Comerica (CMA) 10-K 15 Feb 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 09, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Entity Registrant Name	Comerica INC /NEW/
Entity Central Index Key	28,412
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		172,813,294
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 12,665,000,000

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and due from banks		$ 1,438	$ 1,249
Interest-bearing deposits with banks		4,407	5,969
Other short-term investments		96	92
Investment securities available-for-sale	[1]	10,938	10,787
Investment securities held-to-maturity		1,266	1,582
Commercial loans		31,060	30,994
Real estate construction loans		2,961	2,869
Commercial mortgage loans		9,159	8,931
Lease financing		468	572
International loans		983	1,258
Residential mortgage loans		1,988	1,942
Consumer loans		2,554	2,522
Total loans		49,173	49,088
Less allowance for loan losses		(712)	(730)
Net loans		48,461	48,358
Premises and equipment		466	501
Accrued income and other assets		4,495	4,440
Total assets		71,567	72,978
LIABILITIES AND SHAREHOLDERS' EQUITY
Noninterest-bearing deposits		32,071	31,540
Money market and interest-bearing checking deposits		21,500	22,556
Savings deposits		2,152	2,064
Customer certificates of deposit		2,165	2,806
Foreign office time deposits		15	19
Total interest-bearing deposits		25,832	27,445
Total deposits		57,903	58,985
Short-term borrowings		10	25
Accrued expenses and other liabilities		1,069	1,012
Medium- and long-term debt		4,622	5,160
Total liabilities		63,604	65,182
Common stock - $5 par value: Authorized - 325,000,000 shares; Issued - 228,164,824 shares		1,141	1,141
Capital surplus		2,122	2,135
Accumulated other comprehensive loss		(451)	(383)
Retained earnings		7,887	7,331
Less cost of common stock in treasury - 55,306,483 shares at 12/31/17 and 52,851,156 shares at 12/31/16		(2,736)	(2,428)
Total shareholders' equity		7,963	7,796
Total liabilities and shareholders' equity		$ 71,567	$ 72,978
[1]	Included auction-rate securities at amortized cost and fair value of $51 million and $49 million, respectively, as of December 31, 2017 and $55 million and $54 million, respectively, as of December 31, 2016.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common stock, par value	$ 5	$ 5
Common stock, authorized shares	325,000,000	325,000,000
Common stock, issued shares	228,164,824	228,164,824
Shares in treasury	55,306,483	52,851,156

Consolidated Statements Of Inco

Consolidated Statements Of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INTEREST INCOME
Interest and fees on loans	$ 1,872	$ 1,635	$ 1,551
Interest on investment securities	250	247	216
Interest on short-term investments	60	27	17
Total interest income	2,182	1,909	1,784
INTEREST EXPENSE
Interest on deposits	42	40	43
Interest on short-term borrowings	3	0	0
Interest on medium- and long-term debt	76	72	52
Total interest expense	121	112	95
Net interest income	2,061	1,797	1,689
Provision for credit losses	74	248	147
Net interest income after provision for credit losses	1,987	1,549	1,542
NONINTEREST INCOME
Card fees	333	303	276
Service charges on deposit accounts	227	219	223
Fiduciary income	198	190	187
Commercial lending fees	85	89	99
Letter of credit fees	45	50	53
Bank-owned life insurance	43	42	40
Foreign exchange income	45	42	40
Brokerage fees	23	19	17
Net securities losses	(3)	(5)	(2)
Other noninterest income	111	102	102
Total noninterest income	1,107	1,051	1,035
NONINTEREST EXPENSES
Salaries and benefits expense	912	961	1,009
Outside processing fee expense	366	336	318
Net occupancy expense	154	157	159
Equipment expense	45	53	53
Restructuring charges	45	93	0
Software expense	126	119	99
FDIC insurance expense	51	54	37
Advertising expense	28	21	24
Litigation-related expense	(2)	1	(32)
Other noninterest expenses	135	135	160
Total noninterest expenses	1,860	1,930	1,827
Income before income taxes	1,234	670	750
Provision for income taxes	491	193	229
Net Income	743	477	521
Less income allocated to participating securities	5	4	6
Net income attributable to common shares	$ 738	$ 473	$ 515
Basic earnings per common share	$ 4.23	$ 2.74	$ 2.93
Diluted earnings per common share	$ 4.14	$ 2.68	$ 2.84
Cash dividends declared on common stock	$ 193	$ 154	$ 148
Cash dividends declared per common share	$ 1.09	$ 0.89	$ 0.83

