage servicing rights asset and the mortgage servicing rights valuation allowance was as follows. 2017 2016 2015 ($ in Thousands) Mortgage servicing rights Mortgage servicing rights at beginning of year $ 62,085 $ 62,150 $ 61,379 Additions 7,167 12,262 12,372 Amortization (10,084 ) (12,327 ) (11,601 ) Mortgage servicing rights at end of year $ 59,168 $ 62,085 $ 62,150 Valuation allowance at beginning of year (609 ) (809 ) (1,234 ) (Additions) recoveries, net (175 ) 200 425 Valuation allowance at end of year (784 ) (609 ) (809 ) Mortgage servicing rights, net $ 58,384 $ 61,476 $ 61,341 Fair value of mortgage servicing rights $ 64,387 $ 73,149 $ 70,686 Portfolio of residential mortgage loans serviced for others (“servicing portfolio”) $ 7,646,846 $ 7,974,742 $ 7,915,224 Mortgage servicing rights, net to servicing portfolio 0.76 % 0.77 % 0.77 % Mortgage servicing rights expense (a) $ 10,259 $ 12,127 $ 11,176 (a) Includes the amortization of mortgage servicing rights and additions / recoveries to the valuation allowance of mortgage servicing rights, and is a component of mortgage banking, net in the consolidated statements of income. The following table shows the estimated future amortization expense for amortizing intangible assets. The projections of amortization expense are based on existing asset balances, the current interest rate environment, and prepayment speeds as of December 31, 2017 . The actual amortization expense the Corporation recognizes in any given period may be significantly different depending upon acquisition or sale activities, changes in interest rates, prepayment speeds, market conditions, regulatory requirements, and events or circumstances that indicate the carrying amount of an asset may not be recoverable. Estimated Amortization Expense Other Intangibles Mortgage Servicing Rights ($ in Thousands) Year ending December 31, 2018 $ 1,971 $ 9,590 2019 1,672 8,051 2020 1,555 6,747 2021 1,531 5,670 2022 1,508 4,783 Beyond 2022 7,343 24,327 Total Estimated Amortization Expense $ 15,580 $ 59,168

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises and Equipment	Premises and Equipment See Note 1 for the Corporation’s accounting policy for premises and equipment. A summary of premises and equipment at December 31 was as follows. 2017 2016 ($ in Thousands) Estimated Useful Lives Cost Accumulated Depreciation Net Book Value Net Book Value Land — $ 59,257 $ — $ 59,257 $ 57,471 Land improvements 3 – 15 years 13,115 6,802 6,313 6,643 Buildings and improvements 5 – 39 years 341,947 143,516 198,431 202,152 Computers 3 – 5 years 42,604 31,526 11,078 9,051 Furniture, fixtures and other equipment 3 – 15 years 161,699 119,650 42,049 42,549 Leasehold improvements 3 – 15 years 34,701 20,866 13,835 12,449 Total premises and equipment $ 653,323 $ 322,360 $ 330,963 $ 330,315 Depreciation and amortization of premises and equipment totaled $32 million in 2017 , $32 million in 2016 , and $33 million in 2015 . The Corporation conducts a portion of its business through certain facilities and equipment under noncancelable operating leases. The Corporation also leases a subdivision of some of its facilities and receives rental income from such lease agreements. The approximate minimum annual rental payments and rental receipts under noncancelable agreements and leases with remaining terms in excess of one year are as follows. ($ in Thousands) Payments Receipts 2018 $ 9,815 $ 3,783 2019 9,686 4,415 2020 8,886 1,996 2021 8,085 1,676 2022 5,796 724 Thereafter 22,447 774 Total $ 64,715 $ 13,368 Total rental expense under leases, net of lease income, totaled $6 million in 2017 , $8 million in 2016 , and $13 million in 2015 , respectively. The reduction of rental expense was mainly driven by leasing income generated by the Milwaukee Center (purchased April 2016) of $5 million in 2017 and $4 million

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Deposits	Deposits The distribution of deposits at December 31 was as follows. 2017 2016 ($ in Thousands) Noninterest-bearing demand $ 5,478,416 $ 5,392,208 Savings 1,524,992 1,431,494 Interest-bearing demand 4,603,157 4,687,656 Money market 8,830,328 8,770,963 Brokered CDs 18,609 52,725 Other time 2,330,460 1,553,402 Total deposits $ 22,785,962 $ 21,888,448 Time deposits of $100,000 or more were $1.4 billion and $571 million at December 31, 2017 and 2016 , respectively. Time deposits of $250,000 or more were $1.1 billion and $235 million at December 31, 2017 and 2016 , respectively. Aggregate annual maturities of all time deposits at December 31, 2017 , are as follows. Maturities During Year Ending December 31, ($ in Thousands) 2018 $ 1,708,582 2019 298,774 2020 198,206 2021 84,306 2022 57,618 Thereafter 1,583 Total $ 2,349,069

Short-term Funding

Short-term Funding	12 Months Ended
	Dec. 31, 2017
Short-term Debt [Abstract]
Short-term Funding	Short-Term Funding The components of short-term funding (funding with original contractual maturities of one year or less) at December 31 were as follows. 2017 2016 ($ in Thousands) Federal funds purchased $ 141,950 $ 208,150 Securities sold under agreements to repurchase 182,865 300,197 Federal funds purchased and securities sold under agreements to repurchase 324,815 508,347 FHLB advances 284,000 482,000 Commercial paper 67,467 101,688 Other short-term funding 351,467 583,688 Total short-term funding $ 676,282 $ 1,092,035 Securities Sold Under Agreements to Repurchase ("Repurchase Agreements") The Corporation enters into agreements under which it sells securities subject to an obligation to repurchase the same or similar securities. Under these arrangements, the Corporation may transfer legal control over the assets but still retain effective control through an agreement that both entitles and obligates the Corporation to repurchase the assets. The obligation to repurchase the securities is reflected as a liability on the Corporation’s consolidated balance sheets, while the securities underlying the repurchase agreements remain in the respective investment securities asset accounts (i.e., there is no offsetting or netting of the investment securities assets with the repurchase agreement liabilities). The Corporation utilizes securities sold under agreements to repurchase to facilitate the needs of its customers. As of December 31, 2017 , the Corporation pledged agency mortgage-related securities with a fair value of $325 million as collateral for the repurchase agreements. Securities pledged as collateral under repurchase agreements are maintained with the Corporation's safekeeping agents and are monitored on a daily basis due to the market risk of fair value changes in the underlying securities. The Corporation generally pledges excess securities to ensure there is sufficient collateral to satisfy short-term fluctuations in both the repurchase agreement balances and the fair value of the underlying securities. The remaining contractual maturity of the securities sold under agreements to repurchase in the consolidated balance sheets are presented in the following table. Remaining Contractual Maturity of the Agreements Overnight and Continuous Up to 30 days 30-90 days Greater than 90 days Total ($ in Thousands) December 31, 2017 Repurchase agreements Agency mortgage-related securities $ 182,865 $ — $ — $ — $ 182,865 Total $ 182,865 $ — $ — $ — $ 182,865 December 31, 2016 Repurchase agreements Agency mortgage-related securities $ 300,197 $ — $ — $ — $ 300,197 Total $ 300,197 $ — $ — $ — $ 300,197

Long-term Funding

Long-term Funding	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-term Funding	Long-Term Funding The components of long-term funding (funding with original contractual maturities greater than one year) at December 31 were as follows. 2017 2016 ($ in Thousands) FHLB advances $ 2,900,168 $ 2,265,188 Senior notes, at par 250,000 250,000 Subordinated notes, at par 250,000 250,000 Other long-term funding and capitalized costs (2,718 ) (3,393 ) Total long-term funding $ 3,397,450 $ 2,761,795 FHLB Advances: At December 31, 2017 , the long-term FHLB advances had maturity or call dates primarily ranging from 2018 through 2019, and had an average interest rate of 1.26% , compared to 0.50% at December 31, 2016 . The majority of FHLB advances are indexed to the FHLB discount note and re-price at varying intervals. The advances offer flexible, relatively low cost, long-term funding that improves the Corporation’s liquidity profile. Senior Notes: In November 2014, the Corporation issued $250 million of senior notes, due November 2019, and callable October 2019. The senior notes have a fixed coupon interest rate of 2.75% and were issued at a discount. Subordinated Notes: In November 2014, the Corporation issued $250 million of 10 -year subordinated notes, due January 2025, and callable October 2024. The subordinated notes have a fixed coupon interest rate of 4.25% and were issued at a discount. Under agreements with the Federal Home Loan Bank of Chicago, FHLB advances (short-term and long-term) are secured by qualifying mortgages of the subsidiary bank (such as residential mortgage, residential mortgage loans held for sale, home equity, and commercial real estate). At December 31, 2017 , the Corporation had $6.6 billion of total collateral capacity supported by residential mortgage and home equity loans. Total short-term and long-term FHLB advances outstanding at December 31, 2017 , was $3.2 billion . The table below summarizes the maturities of the Corporation’s long-term funding at December 31, 2017 . Year ($ in Thousands) 2018 $ 1,750,000 2019 499,313 2020 155 2021 150,000 2022 — Thereafter 997,982 Total long-term funding $ 3,397,450

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity Preferred Equity: In September 2011, the Corporation issued 2,600,000 depositary shares, each representing a 1/40th interest in a share of the Corporation’s 8.00% Non-Cumulative Perpetual Preferred Stock, Series B, liquidation preference $1,000 per share (the “Series B Preferred Stock”). On July 23, 2013 , the Board of Directors authorized the purchase of up to $10 million of the Corporation’s Series B Preferred Stock. During 2015, the Corporation repurchased approximately 50,000 depositary shares for $1 million . On September 15, 2016 , the Corporation redeemed all remaining depositary shares for $59 million . In June 2015, the Corporation issued 2,600,000 depositary shares, each representing a 1/40th interest in a share of the Corporation’s 6.125% Non-Cumulative Perpetual Preferred Stock, Series C, liquidation preference $1,000 per share (the “Series C Preferred Stock”). Dividends on the Series C Preferred Stock are payable quarterly in arrears only when, as and if declared by the Board of Directors at a rate per annum equal to 6.125% . Shares of the Series C Preferred Stock have priority over the Corporation’s common stock with regard to the payment of dividends and distributions upon liquidation, dissolution or winding up. As such, the Corporation may not pay dividends on or repurchase, redeem, or otherwise acquire for consideration shares of its common stock unless dividends for the Series C Preferred Stock have been declared for that period, and sufficient funds have been set aside to make payment. The Series C Preferred Stock may be redeemed by the Corporation at its option (i) either in whole or in part, from time to time, on any dividend payment date on or after the dividend payment date occurring on June 15, 2020 , or (ii) in whole but not in part, at any time within 90 days following certain regulatory capital treatment events, in each case at a redemption price of $1,000 per share (equivalent to $25 per depositary share), plus any applicable dividends. Except in certain limited circumstances, the Series C Preferred Stock does not have any voting rights. On August 28, 2015 , the Board of Directors authorized the repurchase of up to $10 million of the Corporation's Series C Preferred Stock. As of December 31, 2017 , $10 million remained available under this repurchase authorization. In September 2016, the Corporation issued 4,000,000 depositary shares, each representing a 1/40th interest in a share of the Corporation’s 5.375% Non-Cumulative Perpetual Preferred Stock, Series D, liquidation preference $1,000 per share (the “Series D Preferred Stock”). Dividends on the Series D Preferred Stock are payable quarterly in arrears only when, as and if declared by the Board of Directors at a rate per annum equal to 5.375% . Shares of the Series D Preferred Stock have priority over the Corporation’s common stock with regard to the payment of dividends and distributions upon liquidation, dissolution or winding up. As such, the Corporation may not pay dividends on or repurchase, redeem, or otherwise acquire for consideration shares of its common stock unless dividends for the Series D Preferred Stock have been declared for that period, and sufficient funds have been set aside to make payment. The Series D Preferred Stock may be redeemed by the Corporation at its option (i) either in whole or in part, from time to time, on any dividend payment date on or after the dividend payment date occurring on September 15, 2021 , or (ii) in whole but not in part, at any time within 90 days following certain regulatory capital treatment events, in each case at a redemption price of $1,000 per share (equivalent to $25 per depositary share), plus any applicable dividends. Except in certain limited circumstances, the Series D Preferred Stock does not have any voting rights. On July 25, 2017, the Board of Directors authorized the repurchase of up to $15 million of the Corporation's Series D Preferred Stock. As of December 31, 2017 , $15 million remained available under this repurchase authorization. Common Stock Warrants: In November 2008, under the Capital Purchase Program, the Corporation issued a 10 year warrant to purchase approximately 4 million shares of common stock. The Common Stock Warrants have a term of 10 years and are exercisable at any time, in whole or in part, at an exercise price of $19.77 per share (subject to certain anti-dilution adjustments). On December 6, 2011 , the U.S. Department of Treasury closed an underwritten secondary public offering of the warrants, each representing the right to purchase one share of common stock, par value $0.01 per share, of the Corporation. The public offering price and the allocation of the warrants in the secondary public warrant offering by the U.S. Treasury were determined by an auction process and the Corporation received no proceeds from the public offering. Subsidiary Equity: At December 31, 2017 , subsidiary equity equaled $3.3 billion . See Note 19 for additional information on regulatory requirements for the Bank. Common Stock Repurchases: The Board of Directors authorized the repurchase of common stock during 2015. During 2017, the Corporation repurchased approximately 1.6 million shares for $37 million (or an average cost per common share of $23.59 ), all of which were returned to authorized but unissued shares. During 2016, the Corporation repurchased 1 million shares for $20 million (or an average cost per common share of $17.10 ), all of which were returned to authorized but unissued shares. The Corporation also repurchased shares for minimum tax withholding settlements on equity compensation totaling approximately $9 million ( 370,000 shares at an average cost per common share of $25.08 ) during 2017 compared to repurchases of shares for minimum tax withholding settlements on equity compensation totaling approximately $5 million ( 293,000 shares at an average cost per common share of $17.30 ) for 2016. As of December 31, 2017, approximately $51 million remained available to repurchase shares of common stock under previously approved Board of Director authorizations. The repurchase of shares will be based on market and investment opportunities, capital levels, growth prospects, and regulatory constraints. Such repurchases may occur from time to time in open market purchases, block transactions, private transactions, accelerated share repurchase programs, or similar facilities. Other Comprehensive Income (Loss): See the Consolidated Statements of Comprehensive Income for a summary of activity in other comprehensive income (loss) and see Note 22

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Stock-Based Compensation	Stock-Based Compensation Stock-Based Compensation Plan In March 2013, the Board of Directors, with subsequent approval of the Corporation’s shareholders, approved the adoption of the 2013 Incentive Compensation Plan (“2013 Plan”). In February 2017, the Board of Directors, with subsequent approval of the Corporation’s shareholders, approved the adoption of the 2017 Incentive Compensation Plan (“2017 Plan”). All remaining shares available for grant under the 2013 Plan were rolled into the 2017 Plan. As of December 31, 2017 , approximately 14 million shares remained available for grant under the 2017 Plan. Under the 2017 Plan, options are generally exercisable up to 10 years from the date of grant, have an exercise price that is equal to the closing price of the Corporation’s stock on the grant date, and vest ratably over four years . The Corporation also issues restricted common stock and restricted common stock units to certain key employees (collectively referred to as “restricted stock awards”) under the 2017 Plan. The shares of restricted stock are restricted as to transfer, but are not restricted as to dividend payment or voting rights. Restricted stock units receive dividend equivalents but do not have voting rights. The transfer restrictions lapse over three years or four years , depending upon whether the awards are performance-based or service-based. Performance-based awards are based on earnings per share performance goals, relative total shareholder return, and continued employment or meeting the requirements for retirement and service-based awards are contingent upon continued employment or meeting the requirements for retirement. Performance-based restricted stock awards vest over a performance period of three years and service-based restricted stock awards vest ratably over four years . The 2017 Plan provides that restricted stock awards and stock options will immediately become fully vested upon retirement from the Corporation of those colleagues whose retirement meets the early retirement or normal retirement definitions under the plan (“retirement eligible colleagues”). See Note 1 for the Corporation’s accounting policy for stock based compensation. Accounting for Stock-Based Compensation Assumptions are used in estimating the fair value of stock options granted. The weighted average expected life of the stock option represents the period of time that stock options are expected to be outstanding and is estimated using historical data of stock option exercises and forfeitures. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant. The expected volatility is based on the implied volatility of the Corporation’s stock. The following assumptions were used in estimating the fair value for options granted in 2017 , 2016 and 2015 . 2017 2016 2015 Dividend yield 2.00 % 2.50 % 2.00 % Risk-free interest rate 2.00 % 2.00 % 2.00 % Weighted average expected volatility 25.00 % 25.00 % 20.00 % Weighted average expected life 5.5 years 5.5 years 6 years Weighted average per share fair value of options $5.30 $3.36 $3.08 A summary of the Corporation’s stock option activity for the year ended December 31, 2017 is presented below. Stock Options Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (000s) Outstanding at December 31, 2016 6,357,843 $ 17.67 6.10 $ 47,902 Granted 799,558 25.61 Exercised (1,551,669 ) 16.87 Forfeited or expired (487,045 ) 31.84 Outstanding at December 31, 2017 5,118,687 $ 18.02 6.48 $ 38,028 Options Exercisable at December 31, 2017 2,831,736 $ 16.31 5.23 $ 25,738 Intrinsic value represents the amount by which the fair market value of the underlying stock exceeds the exercise price of the stock option. For the years ended December 31, 2017 , 2016 , and 2015 the intrinsic value of stock options exercised was $13 million , $9 million , and $7 million , respectively. The total fair value of stock options that vested was $4 million , $3 million and $6 million , respectively, for the years ended December 31, 2017 , 2016 , and 2015 . For the years ended December 31, 2017 , 2016 , and 2015 , the Corporation recognized compensation expense of $4 million for each of the three years, for the vesting of stock options. Included in compensation expense for 2017 was $650,000 of expense for the accelerated vesting of stock options granted to retirement eligible colleagues. At December 31, 2017 , the Corporation had $5 million of unrecognized compensation expense related to stock options that is expected to be recognized over the remaining requisite service periods that extend predominantly through the first quarter 2021 . The following table summarizes information about the Corporation’s restricted stock activity for the year ended December 31, 2017. Restricted Stock Shares Weighted Average Grant Date Fair Value Outstanding at December 31, 2016 2,377,380 $ 17.40 Granted 767,627 25.54 Vested (999,917 ) 18.01 Forfeited (119,019 ) 20.00 Outstanding at December 31, 2017 2,026,071 $ 19.68 The Corporation amortizes the expense related to restricted stock awards as compensation expense over the vesting period specified in the grant. Expense for restricted stock awards of approximately $18 million was recorded for both the years ended December 31, 2017 and 2016 , and $15 million was recorded for the year ended December 31, 2015 . Included in compensation expense for 2017 was approximately $3 million of expense for the accelerated vesting of restricted stock awards granted to retirement eligible colleagues. The Corporation had $18 million of unrecognized compensation costs related to restricted stock awards at December 31, 2017 , that is expected to be recognized over the remaining requisite service periods that extend predominantly through first quarter 2021 . The Corporation has the ability to issue shares from treasury or new shares upon the exercise of stock options or the granting of restricted stock awards. As described in Note 10

Retirement Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Retirement Plans	Retirement Plan The Corporation has a noncontributory defined benefit retirement plan (the Retirement Account Plan) covering substantially all employees who meet participation requirements. The benefits are based primarily on years of service and the employee’s compensation paid. Employees of acquired entities generally participate in the RAP after consummation of the business combinations. Any retirement plans of acquired entities are typically merged into the RAP after completion of the mergers, and credit is usually given to employees for years of service at the acquired institution for vesting and eligibility purposes. The Corporation also provides legacy healthcare access to a limited group of retired employees from a previous acquisition in the Postretirement Plan. There are no other active retiree healthcare plans. The funded status and amounts recognized in the 2017 and 2016 consolidated balance sheets, as measured on December 31, 2017 and 2016 , respectively, for the Retirement Account and Postretirement Plan were as follows. Retirement Account Plan Postretirement Plan Retirement Account Plan Postretirement Plan ($ in Thousands) 2017 2017 2016 2016 Change in Fair Value of Plan Assets Fair value of plan assets at beginning of year $ 295,718 $ — $ 289,599 $ — Actual return on plan assets 41,490 — 17,097 — Employer contributions 6,242 235 — 248 Gross benefits paid (11,841 ) (235 ) (10,978 ) (248 ) Fair value of plan assets at end of year (a) $ 331,609 $ — $ 295,718 $ — Change in Benefit Obligation Net benefit obligation at beginning of year $ 176,825 $ 2,403 $ 171,783 $ 3,436 Service cost 6,955 — 6,780 — Interest cost 7,121 101 7,121 142 Plan amendments — — (823 ) (936 ) Actuarial (gain) loss 7,363 209 2,942 9 Gross benefits paid (11,841 ) (235 ) (10,978 ) (248 ) Net benefit obligation at end of year (a) $ 186,423 $ 2,478 $ 176,825 $ 2,403 Funded (unfunded) status $ 145,186 $ (2,478 ) $ 118,893 $ (2,403 ) Noncurrent assets 145,186 — 118,893 — Current liabilities — (233 ) — (215 ) Noncurrent liabilities — (2,245 ) — (2,188 ) Asset (Liability) Recognized in the Consolidated Balance Sheets $ 145,186 $ (2,478 ) $ 118,893 $ (2,403 ) (a) The fair value of the plan assets represented 178% and 167% of the net benefit obligation of the pension plan at December 31, 2017 and 2016 , respectively. Amounts recognized in accumulated other comprehensive loss, net of tax, as of December 31, 2017 and 2016 follow. Retirement Account Plan Postretirement Plan Retirement Account Plan Postretirement Plan ($ in Thousands) 2017 2017 2016 2016 Prior service cost $ (295 ) $ (531 ) $ (342 ) $ (580 ) Net actuarial loss 24,926 205 35,443 79 Amount not yet recognized in net periodic benefit cost, but recognized in accumulated other comprehensive loss $ 24,631 $ (326 ) $ 35,101 $ (501 ) Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss) (“OCI”), net of tax, in 2017 and 2016 were as follows. Retirement Account Plan Postretirement Retirement Account Plan Postretirement ($ in Thousands) 2017 2017 2016 2016 Net gain (loss) $ 14,482 $ (209 ) $ (6,132 ) $ (9 ) Amortization of prior service cost (73 ) (75 ) (73 ) — Amortization of actuarial loss (gain) 2,278 4 2,115 — Plan amendments — — 823 936 Income tax (expense) benefit (6,219 ) 107 1,168 (353 ) Total Recognized in OCI $ 10,468 $ (173 ) $ (2,099 ) $ 574 The components of net periodic benefit cost for the Retirement Account Plan and Postretirement Plans for 2017 , 2016 , and 2015 were as follows. Retirement Account Plan Postretirement Retirement Account Plan Postretirement Retirement Account Plan Postretirement ($ in Thousands) 2017 2017 2016 2016 2015 2015 Service cost $ 6,955 $ — $ 6,780 $ — $ 11,257 $ — Interest cost 7,121 101 7,121 142 6,617 141 Expected return on plan assets (19,646 ) — (20,287 ) — (21,438 ) — Amortization of: Prior service cost (73 ) (75 ) (73 ) — 50 — Actuarial (gain) loss 2,278 4 2,115 — 2,256 — Total net pension cost $ (3,365 ) $ 30 $ (4,344 ) $ 142 $ (1,258 ) $ 141 As of December 31, 2017 , the estimated actuarial losses and prior service cost that will be amortized during 2018 from accumulated other comprehensive income into net periodic benefit cost for the Retirement Account Plan includes expense of $1.9 million for actuarial losses and income of $75,000 for the prior service cost. For the Postretirement Plan, the estimated actuarial losses and prior service cost that will be amortized during 2018 from accumulated other comprehensive income into net periodic benefit cost includes income of $75,000 for the prior service cost. Actuarial loss expense is estimated to be negligible. Retirement Account Plan Postretirement Plan Retirement Account Plan Postretirement Plan 2017 2017 2016 2016 Weighted average assumptions used to determine benefit obligations Discount rate 3.70 % 3.70 % 4.10 % 4.10 % Rate of increase in compensation levels 3.00 % N/A 4.00 % N/A Weighted average assumptions used to determine net periodic benefit costs Discount rate 4.10 % 4.10 % 4.30 % 4.30 % Rate of increase in compensation levels 4.00 % N/A 4.00 % N/A Expected long-term rate of return on plan assets 6.50 % N/A 7.00 % N/A The overall expected long-term rates of return on the Retirement Account Plan assets were 6.50% for 2017 and 7.00% for 2016 . The expected long-term (more than 20 years) rate of return was estimated using market benchmarks for equities and bonds applied to the Retirement Account Plan’s anticipated asset allocations. The expected return on equities was computed utilizing a valuation framework, which projected future returns based on current equity valuations rather than historical returns. The actual rate of return for the Retirement Account Plan assets was 14.60% and 6.36% for 2017 and 2016 , respectively. The Retirement Account Plan’s investments are exposed to various risks, such as interest rate, market, and credit risks. Due to the level of risks associated with certain investments and the level of uncertainty related to changes in the value of the investments, it is at least reasonably possible that changes in risks in the near term could materially affect the amounts reported. The investment objective for the Retirement Account Plan is to maximize total return with a tolerance for average risk. The plan has a diversified portfolio designed to provide liquidity, current income, and growth of income and principal, with anticipated asset allocation ranges of: equity securities 50 to 70% , fixed income securities 30 to 50% , other cash equivalents 0 to 10% , and alternative securities 0 to 15% . Based on changes in economic and market conditions, the Corporation could be outside of the allocation ranges for brief periods of time. The asset allocation for the Retirement Account Plan as of the December 31, 2017 and 2016 measurement dates, respectively, by asset category were as follows. Asset Category 2017 2016 Equity securities 60 % 60 % Fixed income securities 37 % 39 % Other 3 % 1 % Total 100 % 100 % The Retirement Account Plan assets include cash equivalents, such as money market accounts, mutual funds, and common / collective trust funds (which include investments in equity and bond securities). Money market accounts are stated at cost plus accrued interest, mutual funds are valued at quoted market prices and investments in common / collective trust funds are valued at the amount at which units in the funds can be withdrawn. Based on these inputs, the following table summarizes the fair value of the Retirement Account Plan’s investments as of December 31, 2017 and 2016 . Fair Value Measurements Using ($ in Thousands) December 31, 2017 Level 1 Level 2 Level 3 Retirement Account Plan Investments Money market account $ 9,577 $ 9,577 $ — $ — Common /collective trust funds 133,210 133,210 — — Mutual funds 188,823 188,823 — — Total Retirement Account Plan Investments $ 331,610 $ 331,610 $ — $ — Fair Value Measurements Using ($ in Thousands) December 31, 2016 Level 1 Level 2 Level 3 Retirement Account Plan Investments Money market account $ 3,624 $ 3,624 $ — $ — Common /collective trust funds 126,741 126,741 — — Mutual funds 165,353 165,353 — — Total Retirement Account Plan Investments $ 295,718 $ 295,718 $ — $ — The Corporation’s funding policy is to pay at least the minimum amount required by the funding requirements of federal law and regulations, with consideration given to the maximum funding amounts allowed. The Corporation regularly reviews the funding of its Retirement Account Plan. The Corporation made contributions of $6 million to its Retirement Account Plan in 2017. The projected benefit payments for the Retirement Account and Postretirement Plans at December 31, 2017 , reflecting expected future services, were as follows. The projected benefit payments were calculated using the same assumptions as those used to calculate the benefit obligations listed above. ($ in Thousands) Retirement Account Plan Postretirement Plan Estimated future benefit payments 2018 $ 14,697 $ 237 2019 14,436 197 2020 15,096 194 2021 15,278 190 2022 16,020 186 2023-2027 71,781 839 The health care trend rate is an assumption as to how much the Postretirement Plan’s medical costs will increase each year in the future. The health care trend rate assumption for pre-65 coverage is 7.5% for 2017 , and 0.5% to 0.25% lower in each succeeding year, to an ultimate rate of 5% for 2024 and future years. The actual increase in 2017 health care premium rates for post-65 coverage was 17% . The health care trend rate assumption for post-65 coverage is 6.5% in 2018 and 0.5% to 0.25% lower in each succeeding year, to an ultimate rate of 5% for 2024 and future years. A one percentage point change in the assumed health care cost trend rate would have the following effect. 2017 2016 ($ in Thousands) 100 bp Increase 100 bp Decrease 100 bp Increase 100 bp Decrease Effect on total of service and interest cost $ 7 $ (6 ) $ 7 $ (6 ) Effect on postretirement benefit obligation $ 162 $ (140 ) $ 173 $ (149 ) The Corporation also has a 401(k) and Employee Stock Ownership Plan (the “401(k) plan”). The Corporation’s contribution is determined by the Compensation and Benefits Committee of the Board of Directors. Total expense related to contributions to the 401(k) plan was $14 million , $14 million , and $11 million in 2017 , 2016 , and 2015

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The current and deferred amounts of income tax expense (benefit) were as follows. Years Ended December 31, 2017 2016 2015 ($ in Thousands) Current Federal $ 76,525 $ 73,781 $ 82,449 State 11,576 2,885 2,560 Total current 88,101 76,666 85,009 Deferred Federal 19,755 3,338 (10,606 ) State 1,647 7,318 7,084 Total deferred 21,402 10,656 (3,522 ) Total income tax expense $ 109,503 $ 87,322 $ 81,487 Temporary differences between the amounts reported in the financial statements and the tax bases of assets and liabilities resulted in deferred taxes. Deferred tax assets and liabilities at December 31 were as follows. 2017 2016 ($ in Thousands) Deferred tax assets Allowance for loan losses $ 66,377 $ 100,891 Allowance for other losses 7,095 11,080 Accrued liabilities 3,884 5,969 Deferred compensation 20,015 33,169 Benefit of tax loss and credit carryforwards 8,438 7,882 Nonaccrual interest 1,619 1,085 Net unrealized losses on available-for-sale securities 15,968 16,980 Net unrealized losses on pension and postretirement benefits 9,928 21,218 Other 3,954 8,128 Total deferred tax assets 137,278 206,402 Valuation allowance for deferred tax assets (269 ) — Total deferred tax assets after valuation allowance 137,009 206,402 Deferred tax liabilities Prepaid expenses 49,695 70,943 Goodwill 19,144 27,365 Mortgage banking activities 10,949 17,569 Deferred loan fee income 11,467 16,474 State deferred taxes 2,001 3,800 Lease financing 535 1,975 Bank premises and equipment 5,063 7,698 Other 4,838 8,594 Total deferred tax liabilities 103,692 154,418 Net deferred tax assets $ 33,317 $ 51,984 At December 31, 2016 , there was no valuation allowance for deferred tax assets. Management had determined that it was more likely than not that these assets could be realized through carry back to taxable income in prior years, future reversals of existing taxable temporary differences and future taxable income. The conclusion was based on the Corporation's historical earnings, its current level of earnings and prospects for continued growth and profitability. At December 31, 2017 the valuation allowance for deferred tax assets of approximately $ 269,000 was related to the deferred tax benefit of specific federal tax loss carryforwards of $3 million from the acquisition of Whitnell & Co. in 2017. 2017 2016 ($ in Thousands) Valuation allowance for deferred tax assets, beginning of year $ — $ — Increase (decrease) in current year 269 — Valuation allowance for deferred tax assets, end of year $ 269 $ — At December 31, 2017 the Corporation had state net operating loss carryforwards of $78 million (of which $16 million was acquired from various acquisitions) that will begin expiring in 2032 . The Corporation acquired Whitnell & Co. in October of 2017 which had federal net operating loss carryforwards at the time of acquisition. As a result of the change in control of the acquired subsidiary, Section 382 of the Internal Revenue Code places an annual limitation on the use of the subsidiary's net operating loss carryforwards. At December 31, 2017 the Corporation had federal net operating loss carryforwards from this acquisition of $3 million . The federal carryforwards, if unused, expire in calendar years 2029 through 2032 . The effective income tax rate differs from the statutory federal tax rate. The major reasons for this difference were as follows. 2017 2016 2015 Federal income tax rate at statutory rate 35.0 % 35.0 % 35.0 % Increases (decreases) resulting from: Tax-exempt interest and dividends (4.1 )% (4.8 )% (5.0 )% State income taxes (net of federal benefit) 2.7 % 2.3 % 2.3 % Bank owned life insurance (1.7 )% (1.7 )% (1.2 )% Tax effect of tax credits and benefits, net of related expenses (0.5 )% (0.8 )% (0.5 )% Tax reserve adjustments (1.2 )% 0.3 % (0.6 )% Net tax benefit from stock-based compensation (1.3 )% (0.4 )% — % Tax Cuts and Jobs Act impact on deferred remeasurement 3.5 % — % — % Other (0.1 )% 0.5 % 0.2 % Effective income tax rate 32.3 % 30.4 % 30.2 % Included in the Company’s income tax expense as of December 31, 2017 is tax expense from the remeasurement of deferred taxes totaling $12 million and an acceleration of amortization expense on the low income housing tax credit investment portfolio of $1 million related to the enactment of the Tax Act. Savings banks acquired by the Corporation in 1997 and 2004 qualified under provisions of the Internal Revenue Code that permitted them to deduct from taxable income an allowance for bad debts that differed from the provision for such losses charged to income for financial reporting purposes. Accordingly, no provision for income taxes has been made for $100 million of retained income at December 31, 2017 . If income taxes had been provided, the deferred tax liability would have been approximately $25 million . Management does not expect this amount to become taxable in the future; therefore, no provision for income taxes has been made. The Corporation and its subsidiaries file income tax returns in the U.S. federal jurisdiction and various state jurisdictions. The Corporation’s federal income tax returns are open and subject to examination from the 2014 tax return year and forward. The years open to examination by state and local government authorities varies by jurisdiction. A reconciliation of the beginning and ending amount of unrecognized tax benefits was as follows. 2017 2016 ($ in Millions) Balance at beginning of year $ 10 $ 9 Subtractions for tax positions related to prior years (5 ) — Subtractions for settlements with tax authorities (1 ) — Additions for tax positions related to current year — 1 Balance at end of year $ 4 $ 10 At December 31, 2017 and 2016 , the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate was $3 million and $7 million , respectively. The Corporation recognizes interest and penalties accrued related to unrecognized tax benefits in the income tax expense line of the consolidated statements of income. Interest and penalty benefit was $1 million as of December 31, 2017 and none as of December 31, 2016 . Accrued interest and penalties were $1 million and $2 million at December 31, 2017 and 2016