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 743	$ 477	$ 521
Net unrealized holding losses arising during the period	(81)	(70)	(55)
Less reclassification adjustment for net securities losses included in net income	0	0	(2)
Less net losses realized as a yield adjustment in interest on investment securities	(3)	(3)	(8)
Change in net unrealized losses before income taxes	(78)	(67)	(45)
Actuarial gain (loss) arising during the period	72	(134)	(57)
Prior service credit arising during the period	0	234	3
Amortization of actuarial net loss	51	46	70
Amortization of prior service (credit) cost	(27)	(7)	1
Change in defined benefit pension and other postretirement plans adjustment before income taxes	96	139	17
Total other comprehensive income (loss) before income taxes	18	72	(28)
(Benefit) provision for income taxes	(1)	26	(11)
Total other comprehensive (loss) income, net of tax	19	46	(17)
Comprehensive Income	$ 762	$ 523	$ 504

Consolidated Statements Of Chan

Consolidated Statements Of Changes In Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Capital Surplus	Accumulated Other Comprehensive Loss	Retained Earnings	Treasury Stock
BALANCE at Dec. 31, 2014	$ 7,402	$ 1,141	$ 2,188	$ (412)	$ 6,744	$ (2,259)
BALANCE (in shares) at Dec. 31, 2014		179
Net income	521				521
Other comprehensive income (loss), net of tax	(17)			(17)
Cash dividends declared on common stock	(148)				(148)
Purchase of common stock	(240)					(240)
Purchase of common stock (in shares)		(5.3)
Purchase and retirement of warrants	(10)		(10)
Net issuance of common stock under employee stock plans	14		(22)		(11)	47
Net issuance of common stock under employee stock plans (in shares)		1
Net issuance of common stock for warrants	0		(21)		(22)	43
Net issuance of common stock for warrants (in shares)		1
Share-based compensation	38		38
BALANCE at Dec. 31, 2015	7,560	$ 1,141	2,173	(429)	7,084	(2,409)
BALANCE (in shares) at Dec. 31, 2015		175.7
Net income	477				477
Other comprehensive income (loss), net of tax	46			46
Cash dividends declared on common stock	(154)				(154)
Purchase of common stock	(310)					(310)
Purchase of common stock (in shares)		(6.8)
Net issuance of common stock under employee stock plans	143		(15)		(27)	185
Net issuance of common stock under employee stock plans (in shares)		4.1
Net issuance of common stock for warrants	0		(57)		(49)	106
Net issuance of common stock for warrants (in shares)		2.3
Share-based compensation	34		34
BALANCE (Cumulative effect of change in accounting principle)	1		3		(2)
BALANCE at Dec. 31, 2016	7,796	$ 1,141	2,135	(383)	7,331	(2,428)
BALANCE (in shares) at Dec. 31, 2016		175.3
Net income	743				743
Other comprehensive income (loss), net of tax	19			19
Cash dividends declared on common stock	(193)				(193)
Purchase of common stock	(544)					(544)
Purchase of common stock (in shares)		(7.5)
Net issuance of common stock under employee stock plans	102		(24)		(26)	152
Net issuance of common stock under employee stock plans (in shares)		3.3
Net issuance of common stock for warrants	0		(30)		(53)	83
Net issuance of common stock for warrants (in shares)		1.8
Share-based compensation	39		39
Reclassification of certain deferred tax effects	0
Reclassification of certain deferred tax effects | Accounting Standards Update 2018-01	87			(87)	87
Other	0		1			(1)
BALANCE at Dec. 31, 2017	$ 7,963	$ 1,141	$ 2,122	$ (451)	$ 7,887	$ (2,736)
BALANCE (in shares) at Dec. 31, 2017		172.9