Derivative and Hedging Activiti

Derivative and Hedging Activities	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative and Hedging Activities	Derivative and Hedging Activities The Corporation facilitates customer borrowing activity by providing various interest rate risk management, commodity hedging, and foreign currency exchange solutions through its capital markets area. To date, all of the notional amounts of customer transactions have been matched with a mirror hedge with another counterparty. The Corporation has used, and may use again in the future, derivative instruments to hedge the variability in interest payments or protect the value of certain assets and liabilities recorded on its consolidated balance sheets from changes in interest rates. The predominant derivative and hedging activities include interest rate-related instruments (swaps and caps), foreign currency exchange forwards, commodity contracts, written options, purchased options, and certain mortgage banking activities. The contract or notional amount of a derivative is used to determine, along with the other terms of the derivative, the amounts to be exchanged between the counterparties. The Corporation is exposed to credit risk in the event of nonperformance by counterparties to financial instruments. To mitigate the counterparty risk, interest rate and commodity-related instruments generally contain language outlining collateral pledging requirements for each counterparty. Collateral must be posted when the market value exceeds certain mutually agreed upon threshold limits. Federal regulations require the Corporation to clear all LIBOR interest rate swaps through a clearing house ("centrally cleared") if possible. Securities are often pledged as collateral for centrally cleared interest rate swaps and derivatives. The Corporation pledged $24 million of investment securities as collateral at December 31, 2017 , and pledged $40 million of investment securities as collateral at December 31, 2016 . Cash is often pledged as collateral for interest rate swaps and derivatives that are not centrally cleared. At December 31, 2017 , the Corporation posted $22 million cash collateral for the margin compared to none at December 31, 2016 . See Note 18 for fair value information and disclosures and see Note 1 for the Corporation's accounting policy for derivative and hedging activities. Derivatives to Accommodate Customer Needs The Corporation enters into various derivative contracts which are designated as free standing derivative contracts. Free standing derivative products are entered into primarily for the benefit of commercial customers seeking to manage their exposures to interest rate risk, foreign currency, and commodity prices. These derivative contracts are not designated against specific assets and liabilities on the balance sheet or forecasted transactions and, therefore, do not qualify for hedge accounting treatment. Such derivative contracts are carried at fair value on the consolidated balance sheets with changes in the fair value recorded as a component of capital market fees, net, and typically include interest rate-related instruments (swaps and caps), foreign currency exchange forwards, and commodity contracts. See Note 15 for additional information and disclosures on balance sheet offsetting. Interest Rate-related Instruments: The Corporation provides interest rate risk management services to commercial customers, primarily forward interest rate swaps and caps. The Corporation’s market risk from unfavorable movements in interest rates related to these derivative contracts is generally economically hedged by concurrently entering into offsetting derivative contracts. The offsetting derivative contracts have identical notional values, terms and indices. Foreign Currency Exchange Forwards: The Corporation provides foreign currency exchange services to customers, primarily forward contracts. Our customers enter into a foreign currency exchange forward with the Corporation as a means for them to mitigate exchange rate risk. The Corporation mitigates its risk by then entering into an offsetting foreign currency exchange derivative contract. Commodity Contracts: Commodity contracts are entered into primarily for the benefit of commercial customers seeking to manage their exposure to fluctuating commodity prices. The Corporation mitigates its risk by then entering into an offsetting commodity derivative contract. The table below identifies the balance sheet category and fair values of the Corporation’s derivative instruments to accommodate customer needs which are not designated as hedging instruments. December 31, 2017 December 31, 2016 ($ in Thousands) Notional Amount Fair Value Balance Sheet Category Notional Amount Fair Balance Sheet Interest rate-related instruments — customer and mirror $ 2,183,687 $ 28,494 Trading assets $ 2,039,323 $ 33,671 Trading assets Interest rate-related instruments — customer and mirror 2,183,687 (28,035 ) Trading liabilities 2,039,323 (33,188 ) Trading liabilities Foreign currency exchange forwards 124,851 2,495 Trading assets 109,675 2,002 Trading assets Foreign currency exchange forwards 118,094 (2,339 ) Trading liabilities 106,251 (1,943 ) Trading liabilities Commodity contracts 457,868 38,686 Trading assets 127,582 16,725 Trading assets Commodity contracts 457,108 (37,286 ) Trading liabilities 128,368 (15,972 ) Trading liabilities Mortgage Derivatives Interest rate lock commitments to originate residential mortgage loans held for sale and forward commitments to sell residential mortgage loans are considered derivative instruments, and the fair value of these commitments is recorded on the consolidated balance sheets with the changes in fair value recorded as a component of mortgage banking, net. Written and Purchased Options (Time Deposit) Historically, the Corporation had entered into written and purchased option derivative instruments to facilitate an equity linked time deposit product (the “Power CD”), which the Corporation ceased offering in September 2013. The Power CD was a time deposit that provided the purchaser a guaranteed return of principal at maturity plus a potential equity return (a written option), while the Corporation received a known stream of funds based on the equity return (a purchased option). The written and purchased options are mirror derivative instruments which are carried at fair value on the consolidated balance sheets. The table below identifies the balance sheet category and fair values of the Corporation’s derivative instruments which are not designated as hedging instruments. December 31, 2017 December 31, 2016 ($ in Thousands) Notional Amount Fair Balance Sheet Notional Amount Fair Balance Sheet Interest rate lock commitments (mortgage) $ 222,736 $ 1,538 Other assets $ 285,345 $ 206 Other assets Forward commitments (mortgage) 164,567 (313 ) Other liabilities 179,600 2,908 Other assets Purchased options (time deposit) 31,063 1,175 Other assets 80,554 2,576 Other assets Written options (time deposit) 31,063 (1,175 ) Other liabilities 80,554 (2,576 ) Other liabilities The table below identifies the income statement category of the gains and losses recognized in income on the Corporation’s derivative instruments not designated as hedging instruments. Income Statement Category of Gain / (Loss) Recognized in Income For the Year Ended December 31, ($ in Thousands) 2017 2016 Derivative Instruments Interest rate-related instruments — customer and mirror, net Capital market fees, net $ (24 ) $ 1,978 Interest rate lock commitments (mortgage) Mortgage banking, net 1,332 (752 ) Forward commitments (mortgage) Mortgage banking, net (3,221 ) 2,505 Foreign currency exchange forwards Capital market fees, net 97 (75 ) Commodity contracts Capital market fees, net 647 630

Balance Sheet Offsetting

Balance Sheet Offsetting	12 Months Ended
	Dec. 31, 2017
Offsetting [Abstract]
Balance Sheet Offsetting	Balance Sheet Offsetting Interest Rate-Related Instruments and Commodity Contracts (“Interest and Commodity Agreements”) The Corporation enters into interest rate-related instruments to facilitate the interest rate risk management strategies of commercial customers. The Corporation also enters into commodity contracts to manage commercial customers exposure to fluctuating commodity prices. The Corporation mitigates these risks by entering into equal and offsetting interest and commodity agreements with highly rated third party financial institutions. The Corporation is party to master netting arrangements with its financial institution counterparties that creates a single net settlement of all legal claims or obligations to pay or receive the net amount of settlement of the individual interest and commodity agreements. Collateral, usually in the form of investment securities and cash, is posted by the counterparty with net liability positions in accordance with contract thresholds. The Corporation does not offset assets and liabilities under these arrangements for financial statement presentation purposes. See Note 14 for additional information on the Corporation’s derivative and hedging activities. Securities Sold Under Agreements to Repurchase (“Repurchase Agreements”) The Corporation enters into agreements under which it sells securities subject to an obligation to repurchase the same or similar securities. These repurchase agreements are accounted for as collateralized financing arrangements (i.e., secured borrowings) and not as a sale and subsequent repurchase of securities (i.e., there is no offsetting or netting of the investment securities assets with the repurchase agreement liabilities). The right of set-off for a repurchase agreement resembles a secured borrowing, whereby the collateral would be used to settle the fair value of the repurchase agreement should the Corporation be in default (e.g., fails to make an interest payment to the counterparty). In addition, the Corporation does not enter into reverse repurchase agreements; therefore, there is no such offsetting to be done with the repurchase agreements. See Note 8 for additional disclosures on repurchase agreements. The following table presents the assets and liabilities subject to an enforceable master netting arrangement. The interest and commodity agreements we have with our commercial customers are not subject to an enforceable master netting arrangement, and therefore, are excluded from this table. Gross amounts not offset in the balance sheet ($ in Thousands) Gross Gross amounts offset in the balance sheet Net amounts presented in the balance sheet Financial instruments Collateral Net amount December 31, 2017 Derivative assets Interest and commodity agreements $ 29,503 $ — $ 29,503 $ (29,503 ) $ — $ — Derivative liabilities Interest and commodity agreements $ 37,164 $ — $ 37,164 $ (29,503 ) $ (7,661 ) $ — December 31, 2016 Derivative assets Interest and commodity agreements $ 18,031 $ — $ 18,031 $ (18,031 ) $ — $ — Derivative liabilities Interest and commodity agreements $ 31,075 $ — $ 31,075 $ (18,031 ) $ (11,148 ) $ 1,896

Commitments, Off-Balance Sheet

Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities	Commitments, Off-Balance Sheet Arrangements, and Legal Proceedings The Corporation utilizes a variety of financial instruments in the normal course of business to meet the financial needs of its customers and to manage its own exposure to fluctuations in interest rates. These financial instruments include lending-related and other commitments (see below) as well as derivative instruments (see Note 14 ). The following is a summary of lending-related commitments. 2017 2016 ($ in Thousands) Commitments to extend credit, excluding commitments to originate residential mortgage loans held for sale (a) (b) $ 8,027,187 $ 8,131,131 Commercial letters of credit (a) 11,886 7,923 Standby letters of credit (c) 235,361 259,632 (a) These off-balance sheet financial instruments are exercisable at the market rate prevailing at the date the underlying transaction will be completed and, thus, are deemed to have no current fair value, or the fair value is based on fees currently charged to enter into similar agreements and is not material at December 31, 2017 and 2016 . (b) Interest rate lock commitments to originate residential mortgage loans held for sale are considered derivative instruments and are disclosed in Note 14 . (c) The Corporation has established a liability of $2 million at December 31, 2017 and $3 million at December 31, 2016 , as an estimate of the fair value of these financial instruments. Lending-related Commitments As a financial services provider, the Corporation routinely enters into commitments to extend credit. Such commitments are subject to the same credit policies and approval process accorded to loans made by the Corporation, with each customer’s creditworthiness evaluated on a case-by-case basis. The commitments generally have fixed expiration dates or other termination clauses and may require the payment of a fee. The Corporation’s exposure to credit loss in the event of nonperformance by the other party to these financial instruments is represented by the contractual amount of those instruments. The amount of collateral obtained, if deemed necessary by the Corporation upon extension of credit, is based on management’s credit evaluation of the customer. Since a significant portion of commitments to extend credit are subject to specific restrictive loan covenants or may expire without being drawn upon, the total commitment amounts do not necessarily represent future cash flow requirements. An allowance for unfunded commitments is maintained at a level believed by management to be sufficient to absorb estimated probable losses related to unfunded commitments (including unfunded loan commitments and letters of credit). The allowance for unfunded commitments totaled $24 million at December 31, 2017 compared to $25 million at December 31, 2016 , and is included in accrued expenses and other liabilities on the consolidated balance sheets. See Note 1 for the Corporation’s accounting policy on the allowance for unfunded commitments. See Note 4 for additional information on the allowance for unfunded commitments. Lending-related commitments include commitments to extend credit, commitments to originate residential mortgage loans held for sale, commercial letters of credit, and standby letters of credit. Commitments to extend credit are legally binding agreements to lend to customers at predetermined interest rates, as long as there is no violation of any condition established in the contracts. Interest rate lock commitments to originate residential mortgage loans held for sale and forward commitments to sell residential mortgage loans are considered derivative instruments, and the fair value of these commitments is recorded on the consolidated balance sheets. The Corporation’s derivative and hedging activity is further described in Note 14 . Commercial and standby letters of credit are conditional commitments issued to guarantee the performance of a customer to a third party. Commercial letters of credit are issued specifically to facilitate commerce and typically result in the commitment being drawn on when the underlying transaction is consummated between the customer and the third party, while standby letters of credit generally are contingent upon the failure of the customer to perform according to the terms of the underlying contract with the third party. Other Commitments The Corporation invests in unconsolidated projects including low-income housing, new market tax credit projects, and historic tax credit projects to promote the revitalization of primarily low-to-moderate-income neighborhoods throughout the local communities of its bank subsidiary. As a limited partner in these unconsolidated projects, the Corporation is allocated tax credits and deductions associated with the underlying projects. The aggregate carrying value of these investments at December 31, 2017 , was $147 million , compared to $68 million at December 31, 2016 . The Corporation has principal investment commitments to provide capital-based financing to private and public companies through either direct investments in specific companies or through investment funds and partnerships. The timing of future cash requirements to fund such commitments is generally dependent on the investment cycle, whereby privately held companies are funded by private equity investors and ultimately sold, merged, or taken public through an initial offering, which can vary based on overall market conditions, as well as the nature and type of industry in which the companies operate. The aggregate carrying value of these investments at December 31, 2017 , was $23 million , compared to $17 million at December 31, 2016 , included in other assets on the consolidated balance sheets. Related to these investments, the Corporation had remaining commitments to fund $119 million at December 31, 2017 , and $69 million at December 31, 2016 . Legal Proceedings The Corporation is party to various pending and threatened claims and legal proceedings arising in the normal course of business activities, some of which involve claims for substantial amounts. Although there can be no assurance as to the ultimate outcomes, the Corporation believes it has meritorious defenses to the claims asserted against it in its currently outstanding matters, including the matters described below, and with respect to such legal proceedings, intends to continue to defend itself vigorously. The Corporation will consider settlement of cases when, in management’s judgment, it is in the best interests of both the Corporation and its shareholders. On at least a quarterly basis, the Corporation assesses its liabilities and contingencies in connection with all pending or threatened claims and litigation, utilizing the most recent information available. On a matter by matter basis, an accrual for loss is established for those matters which the Corporation believes it is probable that a loss may be incurred and that the amount of such loss can be reasonably estimated. Once established, each accrual is adjusted as appropriate to reflect any subsequent developments. Accordingly, management’s estimate will change from time to time, and actual losses may be more or less than the current estimate. For matters where a loss is not probable, or the amount of the loss cannot be estimated, no accrual is established. Resolution of legal claims is inherently unpredictable, and in many legal proceedings various factors exacerbate this inherent unpredictability, including where the damages sought are unsubstantiated or indeterminate, it is unclear whether a case brought as a class action will be allowed to proceed on that basis, discovery is not complete, the proceeding is not yet in its final stages, the matters present legal uncertainties, there are significant facts in dispute, there are a large number of parties (including where it is uncertain how liability, if any, will be shared among multiple defendants), or there is a wide range of potential results. A lawsuit, R.J. ZAYED v. Associated Bank, N.A. , was filed in the United States District Court for the District of Minnesota on January 29, 2013. The lawsuit relates to a Ponzi scheme perpetrated by Oxford Global Partners and related entities (“Oxford”) and individuals and was brought by the receiver for Oxford. Oxford was a depository customer of Associated Bank (the "Bank"). The lawsuit claims that the Bank is liable for failing to uncover the Oxford Ponzi scheme, and specifically alleges the Bank aided and abetted (1) the fraudulent scheme; (2) a breach of fiduciary duty; (3) conversion; and (4) false representations and omissions. The lawsuit seeks unspecified consequential and punitive damages. The District Court granted the Bank’s motion to dismiss the complaint on September 30, 2013. On March 2, 2015, the U.S. Court of Appeals for the Eighth Circuit reversed the District Court and remanded the case back to the District Court for further proceedings. On January 31, 2017, the District Court granted the Bank’s motion for summary judgment. The receiver has appealed the District Court’s summary judgment decision to the Eighth Circuit Court of Appeals. On January 23, 2018, the District Court approved a settlement agreement between the parties. Based on the terms of the settlement agreement, the Bank expects that the litigation will not have a material adverse impact on the Bank regardless of the outcome of the appeal to the Eighth Circuit Court of Appeals. A lawsuit by investors in the same Ponzi scheme, Herman Grad, et al v. Associated Bank, N.A., brought in Brown County, Wisconsin in October 2009 was dismissed by the circuit court, and the dismissal was affirmed by the Wisconsin Court of Appeals in June 2011 in an unpublished opinion. Two complaints were filed against the Bank on January 11, 2016 in the United States Bankruptcy Court for the Northern District of Illinois, Eastern Division in connection with the In re: World Marketing Chicago, LLC, et al Chapter 11 bankruptcy proceeding. In the first complaint, The Official Committee of Unsecured Creditors of World Marketing Chicago, LLC, et al v. Associated Bank, N.A., the plaintiff seeks to avoid guarantees and pledges of collateral given by the debtors to secure a revolving financing commitment of $6 million to the debtors’ parent company from the Bank. The plaintiff alleges a variety of legal theories under federal and state law, including fraudulent conveyance, preferential transfer and conversion, in support of its position. The plaintiff seeks return of approximately $4 million paid to the Bank and the avoidance of the security interest in the collateral securing the remaining indebtedness to the Bank. The Bank intends to vigorously defend this lawsuit. In the second complaint, American Funds Service Company v. Associated Bank, N.A., the plaintiff alleges that approximately $600,000 of funds it had advanced to the World Marketing entities to apply towards future postage fees was swept by the Bank from World Marketing’s bank accounts. Plaintiff seeks the return of such funds from the Bank under several theories, including Sec. 541(d) of the Bankruptcy Code, the creation of a resulting trust, and unjust enrichment. The Bank intends to vigorously defend this lawsuit. It is not possible for management to assess the probability of a material adverse outcome or reasonably estimate the amount of any potential loss at this time with respect to these two lawsuits. Subsequent to the announcement on July 20, 2017, of the Merger Agreement between the Corporation and Bank Mutual, several lawsuits were filed in connection with the proposed merger. On July 28, 2017, two substantially identical purported class action complaints, each by various individual plaintiffs, were filed with the Wisconsin Circuit Court for Milwaukee County on behalf of the respective named plaintiffs and other Bank Mutual shareholders against Bank Mutual, the members of the Bank Mutual board, and the Corporation. The lawsuits are captioned Schumel et al v. Bank Mutual Corporation et al. and Paquin et al. v. Bank Mutual Corporation et al . Both complaints allege state law breach of fiduciary duty claims against the Bank Mutual board for, among other things, seeking to sell Bank Mutual through an allegedly defective process, for an allegedly unfair price and on allegedly unfair terms. On August 30, 2017, a third purported class action complaint, captioned Wollenburg et al. v. Bank Mutual Corporation et al ., was filed in the Wisconsin Circuit Court for Milwaukee County, on behalf of the same class of shareholders and against the same defendants as the prior two complaints. The Wollenburg complaint asserts similar allegations as the prior two complaints, and further alleges that the preliminary proxy statement/prospectus filed with the SEC contains various alleged misstatements or omissions under federal securities law. The Paquin , Schumel and Wollenburg complaints allege that the Corporation aided and abetted Bank Mutual's directors' alleged breaches of fiduciary duty. The parties have entered into a stipulation seeking to consolidate the three actions. On September 13, 2017, the Corporation filed a notice of removal of the Paquin , Schumel and Wollenburg actions to the United States District Court for the Eastern District of Wisconsin. On September 15, 2017, the plaintiffs in the Paquin , Schumel and Wollenburg actions filed identical motions to remand the three cases back to state court, and on September 27, 2017, the defendants filed oppositions to the motions to remand. On October 3, 2017, the defendants filed motions to dismiss the three actions. On September 6, 2017, a fourth purported class action complaint, captioned Parshall et al., v. Bank Mutual Corporation et al ., was filed in the U.S. District Court for the Eastern District of Wisconsin, on behalf of the same class of shareholders and against the same defendants as the prior complaints. The Parshall complaint criticizes the adequacy of the merger consideration and alleges that Bank Mutual, the members of the Bank Mutual board and the Corporation allegedly omitted and/or misrepresented certain information in the registration statement on Form S-4 filed in connection with the proposed merger in violation of the federal securities laws. The lawsuits seek, among other things, to enjoin the consummation of the transaction and damages. The Corporation believes the allegations are without merit. On October 13, 2017, Bank Mutual and the Corporation reached agreement with the plaintiffs in each of the four cases whereby Bank Mutual issued certain additional disclosures in a Form 8-K, and each of the plaintiffs have agreed to dismiss their actions with prejudice as to the named plaintiffs and without prejudice as to the rest of the purported class members. Regulatory Matters On May 22, 2015, the Bank entered into a Conciliation Agreement ("Conciliation Agreement") with the U.S. Department of Housing and Urban Development ("HUD") which resolved the HUD investigation into the Bank's lending practices during the years 2008-2010. The Bank's commitments under the Conciliation Agreement are spread over 3 years and include commitments to do the following in minority communities: make mortgage loans of approximately $196 million ; open one branch and four loan production offices; establish special financing programs; make affordable home repair grants; engage in affirmative marketing outreach; provide financial education programs; and make grants to support community reinvestment training and education. The cost of these commitments will be spread over four calendar years and is not expected to have a material impact on the Corporation's financial condition or results of operation. A variety of consumer products, including mortgage and deposit products, and certain fees and charges related to such products, have come under increased regulatory scrutiny. It is possible that regulatory authorities could bring enforcement actions, including civil money penalties, or take other actions against the Corporation and the Bank in regard to these consumer products. The Bank could also determine of its own accord, or be required by regulators, to refund or otherwise make remediation payments to customers in connection with these products. It is not possible at this time for management to assess the probability of a material adverse outcome or reasonably estimate the amount of any potential loss related to such matters. On March 27, 2017, the Bank received a Community Reinvestment Act ("CRA") rating from the Office of the Comptroller of the Currency of "Satisfactory" for the period from January 1, 2011 through July 27, 2015. As a result of this rating, the restrictions on certain of the Bank's activities that had been imposed under the previous "Needs to Improve" CRA rating are no longer applicable. Mortgage Repurchase Reserve The Corporation sells residential mortgage loans to investors in the normal course of business. Residential mortgage loans sold to others are predominantly conventional residential first lien mortgages originated under our usual underwriting procedures, and are most often sold on a nonrecourse basis, primarily to the GSEs. The Corporation’s agreements to sell residential mortgage loans in the normal course of business usually require certain representations and warranties on the underlying loans sold, related to credit information, loan documentation, collateral, and insurability. Subsequent to being sold, if a material underwriting deficiency or documentation defect is discovered, the Corporation may be obligated to repurchase the loan or reimburse the GSEs for losses incurred (collectively, “make whole requests”). The make whole requests and any related risk of loss under the representations and warranties are largely driven by borrower performance. As a result of make whole requests, the Corporation has repurchased loans with principal balances of approximately $1 million and $2 million during the years ended December 31, 2017 and 2016 , respectively. The loss reimbursement and settlement claims paid for the years ended December 31, 2017 and 2016 , respectively, were negligible. Make whole requests during 2016 and 2017 generally arose from loans sold during the period of January 1, 2012 to December 31, 2017 , which totaled $10 billion at the time of sale, and consisted primarily of loans sold to GSEs. As of December 31, 2017 , approximately $6.1 billion of these sold loans remain outstanding. The balance in the mortgage repurchase reserve at the balance sheet date reflects the estimated amount of potential loss the Corporation could incur from repurchasing a loan, as well as loss reimbursements, indemnifications, and other settlement resolutions. The following summarizes the changes in the mortgage repurchase reserve for the years ended as follows. 2017 2016 ($ in Thousands) Balance at beginning of year $ 900 $ 1,197 Repurchase provision expense 246 456 Adjustments to provision expense — (750 ) Charge offs, net (159 ) (3 ) Balance at end of year $ 987 $ 900 The Corporation may also sell residential mortgage loans with limited recourse (limited in that the recourse period ends prior to the loan’s maturity, usually after certain time and / or loan paydown criteria have been met), whereby repurchase could be required if the loan had defined delinquency issues during the limited recourse periods. At December 31, 2017 , and December 31, 2016 , there were approximately $44 million and $62 million , respectively, of residential mortgage loans sold with such recourse risk. There have been limited instances and immaterial historical losses on repurchases for recourse under the limited recourse criteria. The Corporation has a subordinate position to the FHLB in the credit risk on residential mortgage loans it sold to the FHLB in exchange for a monthly credit enhancement fee. The Corporation has not sold loans to the FHLB with such credit risk retention since February 2005. At December 31, 2017 and December 31, 2016 , there were $73 million and $98 million

Parent Company Only Financial I

Parent Company Only Financial Information	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Parent Company Only Financial Information	Parent Company Only Financial Information Presented below are condensed financial statements for the Parent Company. BALANCE SHEETS December 31, 2017 2016 ($ in Thousands) Assets Cash and due from banks $ 146,877 $ 402,786 Investment securities available for sale, at fair value 11,645 14,389 Notes and interest receivable from subsidiaries 301,378 — Investments in and receivable due from subsidiaries 3,320,090 3,256,763 Other assets 51,466 53,242 Total assets $ 3,831,456 $ 3,727,180 Liabilities and Stockholders' Equity Commercial paper $ 67,467 $ 101,688 Senior notes, at par 250,000 250,000 Subordinated notes, at par 250,000 250,000 Long-term funding capitalized costs (2,718 ) (3,393 ) Total long-term funding 497,282 496,607 Accrued expenses and other liabilities 29,264 37,573 Total liabilities 594,013 635,868 Preferred equity 159,929 159,929 Common equity 3,077,514 2,931,383 Total stockholders’ equity 3,237,443 3,091,312 Total liabilities and stockholders’ equity $ 3,831,456 $ 3,727,180 STATEMENTS OF INCOME For the Years Ended December 31, 2017 2016 2015 ($ in Thousands) Income Dividends from subsidiaries $ 213,000 $ 188,000 $ 205,000 Interest income on notes receivable from subsidiaries 4,175 — — Other income 1,763 4,669 8,441 Total income 218,938 192,669 213,441 Expense Interest expense on short and long-term funding 18,464 21,901 39,576 Other expense 6,927 4,289 4,684 Total expense 25,391 26,190 44,260 Income before income tax expense (benefit) and equity in undistributed net income (loss) of subsidiaries 193,547 166,479 169,181 Income tax expense (benefit) 4,768 3,468 (1,665 ) Income before equity in undistributed net income (loss) of subsidiaries 188,779 163,011 170,846 Equity in undistributed net income (loss) of subsidiaries 40,485 37,263 17,455 Net income 229,264 200,274 188,301 Preferred stock dividends 9,347 8,903 7,155 Net income available to common equity $ 219,917 $ 191,371 $ 181,146 STATEMENTS OF CASH FLOWS For the Years Ended December 31, 2017 2016 2015 ($ in Thousands) Cash Flows from Operating Activities Net income $ 229,264 $ 200,274 $ 188,301 Adjustments to reconcile net income to net cash provided by operating activities: (Increase) decrease in equity in undistributed net income (loss) of subsidiaries (40,485 ) (37,263 ) (17,455 ) (Gain) loss on sales of investment securities, net of impairment write-downs — (466 ) — (Gain) loss on sales of assets, net (88 ) (793 ) (5,673 ) Net change in other assets and other liabilities (9,589 ) 19,708 (10,997 ) Net cash provided by operating activities 179,102 181,460 154,176 Cash Flows from Investing Activities Proceeds from sales of investment securities 2,618 47,719 13,962 Net increase in notes receivable from subsidiaries (300,000 ) — — Purchase of other assets, net of disposals 1,058 2,211 11,964 Net cash provided by (used in) investing activities (296,324 ) 49,930 25,926 Cash Flows from Financing Activities Net increase (decrease) in commercial paper (34,221 ) 33,710 (6,319 ) Repayment of long-term funding — (430,000 ) — Proceeds from issuance of common stock for stock-based compensation plans 27,619 21,748 20,054 Proceeds from issuance of preferred stock — 97,066 62,966 Redemption of preferred stock — (58,903 ) — Purchase of preferred stock — (1,248 ) (1,335 ) Purchase of common stock returned to authorized but unissued (37,031 ) (20,007 ) (93,000 ) Purchase of treasury stock for tax withholding (9,290 ) (5,074 ) (5,154 ) Cash dividends on common stock (76,417 ) (67,855 ) (62,400 ) Cash dividends on preferred stock (9,347 ) (8,903 ) (7,155 ) Net cash used in financing activities (138,687 ) (439,466 ) (92,343 ) Net increase (decrease) in cash and cash equivalents (255,909 ) (208,076 ) 87,759 Cash and cash equivalents at beginning of year 402,786 610,862 523,103 Cash and cash equivalents at end of year 146,877 402,786 610,862

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value represents the estimated price at which an orderly transaction to sell an asset or to transfer a liability would take place between market participants at the measurement date under current market conditions (i.e., an exit price concept). See Note 1 for the Corporation’s accounting policy for fair value measurements. Following is a description of the valuation methodologies used for the Corporation’s more significant instruments measured on a recurring basis at fair value, including the general classification of such instruments pursuant to the valuation hierarchy. Assets and Liabilities Measured at Fair Value on a Recurring Basis Investment Securities Available For Sale: Where quoted prices are available in an active market, investment securities are classified in Level 1 of the fair value hierarchy. If quoted market prices are not available for the specific security, then fair values are estimated by using pricing models, quoted prices of securities with similar characteristics or discounted cash flows, with consideration given to the nature of the quote and the relationship of recently evidenced market activity to the fair value estimate, and are classified in Level 2 of the fair value hierarchy. Lastly, in certain cases where there is limited activity or less transparency around inputs to the estimated fair value, securities are classified within Level 3 of the fair value hierarchy. To validate the fair value estimates, assumptions, and controls, the Corporation looks to transactions for similar instruments and utilizes independent pricing provided by third party vendors or brokers and relevant market indices. While none of these sources are solely indicative of fair value, they serve as directional indicators for the appropriateness of the Corporation’s fair value estimates. The Corporation has determined that the fair value measures of its investment securities are classified predominantly within Level 1 or 2 of the fair value hierarchy. See Note 3 for additional disclosure regarding the Corporation’s investment securities. Residential Loans Held For Sale: Loans held for sale, which consist generally of current production of certain fixed-rate, first-lien residential mortgage loans, are carried at estimated fair value. Effective January 1, 2017, management elected the fair value option to account for all newly originated mortgage loans held for sale which results in the financial impact of changing market conditions being reflected currently in earnings as opposed to being dependent upon the timing of sales. Therefore, the continually adjusted values going forward will better reflect the price the Corporation expects to receive from the sale of such loans. The estimated fair value was based on what secondary markets are currently offering for portfolios with similar characteristics, which the Corporation classifies as a Level 2 fair value measurement. Derivative Financial Instruments (Interest Rate-Related Instruments): The Corporation has used, and may use again in the future, interest rate swaps to manage its interest rate risk. In addition, the Corporation offers interest rate-related instruments (swaps and caps) to service our customers’ needs, for which the Corporation simultaneously enters into offsetting derivative financial instruments (i.e., mirror interest rate-related instruments) with third parties to manage its interest rate risk associated with these financial instruments. The valuation of the Corporation’s derivative financial instruments is determined using discounted cash flow analysis on the expected cash flows of each derivative and also includes a nonperformance / credit risk component (credit valuation adjustment). See Note 14 for additional disclosure regarding the Corporation’s interest rate-related instruments. The discounted cash flow analysis component in the fair value measurement reflects the contractual terms of the derivative financial instruments, including the period to maturity, and uses observable market-based inputs, including interest rate curves and implied volatilities. More specifically, the fair values of interest rate swaps are determined using the market standard methodology of netting the discounted future fixed cash receipts (or payments), with the variable cash payments (or receipts) based on an expectation of future interest rates (forward curves) derived from observable market interest rate curves. Likewise, the fair values of interest rate options (i.e., interest rate caps) are determined using the market standard methodology of discounting the future expected cash receipts that would occur if variable interest rates fall below (or rise above) the strike rate of the floors (or caps), with the variable interest rates used in the calculation of projected receipts on the floor (or cap) based on an expectation of future interest rates derived from observable market interest rate curves and volatilities. The Corporation also incorporates credit valuation adjustments to appropriately reflect both its own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. In adjusting the fair value of its derivative financial instruments for the effect of nonperformance risk, the Corporation has considered the impact of netting and any applicable credit enhancements, such as collateral postings, thresholds, mutual puts, and guarantees. While the Corporation has determined that the majority of the inputs used to value its derivative financial instruments fall within Level 2 of the fair value hierarchy, the credit valuation adjustments utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by itself and its counterparties. The Corporation has assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions as of December 31, 2017 and 2016 , and has determined that the credit valuation adjustments are not significant to the overall valuation of its derivative financial instruments. Therefore, the Corporation has determined that the fair value measures of its derivative financial instruments in their entirety are classified within Level 2 of the fair value hierarchy. Derivative Financial Instruments (Foreign Currency Exchange Forwards): The Corporation provides foreign currency exchange services to customers. In addition, the Corporation may enter into a foreign currency exchange forward to mitigate the exchange rate risk attached to the cash flows of a loan or as an offsetting contract to a forward entered into as a service to our customer. The valuation of the Corporation’s foreign currency exchange forwards is determined using quoted prices of foreign currency exchange forwards with similar characteristics, with consideration given to the nature of the quote and the relationship of recently evidenced market activity to the fair value estimate, and are classified in Level 2 of the fair value hierarchy. See Note 14 for additional disclosures regarding the Corporation’s foreign currency exchange forwards. Derivative Financial Instruments (Commodity Contracts): The Corporation enters into commodity contracts to manage commercial customers' exposure to fluctuating commodity prices, for which the Corporation simultaneously enters into offsetting derivative financial instruments (i.e., mirror commodity contracts) with third parties to manage its risk associated with these financial instruments. The valuation of the Corporation’s commodity contracts is determined using quoted prices of the underlying instruments, and are classified in Level 2 of the fair value hierarchy. See Note 14 for additional disclosures regarding the Corporation’s commodity contracts. The table below presents the Corporation’s financial instruments measured at fair value on a recurring basis as of December 31, 2017 and 2016 , aggregated by the level in the fair value hierarchy within which those measurements fall. Fair Value Hierarchy December 31, 2017 December 31, 2016 ($ in Thousands) Assets Investment securities available for sale U.S. Treasury securities Level 1 $ 996 $ 1,000 Residential mortgage-related securities FNMA / FHLMC Level 2 464,768 639,930 GNMA Level 2 1,913,350 2,004,475 Private-label Level 2 1,059 1,121 GNMA commercial mortgage-related securities Level 2 1,513,277 2,028,898 FFELP asset backed securities Level 2 145,176 — Other securities (debt and equity) Level 1 1,632 1,602 Other securities (debt and equity) Level 2 3,188 3,000 Other securities (debt and equity) Level 3 — 200 Total investment securities available for sale Level 1 2,628 2,602 Total investment securities available for sale Level 2 4,040,818 4,677,424 Total investment securities available for sale Level 3 — 200 Residential loans held for sale (a) Level 2 85,544 — Interest rate-related instruments Level 2 28,494 33,671 Foreign currency exchange forwards Level 2 2,495 2,002 Interest rate lock commitments to originate residential mortgage loans held for sale Level 3 1,538 206 Forward commitments to sell residential mortgage loans Level 3 — 2,908 Commodity contracts Level 2 38,686 16,725 Purchased options (time deposit) Level 2 1,175 2,576 Liabilities Interest rate-related instruments Level 2 $ 28,035 $ 33,188 Foreign currency exchange forwards Level 2 2,339 1,943 Forward commitments to sell residential mortgage loans Level 3 313 — Commodity contracts Level 2 37,286 15,972 Written options (time deposit) Level 2 1,175 2,576 (a) Effective January 1, 2017, residential loans originated for sale are accounted for under the fair value option. Prior periods have not been restated. For more information on this accounting policy change, please refer to Note 1 . The table below presents a rollforward of the balance sheet amounts for the years ended December 31, 2017 and 2016 , for financial instruments measured on a recurring basis and classified within Level 3 of the fair value hierarchy. Investment Securities Available for Sale Derivative Financial Instruments ($ in Thousands) Balance December 31, 2015 $ 200 $ 1,361 Total net gains (losses) included in income Mortgage derivative gain (loss) — 1,753 Balance December 31, 2016 $ 200 $ 3,114 Total net gains (losses) included in income Mortgage derivative gain (loss) — (1,889 ) Transfer out of level 3 securities (a) $ (200 ) $ — Balance December 31, 2017 $ — $ 1,225 (a) During the first quarter of 2017, the $200,000 level 3 investment security was transferred to level 2 based upon new pricing information. For Level 3 assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 , the Corporation utilized the following valuation techniques and significant unobservable inputs. Derivative Financial Instruments (Mortgage Derivative — Interest Rate lock Commitments to Originate Residential Mortgage Loans Held For Sale): The fair value is determined by the change in value from each loan's rate lock date to the expected rate lock expiration date based on the underlying loan attributes, estimated closing ratios, and investor price matrix determined to be reasonably applicable to each loan commitment. The closing ratio calculation takes into consideration historical experience and loan-level attributes, particularly the change in the current interest rates from the time of initial rate lock. The closing ratio is periodically reviewed for reasonableness and reported to the Associated Mortgage Risk Management Committee. At December 31, 2017 , the closing ratio was 85% . Derivative Financial Instruments (Mortgage Derivative—Forward Commitments to Sell Mortgage Loans): Mortgage derivatives include forward commitments to deliver closed end residential mortgage loans into conforming Agency Mortgage Backed Securities (To be Announced, "TBA") or conforming Cash Forward sales. The fair value of such instruments is determined by the difference of current market prices for such traded instruments or available from forward cash delivery commitments and the original traded price for such commitments. The Corporation also relies on an internal valuation model to estimate the fair value of its forward commitments to sell residential mortgage loans (i.e., an estimate of what the Corporation would receive or pay to terminate the forward delivery contract based on market prices for similar financial instruments), which includes matching specific terms and maturities of the forward commitments against applicable investor pricing available. While there are Level 2 and 3 inputs used in the valuation models, the Corporation has determined that the majority of the inputs significant in the valuation of both of the mortgage derivatives fall within Level 3 of the fair value hierarchy. See Note 14 for additional disclosure regarding the Corporation’s mortgage derivatives. Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis Following is a description of the valuation methodologies used for the Corporation’s more significant instruments measured on a nonrecurring basis at the lower of amortized cost or estimated fair value, including the general classification of such instruments pursuant to the valuation hierarchy. Commercial Loans Held For Sale: Loans held for sale are carried at the lower of cost or estimated fair value. The estimated fair value is based on a discounted cash flow analysis, which the Corporation classifies as a Level 2 nonrecurring fair value measurement. Other Real Estate Owned: Certain other real estate owned, upon initial recognition, was re-measured and reported at fair value through a charge off to the allowance for loan losses based upon the estimated fair value of the other real estate owned, less estimated selling costs. The fair value of other real estate owned, upon initial recognition or subsequent impairment, was estimated using appraised values, which the Corporation classifies as a Level 2 nonrecurring fair value measurement. For Level 3 assets and liabilities measured at fair value on a nonrecurring basis as of December 31, 2017, the Corporation utilized the following valuation techniques and significant unobservable inputs. Impaired Loans: The Corporation considers a loan impaired when it is probable that the Corporation will be unable to collect all amounts due according to the original contractual terms of the note agreement, including both principal and interest. Management has determined that commercial and consumer loan relationships that have nonaccrual status or have had their terms restructured in a troubled debt restructuring meet this impaired loan definition. For individually evaluated impaired loans, the amount of impairment is based upon the present value of expected future cash flows discounted at the loan’s effective interest rate, the estimated fair value of the underlying collateral for collateral-dependent loans, or the estimated liquidity of the note. See Note 4 for additional information regarding the Corporation’s impaired loans. Mortgage Servicing Rights: Mortgage servicing rights do not trade in an active, open market with readily observable prices. While sales of mortgage servicing rights do occur, the precise terms and conditions typically are not readily available to allow for a “quoted price for similar assets” comparison. Accordingly, the Corporation utilizes an independent valuation from a third party which uses a discounted cash flow model to estimate the fair value of its mortgage servicing rights. The valuation model incorporates prepayment assumptions to project mortgage servicing rights cash flows based on the current interest rate scenario, which is then discounted to estimate an expected fair value of the mortgage servicing rights. The valuation model considers portfolio characteristics of the underlying mortgages, contractually specified servicing fees, prepayment assumptions, discount rate assumptions, delinquency rates, late charges, other ancillary revenue, costs to service, and other economic factors. The Corporation periodically reviews and assesses the underlying inputs and assumptions used in the model. In addition, the Corporation compares its fair value estimates and assumptions to observable market data for mortgage servicing rights, where available, and to recent market activity and actual portfolio experience. Due to the nature of the valuation inputs, mortgage servicing rights are classified within Level 3 of the fair value hierarchy. The Corporation uses the amortization method (i.e., lower of amortized cost or estimated fair value measured on a nonrecurring basis), not fair value measurement accounting, for its mortgage servicing rights assets. The discounted cash flow analyses that generate expected market prices utilize the observable characteristics of the mortgage servicing rights portfolio, as well as certain unobservable valuation parameters. The significant unobservable inputs used in the fair value measurement of the Corporation’s mortgage servicing rights are the weighted average constant prepayment rate and weighted average discount rate. Significant increases (decreases) in any of those inputs in isolation could result in a significantly lower (higher) fair value measurement. These parameter assumptions fall within a range that the Corporation, in consultation with an independent third party, believes purchasers of servicing would apply to such portfolios sold into the current secondary servicing market. Discussions are held with members from Treasury and the Community, Consumer, and Business segment to reconcile the fair value estimates and the key assumptions used by the respective parties in arriving at those estimates. The Associated Mortgage Risk Management Committee is responsible for providing control over the valuation methodology and key assumptions. To assess the reasonableness of the fair value measurement, the Corporation also compares the fair value and constant prepayment rate to a value calculated by an independent third party on an annual basis. See Note 5 for additional disclosure regarding the Corporation’s mortgage servicing rights. The table below presents the Corporation’s assets measured at fair value on a nonrecurring basis, aggregated by the level in the fair value hierarchy within which those measurements fall. Income Statement Category of Adjustment Recognized in Income Fair Value Hierarchy Fair Value ($ in Thousands) December 31, 2017 Assets Impaired loans (a) Level 3 $ 92,534 Provision for credit losses (c) $ (32,159 ) Other real estate owned Level 2 2,604 Foreclosure / OREO expense, net (939 ) Mortgage servicing rights Level 3 64,387 Mortgage banking, net (175 ) December 31, 2016 Assets Commercial loans held for sale Level 2 $ 12,474 Provision for credit losses $ (559 ) Residential loans held for sale (b) Level 2 108,010 Mortgage banking, net (3,760 ) Impaired loans (a) Level 3 79,270 Provision for credit losses (c) (75,194 ) Other real estate owned Level 2 9,752 Foreclosure / OREO expense, net (1,091 ) Mortgage servicing rights Level 3 73,149 Mortgage banking, net 200 (a) Represents individually evaluated impaired loans, net of the related allowance for loan losses. (b) Effective January 1, 2017, residential loans originated for sale are accounted for under the fair value option. Prior periods have not been restated. For more information on this accounting policy change, please refer to Note 3 . (c) Represents provision for credit losses on individually evaluated impaired loans. The change in provision for credit loss is primarily due to the oil and gas portfolio. For more information on the oil and gas portfolio, see Note 4 . Certain nonfinancial assets and nonfinancial liabilities measured at fair value on a nonrecurring basis include the fair value analysis in the second step of a goodwill impairment test, and intangible assets and other nonfinancial long-lived assets measured at fair value for impairment assessment. The Corporation's significant Level 3 measurements which employ unobservable inputs that are readily quantifiable pertain to mortgage servicing rights and impaired loans. The table below presents information about these inputs and further discussion is found above. December 31, 2017 Valuation Technique Significant Unobservable Input Weighted Average Input Applied Mortgage servicing rights Discounted cash flow Discount rate 11% Mortgage servicing rights Discounted cash flow Constant prepayment rate 11% Impaired loans Appraisals / Discounted cash flow Collateral / Discount factor 19% Fair Value of Financial Instruments The Corporation is required to disclose estimated fair values for its financial instruments. Fair value estimates, methods, and assumptions are set forth below for the Corporation’s financial instruments. December 31, 2017 December 31, 2016 Fair Value Hierarchy Level Carrying Amount Fair Value Carrying Amount Fair Value ($ in Thousands) Financial assets Cash and due from banks Level 1 $ 483,666 $ 483,666 $ 446,558 $ 446,558 Interest-bearing deposits in other financial institutions Level 1 199,702 199,702 149,175 149,175 Federal funds sold and securities purchased under agreements to resell Level 1 32,650 32,650 46,500 46,500 Investment securities held to maturity Level 2 2,282,853 2,283,574 1,273,536 1,264,674 Investment securities available for sale Level 1 2,628 2,628 2,602 2,602 Investment securities available for sale Level 2 4,040,818 4,040,818 4,677,424 4,677,424 Investment securities available for sale Level 3 — — 200 200 FHLB and Federal Reserve Bank stocks Level 2 165,331 165,331 140,001 140,001 Commercial loans held for sale Level 2 — — 12,474 12,474 Residential loans held for sale Level 2 85,544 85,544 108,010 108,010 Loans, net Level 3 20,519,111 20,314,984 19,776,381 19,680,317 Bank and corporate owned life insurance Level 2 591,057 591,057 585,290 585,290 Derivatives (trading and other assets) Level 2 70,850 70,850 54,974 54,974 Derivatives (trading and other assets) Level 3 1,538 1,538 3,114 3,114 Financial liabilities Noninterest-bearing demand, savings, interest-bearing demand, and money market accounts Level 3 $ 20,436,893 $ 20,436,893 $ 20,282,321 $ 20,282,321 Brokered CDs and other time deposits Level 2 2,349,069 2,349,069 1,606,127 1,606,127 Short-term funding Level 2 676,282 676,282 1,092,035 1,092,035 Long-term funding Level 2 3,397,450 3,411,368 2,761,795 2,791,841 Standby letters of credit (a) Level 2 2,402 2,402 2,566 2,566 Derivatives (trading and other liabilities) Level 2 68,835 68,835 53,679 53,679 Derivatives (trading and other liabilities) Level 3 313 313 — — (a) The commitment on standby letters of credit was $235 million and $260 million at December 31, 2017 and 2016 , respectively. See Note 16 for additional information on the standby letters of credit and for information on the fair value of lending-related commitments. Cash and due from banks, interest-bearing deposits in other financial institutions, and federal funds sold and securities purchased under agreements to resell: For these short-term instruments, the carrying amount is a reasonable estimate of fair value. Investment securities (held to maturity and available for sale): The fair value of investment securities is based on quoted prices in active markets, or if quoted prices are not available for a specific security, then fair values are estimated by using pricing models, quoted prices of securities with similar characteristics, or discounted cash flows. FHLB and Federal Reserve Bank stocks: The carrying amount is a reasonable fair value estimate for the Federal Reserve Bank and FHLB stocks given their “restricted” nature (i.e., the stock can only be sold back to the respective institutions (FHLB or Federal Reserve Bank) or another member institution at par). Loans held for sale: The fair value estimation process for the loans held for sale portfolio is segregated by loan type. The estimated fair value for residential loans held for sale was based on what secondary markets are currently offering for portfolios with similar characteristics. The estimated fair value for commercial loans held for sale was based on a discounted cash flow analysis. Loans, net: The fair value estimation process for the loan portfolio uses an exit price concept and reflects discounts the Corporation believes are consistent with liquidity discounts in the market place. Fair values are estimated for portfolios of loans with similar financial characteristics. Loans are segregated by type such as commercial and industrial, real estate construction, commercial real estate (owner occupied and investor), residential mortgage, home equity, and other consumer. The fair value of loans is estimated by discounting the future cash flows using the current rates at which similar loans would be made to borrowers with similar credit ratings and for similar maturities. The fair value analysis also included other assumptions to estimate fair value, intended to approximate those a market participant would use in an orderly transaction, with adjustments for discount rates, interest rates, liquidity, and credit spreads, as appropriate. Bank and corporate owned life insurance ("BOLI" and "COLI"): The fair value of BOLI and COLI approximates the carrying amount, because upon liquidation of these investments, the Corporation would receive the cash surrender value which equals the carrying amount. The Corporation has not purchased any new BOLI or COLI policies since 2008. Deposits: The fair value of deposits with no stated maturity such as noninterest-bearing demand, savings, interest-bearing demand, and money market accounts, is equal to the amount payable on demand as of the balance sheet date. The fair value of Brokered CDs and other time deposits is based on the discounted value of contractual cash flows. The discount rate is estimated using the rates currently offered for deposits of similar remaining maturities. However, if the estimated fair value of Brokered CDs and other time deposits is less than the carrying value, the carrying value is reported as the fair value. Short-term funding: The carrying amount is a reasonable estimate of fair value for existing short-term funding. Long-term funding: Rates currently available to the Corporation for debt with similar terms and remaining maturities are used to estimate the fair value of existing long-term funding. Standby letters of credit: The fair value of standby letters of credit represents deferred fees arising from the related off-balance sheet financial instruments. These deferred fees approximate the fair value of these instruments and are based on several factors, including the remaining terms of the agreement and the credit standing of the customer. Derivatives (trading and other): A detailed description of the Corporation's derivative instruments can be found under the "Assets and Liabilities Measured at Fair Value on a Recurring Basis" section of this footnote. Limitations:

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Regulatory Matters	Regulatory Matters Restrictions on Cash and Due From Banks The Corporation’s bank subsidiary is required to maintain certain vault cash and reserve balances with the Federal Reserve Bank to meet specific reserve requirements. These requirements approximated $73 million at December 31, 2017 . Regulatory Capital Requirements The Corporation and its subsidiary bank are subject to various regulatory capital requirements administered by the federal banking agencies. Failure to meet minimum capital requirements can initiate certain mandatory and possible additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Corporation’s financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, the Corporation must meet specific capital guidelines that involve quantitative measures of the Corporation’s assets, liabilities, and certain off-balance sheet items as calculated under regulatory accounting practices. The Corporation’s capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings, and other factors. Quantitative measures established by regulation to ensure capital adequacy require the Corporation to maintain minimum amounts and ratios (set forth in the table below) of total and Common equity Tier 1 capital (as defined in the regulations) to risk-weighted assets (as defined), and of Tier 1 capital (as defined) to average assets (as defined). Management believes, as of December 31, 2017 and 2016 , that the Corporation meets all capital adequacy requirements to which it is subject. For additional information on the capital requirements applicable for the Corporation and the Bank, please see Part I, Item 1. As of December 31, 2017 and 2016 , the most recent notifications from the Office of the Comptroller of the Currency and the Federal Deposit Insurance Corporation categorized the subsidiary bank as well capitalized under the regulatory framework for prompt corrective action. To be categorized as well capitalized, the subsidiary bank must maintain minimum ratios as set forth in the table. There are no conditions or events since that notification that management believes have changed the institution’s category. The actual capital amounts and ratios of the Corporation and its significant subsidiary are presented below. No deductions from capital were made for interest rate risk in 2017 or 2016 . Actual For Capital Adequacy Purposes To Be Well Capitalized Under Prompt Corrective Action Provisions (b) Amount Ratio (a) Amount Ratio (a) Amount Ratio (a) ($ in Thousands) As of December 31 , 2017 Associated Banc-Corp Total capital $ 2,848,851 13.22 % $ 1,723,557 ≥ 8.00 % Tier 1 capital 2,331,245 10.82 % 1,292,668 ≥ 6.00 % Common equity Tier 1 capital 2,171,508 10.08 % 969,501 ≥ 4.50 % Leverage 2,331,245 8.02 % 1,162,929 ≥ 4.00 % Associated Bank, N.A. Total capital $ 2,625,945 12.24 % $ 1,716,910 ≥ 8.00 % $ 2,146,138 ≥ 10.00 % Tier 1 capital 2,357,354 10.98 % 1,287,683 ≥ 6.00 % 1,716,910 ≥ 8.00 % Common equity Tier 1 capital 2,157,354 10.05 % 965,762 ≥ 4.50 % 1,394,989 ≥ 6.50 % Leverage 2,357,354 8.13 % 1,159,959 ≥ 4.00 % 1,449,448 ≥ 5.00 % As of December 31 , 2016 Associated Banc-Corp Total capital $ 2,706,760 12.68 % $ 1,707,276 ≥ 8.00 % Tier 1 capital 2,191,798 10.27 % 1,280,457 ≥ 6.00 % Common equity Tier 1 capital 2,032,587 9.52 % 960,343 ≥ 4.50 % Leverage 2,191,798 7.83 % 1,119,685 ≥ 4.00 % Associated Bank, N.A. Total capital $ 2,565,062 12.07 % $ 1,700,737 ≥ 8.00 % $ 2,125,921 ≥ 10.00 % Tier 1 capital 2,298,812 10.81 % 1,275,553 ≥ 6.00 % 1,700,737 ≥ 8.00 % Common equity Tier 1 capital 2,098,812 9.87 % 956,664 ≥ 4.50 % 1,381,849 ≥ 6.50 % Leverage 2,298,812 8.24 % 1,115,731 ≥ 4.00 % 1,394,663 ≥ 5.00 % (a) When fully phased-in on January 1, 2019, the Basel III capital rules include a capital conservation buffer of 2.5% that is added on top of each of the minimum risk-based capital ratios noted above. Implementation began on January 1, 2016 at the 0.625% level and will increase each subsequent January 1, until it reaches 2.5% on January 1, 2019.

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share See Note 1 for the Corporation’s accounting policy on earnings per common share. Presented below are the calculations for basic and diluted earnings per common share. For the Years Ended December 31, 2017 2016 2015 ($ in Thousands, Except Per Share Data) Net income $ 229,264 $ 200,274 $ 188,301 Preferred stock dividends (9,347 ) (8,903 ) (7,155 ) Net income available to common equity $ 219,917 $ 191,371 $ 181,146 Common shareholder dividends (75,967 ) (67,100 ) (61,774 ) Unvested share-based payment awards (450 ) (755 ) (626 ) Undistributed earnings $ 143,500 $ 123,516 $ 118,746 Undistributed earnings allocated to common shareholders 142,593 122,205 117,498 Undistributed earnings allocated to unvested share-based payment awards 907 1,311 1,248 Undistributed earnings $ 143,500 $ 123,516 $ 118,746 Basic Distributed earnings to common shareholders $ 75,967 $ 67,100 $ 61,774 Undistributed earnings allocated to common shareholders 142,593 122,205 117,498 Total common shareholders earnings, basic $ 218,560 $ 189,305 $ 179,272 Diluted Distributed earnings to common shareholders $ 75,967 $ 67,100 $ 61,774 Undistributed earnings allocated to common shareholders 142,593 122,205 117,498 Total common shareholders earnings, diluted $ 218,560 $ 189,305 $ 179,272 Weighted average common shares outstanding 150,877 148,769 149,350 Effect of dilutive common stock awards $ 2,038 $ 1,192 $ 1,253 Effect of dilutive common stock warrants 732 — — Diluted weighted average common shares outstanding 153,647 149,961 150,603 Basic earnings per common share $ 1.45 $ 1.27 $ 1.20 Diluted earnings per common share $ 1.42 $ 1.26 $ 1.19 Anti-dilutive common stock options of approximately 1 million at the year ended December 31, 2017, 2016 and 2015 were excluded from the earnings per common share calculation. Warrants to purchase approximately 4 million

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Reporting	Segment Reporting The Corporation utilizes a risk-based internal profitability measurement system to provide strategic business unit reporting. The profitability measurement system is based on internal management methodologies designed to produce consistent results and reflect the underlying economics of the units. Certain strategic business units have been combined for segment information reporting purposes where the nature of the products and services, the type of customer and the distribution of those products and services are similar. The three reportable segments are Corporate and Commercial Specialty; Community, Consumer, and Business; and Risk Management and Shared Services. The financial information of the Corporation’s segments has been compiled utilizing the accounting policies described in Note 1 , with certain exceptions. The more significant of these exceptions are described herein. The Corporation allocates net interest income using an internal FTP methodology that charges users of funds (assets) and credits providers of funds (liabilities, primarily deposits) based on the maturity, prepayment and / or repricing characteristics of the assets and liabilities. The net effect of this allocation is recorded in the Risk Management and Shared Services segment. A credit provision is allocated to segments based on the expected long-term annual net charge off rates attributable to the credit risk of loans managed by the segment during the period. In contrast, the level of the consolidated provision for credit losses is determined based on an incurred loss model using the methodologies described in Note 1 to assess the overall appropriateness of the allowance for loan losses and the allowance for unfunded commitments. The net effect of the credit provision is recorded in Risk Management and Shared Services. Indirect expenses incurred by certain centralized support areas are allocated to segments based on actual usage (for example, volume measurements) and other criteria. Certain types of administrative expense and bank-wide expense accruals (including amortization of core deposit and other intangible assets associated with acquisitions) are generally not allocated to segments. Income taxes are allocated to segments based on the Corporation’s tax rate, with certain segments adjusted for any tax-exempt income or non-deductible expenses, the net tax residual is recorded in Risk Management and Shared Services. Equity is allocated to the segments based on regulatory capital requirements and in proportion to an assessment of the inherent risks associated with the business of the segment (including interest, credit and operating risk). The management accounting policies and processes utilized in compiling segment financial information are highly subjective and, unlike financial accounting, are not based on authoritative guidance similar to U.S. generally accepted accounting principles. As a result, reported segments and the financial information of the reported segments are not necessarily comparable with similar information reported by other financial institutions. Furthermore, changes in management structure or allocation methodologies and procedures may result in changes in previously reported segment financial data. During 2016 , certain presentation changes were made and, accordingly, 2015 results have been restated and presented on a comparable basis, except as noted above for the enhanced FTP methodology. A description of each business segment is presented below. Corporate and Commercial Specialty: The Corporate and Commercial Specialty segment serves a wide range of customers including larger businesses, developers, not-for-profits, municipalities, and financial institutions. In serving this segment we compete based on an in-depth understanding of our customers’ financial needs, the ability to match market competitive solutions to those needs, and the highest standards of relationship and service excellence in the delivery of these services. Delivery of services is provided through our corporate and commercial units, our commercial real estate unit, as well as our specialized industries and commercial financial services units. Within this segment we provide the following products and services: (1) lending solutions, such as commercial loans and lines of credit, commercial real estate financing, construction loans, letters of credit, leasing, asset based lending, and, for our larger clients, loan syndications; (2) deposit and cash management solutions such as commercial checking and interest-bearing deposit products, cash vault and night depository services, liquidity solutions, payables and receivables solutions, and information services, and (3) specialized financial services such as interest rate risk management, foreign exchange solutions, and commodity hedging. Community, Consumer, and Business: The Community, Consumer, and Business segment serves individuals, as well as small and mid-sized businesses. In serving this segment we compete based on providing a broad range of solutions to meet the needs of our customers in their entire financial lifecycle, convenient access to our services through multiple channels such as branches, phone based services, online and mobile banking, and a relationship based business model which assists our customers in navigating any changes and challenges in their financial circumstances. Delivery of services is provided through our various consumer banking, community banking, and private client units. Within this segment we provide the following products and services: (1) lending solutions such as residential mortgages, home equity loans and lines of credit, personal and installment loans, real estate financing, business loans, and business lines of credit; (2) deposit and transactional solutions such as checking, credit, debit and pre-paid cards, online banking and bill pay, and money transfer services; (3) investable funds solutions such as savings, money market deposit accounts, IRA accounts, certificates of deposit, fixed and variable annuities, full-service, discount and on-line investment brokerage; investment advisory services; trust and investment management accounts; (4) insurance and benefits related products and services; and (5) fiduciary services such as administration of pension, profit-sharing and other employee benefit plans, fiduciary and corporate agency services, and institutional asset management. Risk Management and Shared Services: The Risk Management and Shared Services segment includes Corporate Risk Management, Credit Administration, Finance, Treasury, Operations and Technology, which are key shared functions. The segment also includes Parent Company activity, intersegment eliminations and residual revenue and expenses, representing the difference between actual amounts incurred and the amounts allocated to operating segments, including interest rate risk residuals (FTP mismatches) and credit risk and provision residuals (long term credit charge mismatches). The earning assets within this segment include the Corporation’s investment portfolio, and capital includes both allocated and any remaining unallocated capital. Information about the Corporation’s segments is presented below. Segment Income Statement Data Corporate and Commercial Specialty Community, Consumer, and Business Risk Management and Shared Services Consolidated Total For the Years Ended December 31, ($ in Thousands) 2017 Net interest income $ 357,051 $ 361,361 $ 22,808 $ 741,220 Noninterest income 52,297 266,250 14,133 332,680 Total revenue 409,348 627,611 36,941 1,073,900 Credit provision (a) 42,298 20,400 (36,698 ) 26,000 Noninterest expense 156,890 490,908 61,335 709,133 Income before income taxes 210,160 116,303 12,304 338,767 Income tax expense (benefit) 71,655 40,706 (2,858 ) 109,503 Net income $ 138,505 $ 75,597 $ 15,162 $ 229,264 Return on average allocated capital (ROCET1) (b) 12.4 % 12.9 % 1.4 % 10.4 % 2016 Net interest income $ 328,603 $ 350,551 $ 28,119 $ 707,273 Noninterest income 47,776 277,942 27,165 352,883 Total revenue 376,379 628,493 55,284 1,060,156 Credit provision (a) 50,397 24,185 (4,582 ) 70,000 Noninterest expense 148,493 502,285 51,782 702,560 Income before income taxes 177,489 102,023 8,084 287,596 Income tax expense (benefit) 59,261 35,708 (7,647 ) 87,322 Net income $ 118,228 $ 66,315 $ 15,731 $ 200,274 Return on average allocated capital (ROCET1) (b) 11.0 % 10.5 % 2.8 % 9.9 % 2015 Net interest income $ 310,072 $ 349,134 $ 17,072 $ 676,278 Noninterest income 46,742 265,503 17,112 329,357 Total revenue 356,814 614,637 34,184 1,005,635 Credit provision (a) 41,913 25,614 (30,027 ) 37,500 Noninterest expense 141,912 492,284 64,151 698,347 Income before income taxes 172,989 96,739 60 269,788 Income tax expense 59,200 33,859 (11,572 ) 81,487 Net income $ 113,789 $ 62,880 $ 11,632 $ 188,301 Return on average allocated capital (ROCET1) (b) 11.6 % 9.8 % 2.1 % 9.9 % Segment Balance Sheet Data Corporate and Commercial Specialty Community, Consumer, and Business Risk Management and Shared Services Consolidated Total ($ in Thousands) Average Balances 2017 Average earning assets $ 10,820,998 $ 9,456,549 $ 6,722,337 $ 26,999,884 Average loans 10,811,827 9,452,253 328,303 20,592,383 Average deposits 6,938,913 11,711,407 3,273,282 21,923,602 Average allocated capital (CET1) (b) $ 1,117,761 $ 586,417 $ 405,281 $ 2,109,459 2016 Average earning assets $ 10,178,813 $ 9,309,028 $ 6,538,820 $ 26,026,661 Average loans 10,169,300 9,307,723 173,644 19,650,667 Average deposits 5,904,238 11,451,759 3,649,775 21,005,772 Average allocated capital (CET1) (b) $ 1,070,598 $ 629,540 $ 240,253 $ 1,940,391 2015 Average earning assets $ 9,383,971 $ 8,810,015 $ 6,377,101 $ 24,571,087 Average loans 9,374,191 8,809,673 68,400 18,252,264 Average deposits 5,856,530 10,898,602 3,147,955 19,903,087 Average allocated capital (CET1) (b) $ 977,406 $ 640,181 $ 216,010 $ 1,833,597 (a) The consolidated credit provision is equal to the actual reported provision for credit losses. (b)

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The following table summarizes the components of accumulated other comprehensive income (loss) at December 31, 2017 , 2016 , and 2015 , changes during the years then ended, and reclassifications out of accumulated other comprehensive income (loss) during the years ended December 31, 2017 , 2016 , and 2015 , respectively. Investments Securities Available For Sale Defined Benefit Pension and Postretirement Obligations Accumulated Other Comprehensive Income (Loss) ($ in Thousands) Balance, December 31, 2014 $ 18,512 $ (23,362 ) $ (4,850 ) Other comprehensive income (loss) before reclassifications (20,439 ) (17,892 ) (38,331 ) Amounts reclassified from accumulated other comprehensive income (loss) Investment securities gain (loss), net (8,133 ) — (8,133 ) Personnel expense — 2,306 2,306 Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities) (555 ) — (555 ) Income tax (expense) benefit 11,074 5,873 16,947 Net other comprehensive income (loss) during period (18,053 ) (9,713 ) (27,766 ) Balance, December 31, 2015 $ 459 $ (33,075 ) $ (32,616 ) Other comprehensive income (loss) before reclassifications (17,900 ) (6,141 ) (24,041 ) Amounts reclassified from accumulated other comprehensive income (loss) Investment securities gain (loss), net (9,316 ) — (9,316 ) Personnel expense — 3,801 3,801 Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities) (5,887 ) — (5,887 ) Income tax (expense) benefit 12,565 815 13,380 Net other comprehensive income (loss) during period (20,538 ) (1,525 ) (22,063 ) Balance, December 31, 2016 $ (20,079 ) $ (34,600 ) $ (54,679 ) Other comprehensive income (loss) before reclassifications (27,040 ) 14,273 (12,767 ) Amounts reclassified from accumulated other comprehensive income (loss) Personnel expense — 2,134 2,134 Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities) (2,665 ) — (2,665 ) Income tax (expense) benefit 11,331 (6,112 ) 5,219 Net other comprehensive income (loss) during period (18,374 ) 10,295 (8,079 ) Balance, December 31, 2017 $ (38,453 ) $ (24,305 ) $ (62,758 )

Recent Development Recent Devel

Recent Development Recent Development Details (Notes)	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	Note 23 Recent Developments On February 1, 2018, the Corporation acquired Bank Mutual Corporation ("Bank Mutual") pursuant to an Agreement and Plan of Merger, dated as of July 20, 2017 (the "Merger Agreement"), under which Bank Mutual merged with and into the Corporation. Under the terms of the Merger Agreement, Bank Mutual’s shareholders received 0.422