Consolidated Statements Of Cha7

Consolidated Statements Of Changes In Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Cash dividends declared on common stock, per share	$ 1.09	$ 0.89	$ 0.83

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES
Net income	$ 743	$ 477	$ 521
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	74	248	147
Provision (benefit) for deferred income taxes	79	(51)	(71)
Depreciation and amortization	121	121	118
Net periodic defined benefit (credit) cost	(18)	6	48
Share-based compensation expense	39	34	38
Net amortization of securities	6	8	13
Accretion of loan purchase discount	(3)	(4)	(7)
Net securities losses	0	0	(2)
Net gains on sales of foreclosed property	(3)	(4)	(2)
Net change in accrued income receivable	(33)	(20)	(12)
Net change in accrued expenses payable	41	37	(35)
Other, net	57	(350)	105
Net cash provided by operating activities	1,103	502	865
INVESTING ACTIVITIES
Maturities and redemptions of investment securities available-for-sale	1,615	1,699	1,757
Sales of investment securities available-for-sale	1,259	0	0
Purchases of investment securities available-for-sale	(3,112)	(2,045)	(4,228)
Maturities and redemptions of investment securities held-to-maturity	319	402	324
Purchases of investment securities held-to-maturity	0	0	(362)
Net change in loans	(175)	(136)	(644)
Purchases of Federal Hole Loan Bank stock	(42)	(115)	0
Redemptions of Federal Home Loan Bank stock	42	0	0
Proceeds from sales of foreclosed property	22	20	12
Net increase in premises and equipment	(69)	(95)	(119)
Other, net	3	0	5
Net cash used in investing activities	(138)	(270)	(3,255)
FINANCING ACTIVITIES
Net change in deposits	(1,180)	(998)	2,529
Net change in short-term borrowings	(15)	2	(93)
Maturities and redemptions of medium- and long-term debt	(500)	(650)	(606)
Issuances of medium- and long-term debt	0	2,800	1,016
Terminations of medium- and long-term debt	(16)	0	0
Repurchases of common stock	(552)	(315)	(240)
Cash dividends paid on common stock	(180)	(152)	(147)
Issuances of common stock under employee stock plans	110	152	22
Purchase and retirement of warrants	0	0	(10)
Other, net	(5)	0	(5)
Net cash (used in) provided by financing activities	(2,338)	839	2,466
Net (decrease) increase in cash and cash equivalents	(1,373)	1,071	76
Cash and cash equivalents at beginning of period	7,218	6,147	6,071
Cash and cash equivalents at end of period	5,845	7,218	6,147
Interest paid	122	111	94
Income taxes paid	336	151	88
Noncash investing and financing activities:
Loans transferred to other real estate	8	21	12
Loans transferred from portfolio to held-for-sale	0	0	28
Loans transferred from held-for-sale to portfolio	0	17	0
Lease residual transferred to other assets	$ 0	$ 0	$ 16