Summary of Significant Accoun32

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Business and Basis of Financial Statement Presentation	Business Associated Banc-Corp (individually referred to herein as the "Parent Company" and together with all of its subsidiaries and affiliates, collectively referred to herein as the "Corporation") is a bank holding company headquartered in Wisconsin. The Corporation provides a full range of banking and related financial services to consumer and commercial customers through its network of bank and nonbank subsidiaries. The Corporation is subject to competition from other financial and non-financial institutions that offer similar or competing products and services. The Corporation is regulated by federal and state agencies and is subject to periodic examinations by those agencies. Basis of Financial Statement Presentation The consolidated financial statements include the accounts of the Parent Company and its wholly-owned subsidiaries. Investments in unconsolidated entities (none of which are considered to be variable interest entities in which the Corporation is the primary beneficiary) are accounted for using the cost method of accounting when the Corporation has determined that the cost method is appropriate. Investments not meeting the criteria for cost method accounting are accounted for using the equity method of accounting. Investments in unconsolidated entities are included in other assets, and the Corporation’s share of income or loss is recorded in other noninterest income, while distributions in excess of the investment are recorded in gain on assets. All significant intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	In preparing the consolidated financial statements, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and revenues and expenses for the period. Actual results could differ significantly from those estimates. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, goodwill impairment assessment, mortgage servicing rights valuation, and income taxes. Management has evaluated subsequent events for potential recognition or disclosure.
Investment Securities	Investment Securities Securities are classified as held to maturity or available for sale at the time of purchase. Investment securities classified as held to maturity, which management has the positive intent and ability to hold to maturity, are reported at amortized cost. Investment securities classified as available for sale, which management has the intent and ability to hold for an indefinite period of time, but not necessarily to maturity, are carried at fair value, with unrealized gains and losses, net of related deferred income taxes, included in stockholders’ equity as a separate component of other comprehensive income. Any decision to sell investment securities available for sale would be based on various factors, including, but not limited to, asset / liability management strategies, changes in interest rates or prepayment risks, liquidity needs, or regulatory capital considerations. Realized gains or losses on investment security sales (using specific identification method) are included in investment securities gains (losses), net, in the consolidated statements of income. Premiums and discounts are amortized or accreted into interest income over the estimated life (earlier of call date, maturity, or estimated life) of the related security, using a prospective method that approximates level yield. In certain situations, management may elect to transfer certain investment securities from the available for sale classification to the held to maturity classification. In such cases, the investment securities are reclassified at fair value at the time of transfer. Any unrealized gain or loss included in accumulated other comprehensive income (loss) at the time of transfer is retained therein and amortized over the remaining life of the investment security as an adjustment to yield. Declines in the fair value of investment securities (with certain exceptions for debt securities noted below) that are deemed to be other-than-temporary are charged to earnings as a realized loss, and a new cost basis for the investment security is established. In evaluating other-than-temporary impairment, management considers the length of time and extent to which the security has been in an unrealized loss position, changes in security ratings, the financial condition and near-term prospects of the issuer, as well as security and industry specific economic conditions. In addition, the Corporation considers the intent and ability to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value in the near term. Declines in the fair value of debt securities below amortized cost are deemed to be other-than-temporary in circumstances where: (1) the Corporation has the intent to sell a security; (2) it is more likely than not that the Corporation will be required to sell the security before recovery of its amortized cost basis; or (3) the Corporation does not expect to recover the entire amortized cost basis of the security. If the Corporation intends to sell a security or if it is more likely than not that the Corporation will be required to sell the security before recovery, an other-than-temporary impairment write-down is recognized in earnings equal to the difference between the security’s amortized cost basis and its fair value. If an entity does not intend to sell the security or it is more likely than not that it will not be required to sell the security before recovery, the other-than-temporary impairment write-down is separated into an amount representing credit loss, which is recognized in earnings, and an amount related to all other factors, which is recognized in other comprehensive income. Declines in value determined to be other-than-temporary are included in investment securities gains (losses), net, in the consolidated statements of income. See Note 3
Federal Home Loan Bank (FHLB) and Federal Reserve Bank Stocks	Federal Home Loan Bank (“FHLB”) and Federal Reserve Bank Stocks The Corporation is required to maintain Federal Reserve stock and FHLB stock as a member of both the Federal Reserve System and the FHLB, and in amounts as required by these institutions. These equity securities are “restricted” in that they can only be sold back to the respective institutions or another member institution at par. Therefore, they are less liquid than other marketable equity securities and their fair value is equal to amortized cost. See Note 3
Loans Held for Sale	Loans Held for Sale Residential Loans Held for Sale: Loans held for sale, which consist generally of current production of certain fixed-rate, first-lien residential mortgage loans, are now carried at estimated fair value. Effective January 1, 2017, management elected the fair value option to account for all newly originated mortgage loans held for sale which results in the financial impact of changing market conditions being reflected currently in earnings as opposed to being dependent upon the timing of sales. The estimated fair value was based on what secondary markets are currently offering for portfolios with similar characteristics, which the Corporation classifies as a Level 2 fair value measurement. Commercial Loans Held for Sale:
Loans	Loans Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off are reported at their outstanding principal balances, net of any deferred fees and costs on originated loans. Origination fee income received on loans and amounts representing the estimated direct costs of origination are deferred and amortized to interest income over the life of the loan using the effective interest method. An allowance for loan losses is established for estimated credit losses in the loan portfolio. See Allowance for Loan Losses below for further policy discussion. Nonaccrual Loans: Management considers a loan to be impaired when it is probable that the Corporation will be unable to collect all amounts due according to the original contractual terms of the note agreement, including both principal and interest. This determination is based on management's review of current information and other events regarding the borrowers’ ability to repay their obligations. Management has determined that commercial and consumer loan relationships that have nonaccrual status or have had their terms restructured in a troubled debt restructuring meet this impaired loan definition. Interest income on loans is based on the principal balance outstanding computed using the effective interest method. The accrual of interest income for commercial loans is discontinued when there is a clear indication that the borrower’s cash flow may not be sufficient to meet payments as they become due, while the accrual of interest income for consumer loans is discontinued when loans reach specific delinquency levels. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Loans are generally placed on nonaccrual status when contractually past due 90 days or more as to interest or principal payments, unless the loan is well secured and in the process of collection. Additionally, whenever management becomes aware of facts or circumstances that may adversely impact the collectability of principal or interest on loans, it is management’s practice to place such loans on a nonaccrual status immediately, rather than delaying such action until the loans become 90 days past due. When a loan is placed on nonaccrual status, previously accrued and uncollected interest is reversed, amortization of related deferred loan fees or costs is suspended, and income is recorded only to the extent that interest payments are subsequently received in cash and a determination has been made that the principal and interest of the loan is collectible. If collectability of the principal and interest is in doubt, payments received are applied to loan principal. While a loan is in nonaccrual status, some or all of the cash interest payments received may be treated as interest income on a cash basis as long as the remaining recorded investment in the loan (i.e., after charge off of identified losses, if any) is deemed to be fully collectible. The determination as to the ultimate collectability of the loan's remaining recorded investment must be supported by a current, well documented credit evaluation of the borrower’s financial condition and prospects for repayment, including consideration of the borrower’s sustained historical repayment performance and other relevant factors. A nonaccrual loan is returned to accrual status when all delinquent principal and interest payments become current in accordance with the terms of the loan agreement, the borrower has demonstrated a period of sustained repayment performance, and the ultimate collectability of the total contractual principal and interest is no longer in doubt. A sustained period of repayment performance generally would be a minimum of six months. See Note 4
Troubled Debt Restructurings (Restructured Loans)	Troubled Debt Restructurings (“Restructured Loans”): Loans are considered restructured loans if concessions have been granted to borrowers that are experiencing financial difficulty. The concessions granted generally involve the modification of terms of the loan, such as changes in payment schedule or interest rate, which generally would not otherwise be considered. Restructured loans can involve loans remaining on nonaccrual, moving to nonaccrual, or continuing on accrual status, depending on the individual facts and circumstances of the borrower. Nonaccrual restructured loans are included and treated with all other nonaccrual loans. In addition, all accruing restructured loans are reported as troubled debt restructurings, which are considered and accounted for as impaired loans. Generally, restructured loans remain on nonaccrual until the customer has attained a sustained period of repayment performance under the modified loan terms (generally a minimum of six months). However, performance prior to the restructuring, or significant events that coincide with the restructuring, are considered in assessing whether the borrower can meet the new terms and whether the loan should be returned to or maintained on accrual status. If the borrower’s ability to meet the revised payment schedule is not reasonably assured, the loan remains on nonaccrual status. See Note 4
Allowance for Loan Losses	Allowance for Loan Losses: The allowance for loan losses is a reserve for estimated credit losses on individually evaluated loans determined to be impaired as well as estimated credit losses inherent in the loan portfolio, and is based on quarterly evaluations of the collectability and historical loss experience of loans. Actual credit losses, net of recoveries, are deducted from the allowance for loan losses. A provision for loan losses, which is a charge against earnings, is recorded to bring the allowance for loan losses to a level that, in management’s judgment, is appropriate to absorb probable losses in the loan portfolio. The methodology applied by the Corporation, designed to assess the appropriateness of the allowance for loan losses, is based upon management’s ongoing review and grading of the loan portfolio into criticized loan categories (defined as specific loans warranting either specific allocation, or a criticized status of special mention, substandard, doubtful, or loss). The methodology also focuses on evaluation of several factors, including but not limited to: evaluation of facts and issues related to specific loans, management’s ongoing review and grading of the loan portfolio, consideration of historical loan loss and delinquency experience on each portfolio category, trends in past due and nonaccrual loans, the level of potential problem loans, the risk characteristics of the various classifications of loans, changes in the size and character of the loan portfolio, concentrations of loans to specific borrowers or industries, existing economic conditions, the fair value of underlying collateral, and other qualitative and quantitative factors which could affect potential credit losses. Because each of the criteria used is subject to change, the analysis of the allowance for loan losses is not necessarily indicative of the trend of future loan losses in any particular loan category. The total allowance for loan losses is available to absorb losses from any segment of the loan portfolio. When an individual loan is determined to be impaired, the allowance for loan losses attributable to the loan is allocated based on management’s estimate of the borrower’s ability to repay the loan given the availability of collateral, other sources of cash flows, as well as evaluation of legal options available to the Corporation. The amount of impairment is measured based upon the present value of expected future cash flows discounted at the loan’s effective interest rate, the fair value of the underlying collateral less applicable selling costs, or the observable market price of the loan. If foreclosure is probable or the loan is collateral dependent, impairment is measured using the fair value of the loan’s collateral, less costs to sell. Large groups of homogeneous loans, such as residential mortgage, home equity, and other consumer, are collectively evaluated for impairment. Management believes that the level of the allowance for loan losses is appropriate. While management uses currently available information to recognize losses on loans, future adjustments to the allowance for loan losses may be necessary based on newly received appraisals, updated commercial customer financial statements, rapidly deteriorating cash flow, and changes in economic conditions that affect our customers. In addition, various regulatory agencies, as an integral part of their examination process, periodically review the Corporation’s allowance for loan losses. Such agencies may require additions to the allowance for loan losses or may require that certain loan balances be charged off or downgraded into criticized loan categories when their credit evaluations differ from those of management based on their judgments about information available to them at the time of their examinations. See Loans and Troubled Debt Restructurings above for further policy discussion and see Note 4
Other Real Estate Owned	Other Real Estate Owned Other real estate owned is included in other assets in the consolidated balance sheets and is comprised of property acquired through a foreclosure proceeding or acceptance of a deed-in-lieu of foreclosure, and loans classified as in-substance foreclosure. Other real estate owned is recorded at the fair value of the underlying property collateral, less estimated selling costs. This fair value becomes the new cost basis for the foreclosed asset. The initial write-down, if any, will be recorded as a charge off against the
Reserve for Unfunded Commitments	Allowance for Unfunded Commitments The allowance for unfunded commitments is maintained at a level believed by management to be sufficient to absorb estimated probable losses related to unfunded credit facilities (including unfunded loan commitments and letters of credit) and is included in accrued expenses and other liabilities in the consolidated balance sheets. The determination of the appropriate level of the allowance for unfunded commitments is based upon an evaluation of the unfunded credit facilities, including an assessment of historical commitment utilization experience and credit risk grading of the loan. Net adjustments to the allowance for unfunded commitments are included in the provision for credit losses in the consolidated statements of income. See Note 4 and Note 16
Mortgage Repurchase Reserve	Mortgage Repurchase Reserve The Corporation sells residential mortgage loans to investors in the normal course of business. Residential mortgage loans sold to investors are predominantly conventional residential first lien mortgages originated under the usual underwriting procedures, and are most often sold on a nonrecourse basis, primarily to the Government Sponsored Enterprises ("GSE"). The Corporation’s agreements to sell residential mortgage loans usually require certain representations and warranties on the underlying loans sold, related to credit information, loan documentation, collateral, and insurability, which if subsequently untrue or breached, could require the Corporation to indemnify or repurchase certain loans affected. To a much lesser degree, the Corporation may sell residential mortgage loans with limited recourse (limited in that the recourse period ends prior to the loan’s maturity, usually after certain time and / or loan paydown criteria have been met), whereby indemnification or repurchase could be required if the loan had defined delinquency issues during the limited recourse periods. The balance in the repurchase reserve at the balance sheet date reflects the estimated amount of potential loss the Corporation could incur from repurchasing a loan (“put back” requests), as well as loss reimbursements, indemnification, and other settlement resolutions (“make whole” payments). See Note 16
Premises and Equipment and Software	Premises and Equipment and Software Premises and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization are computed on the straight-line method over the estimated useful lives of the related assets or the lease term. Maintenance and repairs are charged to expense as incurred, while additions or major improvements are capitalized and depreciated over the estimated useful lives. Leasehold improvements are amortized on a straight-line basis over the lesser of the lease terms or the estimated useful lives of the improvements. Software, included in other assets in the consolidated balance sheets, is amortized on a straight-line basis over the lesser of the contract terms or the estimated useful life of the software. See Note 6
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill and Other Intangible Assets: The excess of the cost of an acquisition over the fair value of the net assets acquired consists primarily of goodwill, core deposit intangibles, and other identifiable intangibles (primarily related to customer relationships acquired). Core deposit intangibles have estimated finite lives and are amortized on an accelerated basis to expense over a 10 -year period. The other intangibles have estimated finite lives and are amortized on an accelerated basis to expense over their weighted average life (a weighted average life of 11 years for 2017 and 12 years for 2016 ). The Corporation reviews long-lived assets and certain identifiable intangibles for impairment at least annually, or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, in which case an impairment charge would be recorded. Goodwill is not amortized but, instead, is subject to impairment tests on at least an annual basis, and more frequently if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. The impairment testing process is conducted by assigning net assets and goodwill to each reporting unit. An initial qualitative evaluation is made to assess the likelihood of impairment and determine whether further quantitative testing to calculate the fair value is necessary. When the qualitative evaluation indicates that impairment is more likely than not, quantitative testing is required whereby the fair value of each reporting unit is calculated and compared to the recorded book value, “step one.” If the calculated fair value of the reporting unit exceeds its carrying value, goodwill is not considered impaired and “step two” is not considered necessary. If the carrying value of a reporting unit exceeds its calculated fair value, the impairment test continues (“step two”) by comparing the carrying value of the reporting unit’s goodwill to the implied fair value of goodwill. The implied fair value is computed by adjusting all assets and liabilities of the reporting unit to current fair value with the offset adjustment to goodwill. The adjusted goodwill balance is the implied fair value of the goodwill. An impairment charge is recognized if the carrying value of goodwill exceeds the implied fair value of goodwill. See Note 5 for additional information on goodwill and other intangible assets. Mortgage Servicing Rights: The Corporation sells residential mortgage loans in the secondary market and typically retains the right to service the loans sold. Upon sale, a mortgage servicing rights asset is capitalized, which represents the then current fair value of future net cash flows expected to be realized for performing servicing activities. Mortgage servicing rights, when purchased, are initially recorded at fair value. As the Corporation has not elected to subsequently measure any class of servicing assets under the fair value measurement method, the Corporation follows the amortization method. Mortgage servicing rights are amortized in proportion to and over the period of estimated net servicing income, and assessed for impairment at each reporting date. Mortgage servicing rights are carried at the lower of the initial capitalized amount, net of accumulated amortization, or estimated fair value, in the consolidated balance sheets. The Corporation periodically evaluates its mortgage servicing rights asset for impairment. Impairment is assessed based on fair value at each reporting date using estimated prepayment speeds of the underlying mortgage loans serviced and stratifications based on the risk characteristics of the underlying loans (predominantly loan type and note interest rate). As mortgage interest rates fall, prepayment speeds are usually faster and the value of the mortgage servicing rights asset generally decreases, requiring additional valuation reserve. Conversely, as mortgage interest rates rise, prepayment speeds are usually slower and the value of the mortgage servicing rights asset generally increases, requiring less valuation reserve. A valuation allowance is established, through a charge to earnings, to the extent the amortized cost of the mortgage servicing rights exceeds the estimated fair value by stratification. If it is later determined that all or a portion of the temporary impairment no longer exists for a stratification, the valuation is reduced through a recovery to earnings. An other-than-temporary impairment (i.e., recoverability is considered remote when considering interest rates and loan pay off activity) is recognized as a write-down of the mortgage servicing rights asset and the related valuation allowance (to the extent a valuation allowance is available) and then against earnings. A direct write-down permanently reduces the carrying value of the mortgage servicing rights asset and valuation allowance, precluding subsequent recoveries. See Note 5
Income Taxes	Income Taxes Amounts provided for income tax expense are based on income reported for financial statement purposes and do not necessarily represent amounts currently payable under tax laws. Deferred income taxes, which arise principally from temporary differences between the amounts reported in the financial statements and the tax bases of assets and liabilities, are included in the amounts provided for income taxes. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income and tax planning strategies which will create taxable income during the periods in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities, the amount of taxes paid in available carryback years, projected future taxable income, and, if necessary, tax planning strategies in making this assessment. The Corporation files a consolidated federal income tax return and separate or combined state income tax returns. Accordingly, amounts equal to tax benefits of those subsidiaries having taxable federal or state losses or credits are offset by other subsidiaries that incur federal or state tax liabilities. It is the Corporation’s policy to provide for uncertainty in income taxes as a part of income tax expense based upon management’s assessment of whether a tax benefit is more likely than not to be sustained upon examination by tax authorities. At December 31, 2017 and 2016 , the Corporation believes it has appropriately accounted for any unrecognized tax benefits. To the extent the Corporation prevails in matters for which a liability for an unrecognized tax benefit was established or is required to pay amounts in excess of the liability established, the Corporation’s effective tax rate in a given financial statement period may be impacted. See Note 13
Derivative and Hedging Activities	Derivative and Hedging Activities Derivative instruments, including derivative instruments embedded in other contracts, are carried at fair value on the consolidated balance sheets with changes in the fair value recorded to earnings or accumulated other comprehensive income, as appropriate. On the date the derivative contract is entered into, the Corporation designates the derivative as a fair value hedge (i.e., a hedge of the fair value of a recognized asset or liability), a cash flow hedge (i.e., a hedge of the variability of cash flows to be received or paid related to a recognized asset or liability), or a free-standing derivative instrument. For a derivative designated as a fair value hedge, the changes in the fair value of the derivative instrument and the changes in the fair value of the hedged asset or liability are recognized in current period earnings as an increase or decrease to the carrying value of the hedged item on the balance sheet and in the related income statement account. For a derivative designated as a cash flow hedge, the effective portions of changes in the fair value of a derivative instrument are recorded in other comprehensive income and the ineffective portions of changes in the fair value of a derivative instrument are recognized in current period earnings as an adjustment to the related income statement account. Amounts within accumulated other comprehensive income are reclassified into earnings in the period the hedged item affects earnings. For a derivative designated as a free-standing derivative instrument, changes in fair value are reported in current period earnings. At December 31, 2017 and 2016 , the Corporation only had free-standing derivative instruments to facilitate customer borrowing activity. These free-standing derivative instruments included: interest rate risk management, commodity hedging, and foreign currency exchange solutions. See Note 14 for additional information on derivative and hedging activities.
Retirement Plan	Retirement Plans The funded status of the retirement plans are recognized as an asset or liability in the consolidated balance sheets, and changes in that funded status are recognized in the year in which the changes occur through other comprehensive income. Plan assets and benefit obligations are measured as of fiscal year end. The measurement of the projected benefit obligation and pension expense involve actuarial valuation methods and the use of various actuarial and economic assumptions. The Corporation monitors the assumptions and updates them periodically. Due to the long-term nature of the pension plan obligation, actual results may differ significantly from estimations. Such differences are adjusted over time as the assumptions are replaced by facts and values are recalculated. See Note 12
Stock-Based Compensation	Stock-Based Compensation The fair value of stock options granted is estimated on the date of grant using a Black-Scholes option pricing model, while the fair value of restricted common stock awards is their fair market value on the date of grant. The fair values of stock options and restricted stock awards are amortized as compensation expense on a straight-line basis over the vesting period of the grants. Expenses related to stock options and restricted stock awards are fully recognized on the date the colleague meets the definition of normal or early retirement. Compensation expense recognized is included in personnel expense in the consolidated statements of income. See Note 11
Comprehensive Income	Comprehensive Income Comprehensive income includes all changes in stockholders’ equity during a period, except those resulting from transactions with stockholders. In addition to net income, other components of the Corporation’s comprehensive income include the after tax effect of changes in net unrealized gain / loss on securities available for sale and changes in net actuarial gain / loss on defined benefit postretirement plans. Comprehensive income is reported in the accompanying consolidated statements of changes in stockholder’s equity and consolidated statements of comprehensive income. See Note 22
Fair Value Measurements	Fair Value Measurements Fair value represents the estimated price at which an orderly transaction to sell an asset or to transfer a liability would take place between market participants at the measurement date under current market conditions (i.e., an exit price concept). As there is no active market for many of the Corporation’s financial instruments, estimates are made using discounted cash flow or other valuation techniques. Inputs into the valuation methods are subjective in nature, involve uncertainties, and require significant judgment and therefore cannot be determined with precision. Accordingly, the derived fair value estimates presented herein are not necessarily indicative of the amounts the Corporation could realize in a current market exchange. Assets and liabilities are categorized into three levels based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy in which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Corporation’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the asset or liability. See Note 18 for additional information on fair value measurements. Below is a brief description of each fair value level. Level 1 — Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities that the Corporation has the ability to access. Level 2 — Level 2 inputs are inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates, foreign exchange rates, and yield curves that are observable at commonly quoted intervals.
Cash and Cash Equivalents	Cash and Cash EquivalentsFor purposes of the consolidated statements of cash flows, cash and cash equivalents are considered to include cash and due from banks, interest-bearing deposits in other financial institutions, federal funds sold and securities purchased under agreements to resell.
Earnings Per Common Share	Earnings Per Common Share Earnings per common share are calculated utilizing the two-class method. Basic earnings per common share are calculated by dividing the sum of distributed earnings to common shareholders and undistributed earnings allocated to common shareholders by the weighted average number of common shares outstanding. Diluted earnings per common share are calculated by dividing the sum of distributed earnings to common shareholders and undistributed earnings allocated to common shareholders by the weighted average number of common shares outstanding adjusted for the dilutive effect of common stock awards (outstanding stock options and unvested restricted stock awards) and common stock warrants. See Note 20
Fair Value of Financial Instruments	Accounting Policy Election Effective January 1, 2017, residential mortgage loans that are classified as held for sale are accounted using the fair value option method of accounting. Management has elected the fair value option to mitigate accounting mismatches between held for sale loan valuations and corresponding derivative commitments. Prior to January 1, 2017, residential mortgage loans that were classified as held for sale were accounted for at the lower of cost or market method of accounting.
New Accounting Pronouncements Adopted	New Accounting Pronouncements Adopted Standard Description Date of adoption Effect on financial statements ASU 2017-08 Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities The FASB issued amendments to require that certain purchased callable debt securities held at a premium be amortized to the earliest call date. The amendments do not require an accounting change for securities held at a discount, which continue to be amortized to maturity. 1st Quarter 2017 The Corporation early adopted the accounting standard with no material impact on results of operations, financial position, or liquidity. ASU 2017-03 Accounting Changes and Error Corrections (Topic 250) and Investments - Equity Method and Joint Ventures (Topic 323) The FASB issues amendments to require, for ASUs that have not been adopted yet, registrants to determine the potential effects (if material) of those ASUs on their financial statements when adopted and include the appropriate disclosures in the financial statements. If the impact of adoption is unknown or cannot be estimated, a registrant should include a statement noting this and consider adding qualitative disclosures to the financial statements to assist the reader in evaluating the impact of the ASUs, when adopted, on the financial statements. 1st Quarter 2017 No material impact on results of operations, financial position, or liquidity. ASU 2016-17 Consolidation (Topic 810): Interests Held through Related Parties That Are Under Common Control The FASB issued an amendment to address how a reporting entity that is a single decision maker of a variable interest entity treats indirect interests in the entity held through related parties that are under common control with the reporting entity. 1st Quarter 2017 No material impact on results of operations, financial position, or liquidity. ASU 2016-07 Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting The FASB issued an amendment to eliminate the requirement that when an investment qualifies for use of the equity method as a result of an increase in the level of ownership interest or degree of influence, an investor must adjust the investment, results of operations, and retained earnings retroactively on a step-by-step basis as if the equity method had been in effect during all previous periods that the investment had been held. The amendment requires that the equity method investor add the cost of acquiring the additional interests in the investee to the current basis of the investor’s previously held interest and adopt the equity method of accounting as of the date the investment becomes qualified for equity method accounting. Therefore, upon qualifying for the equity method of accounting, no retroactive adjustment of the investment is required. The amendment requires that an entity that has an available-for-sale equity security that becomes qualified for the equity method of accounting recognize through earnings the unrealized holding gain or loss in accumulated other comprehensive income at the date the investment becomes qualified for use of the equity method. Entities should apply the amendment prospectively to increases in the level of ownership interest or degree of influence that result in the adoption of the equity method. 1st Quarter 2017 No material impact on results of operations, financial position, or liquidity.

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investment securities available for sale	December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value ($ in Thousands) Investment securities available for sale U.S. Treasury securities $ 1,003 $ — $ (7 ) $ 996 Residential mortgage-related securities FNMA / FHLMC 457,680 9,722 (2,634 ) 464,768 GNMA 1,944,453 275 (31,378 ) 1,913,350 Private-label 1,067 — (8 ) 1,059 GNMA commercial mortgage-related securities 1,547,173 5 (33,901 ) 1,513,277 FFELP asset backed securities 144,322 867 (13 ) 145,176 Other securities (debt and equity) 4,719 127 (26 ) 4,820 Total investment securities available for sale $ 4,100,417 $ 10,996 $ (67,967 ) $ 4,043,446 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) $ 1,281,320 $ 13,899 $ (3,177 ) $ 1,292,042 Residential mortgage-related securities FNMA / FHLMC 40,995 398 (489 ) 40,904 GNMA 414,440 2,700 (6,400 ) 410,740 GNMA commercial mortgage-related securities 546,098 9,546 (15,756 ) 539,888 Total investment securities held to maturity $ 2,282,853 $ 26,543 $ (25,822 ) $ 2,283,574 December 31, 2016 Amortized Gross Gross Fair Value ($ in Thousands) Investment securities available for sale U.S. Treasury securities $ 1,000 $ — $ — $ 1,000 Residential mortgage-related securities: FNMA / FHLMC 625,234 17,298 (2,602 ) 639,930 GNMA 2,028,301 1,372 (25,198 ) 2,004,475 Private-label 1,134 1 (14 ) 1,121 GNMA commercial mortgage-related securities 2,064,508 356 (35,966 ) 2,028,898 Other securities (debt and equity) 4,718 105 (21 ) 4,802 Total investment securities available for sale $ 4,724,895 $ 19,132 $ (63,801 ) $ 4,680,226 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) $ 1,145,843 $ 3,868 $ (12,036 ) $ 1,137,675 Residential mortgage-related securities FNMA / FHLMC 37,697 439 (693 ) 37,443 GNMA 89,996 216 (656 ) 89,556 Total investment securities held to maturity $ 1,273,536 $ 4,523 $ (13,385 ) $ 1,264,674
Investment securities held to maturity	December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value ($ in Thousands) Investment securities available for sale U.S. Treasury securities $ 1,003 $ — $ (7 ) $ 996 Residential mortgage-related securities FNMA / FHLMC 457,680 9,722 (2,634 ) 464,768 GNMA 1,944,453 275 (31,378 ) 1,913,350 Private-label 1,067 — (8 ) 1,059 GNMA commercial mortgage-related securities 1,547,173 5 (33,901 ) 1,513,277 FFELP asset backed securities 144,322 867 (13 ) 145,176 Other securities (debt and equity) 4,719 127 (26 ) 4,820 Total investment securities available for sale $ 4,100,417 $ 10,996 $ (67,967 ) $ 4,043,446 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) $ 1,281,320 $ 13,899 $ (3,177 ) $ 1,292,042 Residential mortgage-related securities FNMA / FHLMC 40,995 398 (489 ) 40,904 GNMA 414,440 2,700 (6,400 ) 410,740 GNMA commercial mortgage-related securities 546,098 9,546 (15,756 ) 539,888 Total investment securities held to maturity $ 2,282,853 $ 26,543 $ (25,822 ) $ 2,283,574 December 31, 2016 Amortized Gross Gross Fair Value ($ in Thousands) Investment securities available for sale U.S. Treasury securities $ 1,000 $ — $ — $ 1,000 Residential mortgage-related securities: FNMA / FHLMC 625,234 17,298 (2,602 ) 639,930 GNMA 2,028,301 1,372 (25,198 ) 2,004,475 Private-label 1,134 1 (14 ) 1,121 GNMA commercial mortgage-related securities 2,064,508 356 (35,966 ) 2,028,898 Other securities (debt and equity) 4,718 105 (21 ) 4,802 Total investment securities available for sale $ 4,724,895 $ 19,132 $ (63,801 ) $ 4,680,226 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) $ 1,145,843 $ 3,868 $ (12,036 ) $ 1,137,675 Residential mortgage-related securities FNMA / FHLMC 37,697 439 (693 ) 37,443 GNMA 89,996 216 (656 ) 89,556 Total investment securities held to maturity $ 1,273,536 $ 4,523 $ (13,385 ) $ 1,264,674
Amortized cost and fair values of investment securities available for sale by contractual maturity	The expected maturities of investment securities available for sale and held to maturity at December 31, 2017 , are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Available for Sale Held to Maturity Amortized Cost Fair Value Amortized Cost Fair Value ($ in Thousands) Due in one year or less $ 1,001 $ 1,001 $ 50,089 $ 44,781 Due after one year through five years 4,703 4,669 226,053 229,939 Due after five years through ten years — — 322,413 324,380 Due after ten years — — 682,765 692,942 Total debt securities 5,704 5,670 1,281,320 1,292,042 Residential mortgage-related securities FNMA / FHLMC 457,680 464,768 40,995 40,904 GNMA 1,944,453 1,913,350 414,440 410,740 Private-label 1,067 1,059 — — GNMA commercial mortgage-related securities 1,547,173 1,513,277 546,098 539,888 FFELP asset backed securities 144,322 145,176 — — Equity securities 18 146 — — Total investment securities $ 4,100,417 $ 4,043,446 $ 2,282,853 $ 2,283,574 Ratio of Fair Value to Amortized Cost 98.6 % 100.0 %
Realized gains and losses and proceeds from sale	Total proceeds and gross realized gains and losses from sales of investment securities for each of the three years ended December 31 were as follows. There were no other-than-temporary impairment write-downs on investment securities for 2017 , 2016 , or 2015 . 2017 2016 2015 ($ in Thousands) Gross gains on available for sale securities $ — $ 9,485 $ 12,270 Gross gains on held to maturity securities 439 33 — Total gains 439 9,518 12,270 Gross losses on available for sale securities — (202 ) (4,137 ) Gross losses on held to maturity securities (5 ) — — Total losses (5 ) (202 ) (4,137 ) Investment securities gains, net $ 434 $ 9,316 $ 8,133 Proceeds from sales of investment securities $ 18,467 $ 549,555 $ 1,601,947
Unrealized losses and fair value of available for sale and held to maturity securities, by investment category and time length	The following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time individual securities have been in a continuous unrealized loss position, at December 31, 2017 . Less than 12 months 12 months or more Total December 31, 2017 Number of Securities Unrealized Losses Fair Value Number of Securities Unrealized Losses Fair Value Unrealized Losses Fair Value ($ in Thousands) Investment securities available for sale U.S. Treasury securities 1 $ (7 ) $ 996 — $ — $ — $ (7 ) $ 996 Residential mortgage-related securities FNMA / FHLMC 9 (572 ) 69,939 9 (2,062 ) 142,093 (2,634 ) 212,032 GNMA 44 (8,927 ) 1,028,221 25 (22,451 ) 737,198 (31,378 ) 1,765,419 Private-label — — — 1 (8 ) 1,059 (8 ) 1,059 GNMA commercial mortgage-related securities 33 (5,554 ) 480,514 70 (28,347 ) 1,026,642 (33,901 ) 1,507,156 FFELP asset backed securities 1 (13 ) 12,158 — — — (13 ) 12,158 Other securities (debt and equity) 4 (26 ) 1,675 — — — (26 ) 1,675 Total 92 $ (15,099 ) $ 1,593,503 105 $ (52,868 ) $ 1,906,992 $ (67,967 ) $ 3,500,495 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) 157 $ (746 ) $ 122,761 132 $ (2,431 ) $ 127,043 $ (3,177 ) $ 249,804 Residential mortgage-related securities FNMA / FHLMC 8 (73 ) 13,143 10 (417 ) 16,262 (490 ) 29,405 GNMA 35 (3,373 ) 268,388 18 (3,026 ) 120,892 (6,399 ) 389,280 GNMA commercial mortgage-related securities 2 (299 ) 52,997 23 (15,457 ) 486,891 (15,756 ) 539,888 Total 202 $ (4,491 ) $ 457,289 183 $ (21,331 ) $ 751,088 $ (25,822 ) $ 1,208,377 For comparative purposes, the following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2016 . Less than 12 months 12 months or more Total December 31, 2016 Number Unrealized Fair Number Unrealized Fair Unrealized Fair ($ in Thousands) Investment securities available for sale Residential mortgage-related securities FNMA / FHLMC 14 $ (2,602 ) $ 244,252 — $ — $ — $ (2,602 ) $ 244,252 GNMA 54 (25,198 ) 1,723,523 — — — (25,198 ) 1,723,523 Private-label — — — 1 (14 ) 1,119 (14 ) 1,119 GNMA commercial mortgage-related securities 74 (16,445 ) 1,427,889 21 (19,521 ) 429,258 (35,966 ) 1,857,147 Other securities (debt and equity) 3 (21 ) 1,479 — — — (21 ) 1,479 Total 145 $ (44,266 ) $ 3,397,143 22 $ (19,535 ) $ 430,377 $ (63,801 ) $ 3,827,520 Investment securities held to maturity Obligations of state and political subdivisions (municipal securities) 700 $ (11,937 ) $ 414,186 4 $ (99 ) $ 1,752 $ (12,036 ) $ 415,938 Residential mortgage-related securities FNMA / FHLMC 14 (441 ) 17,477 1 (252 ) 6,031 (693 ) 23,508 GNMA 39 (656 ) 64,633 — — — (656 ) 64,633 Total 753 $ (13,034 ) $ 496,296 5 $ (351 ) $ 7,783 $ (13,385 ) $ 504,079

Loans (Tables)

Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Loan composition	Loans at December 31 are summarized below. 2017 2016 ($ in Thousands) Commercial and industrial $ 6,399,693 $ 6,489,014 Commercial real estate - owner occupied 802,209 897,724 Commercial and business lending 7,201,902 7,386,738 Commercial real estate - investor 3,315,254 3,574,732 Real estate construction 1,451,684 1,432,497 Commercial real estate lending 4,766,938 5,007,229 Total commercial 11,968,840 12,393,967 Residential mortgage 7,546,534 6,332,327 Home equity 883,804 934,443 Other consumer 385,813 393,979 Total consumer 8,816,151 7,660,749 Total loans $ 20,784,991 $ 20,054,716
Loans And Leases Receivable Related Parties	The Corporation has granted loans to its directors, executive officers, or their related interests. These loans were made on substantially the same terms, including rates and collateral, as those prevailing at the time for comparable transactions with other unrelated customers, and do not involve more than a normal risk of collection. These loans to related parties are summarized below. 2017 2016 ($ in Thousands) Balance at beginning of year $ 27,589 $ 36,597 New loans 5,329 10,677 Repayments (7,632 ) (11,089 ) Change due to status of executive officers and directors (5,026 ) (8,596 ) Balance at end of year $ 20,260 $ 27,589
Commercial and consumer loans by credit quality indicator	The following table presents commercial and consumer loans by credit quality indicator at December 31, 2017 . Pass Special Mention Potential Problem Nonaccrual Total ($ in Thousands) Commercial and industrial $ 6,015,884 $ 157,245 $ 113,778 $ 112,786 $ 6,399,693 Commercial real estate - owner occupied 723,291 14,181 41,997 22,740 802,209 Commercial and business lending 6,739,175 171,426 155,775 135,526 7,201,902 Commercial real estate - investor 3,266,389 24,845 19,291 4,729 3,315,254 Real estate construction 1,421,504 29,206 — 974 1,451,684 Commercial real estate lending 4,687,893 54,051 19,291 5,703 4,766,938 Total commercial 11,427,068 225,477 175,066 141,229 11,968,840 Residential mortgage 7,490,860 426 1,616 53,632 7,546,534 Home equity 868,958 1,137 195 13,514 883,804 Other consumer 384,990 652 — 171 385,813 Total consumer 8,744,808 2,215 1,811 67,317 8,816,151 Total loans $ 20,171,876 $ 227,692 $ 176,877 $ 208,546 $ 20,784,991 The following table presents commercial and consumer loans by credit quality indicator at December 31, 2016 . Pass Special Mention Potential Problem Nonaccrual Total ($ in Thousands) Commercial and industrial $ 5,937,119 $ 141,328 $ 227,196 $ 183,371 $ 6,489,014 Commercial real estate - owner occupied 805,871 17,785 64,524 9,544 897,724 Commercial and business lending 6,742,990 159,113 291,720 192,915 7,386,738 Commercial real estate - investor 3,491,217 14,236 51,228 18,051 3,574,732 Real estate construction 1,429,083 105 2,465 844 1,432,497 Commercial real estate lending 4,920,300 14,341 53,693 18,895 5,007,229 Total commercial 11,663,290 173,454 345,413 211,810 12,393,967 Residential mortgage 6,275,162 1,314 5,615 50,236 6,332,327 Home equity 919,740 1,588 114 13,001 934,443 Other consumer 393,161 562 — 256 393,979 Total consumer 7,588,063 3,464 5,729 63,493 7,660,749 Total loans $ 19,251,353 $ 176,918 $ 351,142 $ 275,303 $ 20,054,716
Summarized details of Loans	The following table presents loans by past due status at December 31, 2017 . Current 30-59 Days Past Due 60-89 Days Past Due 90 Days or More Past Due (a) Nonaccrual (b) Total ($ in Thousands) Commercial and industrial $ 6,286,369 $ 170 $ 101 $ 267 $ 112,786 $ 6,399,693 Commercial real estate - owner occupied 779,421 48 — — 22,740 802,209 Commercial and business lending 7,065,790 218 101 267 135,526 7,201,902 Commercial real estate - investor 3,310,000 374 — 151 4,729 3,315,254 Real estate construction 1,450,459 168 83 — 974 1,451,684 Commercial real estate lending 4,760,459 542 83 151 5,703 4,766,938 Total commercial 11,826,249 760 184 418 141,229 11,968,840 Residential mortgage 7,483,350 9,186 366 — 53,632 7,546,534 Home equity 863,465 5,688 1,137 — 13,514 883,804 Other consumer 382,186 1,227 780 1,449 171 385,813 Total consumer 8,729,001 16,101 2,283 1,449 67,317 8,816,151 Total loans $ 20,555,250 $ 16,861 $ 2,467 $ 1,867 $ 208,546 $ 20,784,991 (a) The recorded investment in loans past due 90 days or more and still accruing totaled $2 million at December 31, 2017 (the same as the reported balances for the accruing loans noted above). (b) Of the total nonaccrual loans, $135 million or 65% were current with respect to payment at December 31, 2017 . The following table presents loans by past due status at December 31, 2016 . Current 30-59 Days Past Due 60-89 Days Past Due 90 Days or More Past Due (a) Nonaccrual (b) Total ($ in Thousands) Commercial and industrial $ 6,303,994 $ 965 $ 448 $ 236 $ 183,371 $ 6,489,014 Commercial real estate - owner occupied 886,796 968 416 — 9,544 897,724 Commercial and business lending 7,190,790 1,933 864 236 192,915 7,386,738 Commercial real estate - investor 3,555,750 431 500 — 18,051 3,574,732 Real estate construction 1,431,284 264 105 — 844 1,432,497 Commercial real estate lending 4,987,034 695 605 — 18,895 5,007,229 Total commercial 12,177,824 2,628 1,469 236 211,810 12,393,967 Residential mortgage 6,273,949 7,298 844 — 50,236 6,332,327 Home equity 915,593 4,265 1,584 — 13,001 934,443 Other consumer 389,157 2,471 718 1,377 256 393,979 Total consumer 7,578,699 14,034 3,146 1,377 63,493 7,660,749 Total loans $ 19,756,523 $ 16,662 $ 4,615 $ 1,613 $ 275,303 $ 20,054,716 (a) The recorded investment in loans past due 90 days or more and still accruing totaled $2 million at December 31, 2016 (the same as the reported balances for the accruing loans noted above). (b) Of the total nonaccrual loans, $224 million or 81% were current with respect to payment at December 31, 2016
Summarized details of impaired Loans	The following table presents impaired loans individually evaluated under ASC Topic 310 at December 31, 2017 . Recorded Unpaid Related Average Interest ($ in Thousands) Loans with a related allowance Commercial and industrial $ 81,649 $ 83,579 $ 10,838 $ 58,494 $ 2,629 Commercial real estate - owner occupied 23,796 23,937 2,973 12,124 736 Commercial and business lending 105,445 107,516 13,811 70,618 3,365 Commercial real estate - investor 17,823 17,862 1,597 16,924 1,694 Real estate construction 467 578 86 484 29 Commercial real estate lending 18,290 18,440 1,683 17,408 1,723 Total commercial 123,735 125,956 15,494 88,026 5,088 Residential mortgage 40,561 42,922 6,512 40,411 1,614 Home equity 10,250 10,986 3,718 10,521 549 Other consumer 1,135 1,138 122 1,140 3 Total consumer 51,946 55,046 10,352 52,072 2,166 Total loans $ 175,681 $ 181,002 $ 25,846 $ 140,098 $ 7,254 Loans with no related allowance Commercial and industrial $ 60,595 $ 82,839 $ — $ 89,275 $ 492 Commercial real estate - owner occupied 2,438 2,829 — 1,948 36 Commercial and business lending 63,033 85,668 — 91,223 528 Commercial real estate - investor 1,295 1,295 — — 45 Real estate construction — — — — — Commercial real estate lending 1,295 1,295 — — 45 Total commercial 64,328 86,963 — 91,223 573 Residential mortgage 6,925 7,204 — 4,999 217 Home equity 641 645 — 540 7 Other consumer — — — — — Total consumer 7,566 7,849 — 5,539 224 Total loans $ 71,894 $ 94,812 $ — $ 96,762 $ 797 Total Commercial and industrial $ 142,244 $ 166,418 $ 10,838 $ 147,769 $ 3,121 Commercial real estate - owner occupied 26,234 26,766 2,973 14,072 772 Commercial and business lending 168,478 193,184 13,811 161,841 3,893 Commercial real estate - investor 19,118 19,157 1,597 16,924 1,739 Real estate construction 467 578 86 484 29 Commercial real estate lending 19,585 19,735 1,683 17,408 1,768 Total commercial 188,063 212,919 15,494 179,249 5,661 Residential mortgage 47,486 50,126 6,512 45,410 1,831 Home equity 10,891 11,631 3,718 11,061 556 Other consumer 1,135 1,138 122 1,140 3 Total consumer 59,512 62,895 10,352 57,611 2,390 Total loans (a) $ 247,575 $ 275,814 $ 25,846 $ 236,860 $ 8,051 (a) The net recorded investment (defined as recorded investment, net of the related allowance) of the impaired loans represented 80% of the unpaid principal balance at December 31, 2017 . The following table presents impaired loans individually evaluated under ASC Topic 310 at December 31, 2016 . Recorded Investment Unpaid Principal Balance Related Allowance Average Recorded Investment Interest Income Recognized ($ in Thousands) Loans with a related allowance Commercial and industrial $ 99,786 $ 105,175 $ 21,047 $ 104,808 $ 2,345 Commercial real estate - owner occupied 5,544 5,568 23 5,840 263 Commercial and business lending 105,330 110,743 21,070 110,648 2,608 Commercial real estate - investor 26,764 27,031 3,410 30,665 2,120 Real estate construction 509 648 84 529 31 Commercial real estate lending 27,273 27,679 3,494 31,194 2,151 Total commercial 132,603 138,422 24,564 141,842 4,759 Residential mortgage 37,902 39,979 6,438 38,608 1,551 Home equity 11,070 11,909 3,943 11,420 627 Other consumer 1,012 1,023 109 1,021 2 Total consumer 49,984 52,911 10,490 51,049 2,180 Total loans $ 182,587 $ 191,333 $ 35,054 $ 192,891 $ 6,939 Loans with no related allowance Commercial and industrial $ 113,485 $ 134,863 $ — $ 117,980 $ 1,519 Commercial real estate - owner occupied 8,439 9,266 — 8,759 138 Commercial and business lending 121,924 144,129 — 126,739 1,657 Commercial real estate - investor 6,144 6,478 — 7,092 — Real estate construction — — — — — Commercial real estate lending 6,144 6,478 — 7,092 — Total commercial 128,068 150,607 — 133,831 1,657 Residential mortgage 5,974 6,998 — 6,610 184 Home equity 106 107 — 107 4 Other consumer — — — — — Total consumer 6,080 7,105 — 6,717 188 Total loans $ 134,148 $ 157,712 $ — $ 140,548 $ 1,845 Total Commercial and industrial $ 213,271 $ 240,038 $ 21,047 $ 222,788 $ 3,864 Commercial real estate - owner occupied 13,983 14,834 23 14,599 401 Commercial and business lending 227,254 254,872 21,070 237,387 4,265 Commercial real estate - investor 32,908 33,509 3,410 37,757 2,120 Real estate construction 509 648 84 529 31 Commercial real estate lending 33,417 34,157 3,494 38,286 2,151 Total commercial 260,671 289,029 24,564 275,673 6,416 Residential mortgage 43,876 46,977 6,438 45,218 1,735 Home equity 11,176 12,016 3,943 11,527 631 Other consumer 1,012 1,023 109 1,021 2 Total consumer 56,064 60,016 10,490 57,766 2,368 Total loans (a) $ 316,735 $ 349,045 $ 35,054 $ 333,439 $ 8,784 (a) The net recorded investment (defined as recorded investment, net of the related allowance) of the impaired loans represented 81% of the unpaid principal balance at December 31, 2016
Nonaccrual and performing restructured loans	December 31, 2017 December 31, 2016 December 31, 2015 Performing Restructured Loans Nonaccrual Restructured Loans (a) Performing Restructured Loans Nonaccrual Restructured Loans (a) Performing Restructured Loans Nonaccrual Restructured Loans (a) ($ in Thousands) Commercial and industrial $ 30,047 $ 1,776 $ 31,884 $ 1,276 $ 29,293 $ 1,714 Commercial real estate - owner occupied 3,989 — 5,490 2,220 7,877 2,703 Commercial real estate - investor 14,389 — 15,289 924 21,915 3,936 Real estate construction 310 157 359 150 510 177 Residential mortgage 17,068 18,991 18,100 21,906 19,870 24,592 Home equity 7,705 2,537 7,756 2,877 7,069 4,522 Other consumer 1,110 25 979 32 829 40 Total restructured loans $ 74,618 $ 23,486 $ 79,857 $ 29,385 $ 87,363 $ 37,684 (a)
Summary of restructured loans	The following table provides the number of loans modified in a troubled debt restructuring by loan portfolio during the years ended December 31, 2017 , 2016 and 2015 , respectively, and the recorded investment and unpaid principal balance as of December 31, 2017 , 2016 and 2015 , respectively. Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Number of Loans Recorded Investment (a) Unpaid Principal Balance (b) Number of Loans Recorded Investment (a) Unpaid Principal Balance (b) Number Recorded (a) Unpaid (b) ($ in Thousands) Commercial and industrial 8 $ 3,991 $ 6,339 8 $ 1,509 $ 1,526 12 $ 2,219 $ 2,900 Commercial real estate - owner occupied 2 690 690 1 116 122 5 3,694 3,901 Commercial real estate - investor — — — — — — 5 21,573 21,640 Real estate construction — — — 1 65 91 4 78 79 Residential mortgage 45 4,238 4,364 63 5,535 5,792 97 10,464 10,996 Home equity 22 507 507 57 2,030 2,084 88 3,103 3,249 Other consumer — — — 1 15 16 — — — Total 77 $ 9,426 $ 11,900 131 $ 9,270 $ 9,631 211 $ 41,131 $ 42,765 (a) Represents post-modification outstanding recorded investment. (b)
Troubled debt restructurings subsequent redefault	The following table provides the number of loans modified in a troubled debt restructuring during the previous twelve months which subsequently defaulted during the year ended December 31, 2017 , 2016 and 2015 , respectively, as well as the recorded investment in these restructured loans as of December 31, 2017 , 2016 and 2015 , respectively. Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Recorded ($ in Thousands) Commercial and industrial 2 $ — — $ — 2 $ 197 Residential mortgage 36 3,137 44 4,102 61 6,815 Home equity 27 735 23 457 28 1,220 Other consumer 1 7 1 15 — — Total 66 $ 3,879 68 $ 4,574 91 $ 8,232
Changes in the allowance for loan losses by portfolio segment	A summary of the changes in the allowance for loan losses by portfolio segment for the year ended December 31, 2017 , was as follows. Commercial and industrial Commercial real estate - owner occupied Commercial real estate - investor Real estate construction Residential mortgage Home equity Other consumer Total ($ in Thousands) December 31, 2016 $ 140,126 $ 14,034 $ 45,285 $ 26,932 $ 27,046 $ 20,364 $ 4,548 $ 278,335 Charge offs (44,533 ) (344 ) (991 ) (604 ) (2,611 ) (2,724 ) (4,439 ) (56,246 ) Recoveries 11,465 173 242 74 927 3,194 716 16,791 Net charge offs (33,068 ) (171 ) (749 ) (530 ) (1,684 ) 470 (3,723 ) (39,455 ) Provision for loan losses 16,010 (3,511 ) (3,477 ) 7,968 4,245 1,292 4,473 27,000 December 31, 2017 $ 123,068 $ 10,352 $ 41,059 $ 34,370 $ 29,607 $ 22,126 $ 5,298 $ 265,880 Allowance for loan losses Individually evaluated for impairment $ 10,838 $ 2,973 $ 1,597 $ 86 $ 6,512 $ 3,718 $ 122 $ 25,846 Collectively evaluated for impairment 112,230 7,379 39,462 34,284 23,095 18,408 5,176 240,034 Total allowance for loan losses $ 123,068 $ 10,352 $ 41,059 $ 34,370 $ 29,607 $ 22,126 $ 5,298 $ 265,880 Loans Individually evaluated for impairment $ 142,244 $ 26,234 $ 19,118 $ 467 $ 47,486 $ 10,891 $ 1,135 $ 247,575 Collectively evaluated for impairment 6,257,449 775,975 3,296,136 1,451,217 7,499,048 872,913 384,678 20,537,416 Total loans $ 6,399,693 $ 802,209 $ 3,315,254 $ 1,451,684 $ 7,546,534 $ 883,804 $ 385,813 $ 20,784,991 For comparison purposes, a summary of the changes in the allowance for loan losses by portfolio segment for the year ended December 31, 2016 , was as follows. Commercial and industrial Commercial real estate - owner occupied Commercial real estate - investor Real estate construction Residential mortgage Home equity Other consumer Total ($ in Thousands) December 31, 2015 $ 129,959 $ 18,680 $ 43,018 $ 25,266 $ 28,261 $ 23,555 $ 5,525 $ 274,264 Charge offs (71,016 ) (512 ) (1,504 ) (558 ) (4,332 ) (4,686 ) (3,831 ) (86,439 ) Recoveries 14,543 74 1,624 203 755 3,491 820 21,510 Net charge offs (56,473 ) (438 ) 120 (355 ) (3,577 ) (1,195 ) (3,011 ) (64,929 ) Provision for loan losses 66,640 (4,208 ) 2,147 2,021 2,362 (1,996 ) 2,034 69,000 December 31, 2016 $ 140,126 $ 14,034 $ 45,285 $ 26,932 $ 27,046 $ 20,364 $ 4,548 $ 278,335 Allowance for loan losses Individually evaluated for impairment $ 21,047 $ 23 $ 3,410 $ 84 $ 6,438 $ 3,943 $ 109 $ 35,054 Collectively evaluated for impairment 119,079 14,011 41,875 26,848 20,608 16,421 4,439 243,281 Total allowance for loan losses $ 140,126 $ 14,034 $ 45,285 $ 26,932 $ 27,046 $ 20,364 $ 4,548 $ 278,335 Loans Individually evaluated for impairment $ 213,271 $ 13,983 $ 32,908 $ 509 $ 43,876 $ 11,176 $ 1,012 $ 316,735 Collectively evaluated for impairment 6,275,743 883,741 3,541,824 1,431,988 6,288,451 923,267 392,967 19,737,981 Total loans $ 6,489,014 $ 897,724 $ 3,574,732 $ 1,432,497 $ 6,332,327 $ 934,443 $ 393,979 $ 20,054,716
Changes in the allowance for loan losses by oil and gas segment	The allowance related to the oil and gas portfolio was $27 million at December 31, 2017 and represented 4.5% of total oil and gas loans. Year Ended December 31, 2017 Year Ended December 31, 2016 ($ in Millions) Balance at beginning of period $ 38 $ 42 Charge offs (25 ) (59 ) Recoveries — — Net Charge offs (25 ) (59 ) Provision for loan losses 14 55 Balance at end of period $ 27 $ 38 Allowance for loan losses Individually evaluated for impairment $ 5 $ 14 Collectively evaluated for impairment 22 24 Total allowance for loan losses $ 27 $ 38 Loans Individually evaluated for impairment $ 77 $ 147 Collectively evaluated for impairment 523 521 Total loans $ 600 $ 668
Changes in the allowance for unfunded commitments	A summary of the changes in the allowance for unfunded commitments was as follows. Years Ended December 31, 2017 2016 2015 ($ in Thousands) Allowance for Unfunded Commitments Balance at beginning of period $ 25,400 $ 24,400 $ 24,900 Provision for unfunded commitments (1,000 ) 1,000 (500 ) Balance at end of period $ 24,400 $ 25,400 $ 24,400

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of core deposit intangibles and other intangibles	For core deposit intangibles and other intangibles, changes in the gross carrying amount, accumulated amortization, and net book value were as follows. 2017 2016 2015 ($ in Thousands) Core deposit intangibles Gross carrying amount $ 4,385 $ 4,385 $ 19,545 Accumulated amortization (4,385 ) (4,273 ) (19,152 ) Net book value $ — $ 112 $ 393 Amortization during the year $ 112 $ 281 $ 1,404 Other intangibles Gross carrying amount $ 34,572 $ 32,410 $ 31,398 Accumulated amortization (18,992 ) (17,145 ) (15,333 ) Net book value $ 15,580 $ 15,265 $ 16,065 Additions during the period $ 2,162 $ 1,012 $ 12,115 Amortization during the year $ 1,847 $ 1,812 $ 1,690
Summary of changes in balance of mortgage servicing rights asset and mortgage servicing rights valuation allowance	A summary of changes in the balance of the mortgage servicing rights asset and the mortgage servicing rights valuation allowance was as follows. 2017 2016 2015 ($ in Thousands) Mortgage servicing rights Mortgage servicing rights at beginning of year $ 62,085 $ 62,150 $ 61,379 Additions 7,167 12,262 12,372 Amortization (10,084 ) (12,327 ) (11,601 ) Mortgage servicing rights at end of year $ 59,168 $ 62,085 $ 62,150 Valuation allowance at beginning of year (609 ) (809 ) (1,234 ) (Additions) recoveries, net (175 ) 200 425 Valuation allowance at end of year (784 ) (609 ) (809 ) Mortgage servicing rights, net $ 58,384 $ 61,476 $ 61,341 Fair value of mortgage servicing rights $ 64,387 $ 73,149 $ 70,686 Portfolio of residential mortgage loans serviced for others (“servicing portfolio”) $ 7,646,846 $ 7,974,742 $ 7,915,224 Mortgage servicing rights, net to servicing portfolio 0.76 % 0.77 % 0.77 % Mortgage servicing rights expense (a) $ 10,259 $ 12,127 $ 11,176 (a)
Summary of estimated future amortization expense	The following table shows the estimated future amortization expense for amortizing intangible assets. The projections of amortization expense are based on existing asset balances, the current interest rate environment, and prepayment speeds as of December 31, 2017 . The actual amortization expense the Corporation recognizes in any given period may be significantly different depending upon acquisition or sale activities, changes in interest rates, prepayment speeds, market conditions, regulatory requirements, and events or circumstances that indicate the carrying amount of an asset may not be recoverable. Estimated Amortization Expense Other Intangibles Mortgage Servicing Rights ($ in Thousands) Year ending December 31, 2018 $ 1,971 $ 9,590 2019 1,672 8,051 2020 1,555 6,747 2021 1,531 5,670 2022 1,508 4,783 Beyond 2022 7,343 24,327 Total Estimated Amortization Expense $ 15,580 $ 59,168

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of Premises and Equipment	A summary of premises and equipment at December 31 was as follows. 2017 2016 ($ in Thousands) Estimated Useful Lives Cost Accumulated Depreciation Net Book Value Net Book Value Land — $ 59,257 $ — $ 59,257 $ 57,471 Land improvements 3 – 15 years 13,115 6,802 6,313 6,643 Buildings and improvements 5 – 39 years 341,947 143,516 198,431 202,152 Computers 3 – 5 years 42,604 31,526 11,078 9,051 Furniture, fixtures and other equipment 3 – 15 years 161,699 119,650 42,049 42,549 Leasehold improvements 3 – 15 years 34,701 20,866 13,835 12,449 Total premises and equipment $ 653,323 $ 322,360 $ 330,963 $ 330,315
Minimum annual rentals and commitments under noncancelable operating leases	The approximate minimum annual rental payments and rental receipts under noncancelable agreements and leases with remaining terms in excess of one year are as follows. ($ in Thousands) Payments Receipts 2018 $ 9,815 $ 3,783 2019 9,686 4,415 2020 8,886 1,996 2021 8,085 1,676 2022 5,796 724 Thereafter 22,447 774 Total $ 64,715 $ 13,368

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Deposits by type	The distribution of deposits at December 31 was as follows. 2017 2016 ($ in Thousands) Noninterest-bearing demand $ 5,478,416 $ 5,392,208 Savings 1,524,992 1,431,494 Interest-bearing demand 4,603,157 4,687,656 Money market 8,830,328 8,770,963 Brokered CDs 18,609 52,725 Other time 2,330,460 1,553,402 Total deposits $ 22,785,962 $ 21,888,448
Time deposits by maturity	Aggregate annual maturities of all time deposits at December 31, 2017 , are as follows. Maturities During Year Ending December 31, ($ in Thousands) 2018 $ 1,708,582 2019 298,774 2020 198,206 2021 84,306 2022 57,618 Thereafter 1,583 Total $ 2,349,069

Short-term Funding (Tables)

Short-term Funding (Tables)	12 Months Ended
	Dec. 31, 2017
Short-term Debt [Abstract]
Short-term funding	The components of short-term funding (funding with original contractual maturities of one year or less) at December 31 were as follows. 2017 2016 ($ in Thousands) Federal funds purchased $ 141,950 $ 208,150 Securities sold under agreements to repurchase 182,865 300,197 Federal funds purchased and securities sold under agreements to repurchase 324,815 508,347 FHLB advances 284,000 482,000 Commercial paper 67,467 101,688 Other short-term funding 351,467 583,688 Total short-term funding $ 676,282 $ 1,092,035
Schedule of Repurchase Agreements	The remaining contractual maturity of the securities sold under agreements to repurchase in the consolidated balance sheets are presented in the following table. Remaining Contractual Maturity of the Agreements Overnight and Continuous Up to 30 days 30-90 days Greater than 90 days Total ($ in Thousands) December 31, 2017 Repurchase agreements Agency mortgage-related securities $ 182,865 $ — $ — $ — $ 182,865 Total $ 182,865 $ — $ — $ — $ 182,865 December 31, 2016 Repurchase agreements Agency mortgage-related securities $ 300,197 $ — $ — $ — $ 300,197 Total $ 300,197 $ — $ — $ — $ 300,197

Long-term Funding (Tables)

Long-term Funding (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-term Funding	The components of long-term funding (funding with original contractual maturities greater than one year) at December 31 were as follows. 2017 2016 ($ in Thousands) FHLB advances $ 2,900,168 $ 2,265,188 Senior notes, at par 250,000 250,000 Subordinated notes, at par 250,000 250,000 Other long-term funding and capitalized costs (2,718 ) (3,393 ) Total long-term funding $ 3,397,450 $ 2,761,795
Maturities of Long-term funding	The table below summarizes the maturities of the Corporation’s long-term funding at December 31, 2017 . Year ($ in Thousands) 2018 $ 1,750,000 2019 499,313 2020 155 2021 150,000 2022 — Thereafter 997,982 Total long-term funding $ 3,397,450

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Fair value assumptions of stock options	The following assumptions were used in estimating the fair value for options granted in 2017 , 2016 and 2015 . 2017 2016 2015 Dividend yield 2.00 % 2.50 % 2.00 % Risk-free interest rate 2.00 % 2.00 % 2.00 % Weighted average expected volatility 25.00 % 25.00 % 20.00 % Weighted average expected life 5.5 years 5.5 years 6 years Weighted average per share fair value of options $5.30 $3.36 $3.08
Summary of Company's Stock Option Activities	A summary of the Corporation’s stock option activity for the year ended December 31, 2017 is presented below. Stock Options Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (000s) Outstanding at December 31, 2016 6,357,843 $ 17.67 6.10 $ 47,902 Granted 799,558 25.61 Exercised (1,551,669 ) 16.87 Forfeited or expired (487,045 ) 31.84 Outstanding at December 31, 2017 5,118,687 $ 18.02 6.48 $ 38,028 Options Exercisable at December 31, 2017 2,831,736 $ 16.31 5.23 $ 25,738
Summary of Restricted Stock Awards Activity (Excluding Salary Shares)	The following table summarizes information about the Corporation’s restricted stock activity for the year ended December 31, 2017. Restricted Stock Shares Weighted Average Grant Date Fair Value Outstanding at December 31, 2016 2,377,380 $ 17.40 Granted 767,627 25.54 Vested (999,917 ) 18.01 Forfeited (119,019 ) 20.00 Outstanding at December 31, 2017 2,026,071 $ 19.68

Retirement Plans (Tables)

Retirement Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Change in Benefit Obligation	The funded status and amounts recognized in the 2017 and 2016 consolidated balance sheets, as measured on December 31, 2017 and 2016 , respectively, for the Retirement Account and Postretirement Plan were as follows. Retirement Account Plan Postretirement Plan Retirement Account Plan Postretirement Plan ($ in Thousands) 2017 2017 2016 2016 Change in Fair Value of Plan Assets Fair value of plan assets at beginning of year $ 295,718 $ — $ 289,599 $ — Actual return on plan assets 41,490 — 17,097 — Employer contributions 6,242 235 — 248 Gross benefits paid (11,841 ) (235 ) (10,978 ) (248 ) Fair value of plan assets at end of year (a) $ 331,609 $ — $ 295,718 $ — Change in Benefit Obligation Net benefit obligation at beginning of year $ 176,825 $ 2,403 $ 171,783 $ 3,436 Service cost 6,955 — 6,780 — Interest cost 7,121 101 7,121 142 Plan amendments — — (823 ) (936 ) Actuarial (gain) loss 7,363 209 2,942 9 Gross benefits paid (11,841 ) (235 ) (10,978 ) (248 ) Net benefit obligation at end of year (a) $ 186,423 $ 2,478 $ 176,825 $ 2,403 Funded (unfunded) status $ 145,186 $ (2,478 ) $ 118,893 $ (2,403 ) Noncurrent assets 145,186 — 118,893 — Current liabilities — (233 ) — (215 ) Noncurrent liabilities — (2,245 ) — (2,188 ) Asset (Liability) Recognized in the Consolidated Balance Sheets $ 145,186 $ (2,478 ) $ 118,893 $ (2,403 ) (a) The fair value of the plan assets represented 178% and 167% of the net benefit obligation of the pension plan at December 31, 2017 and 2016
AOCI Components	Amounts recognized in accumulated other comprehensive loss, net of tax, as of December 31, 2017 and 2016 follow. Retirement Account Plan Postretirement Plan Retirement Account Plan Postretirement Plan ($ in Thousands) 2017 2017 2016 2016 Prior service cost $ (295 ) $ (531 ) $ (342 ) $ (580 ) Net actuarial loss 24,926 205 35,443 79 Amount not yet recognized in net periodic benefit cost, but recognized in accumulated other comprehensive loss $ 24,631 $ (326 ) $ 35,101 $ (501 )
Changes in OCI	Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss) (“OCI”), net of tax, in 2017 and 2016 were as follows. Retirement Account Plan Postretirement Retirement Account Plan Postretirement ($ in Thousands) 2017 2017 2016 2016 Net gain (loss) $ 14,482 $ (209 ) $ (6,132 ) $ (9 ) Amortization of prior service cost (73 ) (75 ) (73 ) — Amortization of actuarial loss (gain) 2,278 4 2,115 — Plan amendments — — 823 936 Income tax (expense) benefit (6,219 ) 107 1,168 (353 ) Total Recognized in OCI $ 10,468 $ (173 ) $ (2,099 ) $ 574
Net period benefit cost for the pension and postretirement plans	The components of net periodic benefit cost for the Retirement Account Plan and Postretirement Plans for 2017 , 2016 , and 2015 were as follows. Retirement Account Plan Postretirement Retirement Account Plan Postretirement Retirement Account Plan Postretirement ($ in Thousands) 2017 2017 2016 2016 2015 2015 Service cost $ 6,955 $ — $ 6,780 $ — $ 11,257 $ — Interest cost 7,121 101 7,121 142 6,617 141 Expected return on plan assets (19,646 ) — (20,287 ) — (21,438 ) — Amortization of: Prior service cost (73 ) (75 ) (73 ) — 50 — Actuarial (gain) loss 2,278 4 2,115 — 2,256 — Total net pension cost $ (3,365 ) $ 30 $ (4,344 ) $ 142 $ (1,258 ) $ 141
Weighted Average Benefit Assumptions	Retirement Account Plan Postretirement Plan Retirement Account Plan Postretirement Plan 2017 2017 2016 2016 Weighted average assumptions used to determine benefit obligations Discount rate 3.70 % 3.70 % 4.10 % 4.10 % Rate of increase in compensation levels 3.00 % N/A 4.00 % N/A Weighted average assumptions used to determine net periodic benefit costs Discount rate 4.10 % 4.10 % 4.30 % 4.30 % Rate of increase in compensation levels 4.00 % N/A 4.00 % N/A Expected long-term rate of return on plan assets 6.50 % N/A 7.00 % N/A
Plan Asset Allocation Percentages	The asset allocation for the Retirement Account Plan as of the December 31, 2017 and 2016 measurement dates, respectively, by asset category were as follows. Asset Category 2017 2016 Equity securities 60 % 60 % Fixed income securities 37 % 39 % Other 3 % 1 % Total 100 % 100 %
Pension Plan Investments	Based on these inputs, the following table summarizes the fair value of the Retirement Account Plan’s investments as of December 31, 2017 and 2016 . Fair Value Measurements Using ($ in Thousands) December 31, 2017 Level 1 Level 2 Level 3 Retirement Account Plan Investments Money market account $ 9,577 $ 9,577 $ — $ — Common /collective trust funds 133,210 133,210 — — Mutual funds 188,823 188,823 — — Total Retirement Account Plan Investments $ 331,610 $ 331,610 $ — $ — Fair Value Measurements Using ($ in Thousands) December 31, 2016 Level 1 Level 2 Level 3 Retirement Account Plan Investments Money market account $ 3,624 $ 3,624 $ — $ — Common /collective trust funds 126,741 126,741 — — Mutual funds 165,353 165,353 — — Total Retirement Account Plan Investments $ 295,718 $ 295,718 $ — $ —
Expected Benefit Payments	The projected benefit payments for the Retirement Account and Postretirement Plans at December 31, 2017 , reflecting expected future services, were as follows. The projected benefit payments were calculated using the same assumptions as those used to calculate the benefit obligations listed above. ($ in Thousands) Retirement Account Plan Postretirement Plan Estimated future benefit payments 2018 $ 14,697 $ 237 2019 14,436 197 2020 15,096 194 2021 15,278 190 2022 16,020 186 2023-2027 71,781 839
One Percentage Point Change in Assumed Health Care Cost	A one percentage point change in the assumed health care cost trend rate would have the following effect. 2017 2016 ($ in Thousands) 100 bp Increase 100 bp Decrease 100 bp Increase 100 bp Decrease Effect on total of service and interest cost $ 7 $ (6 ) $ 7 $ (6 ) Effect on postretirement benefit obligation $ 162 $ (140 ) $ 173 $ (149 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current and Deferred Income Tax Expense (Benefit)	The current and deferred amounts of income tax expense (benefit) were as follows. Years Ended December 31, 2017 2016 2015 ($ in Thousands) Current Federal $ 76,525 $ 73,781 $ 82,449 State 11,576 2,885 2,560 Total current 88,101 76,666 85,009 Deferred Federal 19,755 3,338 (10,606 ) State 1,647 7,318 7,084 Total deferred 21,402 10,656 (3,522 ) Total income tax expense $ 109,503 $ 87,322 $ 81,487
Schedule of Deferred Tax Assets and Liabilities	Temporary differences between the amounts reported in the financial statements and the tax bases of assets and liabilities resulted in deferred taxes. Deferred tax assets and liabilities at December 31 were as follows. 2017 2016 ($ in Thousands) Deferred tax assets Allowance for loan losses $ 66,377 $ 100,891 Allowance for other losses 7,095 11,080 Accrued liabilities 3,884 5,969 Deferred compensation 20,015 33,169 Benefit of tax loss and credit carryforwards 8,438 7,882 Nonaccrual interest 1,619 1,085 Net unrealized losses on available-for-sale securities 15,968 16,980 Net unrealized losses on pension and postretirement benefits 9,928 21,218 Other 3,954 8,128 Total deferred tax assets 137,278 206,402 Valuation allowance for deferred tax assets (269 ) — Total deferred tax assets after valuation allowance 137,009 206,402 Deferred tax liabilities Prepaid expenses 49,695 70,943 Goodwill 19,144 27,365 Mortgage banking activities 10,949 17,569 Deferred loan fee income 11,467 16,474 State deferred taxes 2,001 3,800 Lease financing 535 1,975 Bank premises and equipment 5,063 7,698 Other 4,838 8,594 Total deferred tax liabilities 103,692 154,418 Net deferred tax assets $ 33,317 $ 51,984
Summary of Valuation Allowance [Table Text Block]	At December 31, 2017 the valuation allowance for deferred tax assets of approximately $ 269,000 was related to the deferred tax benefit of specific federal tax loss carryforwards of $3 million from the acquisition of Whitnell & Co. in 2017. 2017 2016 ($ in Thousands) Valuation allowance for deferred tax assets, beginning of year $ — $ — Increase (decrease) in current year 269 — Valuation allowance for deferred tax assets, end of year $ 269 $ —
Schedule of Effective Income Tax Rate Reconciliation	The effective income tax rate differs from the statutory federal tax rate. The major reasons for this difference were as follows. 2017 2016 2015 Federal income tax rate at statutory rate 35.0 % 35.0 % 35.0 % Increases (decreases) resulting from: Tax-exempt interest and dividends (4.1 )% (4.8 )% (5.0 )% State income taxes (net of federal benefit) 2.7 % 2.3 % 2.3 % Bank owned life insurance (1.7 )% (1.7 )% (1.2 )% Tax effect of tax credits and benefits, net of related expenses (0.5 )% (0.8 )% (0.5 )% Tax reserve adjustments (1.2 )% 0.3 % (0.6 )% Net tax benefit from stock-based compensation (1.3 )% (0.4 )% — % Tax Cuts and Jobs Act impact on deferred remeasurement 3.5 % — % — % Other (0.1 )% 0.5 % 0.2 % Effective income tax rate 32.3 % 30.4 % 30.2 %
Summary Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits was as follows. 2017 2016 ($ in Millions) Balance at beginning of year $ 10 $ 9 Subtractions for tax positions related to prior years (5 ) — Subtractions for settlements with tax authorities (1 ) — Additions for tax positions related to current year — 1 Balance at end of year $ 4 $ 10

Derivative and Hedging Activi43

Derivative and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Balance sheet category and fair values of derivative instruments not designated as hedging instruments	The table below identifies the balance sheet category and fair values of the Corporation’s derivative instruments to accommodate customer needs which are not designated as hedging instruments. December 31, 2017 December 31, 2016 ($ in Thousands) Notional Amount Fair Value Balance Sheet Category Notional Amount Fair Balance Sheet Interest rate-related instruments — customer and mirror $ 2,183,687 $ 28,494 Trading assets $ 2,039,323 $ 33,671 Trading assets Interest rate-related instruments — customer and mirror 2,183,687 (28,035 ) Trading liabilities 2,039,323 (33,188 ) Trading liabilities Foreign currency exchange forwards 124,851 2,495 Trading assets 109,675 2,002 Trading assets Foreign currency exchange forwards 118,094 (2,339 ) Trading liabilities 106,251 (1,943 ) Trading liabilities Commodity contracts 457,868 38,686 Trading assets 127,582 16,725 Trading assets Commodity contracts 457,108 (37,286 ) Trading liabilities 128,368 (15,972 ) Trading liabilities
Summary Of Other derivative instruments not designated as hedging instruments	The table below identifies the balance sheet category and fair values of the Corporation’s derivative instruments which are not designated as hedging instruments. December 31, 2017 December 31, 2016 ($ in Thousands) Notional Amount Fair Balance Sheet Notional Amount Fair Balance Sheet Interest rate lock commitments (mortgage) $ 222,736 $ 1,538 Other assets $ 285,345 $ 206 Other assets Forward commitments (mortgage) 164,567 (313 ) Other liabilities 179,600 2,908 Other assets Purchased options (time deposit) 31,063 1,175 Other assets 80,554 2,576 Other assets Written options (time deposit) 31,063 (1,175 ) Other liabilities 80,554 (2,576 ) Other liabilities
Gain (loss) on derivative instruments not designated as hedging instruments	The table below identifies the income statement category of the gains and losses recognized in income on the Corporation’s derivative instruments not designated as hedging instruments. Income Statement Category of Gain / (Loss) Recognized in Income For the Year Ended December 31, ($ in Thousands) 2017 2016 Derivative Instruments Interest rate-related instruments — customer and mirror, net Capital market fees, net $ (24 ) $ 1,978 Interest rate lock commitments (mortgage) Mortgage banking, net 1,332 (752 ) Forward commitments (mortgage) Mortgage banking, net (3,221 ) 2,505 Foreign currency exchange forwards Capital market fees, net 97 (75 ) Commodity contracts Capital market fees, net 647 630

Balance Sheet Offsetting (Table

Balance Sheet Offsetting (Tables)	12 Months Ended
	Dec. 31, 2017
Offsetting [Abstract]
Balance Sheet Offsetting of Derivative Assets and Liabilities	The following table presents the assets and liabilities subject to an enforceable master netting arrangement. The interest and commodity agreements we have with our commercial customers are not subject to an enforceable master netting arrangement, and therefore, are excluded from this table. Gross amounts not offset in the balance sheet ($ in Thousands) Gross Gross amounts offset in the balance sheet Net amounts presented in the balance sheet Financial instruments Collateral Net amount December 31, 2017 Derivative assets Interest and commodity agreements $ 29,503 $ — $ 29,503 $ (29,503 ) $ — $ — Derivative liabilities Interest and commodity agreements $ 37,164 $ — $ 37,164 $ (29,503 ) $ (7,661 ) $ — December 31, 2016 Derivative assets Interest and commodity agreements $ 18,031 $ — $ 18,031 $ (18,031 ) $ — $ — Derivative liabilities Interest and commodity agreements $ 31,075 $ — $ 31,075 $ (18,031 ) $ (11,148 ) $ 1,896

Commitments, Off-Balance Shee45

Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Summary of lending-related and other commitments	The following is a summary of lending-related commitments. 2017 2016 ($ in Thousands) Commitments to extend credit, excluding commitments to originate residential mortgage loans held for sale (a) (b) $ 8,027,187 $ 8,131,131 Commercial letters of credit (a) 11,886 7,923 Standby letters of credit (c) 235,361 259,632 (a) These off-balance sheet financial instruments are exercisable at the market rate prevailing at the date the underlying transaction will be completed and, thus, are deemed to have no current fair value, or the fair value is based on fees currently charged to enter into similar agreements and is not material at December 31, 2017 and 2016 . (b) Interest rate lock commitments to originate residential mortgage loans held for sale are considered derivative instruments and are disclosed in Note 14 . (c) The Corporation has established a liability of $2 million at December 31, 2017 and $3 million at December 31, 2016
Summary of changes in the residential mortgage repurchase reserve	The following summarizes the changes in the mortgage repurchase reserve for the years ended as follows. 2017 2016 ($ in Thousands) Balance at beginning of year $ 900 $ 1,197 Repurchase provision expense 246 456 Adjustments to provision expense — (750 ) Charge offs, net (159 ) (3 ) Balance at end of year $ 987 $ 900

Parent Company Only Financial46

Parent Company Only Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Parent Company Balance Sheet	BALANCE SHEETS December 31, 2017 2016 ($ in Thousands) Assets Cash and due from banks $ 146,877 $ 402,786 Investment securities available for sale, at fair value 11,645 14,389 Notes and interest receivable from subsidiaries 301,378 — Investments in and receivable due from subsidiaries 3,320,090 3,256,763 Other assets 51,466 53,242 Total assets $ 3,831,456 $ 3,727,180 Liabilities and Stockholders' Equity Commercial paper $ 67,467 $ 101,688 Senior notes, at par 250,000 250,000 Subordinated notes, at par 250,000 250,000 Long-term funding capitalized costs (2,718 ) (3,393 ) Total long-term funding 497,282 496,607 Accrued expenses and other liabilities 29,264 37,573 Total liabilities 594,013 635,868 Preferred equity 159,929 159,929 Common equity 3,077,514 2,931,383 Total stockholders’ equity 3,237,443 3,091,312 Total liabilities and stockholders’ equity $ 3,831,456 $ 3,727,180
Parent Company Income Statement	STATEMENTS OF INCOME For the Years Ended December 31, 2017 2016 2015 ($ in Thousands) Income Dividends from subsidiaries $ 213,000 $ 188,000 $ 205,000 Interest income on notes receivable from subsidiaries 4,175 — — Other income 1,763 4,669 8,441 Total income 218,938 192,669 213,441 Expense Interest expense on short and long-term funding 18,464 21,901 39,576 Other expense 6,927 4,289 4,684 Total expense 25,391 26,190 44,260 Income before income tax expense (benefit) and equity in undistributed net income (loss) of subsidiaries 193,547 166,479 169,181 Income tax expense (benefit) 4,768 3,468 (1,665 ) Income before equity in undistributed net income (loss) of subsidiaries 188,779 163,011 170,846 Equity in undistributed net income (loss) of subsidiaries 40,485 37,263 17,455 Net income 229,264 200,274 188,301 Preferred stock dividends 9,347 8,903 7,155 Net income available to common equity $ 219,917 $ 191,371 $ 181,146
Parent Company Statement of Cash Flows	STATEMENTS OF CASH FLOWS For the Years Ended December 31, 2017 2016 2015 ($ in Thousands) Cash Flows from Operating Activities Net income $ 229,264 $ 200,274 $ 188,301 Adjustments to reconcile net income to net cash provided by operating activities: (Increase) decrease in equity in undistributed net income (loss) of subsidiaries (40,485 ) (37,263 ) (17,455 ) (Gain) loss on sales of investment securities, net of impairment write-downs — (466 ) — (Gain) loss on sales of assets, net (88 ) (793 ) (5,673 ) Net change in other assets and other liabilities (9,589 ) 19,708 (10,997 ) Net cash provided by operating activities 179,102 181,460 154,176 Cash Flows from Investing Activities Proceeds from sales of investment securities 2,618 47,719 13,962 Net increase in notes receivable from subsidiaries (300,000 ) — — Purchase of other assets, net of disposals 1,058 2,211 11,964 Net cash provided by (used in) investing activities (296,324 ) 49,930 25,926 Cash Flows from Financing Activities Net increase (decrease) in commercial paper (34,221 ) 33,710 (6,319 ) Repayment of long-term funding — (430,000 ) — Proceeds from issuance of common stock for stock-based compensation plans 27,619 21,748 20,054 Proceeds from issuance of preferred stock — 97,066 62,966 Redemption of preferred stock — (58,903 ) — Purchase of preferred stock — (1,248 ) (1,335 ) Purchase of common stock returned to authorized but unissued (37,031 ) (20,007 ) (93,000 ) Purchase of treasury stock for tax withholding (9,290 ) (5,074 ) (5,154 ) Cash dividends on common stock (76,417 ) (67,855 ) (62,400 ) Cash dividends on preferred stock (9,347 ) (8,903 ) (7,155 ) Net cash used in financing activities (138,687 ) (439,466 ) (92,343 ) Net increase (decrease) in cash and cash equivalents (255,909 ) (208,076 ) 87,759 Cash and cash equivalents at beginning of year 402,786 610,862 523,103 Cash and cash equivalents at end of year 146,877 402,786 610,862