Basis of Presentation and Accou

Basis of Presentation and Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation and Accounting Policies	BASIS OF PRESENTATION AND ACCOUNTING POLICIES Organization Comerica Incorporated (the Corporation) is a registered financial holding company headquartered in Dallas, Texas. The Corporation’s major business segments are the Business Bank, the Retail Bank and Wealth Management. The Corporation operates in three primary geographic markets: Michigan, California and Texas. For further discussion of each business segment and primary geographic market, refer to Note 23 . The Corporation and its banking subsidiaries are regulated at both the state and federal levels. The accounting and reporting policies of the Corporation conform to United States (U.S.) generally accepted accounting principles (GAAP). The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect reported amounts and disclosures. Actual results could differ from these estimates. Certain amounts in the financial statements for prior years have been reclassified to conform to the current financial statement presentation. The following summarizes the significant accounting policies of the Corporation applied in the preparation of the accompanying consolidated financial statements. Principles of Consolidation The consolidated financial statements include the accounts of the Corporation and the accounts of those subsidiaries that are majority owned and in which the Corporation has a controlling financial interest. The Corporation consolidates entities not determined to be variable interest entities (VIEs) when it holds a controlling financial interest and uses the cost or equity method when it holds less than a controlling financial interest. In consolidation, all significant intercompany accounts and transactions are eliminated. The results of operations of companies acquired are included from the date of acquisition. The Corporation holds investments in certain legal entities that are considered VIEs. In general, a VIE is an entity that either (1) has an insufficient amount of equity to carry out its principal activities without additional subordinated financial support, (2) has a group of equity owners that are unable to make significant decisions about its activities, or (3) has a group of equity owners that do not have the obligation to absorb losses or the right to receive returns generated by its operations. If any of these characteristics are present, the entity is subject to a variable interests consolidation model, and consolidation is based on variable interests, not on voting interests. Variable interests are defined as contractual ownership or other money interests in an entity that change with fluctuations in the entity’s net asset value. The primary beneficiary is required to consolidate the VIE. The primary beneficiary is defined as the party that has both the power to direct the activities of the VIE that most significantly impact the entity’s economic performance and the obligation to absorb losses or the right to receive benefits that could be significant to the VIE. The maximum potential exposure to losses relative to investments in VIEs is generally limited to the sum of the outstanding book basis and unfunded commitments for future investments. The Corporation evaluates its investments in VIEs, both at inception and when there is a change in circumstances that requires reconsideration, to determine if the Corporation is the primary beneficiary and consolidation is required. The Corporation accounts for unconsolidated VIEs using either the proportional, cost or equity method. These investments comprise investments in community development projects which generate tax credits to their investors and are included in "accrued income and other assets" on the consolidated balance sheets. The proportional method is used for investments in affordable housing projects that qualify for the low-income housing tax credit (LIHTC). The equity method is used for other investments where the Corporation has the ability to exercise significant influence over the entity’s operation and financial policies. Other unconsolidated equity investments that do not meet the criteria to be accounted for under the equity method are accounted for under the cost method. Amortization and other write-downs of LIHTC investments are presented on a net basis as a component of the "provision for income taxes," while income, amortization and write-downs from cost and equity method investments are recorded in “other noninterest income” on the consolidated statements of income. Assets held in an agency or fiduciary capacity are not assets of the Corporation and are not included in the consolidated financial statements. See Note 9 for additional information about the Corporation’s involvement with VIEs. Fair Value Measurements The Corporation utilizes fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures. The determination of fair values of financial instruments often requires the use of estimates. In cases where quoted market values in an active market are not available, the Corporation uses present value techniques and other valuation methods to estimate the fair values of its financial instruments. These valuation methods require considerable judgment and the resulting estimates of fair value can be significantly affected by the assumptions made and methods used. Fair value is an estimate of the exchange price that would be received to sell an asset or paid to transfer a liability in an orderly transaction (i.e., not a forced transaction, such as a liquidation or distressed sale) between market participants at the measurement date. Fair value is based on the assumptions market participants would use when pricing an asset or liability. Trading securities, investment securities available-for-sale, derivatives and deferred compensation plans are recorded at