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Assets and liabilities measured on recurring basis at fair value	The table below presents the Corporation’s financial instruments measured at fair value on a recurring basis as of December 31, 2017 and 2016 , aggregated by the level in the fair value hierarchy within which those measurements fall. Fair Value Hierarchy December 31, 2017 December 31, 2016 ($ in Thousands) Assets Investment securities available for sale U.S. Treasury securities Level 1 $ 996 $ 1,000 Residential mortgage-related securities FNMA / FHLMC Level 2 464,768 639,930 GNMA Level 2 1,913,350 2,004,475 Private-label Level 2 1,059 1,121 GNMA commercial mortgage-related securities Level 2 1,513,277 2,028,898 FFELP asset backed securities Level 2 145,176 — Other securities (debt and equity) Level 1 1,632 1,602 Other securities (debt and equity) Level 2 3,188 3,000 Other securities (debt and equity) Level 3 — 200 Total investment securities available for sale Level 1 2,628 2,602 Total investment securities available for sale Level 2 4,040,818 4,677,424 Total investment securities available for sale Level 3 — 200 Residential loans held for sale (a) Level 2 85,544 — Interest rate-related instruments Level 2 28,494 33,671 Foreign currency exchange forwards Level 2 2,495 2,002 Interest rate lock commitments to originate residential mortgage loans held for sale Level 3 1,538 206 Forward commitments to sell residential mortgage loans Level 3 — 2,908 Commodity contracts Level 2 38,686 16,725 Purchased options (time deposit) Level 2 1,175 2,576 Liabilities Interest rate-related instruments Level 2 $ 28,035 $ 33,188 Foreign currency exchange forwards Level 2 2,339 1,943 Forward commitments to sell residential mortgage loans Level 3 313 — Commodity contracts Level 2 37,286 15,972 Written options (time deposit) Level 2 1,175 2,576 (a) Effective January 1, 2017, residential loans originated for sale are accounted for under the fair value option. Prior periods have not been restated. For more information on this accounting policy change, please refer to Note 1
Assets and liabilities measured at fair value using significant unobservable inputs (level 3)	The table below presents a rollforward of the balance sheet amounts for the years ended December 31, 2017 and 2016 , for financial instruments measured on a recurring basis and classified within Level 3 of the fair value hierarchy. Investment Securities Available for Sale Derivative Financial Instruments ($ in Thousands) Balance December 31, 2015 $ 200 $ 1,361 Total net gains (losses) included in income Mortgage derivative gain (loss) — 1,753 Balance December 31, 2016 $ 200 $ 3,114 Total net gains (losses) included in income Mortgage derivative gain (loss) — (1,889 ) Transfer out of level 3 securities (a) $ (200 ) $ — Balance December 31, 2017 $ — $ 1,225 (a) During the first quarter of 2017, the $200,000
Assets and liabilities measured on nonrecurring basis at fair value	The table below presents the Corporation’s assets measured at fair value on a nonrecurring basis, aggregated by the level in the fair value hierarchy within which those measurements fall. Income Statement Category of Adjustment Recognized in Income Fair Value Hierarchy Fair Value ($ in Thousands) December 31, 2017 Assets Impaired loans (a) Level 3 $ 92,534 Provision for credit losses (c) $ (32,159 ) Other real estate owned Level 2 2,604 Foreclosure / OREO expense, net (939 ) Mortgage servicing rights Level 3 64,387 Mortgage banking, net (175 ) December 31, 2016 Assets Commercial loans held for sale Level 2 $ 12,474 Provision for credit losses $ (559 ) Residential loans held for sale (b) Level 2 108,010 Mortgage banking, net (3,760 ) Impaired loans (a) Level 3 79,270 Provision for credit losses (c) (75,194 ) Other real estate owned Level 2 9,752 Foreclosure / OREO expense, net (1,091 ) Mortgage servicing rights Level 3 73,149 Mortgage banking, net 200 (a) Represents individually evaluated impaired loans, net of the related allowance for loan losses. (b) Effective January 1, 2017, residential loans originated for sale are accounted for under the fair value option. Prior periods have not been restated. For more information on this accounting policy change, please refer to Note 3 . (c)
Schedule of assumptions for fair value as of balance sheet date of assets or liabilities that relate to transferor's continuing involvement	The table below presents information about these inputs and further discussion is found above. December 31, 2017 Valuation Technique Significant Unobservable Input Weighted Average Input Applied Mortgage servicing rights Discounted cash flow Discount rate 11% Mortgage servicing rights Discounted cash flow Constant prepayment rate 11% Impaired loans Appraisals / Discounted cash flow Collateral / Discount factor 19%
Estimated fair values of financial instruments	Fair value estimates, methods, and assumptions are set forth below for the Corporation’s financial instruments. December 31, 2017 December 31, 2016 Fair Value Hierarchy Level Carrying Amount Fair Value Carrying Amount Fair Value ($ in Thousands) Financial assets Cash and due from banks Level 1 $ 483,666 $ 483,666 $ 446,558 $ 446,558 Interest-bearing deposits in other financial institutions Level 1 199,702 199,702 149,175 149,175 Federal funds sold and securities purchased under agreements to resell Level 1 32,650 32,650 46,500 46,500 Investment securities held to maturity Level 2 2,282,853 2,283,574 1,273,536 1,264,674 Investment securities available for sale Level 1 2,628 2,628 2,602 2,602 Investment securities available for sale Level 2 4,040,818 4,040,818 4,677,424 4,677,424 Investment securities available for sale Level 3 — — 200 200 FHLB and Federal Reserve Bank stocks Level 2 165,331 165,331 140,001 140,001 Commercial loans held for sale Level 2 — — 12,474 12,474 Residential loans held for sale Level 2 85,544 85,544 108,010 108,010 Loans, net Level 3 20,519,111 20,314,984 19,776,381 19,680,317 Bank and corporate owned life insurance Level 2 591,057 591,057 585,290 585,290 Derivatives (trading and other assets) Level 2 70,850 70,850 54,974 54,974 Derivatives (trading and other assets) Level 3 1,538 1,538 3,114 3,114 Financial liabilities Noninterest-bearing demand, savings, interest-bearing demand, and money market accounts Level 3 $ 20,436,893 $ 20,436,893 $ 20,282,321 $ 20,282,321 Brokered CDs and other time deposits Level 2 2,349,069 2,349,069 1,606,127 1,606,127 Short-term funding Level 2 676,282 676,282 1,092,035 1,092,035 Long-term funding Level 2 3,397,450 3,411,368 2,761,795 2,791,841 Standby letters of credit (a) Level 2 2,402 2,402 2,566 2,566 Derivatives (trading and other liabilities) Level 2 68,835 68,835 53,679 53,679 Derivatives (trading and other liabilities) Level 3 313 313 — — (a) The commitment on standby letters of credit was $235 million and $260 million at December 31, 2017 and 2016 , respectively. See Note 16

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations	Actual For Capital Adequacy Purposes To Be Well Capitalized Under Prompt Corrective Action Provisions (b) Amount Ratio (a) Amount Ratio (a) Amount Ratio (a) ($ in Thousands) As of December 31 , 2017 Associated Banc-Corp Total capital $ 2,848,851 13.22 % $ 1,723,557 ≥ 8.00 % Tier 1 capital 2,331,245 10.82 % 1,292,668 ≥ 6.00 % Common equity Tier 1 capital 2,171,508 10.08 % 969,501 ≥ 4.50 % Leverage 2,331,245 8.02 % 1,162,929 ≥ 4.00 % Associated Bank, N.A. Total capital $ 2,625,945 12.24 % $ 1,716,910 ≥ 8.00 % $ 2,146,138 ≥ 10.00 % Tier 1 capital 2,357,354 10.98 % 1,287,683 ≥ 6.00 % 1,716,910 ≥ 8.00 % Common equity Tier 1 capital 2,157,354 10.05 % 965,762 ≥ 4.50 % 1,394,989 ≥ 6.50 % Leverage 2,357,354 8.13 % 1,159,959 ≥ 4.00 % 1,449,448 ≥ 5.00 % As of December 31 , 2016 Associated Banc-Corp Total capital $ 2,706,760 12.68 % $ 1,707,276 ≥ 8.00 % Tier 1 capital 2,191,798 10.27 % 1,280,457 ≥ 6.00 % Common equity Tier 1 capital 2,032,587 9.52 % 960,343 ≥ 4.50 % Leverage 2,191,798 7.83 % 1,119,685 ≥ 4.00 % Associated Bank, N.A. Total capital $ 2,565,062 12.07 % $ 1,700,737 ≥ 8.00 % $ 2,125,921 ≥ 10.00 % Tier 1 capital 2,298,812 10.81 % 1,275,553 ≥ 6.00 % 1,700,737 ≥ 8.00 % Common equity Tier 1 capital 2,098,812 9.87 % 956,664 ≥ 4.50 % 1,381,849 ≥ 6.50 % Leverage 2,298,812 8.24 % 1,115,731 ≥ 4.00 % 1,394,663 ≥ 5.00 % (a) When fully phased-in on January 1, 2019, the Basel III capital rules include a capital conservation buffer of 2.5% that is added on top of each of the minimum risk-based capital ratios noted above. Implementation began on January 1, 2016 at the 0.625% level and will increase each subsequent January 1, until it reaches 2.5% on January 1, 2019.

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Calculations for basic and diluted earnings per common share	Presented below are the calculations for basic and diluted earnings per common share. For the Years Ended December 31, 2017 2016 2015 ($ in Thousands, Except Per Share Data) Net income $ 229,264 $ 200,274 $ 188,301 Preferred stock dividends (9,347 ) (8,903 ) (7,155 ) Net income available to common equity $ 219,917 $ 191,371 $ 181,146 Common shareholder dividends (75,967 ) (67,100 ) (61,774 ) Unvested share-based payment awards (450 ) (755 ) (626 ) Undistributed earnings $ 143,500 $ 123,516 $ 118,746 Undistributed earnings allocated to common shareholders 142,593 122,205 117,498 Undistributed earnings allocated to unvested share-based payment awards 907 1,311 1,248 Undistributed earnings $ 143,500 $ 123,516 $ 118,746 Basic Distributed earnings to common shareholders $ 75,967 $ 67,100 $ 61,774 Undistributed earnings allocated to common shareholders 142,593 122,205 117,498 Total common shareholders earnings, basic $ 218,560 $ 189,305 $ 179,272 Diluted Distributed earnings to common shareholders $ 75,967 $ 67,100 $ 61,774 Undistributed earnings allocated to common shareholders 142,593 122,205 117,498 Total common shareholders earnings, diluted $ 218,560 $ 189,305 $ 179,272 Weighted average common shares outstanding 150,877 148,769 149,350 Effect of dilutive common stock awards $ 2,038 $ 1,192 $ 1,253 Effect of dilutive common stock warrants 732 — — Diluted weighted average common shares outstanding 153,647 149,961 150,603 Basic earnings per common share $ 1.45 $ 1.27 $ 1.20 Diluted earnings per common share $ 1.42 $ 1.26 $ 1.19

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Selected segment information	Information about the Corporation’s segments is presented below. Segment Income Statement Data Corporate and Commercial Specialty Community, Consumer, and Business Risk Management and Shared Services Consolidated Total For the Years Ended December 31, ($ in Thousands) 2017 Net interest income $ 357,051 $ 361,361 $ 22,808 $ 741,220 Noninterest income 52,297 266,250 14,133 332,680 Total revenue 409,348 627,611 36,941 1,073,900 Credit provision (a) 42,298 20,400 (36,698 ) 26,000 Noninterest expense 156,890 490,908 61,335 709,133 Income before income taxes 210,160 116,303 12,304 338,767 Income tax expense (benefit) 71,655 40,706 (2,858 ) 109,503 Net income $ 138,505 $ 75,597 $ 15,162 $ 229,264 Return on average allocated capital (ROCET1) (b) 12.4 % 12.9 % 1.4 % 10.4 % 2016 Net interest income $ 328,603 $ 350,551 $ 28,119 $ 707,273 Noninterest income 47,776 277,942 27,165 352,883 Total revenue 376,379 628,493 55,284 1,060,156 Credit provision (a) 50,397 24,185 (4,582 ) 70,000 Noninterest expense 148,493 502,285 51,782 702,560 Income before income taxes 177,489 102,023 8,084 287,596 Income tax expense (benefit) 59,261 35,708 (7,647 ) 87,322 Net income $ 118,228 $ 66,315 $ 15,731 $ 200,274 Return on average allocated capital (ROCET1) (b) 11.0 % 10.5 % 2.8 % 9.9 % 2015 Net interest income $ 310,072 $ 349,134 $ 17,072 $ 676,278 Noninterest income 46,742 265,503 17,112 329,357 Total revenue 356,814 614,637 34,184 1,005,635 Credit provision (a) 41,913 25,614 (30,027 ) 37,500 Noninterest expense 141,912 492,284 64,151 698,347 Income before income taxes 172,989 96,739 60 269,788 Income tax expense 59,200 33,859 (11,572 ) 81,487 Net income $ 113,789 $ 62,880 $ 11,632 $ 188,301 Return on average allocated capital (ROCET1) (b) 11.6 % 9.8 % 2.1 % 9.9 % Segment Balance Sheet Data Corporate and Commercial Specialty Community, Consumer, and Business Risk Management and Shared Services Consolidated Total ($ in Thousands) Average Balances 2017 Average earning assets $ 10,820,998 $ 9,456,549 $ 6,722,337 $ 26,999,884 Average loans 10,811,827 9,452,253 328,303 20,592,383 Average deposits 6,938,913 11,711,407 3,273,282 21,923,602 Average allocated capital (CET1) (b) $ 1,117,761 $ 586,417 $ 405,281 $ 2,109,459 2016 Average earning assets $ 10,178,813 $ 9,309,028 $ 6,538,820 $ 26,026,661 Average loans 10,169,300 9,307,723 173,644 19,650,667 Average deposits 5,904,238 11,451,759 3,649,775 21,005,772 Average allocated capital (CET1) (b) $ 1,070,598 $ 629,540 $ 240,253 $ 1,940,391 2015 Average earning assets $ 9,383,971 $ 8,810,015 $ 6,377,101 $ 24,571,087 Average loans 9,374,191 8,809,673 68,400 18,252,264 Average deposits 5,856,530 10,898,602 3,147,955 19,903,087 Average allocated capital (CET1) (b) $ 977,406 $ 640,181 $ 216,010 $ 1,833,597 (a) The consolidated credit provision is equal to the actual reported provision for credit losses. (b)

Accumulated Other Comprehensi51

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Summary of activity in accumulated other comprehensive income (loss)	The following table summarizes the components of accumulated other comprehensive income (loss) at December 31, 2017 , 2016 , and 2015 , changes during the years then ended, and reclassifications out of accumulated other comprehensive income (loss) during the years ended December 31, 2017 , 2016 , and 2015 , respectively. Investments Securities Available For Sale Defined Benefit Pension and Postretirement Obligations Accumulated Other Comprehensive Income (Loss) ($ in Thousands) Balance, December 31, 2014 $ 18,512 $ (23,362 ) $ (4,850 ) Other comprehensive income (loss) before reclassifications (20,439 ) (17,892 ) (38,331 ) Amounts reclassified from accumulated other comprehensive income (loss) Investment securities gain (loss), net (8,133 ) — (8,133 ) Personnel expense — 2,306 2,306 Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities) (555 ) — (555 ) Income tax (expense) benefit 11,074 5,873 16,947 Net other comprehensive income (loss) during period (18,053 ) (9,713 ) (27,766 ) Balance, December 31, 2015 $ 459 $ (33,075 ) $ (32,616 ) Other comprehensive income (loss) before reclassifications (17,900 ) (6,141 ) (24,041 ) Amounts reclassified from accumulated other comprehensive income (loss) Investment securities gain (loss), net (9,316 ) — (9,316 ) Personnel expense — 3,801 3,801 Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities) (5,887 ) — (5,887 ) Income tax (expense) benefit 12,565 815 13,380 Net other comprehensive income (loss) during period (20,538 ) (1,525 ) (22,063 ) Balance, December 31, 2016 $ (20,079 ) $ (34,600 ) $ (54,679 ) Other comprehensive income (loss) before reclassifications (27,040 ) 14,273 (12,767 ) Amounts reclassified from accumulated other comprehensive income (loss) Personnel expense — 2,134 2,134 Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities) (2,665 ) — (2,665 ) Income tax (expense) benefit 11,331 (6,112 ) 5,219 Net other comprehensive income (loss) during period (18,374 ) 10,295 (8,079 ) Balance, December 31, 2017 $ (38,453 ) $ (24,305 ) $ (62,758 )

Summary of Significant Accoun52

Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Core Deposit Intangibles
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years
Other Intangibles
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	11 years	12 years

Acquisition (Details Textuals)

Acquisition (Details Textuals)	Oct. 02, 2017acquisition	Jul. 20, 2017acquisitionshares	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017acquisition
Business Acquisition [Line Items]
Goodwill acquired during period | $			$ 4,000,000	$ 55,000
Additions to finite-lived intangible assets | $			$ 2,000,000	$ 162,000
Number of Acquisitions					2
Whitnell [Member]
Business Acquisition [Line Items]
Number of Acquisitions	1
Bank Mutual [Member]
Business Acquisition [Line Items]
Number of Acquisitions		1
Consideration shares transferred | shares		0.422

Investment Securities, AFS and

Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment securities available for sale
Amortized Cost	$ 4,100,417	$ 4,724,895
Gross Unrealized Gains	10,996	19,132
Gross Unrealized Losses	(67,967)	(63,801)
Fair Value	4,043,446	4,680,226
Investment securities held to maturity
Amortized Cost	2,282,853	1,273,536
Gross Unrealized Gains	26,543	4,523
Gross Unrealized Losses	(25,822)	(13,385)
Fair Value	2,283,574	1,264,674
U.S. Treasury securities
Investment securities available for sale
Amortized Cost	1,003	1,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7)	0
Fair Value	996	1,000
Obligations of state and political subdivisions (municipal securities)
Investment securities held to maturity
Amortized Cost	1,281,320	1,145,843
Gross Unrealized Gains	13,899	3,868
Gross Unrealized Losses	(3,177)	(12,036)
Fair Value	1,292,042	1,137,675
Private-label
Investment securities available for sale
Amortized Cost	1,067	1,134
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(8)	(14)
Fair Value	1,059	1,121
Investment securities held to maturity
Amortized Cost	0
Fair Value	0
GNMA commercial mortgage-related securities
Investment securities available for sale
Amortized Cost	1,547,173	2,064,508
Gross Unrealized Gains	5	356
Gross Unrealized Losses	(33,901)	(35,966)
Fair Value	1,513,277	2,028,898
Investment securities held to maturity
Amortized Cost	546,098
Gross Unrealized Gains	9,546
Gross Unrealized Losses	(15,756)
Fair Value	539,888
Asset backed Securities
Investment securities available for sale
Amortized Cost	144,322
Gross Unrealized Gains	867
Gross Unrealized Losses	(13)
Fair Value	145,176
Investment securities held to maturity
Amortized Cost	0
Fair Value	0
Other securities (debt and equity)
Investment securities available for sale
Amortized Cost	4,719	4,718
Gross Unrealized Gains	127	105
Gross Unrealized Losses	(26)	(21)
Fair Value	4,820	4,802
FNMA / FHLMC | Residential Related Securities
Investment securities available for sale
Amortized Cost	457,680	625,234
Gross Unrealized Gains	9,722	17,298
Gross Unrealized Losses	(2,634)	(2,602)
Fair Value	464,768	639,930
Investment securities held to maturity
Amortized Cost	40,995	37,697
Gross Unrealized Gains	398	439
Gross Unrealized Losses	(489)	(693)
Fair Value	40,904	37,443
GNMA | Residential Related Securities
Investment securities available for sale
Amortized Cost	1,944,453	2,028,301
Gross Unrealized Gains	275	1,372
Gross Unrealized Losses	(31,378)	(25,198)
Fair Value	1,913,350	2,004,475
Investment securities held to maturity
Amortized Cost	414,440	89,996
Gross Unrealized Gains	2,700	216
Gross Unrealized Losses	(6,400)	(656)
Fair Value	$ 410,740	$ 89,556

Loans, Loan Composition (Detail

Loans, Loan Composition (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 20,784,991	$ 20,054,716
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,399,693	6,489,014
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	802,209	897,724
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,201,902	7,386,738
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,315,254	3,574,732
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,451,684	1,432,497
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,766,938	5,007,229
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	11,968,840	12,393,967
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,546,534	6,332,327
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	883,804	934,443
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	385,813	393,979
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 8,816,151	$ 7,660,749

Investment Securities, AFS an56

Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost
Due in one year or less	$ 1,001
Due after one year through five years	4,703
Due after five years through ten years	0
Due after ten years	0
Total debt securities	5,704
Fair Value
Due in one year or less	1,001
Due after one year through five years	4,669
Due after five years through ten years	0
Due after ten years	0
Total debt securities	5,670
Investment securities available for sale, amortized cost	4,100,417	$ 4,724,895
Investment securities available for sale, at fair value	$ 4,043,446	4,680,226
Ratio of Fair Value to Amortized Cost	98.60%
Amortized Cost
Due in one year or less	$ 50,089
Due after one year through five years	226,053
Due after five years through ten years	322,413
Due after ten years	682,765
Held-to-maturity Debt Securities, Amortized Cost Basis	1,281,320
Amortized Cost	2,282,853	1,273,536
Fair Value
Due in one year or less	44,781
Due after one year through five years	229,939
Due after five years through ten years	324,380
Due after ten years	692,942
Held-to-maturity Securities, Debt Securities	1,292,042
Total debt securities	$ 2,283,574	1,264,674
Ratio of Fair Value to Amortized Cost	100.00%
Private-label
Fair Value
Investment securities available for sale, amortized cost	$ 1,067	1,134
Investment securities available for sale, at fair value	1,059	1,121
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
GNMA commercial mortgage-related securities
Fair Value
Investment securities available for sale, amortized cost	1,547,173	2,064,508
Investment securities available for sale, at fair value	1,513,277	2,028,898
Amortized Cost
Amortized Cost	546,098
Fair Value
Total debt securities	539,888
Asset-backed Securities, Securitized Loans and Receivables [Member]
Fair Value
Investment securities available for sale, amortized cost	144,322
Investment securities available for sale, at fair value	145,176
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
Equity securities
Fair Value
Investment securities available for sale, amortized cost	18
Investment securities available for sale, at fair value	146
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
FNMA / FHLMC | Residential Related Securities
Fair Value
Investment securities available for sale, amortized cost	457,680	625,234
Investment securities available for sale, at fair value	464,768	639,930
Amortized Cost
Amortized Cost	40,995	37,697
Fair Value
Total debt securities	40,904	37,443
GNMA | Residential Related Securities
Fair Value
Investment securities available for sale, amortized cost	1,944,453	2,028,301
Investment securities available for sale, at fair value	1,913,350	2,004,475
Amortized Cost
Amortized Cost	414,440	89,996
Fair Value
Total debt securities	$ 410,740	$ 89,556

Loans, Related Party Loan Rollf

Loans, Related Party Loan Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable, Related Parties [Roll Forward]
Balance at beginning of year	$ 27,589	$ 36,597
New loans	5,329	10,677
Repayments	(7,632)	(11,089)
Changes due to status of executive officers and directors	(5,026)	(8,596)
Balance at end of year	$ 20,260	$ 27,589

Investment Securities, Gains, L

Investment Securities, Gains, Losses, and Proceeds (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains on available for sale securities	$ 0	$ 9,485	$ 12,270
Gross gains on held to maturity securities	439	33	0
Total Gains	439	9,518	12,270
Gross losses on available for sale securities	0	202	4,137
Gross losses on held to maturity securities	(5)	0	0
Total losses	(5)	(202)	(4,137)
Investment securities gains, net	434	9,316	8,133
Proceeds from Sale of Available-for-sale Securities	$ 18,467	$ 549,555	$ 1,601,947

Loans, Loans by Credit Quality

Loans, Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 20,784,991	$ 20,054,716
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	20,171,876	19,251,353
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	227,692	176,918
Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	176,877	351,142
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	208,546	275,303
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,399,693	6,489,014
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,015,884	5,937,119
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	157,245	141,328
Commercial and industrial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	113,778	227,196
Commercial and industrial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	112,786	183,371
Commercial real estate — owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	802,209	897,724
Commercial real estate — owner occupied | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	723,291	805,871
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	14,181	17,785
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	41,997	64,524
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	22,740	9,544
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,201,902	7,386,738
Commercial and business lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,739,175	6,742,990
Commercial and business lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	171,426	159,113
Commercial and business lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	155,775	291,720
Commercial and business lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	135,526	192,915
Commercial real estate — investor
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,315,254	3,574,732
Commercial real estate — investor | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,266,389	3,491,217
Commercial real estate — investor | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	24,845	14,236
Commercial real estate — investor | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	19,291	51,228
Commercial real estate — investor | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,729	18,051
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,451,684	1,432,497
Real estate construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,421,504	1,429,083
Real estate construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	29,206	105
Real estate construction | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	2,465
Real estate construction | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	974	844
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,766,938	5,007,229
Commercial real estate lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,687,893	4,920,300
Commercial real estate lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	54,051	14,341
Commercial real estate lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	19,291	53,693
Commercial real estate lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	5,703	18,895
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	11,968,840	12,393,967
Total commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	11,427,068	11,663,290
Total commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	225,477	173,454
Total commercial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	175,066	345,413
Total commercial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	141,229	211,810
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,546,534	6,332,327
Residential mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,490,860	6,275,162
Residential mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	426	1,314
Residential mortgage | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,616	5,615
Residential mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	53,632	50,236
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	883,804	934,443
Home equity | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	868,958	919,740
Home equity | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,137	1,588
Home equity | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	195	114
Home equity | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	13,514	13,001
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	385,813	393,979
Other consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	384,990	393,161
Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	652	562
Other consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	0
Other consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	171	256
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,816,151	7,660,749
Total consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,744,808	7,588,063
Total consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,215	3,464
Total consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,811	5,729
Total consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 67,317	$ 63,493

Investment Securities, AFS an60

Investment Securities, AFS and HTM Securities Gross Unrealized Losses (Details) $ in Thousands	Dec. 31, 2017USD ($)security	Dec. 31, 2016USD ($)security
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (15,099)	$ (44,266)
Unrealized losses on available for sale securities, 12 months or more	(52,868)	(19,535)
Total unrealized losses on available for sale securities	(67,967)	(63,801)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,593,503	3,397,143
Fair value of unrealized losses on available for sale securities, 12 months or more	1,906,992	430,377
Total fair value of unrealized losses on available for sale securities	$ 3,500,495	$ 3,827,520
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	92	145
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	105	22
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (4,491)	$ (13,034)
Unrealized losses on held to maturity securities, 12 months or more	(21,331)	(351)
Total unrealized losses on held to maturity securities	(25,822)	(13,385)
Fair value of unrealized losses on held to maturity securities, less than 12 months	$ 457,289	$ 496,296
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, 12 Months or Longer | security	183	5
Fair value of unrealized losses on held to maturity securities, 12 months or more	$ 751,088	$ 7,783
Total fair value of unrealized losses on held to maturity securities	$ 1,208,377	$ 504,079
Held-to-maturity, Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions, less than 12 Months | security	202	753
U.S. Treasury securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (7)
Unrealized losses on available for sale securities, 12 months or more	0
Total unrealized losses on available for sale securities	(7)
Fair value of unrealized losses on available for sale securities, less than 12 months	996
Fair value of unrealized losses on available for sale securities, 12 months or more	0
Total fair value of unrealized losses on available for sale securities	$ 996
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	1
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	0
Obligations of state and political subdivisions (municipal securities)
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (746)	$ (11,937)
Unrealized losses on held to maturity securities, 12 months or more	(2,431)	(99)
Total unrealized losses on held to maturity securities	(3,177)	(12,036)
Fair value of unrealized losses on held to maturity securities, less than 12 months	122,761	414,186
Fair value of unrealized losses on held to maturity securities, 12 months or more	127,043	1,752
Total fair value of unrealized losses on held to maturity securities	$ 249,804	$ 415,938
Obligations of state and political subdivisions (municipal securities) | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	157	700
Obligations of state and political subdivisions (municipal securities) | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	132	4
Private-label
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ 0	$ 0
Unrealized losses on available for sale securities, 12 months or more	(8)	(14)
Total unrealized losses on available for sale securities	(8)	(14)
Fair value of unrealized losses on available for sale securities, less than 12 months	0	0
Fair value of unrealized losses on available for sale securities, 12 months or more	1,059	1,119
Total fair value of unrealized losses on available for sale securities	$ 1,059	$ 1,119
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	0	0
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	1	1
GNMA commercial mortgage-related securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (5,554)	$ (16,445)
Unrealized losses on available for sale securities, 12 months or more	(28,347)	(19,521)
Total unrealized losses on available for sale securities	(33,901)	(35,966)
Fair value of unrealized losses on available for sale securities, less than 12 months	480,514	1,427,889
Fair value of unrealized losses on available for sale securities, 12 months or more	1,026,642	429,258
Total fair value of unrealized losses on available for sale securities	$ 1,507,156	$ 1,857,147
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	33	74
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	70	21
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (299)
Unrealized losses on held to maturity securities, 12 months or more	(15,457)
Total unrealized losses on held to maturity securities	(15,756)
Fair value of unrealized losses on held to maturity securities, less than 12 months	52,997
Fair value of unrealized losses on held to maturity securities, 12 months or more	486,891
Total fair value of unrealized losses on held to maturity securities	$ 539,888
GNMA commercial mortgage-related securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	2
GNMA commercial mortgage-related securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	23
Asset-backed Securities, Securitized Loans and Receivables [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (13)
Unrealized losses on available for sale securities, 12 months or more	0
Total unrealized losses on available for sale securities	(13)
Fair value of unrealized losses on available for sale securities, less than 12 months	12,158
Fair value of unrealized losses on available for sale securities, 12 months or more	0
Total fair value of unrealized losses on available for sale securities	$ 12,158
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	1
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	0
Other securities (debt and equity)
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (26)	$ (21)
Unrealized losses on available for sale securities, 12 months or more	0	0
Total unrealized losses on available for sale securities	(26)	(21)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,675	1,479
Fair value of unrealized losses on available for sale securities, 12 months or more	0	0
Total fair value of unrealized losses on available for sale securities	$ 1,675	$ 1,479
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	4	3
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	0	0
FNMA / FHLMC | Residential Related Securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (572)	$ (2,602)
Unrealized losses on available for sale securities, 12 months or more	(2,062)	0
Total unrealized losses on available for sale securities	(2,634)	(2,602)
Fair value of unrealized losses on available for sale securities, less than 12 months	69,939	244,252
Fair value of unrealized losses on available for sale securities, 12 months or more	142,093	0
Total fair value of unrealized losses on available for sale securities	$ 212,032	$ 244,252
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	9	14
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	9	0
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (73)	$ (441)
Unrealized losses on held to maturity securities, 12 months or more	(417)	(252)
Total unrealized losses on held to maturity securities	(490)	(693)
Fair value of unrealized losses on held to maturity securities, less than 12 months	13,143	17,477
Fair value of unrealized losses on held to maturity securities, 12 months or more	16,262	6,031
Total fair value of unrealized losses on held to maturity securities	$ 29,405	$ 23,508
FNMA / FHLMC | Residential Related Securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	8	14
FNMA / FHLMC | Residential Related Securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	10	1
GNMA | Residential Related Securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (8,927)	$ (25,198)
Unrealized losses on available for sale securities, 12 months or more	(22,451)	0
Total unrealized losses on available for sale securities	(31,378)	(25,198)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,028,221	1,723,523
Fair value of unrealized losses on available for sale securities, 12 months or more	737,198	0
Total fair value of unrealized losses on available for sale securities	$ 1,765,419	$ 1,723,523
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	44	54
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	25	0
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (3,373)	$ (656)
Unrealized losses on held to maturity securities, 12 months or more	(3,026)	0
Total unrealized losses on held to maturity securities	(6,399)	(656)
Fair value of unrealized losses on held to maturity securities, less than 12 months	268,388	64,633
Fair value of unrealized losses on held to maturity securities, 12 months or more	120,892	0
Total fair value of unrealized losses on held to maturity securities	$ 389,280	$ 64,633
GNMA | Residential Related Securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	35	39
GNMA | Residential Related Securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	18	0

Loans, Loans by Past Due Status

Loans, Loans by Past Due Status (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summarized details of Loans
Current	$ 20,555,250	$ 19,756,523
Financing Receivable, Recorded Investment, Nonaccrual Status	208,546	275,303
Loans and Leases Receivable, Net of Deferred Income	20,784,991	20,054,716
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	2,000	2,000
Nonaccrual Loans, Current Portion	$ 135,000	$ 224,000
Percent of current nonaccrual loans	65.00%	81.00%
30-59 Days Past Due
Summarized details of Loans
Total Past Due	$ 16,861	$ 16,662
60-89 Days Past Due
Summarized details of Loans
Total Past Due	2,467	4,615
90 Days or More Past Due
Summarized details of Loans
Total Past Due	1,867	1,613
Commercial and industrial
Summarized details of Loans
Current	6,286,369	6,303,994
Financing Receivable, Recorded Investment, Nonaccrual Status	112,786	183,371
Loans and Leases Receivable, Net of Deferred Income	6,399,693	6,489,014
Commercial and industrial | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	170	965
Commercial and industrial | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	101	448
Commercial and industrial | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	267	236
Commercial real estate — owner occupied
Summarized details of Loans
Current	779,421	886,796
Financing Receivable, Recorded Investment, Nonaccrual Status	22,740	9,544
Loans and Leases Receivable, Net of Deferred Income	802,209	897,724
Commercial real estate — owner occupied | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	48	968
Commercial real estate — owner occupied | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	0	416
Commercial real estate — owner occupied | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	0
Commercial and business lending
Summarized details of Loans
Current	7,065,790	7,190,790
Financing Receivable, Recorded Investment, Nonaccrual Status	135,526	192,915
Loans and Leases Receivable, Net of Deferred Income	7,201,902	7,386,738
Commercial and business lending | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	218	1,933
Commercial and business lending | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	101	864
Commercial and business lending | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	267	236
Commercial real estate — investor
Summarized details of Loans
Current	3,310,000	3,555,750
Financing Receivable, Recorded Investment, Nonaccrual Status	4,729	18,051
Loans and Leases Receivable, Net of Deferred Income	3,315,254	3,574,732
Commercial real estate — investor | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	374	431
Commercial real estate — investor | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	0	500
Commercial real estate — investor | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	151	0
Real estate construction
Summarized details of Loans
Current	1,450,459	1,431,284
Financing Receivable, Recorded Investment, Nonaccrual Status	974	844
Loans and Leases Receivable, Net of Deferred Income	1,451,684	1,432,497
Real estate construction | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	168	264
Real estate construction | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	83	105
Real estate construction | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	0
Commercial real estate lending
Summarized details of Loans
Current	4,760,459	4,987,034
Financing Receivable, Recorded Investment, Nonaccrual Status	5,703	18,895
Loans and Leases Receivable, Net of Deferred Income	4,766,938	5,007,229
Commercial real estate lending | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	542	695
Commercial real estate lending | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	83	605
Commercial real estate lending | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	151	0
Total commercial
Summarized details of Loans
Current	11,826,249	12,177,824
Financing Receivable, Recorded Investment, Nonaccrual Status	141,229	211,810
Loans and Leases Receivable, Net of Deferred Income	11,968,840	12,393,967
Total commercial | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	760	2,628
Total commercial | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	184	1,469
Total commercial | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	418	236
Residential mortgage
Summarized details of Loans
Current	7,483,350	6,273,949
Financing Receivable, Recorded Investment, Nonaccrual Status	53,632	50,236
Loans and Leases Receivable, Net of Deferred Income	7,546,534	6,332,327
Residential mortgage | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	9,186	7,298
Residential mortgage | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	366	844
Residential mortgage | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	0
Home equity
Summarized details of Loans
Current	863,465	915,593
Financing Receivable, Recorded Investment, Nonaccrual Status	13,514	13,001
Loans and Leases Receivable, Net of Deferred Income	883,804	934,443
Home equity | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	5,688	4,265
Home equity | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	1,137	1,584
Home equity | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	0
Other consumer
Summarized details of Loans
Current	382,186	389,157
Financing Receivable, Recorded Investment, Nonaccrual Status	171	256
Loans and Leases Receivable, Net of Deferred Income	385,813	393,979
Other consumer | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	1,227	2,471
Other consumer | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	780	718
Other consumer | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	1,449	1,377
Total consumer
Summarized details of Loans
Current	8,729,001	7,578,699
Financing Receivable, Recorded Investment, Nonaccrual Status	67,317	63,493
Loans and Leases Receivable, Net of Deferred Income	8,816,151	7,660,749
Total consumer | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	16,101	14,034
Total consumer | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	2,283	3,146
Total consumer | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	$ 1,449	$ 1,377

Investment Securities (Details

Investment Securities (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity Securities, Sold Security, at Carrying Value	$ 18,000,000
Held-to-maturity Securities, Sold Security, Realized Gain (Loss)	434,000
Available-for-sale Securities, Transferred to Held-to-maturity Securities, at Carrying Value	1,000,000,000
Investment Securities (Textuals) [Abstract]
Proceeds from Sale of Securities		$ 550,000,000	$ 1,600,000,000
Marketable Securities, Gain (Loss)	434,000	9,316,000	$ 8,133,000
Securities pledged as collateral	3,100,000,000	1,800,000,000
Federal Home Loan Bank Stock	89,000,000	65,000,000
Federal Reserve Bank Stock	$ 76,000,000	$ 75,000,000

Loans, Impaired Loans Recorded

Loans, Impaired Loans Recorded Investment, Unpaid Principal Balance, Related Allowance, Average Recorded Investment, and Interest Income Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	$ 247,575	$ 316,735
Unpaid Principal Balance	275,814	349,045
Related Allowance	25,846	35,054
Average Recorded Investment	236,860	333,439
Interest Income Recognized	$ 8,051	$ 8,784
Net Recorded Investment of the Impaired Loans	80.00%	81.00%
Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	$ 175,681	$ 182,587
Unpaid Principal Balance	181,002	191,333
Related Allowance	25,846	35,054
Average Recorded Investment	140,098	192,891
Interest Income Recognized	7,254	6,939
Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	71,894	134,148
Unpaid Principal Balance	94,812	157,712
Related Allowance	0	0
Average Recorded Investment	96,762	140,548
Interest Income Recognized	797	1,845
Commercial and industrial
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	142,244	213,271
Unpaid Principal Balance	166,418	240,038
Related Allowance	10,838	21,047
Average Recorded Investment	147,769	222,788
Interest Income Recognized	3,121	3,864
Commercial and industrial | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	81,649	99,786
Unpaid Principal Balance	83,579	105,175
Related Allowance	10,838	21,047
Average Recorded Investment	58,494	104,808
Interest Income Recognized	2,629	2,345
Commercial and industrial | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	60,595	113,485
Unpaid Principal Balance	82,839	134,863
Related Allowance	0	0
Average Recorded Investment	89,275	117,980
Interest Income Recognized	492	1,519
Commercial real estate — owner occupied
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	26,234	13,983
Unpaid Principal Balance	26,766	14,834
Related Allowance	2,973	23
Average Recorded Investment	14,072	14,599
Interest Income Recognized	772	401
Commercial real estate — owner occupied | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	23,796	5,544
Unpaid Principal Balance	23,937	5,568
Related Allowance	2,973	23
Average Recorded Investment	12,124	5,840
Interest Income Recognized	736	263
Commercial real estate — owner occupied | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	2,438	8,439
Unpaid Principal Balance	2,829	9,266
Related Allowance	0	0
Average Recorded Investment	1,948	8,759
Interest Income Recognized	36	138
Commercial and business lending
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	168,478	227,254
Unpaid Principal Balance	193,184	254,872
Related Allowance	13,811	21,070
Average Recorded Investment	161,841	237,387
Interest Income Recognized	3,893	4,265
Commercial and business lending | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	105,445	105,330
Unpaid Principal Balance	107,516	110,743
Related Allowance	13,811	21,070
Average Recorded Investment	70,618	110,648
Interest Income Recognized	3,365	2,608
Commercial and business lending | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	63,033	121,924
Unpaid Principal Balance	85,668	144,129
Related Allowance	0	0
Average Recorded Investment	91,223	126,739
Interest Income Recognized	528	1,657
Commercial real estate — investor
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	19,118	32,908
Unpaid Principal Balance	19,157	33,509
Related Allowance	1,597	3,410
Average Recorded Investment	16,924	37,757
Interest Income Recognized	1,739	2,120
Commercial real estate — investor | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	17,823	26,764
Unpaid Principal Balance	17,862	27,031
Related Allowance	1,597	3,410
Average Recorded Investment	16,924	30,665
Interest Income Recognized	1,694	2,120
Commercial real estate — investor | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	1,295	6,144
Unpaid Principal Balance	1,295	6,478
Related Allowance	0	0
Average Recorded Investment	0	7,092
Interest Income Recognized	45	0
Real estate construction
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	467	509
Unpaid Principal Balance	578	648
Related Allowance	86	84
Average Recorded Investment	484	529
Interest Income Recognized	29	31
Real estate construction | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	467	509
Unpaid Principal Balance	578	648
Related Allowance	86	84
Average Recorded Investment	484	529
Interest Income Recognized	29	31
Real estate construction | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Commercial real estate lending
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	19,585	33,417
Unpaid Principal Balance	19,735	34,157
Related Allowance	1,683	3,494
Average Recorded Investment	17,408	38,286
Interest Income Recognized	1,768	2,151
Commercial real estate lending | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	18,290	27,273
Unpaid Principal Balance	18,440	27,679
Related Allowance	1,683	3,494
Average Recorded Investment	17,408	31,194
Interest Income Recognized	1,723	2,151
Commercial real estate lending | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	1,295	6,144
Unpaid Principal Balance	1,295	6,478
Related Allowance	0	0
Average Recorded Investment	0	7,092
Interest Income Recognized	45	0
Total commercial
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	188,063	260,671
Unpaid Principal Balance	212,919	289,029
Related Allowance	15,494	24,564
Average Recorded Investment	179,249	275,673
Interest Income Recognized	5,661	6,416
Total commercial | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	123,735	132,603
Unpaid Principal Balance	125,956	138,422
Related Allowance	15,494	24,564
Average Recorded Investment	88,026	141,842
Interest Income Recognized	5,088	4,759
Total commercial | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	64,328	128,068
Unpaid Principal Balance	86,963	150,607
Related Allowance	0	0
Average Recorded Investment	91,223	133,831
Interest Income Recognized	573	1,657
Residential mortgage
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	47,486	43,876
Unpaid Principal Balance	50,126	46,977
Related Allowance	6,512	6,438
Average Recorded Investment	45,410	45,218
Interest Income Recognized	1,831	1,735
Residential mortgage | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	40,561	37,902
Unpaid Principal Balance	42,922	39,979
Related Allowance	6,512	6,438
Average Recorded Investment	40,411	38,608
Interest Income Recognized	1,614	1,551
Residential mortgage | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	6,925	5,974
Unpaid Principal Balance	7,204	6,998
Related Allowance	0	0
Average Recorded Investment	4,999	6,610
Interest Income Recognized	217	184
Home equity
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	10,891	11,176
Unpaid Principal Balance	11,631	12,016
Related Allowance	3,718	3,943
Average Recorded Investment	11,061	11,527
Interest Income Recognized	556	631
Home equity | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	10,250	11,070
Unpaid Principal Balance	10,986	11,909
Related Allowance	3,718	3,943
Average Recorded Investment	10,521	11,420
Interest Income Recognized	549	627
Home equity | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	641	106
Unpaid Principal Balance	645	107
Related Allowance	0	0
Average Recorded Investment	540	107
Interest Income Recognized	7	4
Other consumer
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	1,135	1,012
Unpaid Principal Balance	1,138	1,023
Related Allowance	122	109
Average Recorded Investment	1,140	1,021
Interest Income Recognized	3	2
Other consumer | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	1,135	1,012
Unpaid Principal Balance	1,138	1,023
Related Allowance	122	109
Average Recorded Investment	1,140	1,021
Interest Income Recognized	3	2
Other consumer | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Total consumer
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	59,512	56,064
Unpaid Principal Balance	62,895	60,016
Related Allowance	10,352	10,490
Average Recorded Investment	57,611	57,766
Interest Income Recognized	2,390	2,368
Total consumer | Loans with a related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	51,946	49,984
Unpaid Principal Balance	55,046	52,911
Related Allowance	10,352	10,490
Average Recorded Investment	52,072	51,049
Interest Income Recognized	2,166	2,180
Total consumer | Loans with no related allowance
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	7,566	6,080
Unpaid Principal Balance	7,849	7,105
Related Allowance	0	0
Average Recorded Investment	5,539	6,717
Interest Income Recognized	$ 224	$ 188

Loans, Troubled Debt Restructur

Loans, Troubled Debt Restructurings Performing and Nonaccrual (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Performing Restructured Loans	$ 74,618	$ 79,857	$ 87,363
Nonaccrual Restructured Loans	23,486	29,385	37,684
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Performing Restructured Loans	30,047	31,884	29,293
Nonaccrual Restructured Loans	1,776	1,276	1,714
Commercial real estate — owner occupied
Financing Receivable, Modifications [Line Items]
Performing Restructured Loans	3,989	5,490	7,877
Nonaccrual Restructured Loans	0	2,220	2,703
Commercial real estate — investor
Financing Receivable, Modifications [Line Items]
Performing Restructured Loans	14,389	15,289	21,915
Nonaccrual Restructured Loans	0	924	3,936
Real estate construction
Financing Receivable, Modifications [Line Items]
Performing Restructured Loans	310	359	510
Nonaccrual Restructured Loans	157	150	177
Residential mortgage
Financing Receivable, Modifications [Line Items]
Performing Restructured Loans	17,068	18,100	19,870
Nonaccrual Restructured Loans	18,991	21,906	24,592
Home equity
Financing Receivable, Modifications [Line Items]
Performing Restructured Loans	7,705	7,756	7,069
Nonaccrual Restructured Loans	2,537	2,877	4,522
Other consumer
Financing Receivable, Modifications [Line Items]
Performing Restructured Loans	1,110	979	829
Nonaccrual Restructured Loans	$ 25	$ 32	$ 40

Loans, Loans Modified in a Trou

Loans, Loans Modified in a Troubled Debt Restructuring (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan	Dec. 31, 2015USD ($)loan
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	77	131	211
Recorded Investment	$ 9,426	$ 9,270	$ 41,131
Unpaid Principal Balance	$ 11,900	$ 9,631	$ 42,765
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	8	8	12
Recorded Investment	$ 3,991	$ 1,509	$ 2,219
Unpaid Principal Balance	$ 6,339	$ 1,526	$ 2,900
Commercial real estate — owner occupied
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	2	1	5
Recorded Investment	$ 690	$ 116	$ 3,694
Unpaid Principal Balance	$ 690	$ 122	$ 3,901
Commercial real estate — investor
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0	5
Recorded Investment	$ 0	$ 0	$ 21,573
Unpaid Principal Balance	$ 0	$ 0	$ 21,640
Real estate construction
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	1	4
Recorded Investment	$ 0	$ 65	$ 78
Unpaid Principal Balance	$ 0	$ 91	$ 79
Residential mortgage
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	45	63	97
Recorded Investment	$ 4,238	$ 5,535	$ 10,464
Unpaid Principal Balance	$ 4,364	$ 5,792	$ 10,996
Home equity
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	22	57	88
Recorded Investment	$ 507	$ 2,030	$ 3,103
Unpaid Principal Balance	$ 507	$ 2,084	$ 3,249
Other consumer
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	1	0
Recorded Investment	$ 0	$ 15	$ 0
Unpaid Principal Balance	$ 0	$ 16	$ 0

Loans, Troubled Debt Restruct66

Loans, Troubled Debt Restructurings Subsequent Default (Details)	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan	Dec. 31, 2015USD ($)loan
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	66	68	91
Recorded Investment | $	$ 3,879	$ 4,574	$ 8,232
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	2	0	2
Recorded Investment | $	$ 0	$ 0	$ 197
Residential mortgage
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	36	44	61
Recorded Investment | $	$ 3,137	$ 4,102	$ 6,815
Home equity
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	27	23	28
Recorded Investment | $	$ 735	$ 457	$ 1,220
Other consumer
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	1	1	0
Recorded Investment | $	$ 7	$ 15	$ 0

Loans, Changes in the Allowance

Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	$ 278,335	$ 274,264
Charge offs	(56,246)	(86,439)
Recoveries	16,791	21,510
Net charge offs	(39,455)	(64,929)
Provision for loan losses	27,000	69,000
Balance at end of period	265,880	278,335
Allowance for loan losses:
Individually evaluated for impairment	25,846	35,054
Collectively evaluated for impairment	240,034	243,281
Balance at end of period	265,880	278,335
Loans:
Individually evaluated for impairment	247,575	316,735
Collectively evaluated for impairment	20,537,416	19,737,981
Loans and Leases Receivable, Net of Deferred Income	20,784,991	20,054,716
Commercial and industrial
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	140,126	129,959
Charge offs	(44,533)	(71,016)
Recoveries	11,465	14,543
Net charge offs	(33,068)	(56,473)
Provision for loan losses	16,010	66,640
Balance at end of period	123,068	140,126
Allowance for loan losses:
Individually evaluated for impairment	10,838	21,047
Collectively evaluated for impairment	112,230	119,079
Balance at end of period	123,068	140,126
Loans:
Individually evaluated for impairment	142,244	213,271
Collectively evaluated for impairment	6,257,449	6,275,743
Loans and Leases Receivable, Net of Deferred Income	6,399,693	6,489,014
Commercial real estate — owner occupied
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	14,034	18,680
Charge offs	(344)	(512)
Recoveries	173	74
Net charge offs	(171)	(438)
Provision for loan losses	(3,511)	(4,208)
Balance at end of period	10,352	14,034
Allowance for loan losses:
Individually evaluated for impairment	2,973	23
Collectively evaluated for impairment	7,379	14,011
Balance at end of period	10,352	14,034
Loans:
Individually evaluated for impairment	26,234	13,983
Collectively evaluated for impairment	775,975	883,741
Loans and Leases Receivable, Net of Deferred Income	802,209	897,724
Commercial real estate — investor
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	45,285	43,018
Charge offs	(991)	(1,504)
Recoveries	242	1,624
Net charge offs	(749)	120
Provision for loan losses	(3,477)	2,147
Balance at end of period	41,059	45,285
Allowance for loan losses:
Individually evaluated for impairment	1,597	3,410
Collectively evaluated for impairment	39,462	41,875
Balance at end of period	41,059	45,285
Loans:
Individually evaluated for impairment	19,118	32,908
Collectively evaluated for impairment	3,296,136	3,541,824
Loans and Leases Receivable, Net of Deferred Income	3,315,254	3,574,732
Real estate construction
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	26,932	25,266
Charge offs	(604)	(558)
Recoveries	74	203
Net charge offs	(530)	(355)
Provision for loan losses	7,968	2,021
Balance at end of period	34,370	26,932
Allowance for loan losses:
Individually evaluated for impairment	86	84
Collectively evaluated for impairment	34,284	26,848
Balance at end of period	34,370	26,932
Loans:
Individually evaluated for impairment	467	509
Collectively evaluated for impairment	1,451,217	1,431,988
Loans and Leases Receivable, Net of Deferred Income	1,451,684	1,432,497
Residential mortgage
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	27,046	28,261
Charge offs	(2,611)	(4,332)
Recoveries	927	755
Net charge offs	(1,684)	(3,577)
Provision for loan losses	4,245	2,362
Balance at end of period	29,607	27,046
Allowance for loan losses:
Individually evaluated for impairment	6,512	6,438
Collectively evaluated for impairment	23,095	20,608
Balance at end of period	29,607	27,046
Loans:
Individually evaluated for impairment	47,486	43,876
Collectively evaluated for impairment	7,499,048	6,288,451
Loans and Leases Receivable, Net of Deferred Income	7,546,534	6,332,327
Home equity
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	20,364	23,555
Charge offs	(2,724)	(4,686)
Recoveries	3,194	3,491
Net charge offs	470	(1,195)
Provision for loan losses	1,292	(1,996)
Balance at end of period	22,126	20,364
Allowance for loan losses:
Individually evaluated for impairment	3,718	3,943
Collectively evaluated for impairment	18,408	16,421
Balance at end of period	22,126	20,364
Loans:
Individually evaluated for impairment	10,891	11,176
Collectively evaluated for impairment	872,913	923,267
Loans and Leases Receivable, Net of Deferred Income	883,804	934,443
Other consumer
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	4,548	5,525
Charge offs	(4,439)	(3,831)
Recoveries	716	820
Net charge offs	(3,723)	(3,011)
Provision for loan losses	4,473	2,034
Balance at end of period	5,298	4,548
Allowance for loan losses:
Individually evaluated for impairment	122	109
Collectively evaluated for impairment	5,176	4,439
Balance at end of period	5,298	4,548
Loans:
Individually evaluated for impairment	1,135	1,012
Collectively evaluated for impairment	384,678	392,967
Loans and Leases Receivable, Net of Deferred Income	$ 385,813	$ 393,979

Loans Loans, Changes in the All

Loans Loans, Changes in the Allowance for Loan Losses by Oil and Gas Segment (Details) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year	$ 278,335	$ 274,264
Charge offs	(56,246)	(86,439)
Recoveries	16,791	21,510
Net charge offs	(39,455)	(64,929)
Provision for Loan Losses	27,000	69,000
Balance at end of period	265,880	278,335
Allowance for loan losses
Individually evaluated	25,846	35,054
Collectively evaluated	240,034	243,281
Balance at end of period	265,880	278,335
Loans
Individually evaluated	247,575	316,735
Collectively evaluated	20,537,416	19,737,981
Loans and Leases Receivable, Net of Deferred Income	20,784,991	20,054,716
Oil and Gas Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year	38,000	42,000
Charge offs	(25,000)	(59,000)
Recoveries	0	0
Net charge offs	(25,000)	(59,000)
Provision for Loan Losses	14,000	55,000
Balance at end of period	27,000	38,000
Allowance for loan losses
Individually evaluated	5,000	14,000
Collectively evaluated	22,000	24,000
Balance at end of period	27,000	38,000
Loans
Individually evaluated	77,000	147,000
Collectively evaluated	523,000	521,000
Loans and Leases Receivable, Net of Deferred Income	$ 600,000	$ 668,000

Loans, Changes in the Allowan69

Loans, Changes in the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in the Allowance for Unfunded Commitments
Balance at beginning of period	$ 25,000
Balance at end of period	24,000	$ 25,000
Allowance for Unfunded Commitments
Change in the Allowance for Unfunded Commitments
Balance at beginning of period	25,400	24,400	$ 24,900
Provision for Other Credit Losses	(1,000)	1,000	(500)
Balance at end of period	$ 24,400	$ 25,400	$ 24,400

Loans (Details Textuals)

Loans (Details Textuals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	$ (265,880)	$ (278,335)	$ (274,264)
Financing Receivable, Modifications, Post-Modification Recorded Investment	9,426	9,270	41,131
Restructured Loans Subsequently Accruing	6,000
Ytd Restructured Loans Still On Nonaccrual	3,000
Loans and Leases Receivable, Impaired, Commitment to Lend	9,000
Oil and Gas Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	$ (27,000)	$ (38,000)	$ (42,000)
Percent of Loans	4.50%

Goodwill and Intangible Assets,

Goodwill and Intangible Assets, Summary of Core Deposit and Other Intangibles (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of core deposit intangibles and other intangibles
Additions during the period	$ 2,000,000	$ 162,000
Amortization of other intangible assets			$ 1,959,000	$ 2,093,000	$ 3,094,000
Core Deposit Intangibles
Summary of core deposit intangibles and other intangibles
Gross carrying amount	4,385,000		4,385,000	4,385,000	19,545,000
Accumulated amortization	(4,385,000)		(4,385,000)	(4,273,000)	(19,152,000)
Total Estimated Amortization Expense	0		0	112,000	393,000
Amortization of other intangible assets			112,000	281,000	1,404,000
Other Intangibles
Summary of core deposit intangibles and other intangibles
Gross carrying amount	34,572,000		34,572,000	32,410,000	31,398,000
Accumulated amortization	(18,992,000)		(18,992,000)	(17,145,000)	(15,333,000)
Total Estimated Amortization Expense	$ 15,580,000		15,580,000	15,265,000	16,065,000
Additions during the period			2,162,000	1,012,000	12,115,000
Amortization of other intangible assets			$ 1,847,000	$ 1,812,000	$ 1,690,000

Goodwill and Intangible Asset72

Goodwill and Intangible Assets, Mortgage Servicing Rights Roll-Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Mortgage servicing rights:
Mortgage servicing rights at beginning of year	$ 62,085	$ 62,150	$ 61,379
Additions	7,167	12,262	12,372
Amortization	(10,084)	(12,327)	(11,601)
Mortgage servicing rights at end of year	59,168	62,085	62,150
Valuation Allowance for Impairment of Recognized Servicing Assets [Roll Forward]
Valuation allowance at beginning of year	(609)	(809)	(1,234)
(Additions) recoveries, net	(175)	200	425
Valuation allowance at end of year	(784)	(609)	(809)
Mortgage servicing rights, net	58,384	61,476	61,341
Fair value of mortgage servicing rights	64,387	73,149	70,686
Portfolio of residential mortgage loans serviced for others (“servicing portfolio”)	$ 7,646,846	$ 7,974,742	$ 7,915,224
Mortgage servicing rights, net to servicing portfolio	0.76%	0.77%	0.77%
Mortgage servicing rights expense	$ 10,259	$ 12,127	$ 11,176

Goodwill and Intangible Asset73

Goodwill and Intangible Assets, Estimated Future Amortization Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Core Deposit Intangibles
Estimated future amortization expense
Total Estimated Amortization Expense	$ 0	$ 112	$ 393
Other Intangibles
Estimated future amortization expense
Year ending December 31, 2017	1,971
Year ending December 31, 2018	1,672
Year ending December 31, 2019	1,555
Year ending December 31, 2020	1,531
Year ending December 31, 2021	1,508
Beyond 2,022	7,343
Total Estimated Amortization Expense	15,580	$ 15,265	$ 16,065
Mortgage Servicing Rights
Estimated future amortization expense
Year ending December 31, 2017	9,590
Year ending December 31, 2018	8,051
Year ending December 31, 2019	6,747
Year ending December 31, 2020	5,670
Year ending December 31, 2021	4,783
Beyond 2,022	24,327
Total Estimated Amortization Expense	$ 59,168

Goodwill and Intangible Asset74

Goodwill and Intangible Assets (Details Textuals)	3 Months Ended		12 Months Ended
	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)acquisition	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Business Acquisition [Line Items]
Goodwill, Impairment Loss			$ 0	$ 0	$ 0
Goodwill acquired during period	$ 4,000,000	$ 55,000
Goodwill	976,239,000		$ 976,239,000	$ 971,951,000
Additions to finite-lived intangible assets	$ 2,000,000	162,000
Number of Acquisitions | acquisition			2
Customer Relationships [Member]
Business Acquisition [Line Items]
Additions to finite-lived intangible assets		$ 162,000

Premises and Equipment, Summary

Premises and Equipment, Summary Composition (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 653,323
Accumulated Depreciation	322,360
Net Book Value	330,963	$ 330,315
Land
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	59,257
Accumulated Depreciation	0
Net Book Value	59,257	57,471
Land improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	13,115
Accumulated Depreciation	6,802
Net Book Value	$ 6,313	6,643
Land improvements | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	15 years
Land improvements | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	3 years
Buildings and improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 341,947
Accumulated Depreciation	143,516
Net Book Value	$ 198,431	202,152
Buildings and improvements | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	39 years
Buildings and improvements | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	5 years
Computers
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 42,604
Accumulated Depreciation	31,526
Net Book Value	$ 11,078	9,051
Computers | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	5 years
Computers | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	3 years
Furniture, fixtures and other equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 161,699
Accumulated Depreciation	119,650
Net Book Value	$ 42,049	42,549
Furniture, fixtures and other equipment | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	15 years
Furniture, fixtures and other equipment | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	3 years
Leasehold improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 34,701
Accumulated Depreciation	20,866
Net Book Value	$ 13,835	$ 12,449
Leasehold improvements | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	15 years
Leasehold improvements | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	3 years

Premises and Equipment, Minimum

Premises and Equipment, Minimum Annual Rent Under Operating Lease Agreements (Details) $ in Thousands	Dec. 31, 2017USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Payments, 2018	$ 9,815
Payments, 2019	9,686
Payments, 2020	8,886
Payments, 2021	8,085
Payments, 2022	5,796
Payments, thereafter	22,447
Payments, total	64,715
Operating Leases, Future Minimum Payments Receivable [Abstract]
Receipts, 2018	3,783
Receipts, 2019	4,415
Receipts, 2020	1,996
Receipts, 2021	1,676
Receipts, 2022	724
Receipts, thereafter	774
Receipts, total	$ 13,368

Premises and Equipment (Details

Premises and Equipment (Details Textuals) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 32	$ 32	$ 33
Rental expense under leases	6	8	$ 13
Milwaukee Center
Property, Plant and Equipment [Line Items]
Leasing income	$ 5	$ 4

Deposits, Composition (Details)

Deposits, Composition (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deposits, by Type [Abstract]
Noninterest-bearing demand deposits	$ 5,478,416	$ 5,392,208
Savings	1,524,992	1,431,494
Interest-bearing demand	4,603,157	4,687,656
Money market	8,830,328	8,770,963
Brokered CDs	18,609	52,725
Other time	2,330,460	1,553,402
Total deposits	$ 22,785,962	$ 21,888,448

Short-term Funding, Composition

Short-term Funding, Composition (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt [Abstract]
Federal funds purchased	$ 141,950	$ 208,150
Securities sold under agreements to repurchase	182,865	300,197
Federal funds purchased and securities sold under agreements to repurchase	324,815	508,347
FHLB advances	284,000	482,000
Commercial paper	67,467	101,688
Other short-term funding	351,467	583,688
Total short-term funding	$ 676,282	$ 1,092,035

Deposits, Time Deposit Maturiti

Deposits, Time Deposit Maturities (Details)	Dec. 31, 2017USD ($)
Time Deposits, Fiscal Year Maturity [Abstract]
2,018	$ 1,708,582
2,019	298,774
2,020	198,206
2,021	84,306
2,022	57,618
Thereafter	1,583
Total	$ 2,349,069

Short-term Funding Short-term F

Short-term Funding Short-term Funding, Repurchase Agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Remaining Contractual Maturity of the Agreements
Repurchase agreements	$ 182,865	$ 300,197
Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	182,865	300,197
Overnight and Continuous
Remaining Contractual Maturity of the Agreements
Repurchase agreements	182,865	300,197
Overnight and Continuous | Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	182,865	300,197
Up to 30 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
Up to 30 days | Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
30-90 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
30-90 days | Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
Greater than 90 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
Greater than 90 days | Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	$ 0	$ 0

Deposits (Details Textuals)

Deposits (Details Textuals) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deposits [Abstract]
Time Deposits, $100,000 or More	$ 1,400	$ 571
Time Deposits, $250,000 Or More	$ 1,100	$ 235

Short-term Funding Short-term83

Short-term Funding Short-term Funding (Details Textuals) (Details) $ in Millions	Dec. 31, 2017USD ($)
Short-term Debt [Abstract]
Collateral for repurchase agreements	$ 325

Long-term Funding, Composition

Long-term Funding, Composition (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long-term Funding
FHLB advances	$ 2,900,168	$ 2,265,188
Senior notes, at par	250,000	250,000
Subordinated notes, at par	250,000	250,000
Other Long-term Debt and Capitalized Costs	(2,718)	(3,393)
Total long-term funding	$ 3,397,450	$ 2,761,795

Long-term Funding, Maturities (

Long-term Funding, Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Maturities of Long-term Debt [Abstract]
2,018	$ 1,750,000
2,019	499,313
2,020	155
2,021	150,000
2,022	0
Thereafter	997,982
Total long-term funding	$ 3,397,450	$ 2,761,795

Long-term Funding (Textual) (De

Long-term Funding (Textual) (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2014	Dec. 31, 2017	Dec. 31, 2016
Subordinated Borrowing [Line Items]
Federal Home Loan Bank, Advances, Weighted Average Interest Rate		1.26%	0.50%
Long-term Federal Home Loan Bank Advances		$ 6,600
Federal Home Loan Bank Advances		$ 3,200
Two Thousand Fourteen Senior Notes [Member]
Subordinated Borrowing [Line Items]
New Senior Debt Issued	$ 250
Debt Instrument, Interest Rate, Stated Percentage	2.75%
Two Thousand Fourteen Subordinated Notes [Member]
Subordinated Borrowing [Line Items]
Junior Subordinated Debentures Issued	$ 250
Debt Instrument, Term	10 years
Subordinated Borrowing, Interest Rate	4.25%

Stockholders' Equity (Details T

Stockholders' Equity (Details Textuals)	Sep. 15, 2016USD ($)$ / sharesshares	Jun. 15, 2015$ / sharesshares	Sep. 14, 2011$ / sharesshares	Nov. 30, 2008USD ($)$ / shares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)shares	Sep. 15, 2021	Jul. 25, 2017USD ($)	Aug. 28, 2015USD ($)	Jul. 23, 2013USD ($)	Dec. 06, 2011$ / shares
Stockholders' Equity Note [Abstract]
Subsidiary equity balance | $					$ 3,300,000,000
Class of Stock [Line Items]
Common shares, par value (in usd per share) | $ / shares					$ 0.01	$ 0.01
Purchase of preferred stock | $						$ 1,248,000	$ 1,335,000
Series B Preferred Stock
Class of Stock [Line Items]
Stock repurchase program authorized amount | $											$ 10,000,000
Treasury stock shares acquired (in shares) | shares							50,000
Preferred Stock, Dividend Rate, Percentage			8.00%
Depositary shares issued (in shares) | shares			2,600,000
Depository share ratio			0.025
Purchase of preferred stock | $	$ 59,000,000						$ 1,000,000
Liquidation preference on depositary shares (in usd per share) | $ / shares			$ 1,000
Series C Preferred Stock
Class of Stock [Line Items]
Stock repurchase program authorized amount | $										$ 10,000,000
Remaining authorized repurchase amount | $					$ 10,000,000
Preferred Stock, Dividend Rate, Percentage		6.125%
Depositary shares issued (in shares) | shares		2,600,000
Depository share ratio		0.025
Preferred Stock, Dividend Payment Terms		Jun. 15, 2020
Redemption Price On Depositary Shares | $ / shares		$ 1,000
Liquidation preference on depositary shares (in usd per share) | $ / shares		1,000
Depositary share value (in usd per share) | $ / shares		$ 25
Series D Preferred Stock
Class of Stock [Line Items]
Stock repurchase program authorized amount | $									$ 15,000,000
Remaining authorized repurchase amount | $					$ 15,000,000
Preferred Stock, Dividend Rate, Percentage	5.375%
Depositary shares issued (in shares) | shares	4,000,000
Depository share ratio	0.025
Preferred Stock, Dividend Payment Terms								Sep. 15, 2021
Redemption Price On Depositary Shares | $ / shares	$ 1,000
Liquidation preference on depositary shares (in usd per share) | $ / shares	1,000
Depositary share value (in usd per share) | $ / shares	$ 25
Common Stock
Class of Stock [Line Items]
Treasury stock shares acquired (in shares) | shares					1,600,000	1,000,000
Warrants to purchase shares of common stock (in shares) | $				$ 4,000,000
Term of warrants				10 years
Exercise price of warrants (in usd per share) | $ / shares				$ 19.77
Common shares, par value (in usd per share) | $ / shares												$ 0.01
Treasury stock carrying basis | $					$ 37,000,000	$ 20,000,000
Treasury stock acquired average cost per share (in usd per share) | $ / shares					$ 23.59	$ 17.10
Repurchased amount for minimum tax withholding settlement | $					$ 9,000,000	$ 5,000,000
Repurchased shares for minimum tax withholding settlements (in shares) | shares					370,000	293,000
Minimum tax withholding settlement average cost per share (in usd per share) | $ / shares					$ 25.08	$ 17.30
Remaining authorized repurchase amount | $					$ 51,000,000

Stock-Based Compensation, Stock

Stock-Based Compensation, Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair value assumptions of stock options
Dividend yield	2.00%	2.50%	2.00%
Risk-free interest rate	2.00%	2.00%	2.00%
Weighted average expected volatility	25.00%	25.00%	20.00%
Weighted average expected life	5 years 6 months	5 years 6 months	6 years
Weighted average per share fair value of stock options (in usd per share)	$ 5.30	$ 3.36	$ 3.08
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Stock Options Shares Outstanding, Beginning balance (in shares)	6,357,843
Granted (in shares)	799,558
Exercised (in shares)	(1,551,669)
Forfeited or expired (in shares)	(487,045)
Stock Options Shares Outstanding, Ending balance (in shares)	5,118,687	6,357,843
Options exercisable (in shares)	2,831,736
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Stock Options Outstanding, Weighted Average Exercise Price, Beginning balance (in usd per share)	$ 17.67
Granted, Weighted Average Exercise Price (in usd per share)	25.61
Exercised, Weighted Average Exercise Price (in usd per share)	16.87
Forfeited or expired, Weighted Average Exercise Price (in usd per share)	31.84
Stock Options Outstanding, Weighted Average Exercise Price, Ending balance (in usd per share)	18.02	$ 17.67
Options Exercisable, Weighted Average Exercise Price (in usd per share)	$ 16.31
Stock Options Outstanding, Weighted Average Remaining Contractual Term	6 years 5 months 23 days	6 years 1 month 6 days
Options exercisable, Weighted Average Remaining Contractual Term	5 years 2 months 23 days
Stock Options Outstanding, Aggregate Intrinsic Value	$ 38,028	$ 47,902
Options exercisable, Aggregate Intrinsic Value	$ 25,738

Stock-Based Compensation, Restr

Stock-Based Compensation, Restricted Stock Activity (Details)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding Shares, Beginning balance (in shares) | shares	2,377,380
Granted (in shares) | shares	767,627
Vested (in shares) | shares	(999,917)
Forfeited (in shares) | shares	(119,019)
Outstanding Shares, Ending balance (in shares) | shares	2,026,071
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding, Weighted Average Grant Date Fair Value, Beginning balance (in usd per share) | $ / shares	$ 17.40
Granted, Weighted Average Grant Date Fair Value (in usd per share) | $ / shares	25.54
Vested, Weighted Average Grant Date Fair Value (in usd per share) | $ / shares	18.01
Forfeited, Weighted Average Grant Date Fair Value (in usd per share) | $ / shares	20
Outstanding Weighted Average Grant Date Fair Value, Ending balance (in usd per share) | $ / shares	$ 19.68

Stock-Based Compensation (Detai

Stock-Based Compensation (Details Textuals) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Based Compensation (Textuals) [Abstract]
Intrinsic value of stock options exercised	$ 13,000,000	$ 9,000,000	$ 7,000,000
Total fair value of vested stock options	$ 4,000,000	3,000,000	6,000,000
2017 Incentive Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Period	4 years
Expiration term of awards	10 years
Shares remaining available for grant (in shares)	14
Performance-based Restricted Stock Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Period	3 years
Term of transfer restrictions	3 years
Service-based Restricted Stock Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Period	4 years
Term of transfer restrictions	4 years
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense for accelerated vesting of stock options	$ 650,000
Recognized compensation expense for vesting of stock options	4,000,000	4,000,000	4,000,000
Unvested share-based payment awards	$ 5,000,000
Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized Year For Recognition	first quarter 2021
Restricted Stock Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense for accelerated vesting of stock options	$ 3,000,000
Recognized compensation expense for vesting of stock options	18,000,000	$ 18,000,000	$ 15,000,000
Unvested share-based payment awards	$ 18,000,000
Employee Service Share Based Compensation Nonvested Awards Compensation Cost Not Yet Recognized Year For Recognition	first quarter 2021

Retirement Plans, Pension and P

Retirement Plans, Pension and Postretirement Plans Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets As A Percentage Of Net Benefit Obligation	178.00%	167.00%
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	$ 295,718
Fair value of plan assets at end of year	331,610	$ 295,718
Change in Benefit Obligation
Plan amendments	0	(1,759)	$ 0
Retirement Account Plan
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	295,718	289,599
Actual return on plan assets	41,490	17,097
Employer contributions	6,242	0
Gross benefits paid	(11,841)	(10,978)
Fair value of plan assets at end of year	331,609	295,718	289,599
Change in Benefit Obligation
Net benefit obligation at beginning of year	176,825	171,783
Service cost	6,955	6,780	11,257
Interest cost	7,121	7,121	6,617
Plan amendments	0	(823)
Actuarial (gain) loss	7,363	2,942
Gross benefits paid	(11,841)	(10,978)
Net benefit obligation at end of year	186,423	176,825	171,783
Funded (unfunded) status	145,186	118,893
Noncurrent assets	145,186	118,893
Current liabilities	0	0
Noncurrent liabilities	0	0
Asset (Liability) Recognized in the Consolidated Balance Sheets	145,186	118,893
Postretirement Plan
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	235	248
Gross benefits paid	(235)	(248)
Fair value of plan assets at end of year	0	0	0
Change in Benefit Obligation
Net benefit obligation at beginning of year	2,403	3,436
Service cost	0	0	0
Interest cost	101	142	141
Plan amendments	0	(936)
Actuarial (gain) loss	209	9
Gross benefits paid	(235)	(248)
Net benefit obligation at end of year	2,478	2,403	$ 3,436
Funded (unfunded) status	(2,478)	(2,403)
Noncurrent assets	0	0
Current liabilities	(233)	(215)
Noncurrent liabilities	(2,245)	(2,188)
Asset (Liability) Recognized in the Consolidated Balance Sheets	$ (2,478)	$ (2,403)

Retirement Plans, Amounts Recog

Retirement Plans, Amounts Recognized in Accumulated Other Comprehensive Income Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Retirement Account Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	$ (295)	$ (342)
Net actuarial loss	24,926	35,443
Amount not yet recognized in net periodic benefit cost, but recognized in accumulated other comprehensive loss	24,631	35,101
Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(531)	(580)
Net actuarial loss	205	79
Amount not yet recognized in net periodic benefit cost, but recognized in accumulated other comprehensive loss	$ (326)	$ (501)

Retirement Plans, Other Changes

Retirement Plans, Other Changes in Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost	$ (148)	$ (73)	$ 50
Amortization of actuarial loss (gain)	16,555	(4,026)	(15,636)
Plan amendments	0	1,759	0
Income tax (expense) benefit	(6,112)	815	5,873
Other comprehensive income (loss) on pension and postretirement obligations	10,295	(1,525)	$ (9,713)
Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss)	(209)	(9)
Amortization of prior service cost	(75)	0
Amortization of actuarial loss (gain)	4	0
Plan amendments	0	936
Income tax (expense) benefit	107	(353)
Other comprehensive income (loss) on pension and postretirement obligations	(173)	574
Retirement Account Plan
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss)	14,482	(6,132)
Amortization of prior service cost	(73)	(73)
Amortization of actuarial loss (gain)	2,278	2,115
Plan amendments	0	823
Income tax (expense) benefit	(6,219)	1,168
Other comprehensive income (loss) on pension and postretirement obligations	$ 10,468	$ (2,099)

Retirement Plans, Components of

Retirement Plans, Components of Net Periodic Benefit Cost for the Pension and Postretirement Tables (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Account Plan
Net period benefit cost for the pension and postretirement plans
Service cost	$ 6,955	$ 6,780	$ 11,257
Interest cost	7,121	7,121	6,617
Expected return on plan assets	(19,646)	(20,287)	(21,438)
Prior service cost	(73)	(73)	50
Actuarial (gain) loss	2,278	2,115	2,256
Total net pension cost	(3,365)	(4,344)	(1,258)
Postretirement Plan
Net period benefit cost for the pension and postretirement plans
Service cost	0	0	0
Interest cost	101	142	141
Prior service cost	(75)	0	0
Actuarial (gain) loss	4	0	0
Total net pension cost	$ 30	$ 142	$ 141

Retirement Plans, Weighted Aver

Retirement Plans, Weighted Average Assumptions used to Determine Benefit and Net Periodic Benefit Costs (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Expected long-term rate of return on plan assets	6.50%	7.00%
Retirement Account Plan
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.70%	4.10%
Rate of increase in compensation levels	3.00%	4.00%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.10%	4.30%
Rate of increase in compensation levels	4.00%	4.00%
Expected long-term rate of return on plan assets	6.50%	7.00%
Postretirement Plan
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.70%	4.10%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.10%	4.30%

Retirement Plans, Asset Allocat

Retirement Plans, Asset Allocation for Pension Plan Table (Details)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total	100.00%	100.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total	60.00%	60.00%
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	37.00%	39.00%
Other
Defined Benefit Plan Disclosure [Line Items]
Total	3.00%	1.00%

Retirement Plans, Fair Value of

Retirement Plans, Fair Value of Pension Plan Investments Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Pension Plan Investments
Money market account	$ 9,577	$ 3,624
Common /collective trust funds	133,210	126,741
Mutual funds	188,823	165,353
Total Retirement Account Plan Investments	331,610	295,718
Fair Value, Inputs, Level 1
Pension Plan Investments
Money market account	9,577	3,624
Common /collective trust funds	133,210	126,741
Mutual funds	188,823	165,353
Total Retirement Account Plan Investments	331,610	295,718
Fair Value, Inputs, Level 2
Pension Plan Investments
Money market account	0	0
Common /collective trust funds	0	0
Mutual funds	0	0
Total Retirement Account Plan Investments	0	0
Fair Value, Inputs, Level 3
Pension Plan Investments
Money market account	0	0
Common /collective trust funds	0	0
Mutual funds	0	0
Total Retirement Account Plan Investments	$ 0	$ 0