fair value on a recurring basis. Additionally, from time to time, the Corporation may be required to record other assets and liabilities at fair value on a nonrecurring basis, such as impaired loans, other real estate (primarily foreclosed property), nonmarketable equity securities and certain other assets and liabilities. These nonrecurring fair value adjustments typically involve write-downs of individual assets or application of lower of cost or fair value accounting. Fair value measurements and disclosures guidance establishes a three-level fair value hierarchy based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. The fair value hierarchy gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data. Fair value measurements are separately disclosed by level within the fair value hierarchy. For assets and liabilities recorded at fair value, it is the Corporation’s policy to maximize the use of observable inputs and minimize the use of unobservable inputs when developing fair value measurements. Level 1 Valuation is based upon quoted prices for identical instruments traded in active markets. Level 2 Valuation is based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are less active, and model-based valuation techniques for which all significant assumptions are observable in the market. Level 3 Valuation is generated from model-based techniques that use at least one significant assumption not observable in the market. These unobservable assumptions reflect estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques include use of option pricing models, discounted cash flow models and similar techniques. The Corporation generally utilizes third-party pricing services to value Level 1 and Level 2 trading and investment securities, as well as certain derivatives designated as fair value hedges. Management reviews the methodologies and assumptions used by the third-party pricing services and evaluates the values provided, principally by comparison with other available market quotes for similar instruments and/or analysis based on internal models using available third-party market data. The Corporation may occasionally adjust certain values provided by the third-party pricing service when management believes, as the result of its review, that the adjusted price most appropriately reflects the fair value of the particular security. Fair value measurements for assets and liabilities where limited or no observable market data exists are based primarily upon estimates, often calculated based on the economic and competitive environment, the characteristics of the asset or liability and other factors. Therefore, the results cannot be determined with precision and may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there may be inherent weaknesses in any calculation technique, and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the results of current or future values. Following are descriptions of the valuation methodologies and key inputs used to measure financial assets and liabilities recorded at fair value, as well as a description of the methods and significant assumptions used to estimate fair value disclosures for financial instruments not recorded at fair value in their entirety on a recurring basis. The descriptions include an indication of the level of the fair value hierarchy in which the assets or liabilities are classified. Transfers of assets or liabilities between levels of the fair value hierarchy are recognized at the beginning of the reporting period, when applicable. Cash and due from banks, federal funds sold and interest-bearing deposits with banks Due to their short-term nature, the carrying amount of these instruments approximates the estimated fair value. As such, the Corporation classifies the estimated fair value of these instruments as Level 1. Trading securities and associated deferred compensation plan liabilities Trading securities include securities held for trading purposes as well as assets held related to employee deferred compensation plans. Trading securities and associated deferred compensation plan liabilities are recorded at fair value on a recurring basis and included in “other short-term investments” and “accrued expenses and other liabilities,” respectively, on the consolidated balance sheets. Level 1 trading securities include assets related to employee deferred compensation plans, which are invested in mutual funds, U.S. Treasury securities that are traded by dealers or brokers in active over-the-counter markets and other securities traded on an active exchange, such as the New York Stock Exchange. Deferred compensation plan liabilities represent the fair value of the obligation to the employee, which corresponds to the fair value of the invested assets. Level 2 trading securities include municipal bonds and residential mortgage-backed securities issued by U.S. government-sponsored entities and corporate debt securities. The methods used to value trading securities are the same as the methods used to value investment securities, discussed below. Investment securities Investment securities available-for-sale are recorded at fair value on a recurring basis. The Corporation discloses estimated fair values of investment securities held-to-maturity, which is determined in the same manner as investment securities available-for-sale. Level 1 securities include those traded on an active exchange, such as the New York Stock Exchange, U.S. Treasury securities that are traded by dealers or brokers in active over-the-counter markets and money market funds. Level 2 securities include residential mortgage-backed securities issued by U.S. government agencies and U.S. government-sponsored entities and corporate debt securities. The fair value of Level 2 securities is determined using quoted prices of securities with similar characteristics, or pricing models based on observable market data inputs, primarily