Retirement Plans, Estimated Fut

Retirement Plans, Estimated Future Benefit Payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Retirement Account Plan
Defined Benefit Plan Disclosure [Line Items]
2,018	$ 14,697
2,019	14,436
2,020	15,096
2,021	15,278
2,022	16,020
2023 - 2027	71,781
Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
2,018	237
2,019	197
2,020	194
2,021	190
2,022	186
2023 - 2027	$ 839

Retirement Plans, Effect of 1%

Retirement Plans, Effect of 1% Change in the Assumed Health Care Cost Trend Rate Intro (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Change in assumed health care cost
Effect on total of service and interest cost (increase)	$ 7	$ 7
Effect on total of service and interest cost (decrease)	(6)	(6)
Effect on postretirement benefit obligation (increase)	162	173
Effect on postretirement benefit obligation (decrease)	$ (140)	$ (149)

Retirement Plans (Details Textu

Retirement Plans (Details Textuals) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirements Plans [Line Items]
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	$ 1,900,000
Expected long-term rate of return on plan assets	6.50%	7.00%
Actual return on plan assets percentage	14.60%	6.36%
Total expense related to 401(k)	$ 14,000,000	$ 14,000,000	$ 11,000,000
Pre-65 Health Care Trend Rate [Member]
Retirements Plans [Line Items]
Health care trend rate assumption	7.50%
Defined Benefit Plan, Health Care Cost Trend, Reduction in Trend Rate Maximum	0.50%
Defined Benefit Plan, Health Care Cost Trend, Reduction in Trend Rate Minimum	0.25%
Ultimate future rate	5.00%
Post-65 Health Care Trend [Member]
Retirements Plans [Line Items]
Health care trend rate assumption	6.50%
Defined Benefit Plan, Health Care Cost Trend, Reduction in Trend Rate Maximum	0.50%
Defined Benefit Plan, Health Care Cost Trend, Reduction in Trend Rate Minimum	0.25%
Ultimate future rate	5.00%
Defined Benefit Plan Health Care Cost Rate Change	17.00%
Retirement Account Plan
Retirements Plans [Line Items]
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	$ 75,000
Employer contributions	$ 6,242,000	$ 0
Expected long-term rate of return on plan assets	6.50%	7.00%
Postretirement Plan
Retirements Plans [Line Items]
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	$ 75,000
Employer contributions	$ 235,000	$ 248,000
Minimum [Member] | Equity Securities
Retirements Plans [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%
Minimum [Member] | Fixed income securities
Retirements Plans [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	30.00%
Minimum [Member] | Cash and Cash Equivalents
Retirements Plans [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum [Member] | Alternative Securities
Retirements Plans [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Maximum [Member] | Equity Securities
Retirements Plans [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	70.00%
Maximum [Member] | Fixed income securities
Retirements Plans [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%
Maximum [Member] | Cash and Cash Equivalents
Retirements Plans [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	10.00%
Maximum [Member] | Alternative Securities
Retirements Plans [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	15.00%

Income Taxes, Current and Defer

Income Taxes, Current and Deferred Amounts of Income Tax Expense Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 76,525	$ 73,781	$ 82,449
State	11,576	2,885	2,560
Total current	88,101	76,666	85,009
Deferred:
Federal	19,755	3,338	(10,606)
State	1,647	7,318	7,084
Total deferred	21,402	10,656	(3,522)
Total income tax expense	$ 109,503	$ 87,322	$ 81,487

Income Taxes, Deferred Tax Asse

Income Taxes, Deferred Tax Assets and Liabilities Resulted in Deferred Taxes Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gross deferred tax assets:
Allowance for loan losses	$ 66,377	$ 100,891
Allowance for other losses	7,095	11,080
Accrued liabilities	3,884	5,969
Deferred compensation	20,015	33,169
Benefit of tax loss and credit carryforwards	8,438	7,882
Nonaccrual interest	1,619	1,085
Net unrealized losses on available-for-sale securities	15,968	16,980
Net unrealized losses on pension and postretirement benefits	9,928	21,218
Other	3,954	8,128
Total deferred tax assets	137,278	206,402
Valuation allowance for deferred tax assets	(269)	0	$ 0
Total deferred tax assets after valuation allowance	137,009	206,402
Gross deferred tax liabilities
Prepaid expenses	49,695	70,943
Goodwill	19,144	27,365
Mortgage banking activities	10,949	17,569
Deferred loan fee income	11,467	16,474
State deferred taxes	2,001	3,800
Lease financing	535	1,975
Bank premises and equipment	5,063	7,698
Other	4,838	8,594
Total deferred tax liabilities	103,692	154,418
Net deferred tax assets	$ 33,317	$ 51,984

Income Taxes, Summary of Valuat

Income Taxes, Summary of Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets, Valuation Allowance [Roll Forward]
Valuation allowance for deferred tax assets, beginning of year	$ 0	$ 0
Increase (decrease) in current year	269	0
Valuation allowance for deferred tax assets, end of year	$ 269	$ 0

Income Taxes, Major Reasons for

Income Taxes, Major Reasons for the Difference in Effective Income Tax Rate from the Federal Tax Rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation
Federal income tax rate at statutory rate	35.00%	35.00%	35.00%
Increases (decreases) resulting from:
Tax-exempt interest and dividends	(4.10%)	(4.80%)	(5.00%)
State income taxes (net of federal benefit)	2.70%	2.30%	2.30%
Bank owned life insurance	(1.70%)	(1.70%)	(1.20%)
Tax effect of tax credits and benefits, net of related expenses	(0.50%)	(0.80%)	(0.50%)
Tax reserve adjustments	(1.20%)	0.30%	(0.60%)
Net tax benefit from stock-based compensation	(1.30%)	(0.40%)	0.00%
Tax Cuts and Jobs Act impact on deferred remeasurement	3.50%	0.00%	0.00%
Other	(0.10%)	0.50%	0.20%
Effective income tax rate	32.30%	30.40%	30.20%

Income Taxes, Reconciliation of

Income Taxes, Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 10	$ 9
Subtractions for tax positions related to prior years	(5)	0
Subtractions for settlements with tax authorities	(1)	0
Additions for tax positions related to current year	0	1
Balance at end of year	$ 4	$ 10

Income Taxes, Textuals (Details

Income Taxes, Textuals (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Valuation allowance for deferred tax assets	$ 269,000	$ 0	$ 0
Deferred Other Tax Expense (Benefit)	12,000,000
Other Tax Expense (Benefit)	1,000,000
Bad debt from acquired savings banks	100,000,000
Deferred tax on bad debt from acquired savings banks	25,000,000
Unrecognized tax benefit impact on effective tax rate	3,000,000	7,000,000
Interest and penalty expense (benefit)	(1,000,000)	0
Accrued interest and penalties	1,000,000	$ 2,000,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	78,000,000
Operating tax loss carryforwards from acquisitions	16,000,000
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	3,000,000
Operating tax loss carryforwards from acquisitions	$ 3,000,000

Derivative and Hedging Activ107

Derivative and Hedging Activities, Derivative Instruments Not Designated as Hedging Instruments (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Trading assets | Interest rate-related instruments — customer and mirror
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	$ 2,183,687	$ 2,039,323
Fair Value	28,494	33,671
Trading assets | Foreign currency exchange forwards
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	124,851	109,675
Fair Value	2,495	2,002
Trading assets | Commodity contracts
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	457,868	127,582
Fair Value	38,686	16,725
Trading liabilities | Interest rate-related instruments — customer and mirror
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	2,183,687	2,039,323
Fair Value	(28,035)	(33,188)
Trading liabilities | Foreign currency exchange forwards
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	118,094	106,251
Fair Value	(2,339)	(1,943)
Trading liabilities | Commodity contracts
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	457,108	128,368
Fair Value	(37,286)	(15,972)
Other assets | Interest rate lock commitments (mortgage)
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	222,736	285,345
Fair Value	1,538	206
Other assets | Forward commitments (mortgage)
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount		179,600
Fair Value		2,908
Other assets | Purchased options (time deposit)
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	31,063	80,554
Fair Value	1,175	2,576
Other liabilities | Forward commitments (mortgage)
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	164,567
Fair Value	(313)
Other liabilities | Written options (time deposit)
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Notional Amount	31,063	80,554
Fair Value	$ (1,175)	$ (2,576)

Derivative and Hedging Activ108

Derivative and Hedging Activities, Income Statement Category of the Gains and Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Capital market fees, net | Interest rate-related instruments — customer and mirror
Gain (loss) on derivative instruments not designated as hedging instruments
Gain / (Loss) Recognized in Income	$ (24)	$ 1,978
Capital market fees, net | Foreign currency exchange forwards
Gain (loss) on derivative instruments not designated as hedging instruments
Gain / (Loss) Recognized in Income	97	(75)
Capital market fees, net | Commodity contracts
Gain (loss) on derivative instruments not designated as hedging instruments
Gain / (Loss) Recognized in Income	647	630
Mortgage banking, net | Interest rate lock commitments (mortgage)
Gain (loss) on derivative instruments not designated as hedging instruments
Gain / (Loss) Recognized in Income	1,332	(752)
Mortgage banking, net | Forward commitments (mortgage)
Gain (loss) on derivative instruments not designated as hedging instruments
Gain / (Loss) Recognized in Income	$ (3,221)	$ 2,505

Derivative and Hedging Activ109

Derivative and Hedging Activities (Details Textuals) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Investment securities and cash equivalents pledged as collateral	$ 24	$ 40
Derivative collateral right to reclaim cash	$ 22	$ 0

Balance Sheet Offsetting (Detai

Balance Sheet Offsetting (Details) - Interest Rate Contract - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Offsetting Derivative Assets [Abstract]
Gross amounts recognized	$ 29,503	$ 18,031
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	29,503	18,031
Financial instruments	(29,503)	(18,031)
Collateral	0	0
Net amount	0	0
Offsetting Derivative Liabilities [Abstract]
Gross amounts recognized	37,164	31,075
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	37,164	31,075
Financial instruments	(29,503)	(18,031)
Collateral	(7,661)	(11,148)
Net amount	$ 0	$ 1,896

Commitments, Off-Balance She111

Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities, Summary of Lending Related and Other Commitments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of lending-related and other commitments [Line Items]
Lending related commitments, fair value	$ 0	$ 0
Commitments to extend credit, excluding commitments to originate residential mortgage loans held for sale
Summary of lending-related and other commitments
Lending related commitments	8,027,187	8,131,131
Commercial Letters Of Credit
Summary of lending-related and other commitments
Lending related commitments	11,886	7,923
Standby Letters of Credit
Summary of lending-related and other commitments
Lending related commitments	235,361	259,632
Standby letters of credit, fair value	$ 2,000	$ 3,000

Commitments, Off-Balance She112

Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities Residential Mortgage Repurchase Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Residential mortgage repurchase reserve
Balance at beginning of period	$ 25,000
Balance at end of period	24,000	$ 25,000
Mortgage Repurchase Reserve
Residential mortgage repurchase reserve
Balance at beginning of period	900	1,197
Repurchase provision expense	246	456
Adjustments to provision expense	0	(750)
Charge offs, net	(159)	(3)
Balance at end of period	$ 987	$ 900

Commitments, Off-Balance She113

Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Details Textuals)	Jan. 11, 2016USD ($)complaint	May 22, 2015USD ($)branchloan_production_office	Dec. 31, 2017USD ($)	Jul. 28, 2017complaint	Dec. 31, 2016USD ($)
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
unfunded commitments			$ 24,000,000		$ 25,000,000
Mortgage loan commitment		$ 196,000,000
Number of branch opening commitments | branch		1
Number of loan production offices | loan_production_office		4
Number of complaints filed under legal proceedings | complaint	2
Conciliation Agreement, Commitment Term		3 years
Loans repurchased under make whole requests			1,000,000		2,000,000
Loans sold to outside investors original amount			10,000,000,000
Loans sold to outside investors remaining outstanding amount			6,100,000,000
Residential mortgage loans sold with recourse risk			44,000,000		62,000,000
Residential mortgage loans sold with credit recourse risk			73,000,000		98,000,000
The Official Committee of Unsecured Creditors of World Marketing Chicago LLC v Associated Bank [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Damages sought	$ 6,000,000
Damages sought, cash	4,000,000
American Funds Service Company v Associated Bank [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Damages sought	$ 600,000
Schumel et al. v. Bank Mutual Corporation et al., Paquin et al. v. Bank Mutual Corporation et al. [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Number of complaints filed under legal proceedings | complaint				2
UnconsolidatedProjectsLowIncomeHousing [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Carrying value of investments			147,000,000		68,000,000
Commitments under unconsolidated projects			119,000,000		69,000,000
PrincipalInvestmentCommitment [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Carrying value of investments			$ 23,000,000		$ 17,000,000

Parent Company Only Financia114

Parent Company Only Financial Information, Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash and due from banks	$ 483,666	$ 446,558
Investment securities available for sale, at fair value	4,043,446	4,680,226
Other assets	482,294	421,787
Total assets	30,483,594	29,139,315
Liabilities and stockholders' equity
Commercial paper	67,467	101,688
Senior notes, at par	250,000	250,000
Subordinated notes, at par	250,000	250,000
Other Long-term Debt and Capitalized Costs	2,718	3,393
Total long-term funding	3,397,450	2,761,795
Accrued expenses and other liabilities	318,797	254,622
Total liabilities	27,246,151	26,048,003
Preferred equity	159,929	159,929
Common equity	1,618	1,630
Total stockholders’ equity	3,237,443	3,091,312	$ 2,937,246	$ 2,800,251
Total liabilities and stockholders’ equity	30,483,594	29,139,315
Parent Company Only
Assets
Cash and due from banks	146,877	402,786
Investment securities available for sale, at fair value	11,645	14,389
Notes Receivable, Related Parties, Noncurrent	301,378	0
Investments in and receivable due from subsidiaries	3,320,090	3,256,763
Other assets	51,466	53,242
Total assets	3,831,456	3,727,180
Liabilities and stockholders' equity
Commercial paper	67,467	101,688
Senior notes, at par	250,000	250,000
Subordinated notes, at par	250,000	250,000
Other Long-term Debt and Capitalized Costs	(2,718)	(3,393)
Total long-term funding	497,282	496,607
Accrued expenses and other liabilities	29,264	37,573
Total liabilities	594,013	635,868
Preferred equity	159,929	159,929
Common equity	3,077,514	2,931,383
Total stockholders’ equity	3,237,443	3,091,312
Total liabilities and stockholders’ equity	$ 3,831,456	$ 3,727,180

Parent Company Only Financia115

Parent Company Only Financial Information, Statement of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INCOME
Interest income on notes receivable from subsidiaries	$ 749,000	$ 659,538	$ 615,627
Total income	1,073,900	1,060,156	1,005,635
EXPENSE
Income before income tax expense (benefit) and equity in undistributed net income (loss) of subsidiaries	338,767	287,596	269,788
Income tax expense	109,503	87,322	81,487
Net income	229,264	200,274	188,301
Preferred stock dividends	9,347	8,903	7,155
Net income available to common equity	219,917	191,371	181,146
Parent Company Only
INCOME
Dividends from subsidiaries	213,000	188,000	205,000
Interest income on notes receivable from subsidiaries	4,175	0	0
Other income	1,763	4,669	8,441
Total income	218,938	192,669	213,441
EXPENSE
Interest expense on short and long-term funding	18,464	21,901	39,576
Other expense	6,927	4,289	4,684
Total expense	25,391	26,190	44,260
Income before income tax expense (benefit) and equity in undistributed net income (loss) of subsidiaries	193,547	166,479	169,181
Income tax expense	4,768	3,468	(1,665)
Income before equity in undistributed net income (loss) of subsidiaries	188,779	163,011	170,846
Equity in undistributed net income (loss) of subsidiaries	40,485	37,263	17,455
Net income	229,264	200,274	188,301
Preferred stock dividends	9,347	8,903	7,155
Net income available to common equity	$ 219,917	$ 191,371	$ 181,146

Parent Company Only Financia116

Parent Company Only Financial Information, Statement of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities
Net income	$ 229,264	$ 200,274	$ 188,301
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sales of investment securities, net	(434)	(9,316)	(8,133)
Asset (gains) losses, net	1,244	86	(2,540)
Net change in other assets and other liabilities	(27,497)	26,144	(11,685)
Net cash provided by operating activities	458,368	641,383	301,206
Cash Flows from Investing Activities
Proceeds from Sale of Available-for-sale Securities	18,467	549,555	1,601,947
Net cash used in investing activities	(1,396,858)	(1,653,023)	(1,533,818)
Cash Flows from Financing Activities
Net increase (decrease) in short-term funding	(415,753)	257,619	(233,872)
Repayment of long-term funding	115,020	1,180,038	1,500,035
Proceeds from issuance of common stock for stock-based compensation plans	(27,619)	(21,748)	(20,054)
Proceeds from issuance of preferred stock	0	97,066	62,966
Redemption of preferred stock	0	58,903	0
Purchase of preferred stock	0	(1,248)	(1,335)
Purchase of common stock returned to authorized but unissued	(37,031)	(20,007)	(93,000)
Purchase of treasury stock for tax withholding	(9,290)	(5,074)	(5,154)
Cash dividends on common stock	76,417	67,855	62,400
Cash dividends on preferred stock	9,347	8,903	7,155
Net cash provided by financing activities	1,012,275	1,180,188	674,230
Net increase (decrease) in cash and cash equivalents	73,785	168,548	(558,382)
Cash and cash equivalents at beginning of period	642,233	473,685	1,032,067
Cash and cash equivalents at end of period	716,018	642,233	473,685
Parent Company Only
Cash Flows from Operating Activities
Net income	229,264	200,274	188,301
Adjustments to reconcile net income to net cash provided by operating activities:
(Increase) decrease in equity in undistributed net income (loss) of subsidiaries	(40,485)	(37,263)	(17,455)
Gain on sales of investment securities, net	0	(466)	0
Asset (gains) losses, net	(88)	(793)	(5,673)
Net change in other assets and other liabilities	(9,589)	19,708	(10,997)
Net cash provided by operating activities	179,102	181,460	154,176
Cash Flows from Investing Activities
Proceeds from Sale of Available-for-sale Securities	2,618	47,719	13,962
Increase (Decrease) in Notes Receivable, Related Parties	(300,000)	0	0
Proceeds from Sale of Productive Assets	1,058	2,211	11,964
Net cash used in investing activities	(296,324)	49,930	25,926
Cash Flows from Financing Activities
Net increase (decrease) in short-term funding	(34,221)	33,710	(6,319)
Repayment of long-term funding	0	(430,000)	0
Proceeds from issuance of common stock for stock-based compensation plans	27,619	21,748	20,054
Proceeds from issuance of preferred stock	0	97,066	62,966
Redemption of preferred stock	0	(58,903)	0
Purchase of preferred stock	0	(1,248)	(1,335)
Purchase of common stock returned to authorized but unissued	(37,031)	(20,007)	(93,000)
Purchase of treasury stock for tax withholding	(9,290)	(5,074)	(5,154)
Cash dividends on common stock	(76,417)	(67,855)	(62,400)
Cash dividends on preferred stock	(9,347)	(8,903)	(7,155)
Net cash provided by financing activities	(138,687)	(439,466)	(92,343)
Net increase (decrease) in cash and cash equivalents	(255,909)	(208,076)	87,759
Cash and cash equivalents at beginning of period	402,786	610,862	523,103
Cash and cash equivalents at end of period	$ 146,877	$ 402,786	$ 610,862

Fair Value Measurements, Assets

Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	$ 4,043,446	$ 4,680,226
Trading Assets	69,675	52,398
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	67,660	51,103
Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	2,628	2,602
Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	4,040,818	4,677,424
Trading Assets	70,850	54,974
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	68,835	53,679
Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	0	200
Trading Assets	1,538	3,114
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	313	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 | U.S. Treasury securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	996	1,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 | Other securities (debt and equity)
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,632	1,602
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 | Total investment securities available for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	2,628	2,602
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | FNMA / FHLMC
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	464,768	639,930
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | GNMA
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,913,350	2,004,475
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Private-label
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,059	1,121
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | GNMA commercial mortgage-related securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,513,277	2,028,898
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Federal Family Education Loan Program (FFELP) Guaranteed Loans
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	145,176	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Other securities (debt and equity)
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	3,188	3,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Total investment securities available for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	4,040,818	4,677,424
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Residential Loans Held For Sale Member [Member]
Assets, Fair Value Disclosure [Abstract]
Trading Assets	85,544	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Interest rate-related instruments
Assets, Fair Value Disclosure [Abstract]
Trading Assets	28,494	33,671
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	28,035	33,188
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Foreign currency exchange forwards
Assets, Fair Value Disclosure [Abstract]
Trading Assets	2,495	2,002
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	2,339	1,943
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading Assets	38,686	16,725
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	37,286	15,972
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Purchased options (time deposit)
Assets, Fair Value Disclosure [Abstract]
Trading Assets	1,175	2,576
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	1,175	2,576
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Other securities (debt and equity)
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	0	200
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Total investment securities available for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	0	200
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Interest rate lock commitments to originate residential mortgage loans held for sale
Assets, Fair Value Disclosure [Abstract]
Trading Assets	1,538	206
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Forward commitments to sell residential mortgage loans
Assets, Fair Value Disclosure [Abstract]
Trading Assets	0	2,908
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	$ 313	$ 0

Fair Value Measurements, Ass118

Fair Value Measurements, Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Investment Securities Available for Sale
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Beginning Balance	$ 200	$ 200	$ 200
Mortgage derivative gain (loss)		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(200)	(200)
Ending Balance		0	200
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Mortgage derivative gain (loss)		0	0
Derivative Financial Instruments
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Mortgage derivative gain (loss)		(1,889)	1,753
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	$ 3,114	3,114	1,361
Mortgage derivative gain (loss)		(1,889)	1,753
Ending Balance		$ 1,225	$ 3,114

Fair Value Measurements, Ass119

Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Mortgage servicing rights	$ 58,384	$ 61,476	$ 61,341
Mortgage Servicing Rights (MSR) Impairment (Recovery)	175	(200)	$ (425)
Fair Value, Inputs, Level 2
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Commercial loans held for sale	0	12,474
Mortgage loans held for sale	85,544	108,010
Fair Value, Measurements, Nonrecurring | Fair Value, Inputs, Level 2
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Commercial loans held for sale		12,474
Provision for credit losses		(559)
Mortgage loans held for sale		108,010
Market valuation adjustment, mortgage loans held for sale		(3,760)
Other real estate owned	2,604	9,752
Foreclosure / OREO expense, net	(939)	(1,091)
Fair Value, Measurements, Nonrecurring | Fair Value, Inputs, Level 3
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Impaired loans	92,534	79,270
Provision for Credit Losses, Impaired Loans	(32,159)	(75,194)
Mortgage servicing rights	64,387	73,149
Mortgage Servicing Rights (MSR) Impairment (Recovery)	$ (175)	$ 200

Fair Value Measurements, Schedu

Fair Value Measurements, Schedule of Assumptions for Fair Value as of Balance Sheet Date of Assets or Liabilities (Details) - Fair Value, Inputs, Level 3	12 Months Ended
	Dec. 31, 2017
Servicing Contracts [Member] | Discounted Cash Flow [Member]
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Discount Rate	11.00%
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Prepayment Speed	11.00%
Impaired Finance Receivable [Member] | Appraisals/Discounted Cash Flow [Member]
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Discount Rate	19.00%

Fair Value Measurements, Fair V

Fair Value Measurements, Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial assets
Cash and due from banks	$ 483,666	$ 446,558
Interest-bearing deposits in other financial institutions	199,702	149,175
Federal funds sold and securities purchased under agreements to resell	32,650	46,500
Investment securities held to maturity	2,282,853	1,273,536
Investment securities held to maturity, fair value	2,283,574	1,264,674
Investment securities available for sale	4,043,446	4,680,226
FHLB and Federal Reserve Bank stocks	165,331	140,001
Commercial loans held for sale	0	12,474
Loans, net	20,519,111	19,776,381
Bank and Corporate Owned Life Insurance	591,057	585,290
Trading Assets	69,675	52,398
Financial liabilities
Short-term funding	676,282	1,092,035
Long-term funding	3,397,450	2,761,795
Derivatives (trading and other liabilities)	67,660	51,103
Commitment on standby letters of credit	235,000	260,000
Fair Value, Inputs, Level 1
Financial assets
Cash and due from banks	483,666	446,558
Cash and due from banks, Fair Value	483,666	446,558
Interest-bearing deposits in other financial institutions	199,702	149,175
Interest-bearing deposits in other financial institutions, fair value	199,702	149,175
Federal funds sold and securities purchased under agreements to resell	32,650	46,500
Federal funds sold and securities purchased under agreements to resell, fair value	32,650	46,500
Investment securities available for sale	2,628	2,602
Investment securities available for sale, at fair value	2,628	2,602
Fair Value, Inputs, Level 2
Financial assets
Investment securities held to maturity	2,282,853	1,273,536
Investment securities held to maturity, fair value	2,283,574	1,264,674
Investment securities available for sale	4,040,818	4,677,424
Investment securities available for sale, at fair value	4,040,818	4,677,424
FHLB and Federal Reserve Bank stocks	165,331	140,001
FHLB and Federal Reserve Bank stocks, fair value	165,331	140,001
Commercial loans held for sale	0	12,474
Commercial Loans Held-for-sale, Fair Value Disclosure	0	12,474
Mortgage Loans Held-for-sale	85,544	108,010
Mortgages Held-for-sale, Fair Value Disclosure	85,544	108,010
Bank and Corporate Owned Life Insurance	591,057	585,290
Bank owned life insurance, fair value	591,057	585,290
Trading Assets	70,850	54,974
Derivatives (trading and other assets), fair value	70,850	54,974
Financial liabilities
Brokered CDs and other time deposits	2,349,069	1,606,127
Brokered CDs and other time deposits, fair value	2,349,069	1,606,127
Short-term funding	676,282	1,092,035
Short-term funding, fair value	676,282	1,092,035
Long-term funding	3,397,450	2,761,795
Long-term funding, fair value	3,411,368	2,791,841
Standby letters of credit	2,402	2,566
Standby letters of credit, fair value	2,402	2,566
Derivatives (trading and other liabilities)	68,835	53,679
Derivatives (trading and other liabilities), fair value	68,835	53,679
Fair Value, Inputs, Level 3
Financial assets
Investment securities available for sale	0	200
Investment securities available for sale, at fair value	0	200
Loans, net	20,519,111	19,776,381
Loans, net, fair value	20,314,984	19,680,317
Trading Assets	1,538	3,114
Derivatives (trading and other assets), fair value	1,538	3,114
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market accounts	20,436,893	20,282,321
Noninterest-bearing demand, savings, interest-bearing demand, and money market accounts, fair value	20,436,893	20,282,321
Derivatives (trading and other liabilities)	313	0
Derivatives (trading and other liabilities), fair value	$ 313	$ 0

Fair Value Measurements, Textua

Fair Value Measurements, Textuals (Details)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Closing Ratio	85.00%

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Associated Banc-Corp
Regulatory Capital [Abstract]
Total Capital Actual Amount	$ 2,848,851	$ 2,706,760
Total Capital Actual Ratio	13.22%	12.68%
Total Capital for Capital Adequacy Purposes Amount	$ 1,723,557	$ 1,707,276
Total Capital for Adequacy Purposes Ratio	8.00%	8.00%
Tier 1 Capital Actual Amount	$ 2,331,245	$ 2,191,798
Tier 1 Capital Actual Ratio	10.82%	10.27%
Tier 1 Capital for Adequacy Purposes Amount	$ 1,292,668	$ 1,280,457
Tier 1 Capital for Adequacy Purposes Ratio	6.00%	6.00%
Common Equity Tier One Capital	$ 2,171,508	$ 2,032,587
Common Equity Tier One Capital to Risk Weighted Assets	10.08%	9.52%
Common Equity Tier One Capital Required for Capital Adequacy	$ 969,501	$ 960,343
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier 1 Leverage Capital Actual Amount	$ 2,331,245	$ 2,191,798
Tier 1 Leverage Capital Actual Ratio	8.02%	7.83%
Tier 1 Leverage Capital for Adequacy Purposes Amount	$ 1,162,929	$ 1,119,685
Tier 1 Leverage Capital for Adequacy Purposes Ratio	4.00%	4.00%
Associated Bank, N.A.
Regulatory Capital [Abstract]
Total Capital Actual Amount	$ 2,625,945	$ 2,565,062
Total Capital Actual Ratio	12.24%	12.07%
Total Capital for Capital Adequacy Purposes Amount	$ 1,716,910	$ 1,700,737
Total Capital for Adequacy Purposes Ratio	8.00%	8.00%
Total Capital to be Well Capitalized Amount	$ 2,146,138	$ 2,125,921
Total Capital to be Well Capitalized Ratio	10.00%	10.00%
Tier 1 Capital Actual Amount	$ 2,357,354	$ 2,298,812
Tier 1 Capital Actual Ratio	10.98%	10.81%
Tier 1 Capital for Adequacy Purposes Amount	$ 1,287,683	$ 1,275,553
Tier 1 Capital for Adequacy Purposes Ratio	6.00%	6.00%
Tier 1 Capital To Be Well Capitalized Amount	$ 1,716,910	$ 1,700,737
Tier 1 Capital To Be Well Capitalized Ratio	8.00%	8.00%
Common Equity Tier One Capital	$ 2,157,354	$ 2,098,812
Common Equity Tier One Capital to Risk Weighted Assets	10.05%	9.87%
Common Equity Tier One Capital Required for Capital Adequacy	$ 965,762	$ 956,664
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier 1 Equity Capital to be Well Capitalized Amount	$ 1,394,989	$ 1,381,849
Tier 1 Equity Capital to be Well Capitalized Ratio	6.50%	6.50%
Tier 1 Leverage Capital Actual Amount	$ 2,357,354	$ 2,298,812
Tier 1 Leverage Capital Actual Ratio	8.13%	8.24%
Tier 1 Leverage Capital for Adequacy Purposes Amount	$ 1,159,959	$ 1,115,731
Tier 1 Leverage Capital for Adequacy Purposes Ratio	4.00%	4.00%
Tier 1 Leverage Capital To Be Well Capitalized Amount	$ 1,449,448	$ 1,394,663
Tier 1 Leverage Capital To Be Well Capitalized Ratio	5.00%	5.00%

Regulatory Matters (Details Tex

Regulatory Matters (Details Textuals) $ in Millions	Dec. 31, 2017USD ($)
Regulatory Capital Requirements [Abstract]
Required minimum cash and reserve balances	$ 73

Earnings Per Common Share (Deta

Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Calculations for basic and diluted earnings per common share
Net income	$ 229,264	$ 200,274	$ 188,301
Preferred stock dividends	(9,347)	(8,903)	(7,155)
Net income available to common equity	219,917	191,371	181,146
Common shareholder dividends	(75,967)	(67,100)	(61,774)
Unvested share-based payment awards	(450)	(755)	(626)
Undistributed earnings	143,500	123,516	118,746
Undistributed earnings allocated to common shareholders	142,593	122,205	117,498
Undistributed earnings allocated to unvested share-based payment awards	907	1,311	1,248
Undistributed earnings	143,500	123,516	118,746
Basic
Distributed earnings to common shareholders	75,967	67,100	61,774
Undistributed earnings allocated to common shareholders	142,593	122,205	117,498
Total common shareholders earnings, basic	218,560	189,305	179,272
Diluted
Distributed earnings to common shareholders	75,967	67,100	61,774
Undistributed earnings allocated to common shareholders	142,593	122,205	117,498
Total common shareholders earnings, diluted	$ 218,560	$ 189,305	$ 179,272
Weighted average common shares outstanding	150,877	148,769	149,350
Effect of dilutive common stock awards	2,038	1,192	1,253
Effect of dilutive common stock warrants	732	0	0
Diluted weighted average common shares outstanding	153,647	149,961	150,603
Basic earnings per common share	$ 1.45	$ 1.27	$ 1.20
Diluted earnings per common share	$ 1.42	$ 1.26	$ 1.19

Earnings Per Common Share (Text

Earnings Per Common Share (Textual) (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1	4	4

Segment Reporting (Details)

Segment Reporting (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Income Statement Data Abstract
Net interest income	$ 741,220	$ 707,273	$ 676,278
Noninterest income	332,680	352,883	329,357
Revenues	1,073,900	1,060,156	1,005,635
Credit provision (a)	26,000	70,000	37,500
Noninterest expense	709,133	702,560	698,347
Income before income taxes	338,767	287,596	269,788
Income tax expense (benefit)	109,503	87,322	81,487
Net income	$ 229,264	$ 200,274	$ 188,301
Return on average allocated capital (ROCET1)	10.40%	9.90%	9.90%
Segment Balance Sheet Data
Average earning assets	$ 26,999,884	$ 26,026,661	$ 24,571,087
Average loans	20,592,383	19,650,667	18,252,264
Average deposits	21,923,602	21,005,772	19,903,087
Average allocated capital (CET1)	2,109,459	1,940,391	1,833,597
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	357,051	328,603	310,072
Noninterest income	52,297	47,776	46,742
Revenues	409,348	376,379	356,814
Credit provision (a)	42,298	50,397	41,913
Noninterest expense	156,890	148,493	141,912
Income before income taxes	210,160	177,489	172,989
Income tax expense (benefit)	71,655	59,261	59,200
Net income	$ 138,505	$ 118,228	$ 113,789
Return on average allocated capital (ROCET1)	12.40%	11.00%	11.60%
Segment Balance Sheet Data
Average earning assets	$ 10,820,998	$ 10,178,813	$ 9,383,971
Average loans	10,811,827	10,169,300	9,374,191
Average deposits	6,938,913	5,904,238	5,856,530
Average allocated capital (CET1)	1,117,761	1,070,598	977,406
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	361,361	350,551	349,134
Noninterest income	266,250	277,942	265,503
Revenues	627,611	628,493	614,637
Credit provision (a)	20,400	24,185	25,614
Noninterest expense	490,908	502,285	492,284
Income before income taxes	116,303	102,023	96,739
Income tax expense (benefit)	40,706	35,708	33,859
Net income	$ 75,597	$ 66,315	$ 62,880
Return on average allocated capital (ROCET1)	12.90%	10.50%	9.80%
Segment Balance Sheet Data
Average earning assets	$ 9,456,549	$ 9,309,028	$ 8,810,015
Average loans	9,452,253	9,307,723	8,809,673
Average deposits	11,711,407	11,451,759	10,898,602
Average allocated capital (CET1)	586,417	629,540	640,181
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	22,808	28,119	17,072
Noninterest income	14,133	27,165	17,112
Revenues	36,941	55,284	34,184
Credit provision (a)	(36,698)	(4,582)	(30,027)
Noninterest expense	61,335	51,782	64,151
Income before income taxes	12,304	8,084	60
Income tax expense (benefit)	(2,858)	(7,647)	(11,572)
Net income	$ 15,162	$ 15,731	$ 11,632
Return on average allocated capital (ROCET1)	1.40%	2.80%	2.10%
Segment Balance Sheet Data
Average earning assets	$ 6,722,337	$ 6,538,820	$ 6,377,101
Average loans	328,303	173,644	68,400
Average deposits	3,273,282	3,649,775	3,147,955
Average allocated capital (CET1)	$ 405,281	$ 240,253	$ 216,010

Segment Reporting (Details Text

Segment Reporting (Details Textuals)	12 Months Ended
	Dec. 31, 2017segment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of Reportable Segments	3

Accumulated Other Comprehens129

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (54,679)
Personnel expense	419,778	$ 414,837	$ 404,741
Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities)	(2,665)	(5,887)	(555)
Total other comprehensive income (loss)	(8,079)	(22,063)	(27,766)
Ending Balance	(62,758)	(54,679)
Investments Securities Available For Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(20,079)	459	18,512
Other comprehensive income (loss) before reclassifications	(27,040)	(17,900)	(20,439)
Investment securities gain (loss), net		(9,316)	(8,133)
Personnel expense	0	0	0
Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities)	(2,665)	(5,887)	(555)
Income tax (expense) benefit	11,331	12,565	11,074
Total other comprehensive income (loss)	(18,374)	(20,538)	(18,053)
Ending Balance	(38,453)	(20,079)	459
Defined Benefit Pension and Postretirement Obligations
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(34,600)	(33,075)	(23,362)
Other comprehensive income (loss) before reclassifications	14,273	(6,141)	(17,892)
Investment securities gain (loss), net		0	0
Personnel expense	2,134	3,801	2,306
Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities)	0	0	0
Income tax (expense) benefit	(6,112)	815	5,873
Total other comprehensive income (loss)	10,295	(1,525)	(9,713)
Ending Balance	(24,305)	(34,600)	(33,075)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(54,679)	(32,616)	(4,850)
Other comprehensive income (loss) before reclassifications	(12,767)	(24,041)	(38,331)
Investment securities gain (loss), net		(9,316)	(8,133)
Personnel expense	2,134	3,801	2,306
Interest income (amortization of net unrealized losses (gains) on available for sale securities transferred to held to maturity securities)	(2,665)	(5,887)	(555)
Income tax (expense) benefit	5,219	13,380	16,947
Total other comprehensive income (loss)	(8,079)	(22,063)	(27,766)
Ending Balance	$ (62,758)	$ (54,679)	$ (32,616)

Recent Development (Details)

Recent Development (Details)	Jul. 20, 2017shares
Bank Mutual [Member]
Recent Developments [Line Items]
Consideration shares transferred	0.422