interest rates, spreads and prepayment information. Securities classified as Level 3 represent securities in less liquid markets requiring significant management assumptions when determining fair value. Auction-rate securities comprise Level 3 investment securities available-for-sale. The Corporate Treasury department, with appropriate oversight and approval provided by senior management, is responsible for the valuation of auction-rate securities. Valuation results, including an analysis of changes to the valuation methodology, are provided to senior management for review on a quarterly basis. Loans held-for-sale Loans held-for-sale, included in “other short-term investments” on the consolidated balance sheets, are recorded at the lower of cost or fair value. Loans held-for-sale may be carried at fair value on a nonrecurring basis when fair value is less than cost. The fair value is based on what secondary markets are currently offering for portfolios with similar characteristics. As such, the Corporation classifies both loans held-for-sale subjected to nonrecurring fair value adjustments and the estimated fair value of loans held-for sale as Level 2. Loans The Corporation does not record loans at fair value on a recurring basis. However, the Corporation may establish a specific allowance for an impaired loan based on the fair value of the underlying collateral. Such loan values are reported as nonrecurring fair value measurements. Collateral values supporting individually evaluated impaired loans are evaluated quarterly. When management determines that the fair value of the collateral requires additional adjustments, either as a result of non-current appraisal value or when there is no observable market price, the Corporation classifies the impaired loan as Level 3. The Special Assets Group is responsible for performing quarterly credit quality reviews for all impaired loans as part of the quarterly allowance for loan losses process overseen by the Chief Credit Officer, during which valuation adjustments to updated collateral values are determined. The Corporation discloses fair value estimates for loans. The estimated fair value is determined based on characteristics such as loan category, repricing features and remaining maturity, and includes prepayment and credit loss estimates. For variable rate business loans that reprice frequently, the estimated fair value is based on carrying values adjusted for estimated credit losses inherent in the portfolio at the balance sheet date. For other business loans and retail loans, fair values are estimated using a discounted cash flow model that employs a discount rate that reflects the Corporation's current pricing for loans with similar characteristics and remaining maturity, adjusted by an amount for estimated credit losses inherent in the portfolio at the balance sheet date. The rates take into account the expected yield curve, as well as an adjustment for prepayment risk, when applicable. The Corporation classifies the estimated fair value of loans held for investment as Level 3. Customers’ liability on acceptances outstanding and acceptances outstanding Customers' liability on acceptances outstanding is included in "accrued income and other assets" and acceptances outstanding are included in "accrued expenses and other liabilities" on the consolidated balance sheets. Due to their short-term nature, the carrying amount of these instruments approximates the estimated fair value. As such, the Corporation classifies the estimated fair value of these instruments as Level 1. Derivative assets and derivative liabilities Derivative instruments held or issued for risk management or customer-initiated activities are traded in over-the-counter markets where quoted market prices are not readily available. Fair value for over-the-counter derivative instruments is measured on a recurring basis using internally developed models that use primarily market observable inputs, such as yield curves and option volatilities. Fair value for certain derivatives designated as fair value hedges is determined using third-party pricing services. The Corporation manages credit risk on its derivative positions based on whether the derivatives are being settled through a clearinghouse or bilaterally with each counterparty. For derivative positions settled on a counterparty-by-counterparty basis, the Corporation calculates credit valuation adjustments, included in the fair value of these instruments, on the basis of its relationships at the counterparty portfolio/master netting agreement level. These credit valuation adjustments are determined by applying a credit spread for the counterparty or the Corporation, as appropriate, to the total expected exposure of the derivative after considering collateral and other master netting arrangements. These adjustments, which are considered Level 3 inputs, are based on estimates of current credit spreads to evaluate the likelihood of default. When credit valuation adjustments are significant to the overall fair value of a derivative, the Corporation classifies the over-the-counter derivative valuation in Level 3 of the fair value hierarchy; otherwise, over-the-counter derivative valuations are classified in Level 2. Warrants which contain a net exercise provision or a non-contingent put right embedded in the warrant agreement are accounted for as derivatives and recorded at fair value on a recurring basis using a Black-Scholes valuation model. The Black-Scholes valuation model utilizes five inputs: risk-free rate, expected life, volatility, exercise price, and the per share market value of the underlying company. The Corporation holds a portfolio of warrants for generally nonmarketable equity securities with a fair value of $2 million at December 31, 2017 , included in "accrued income and other assets" on the consolidated balance sheets. These warrants are primarily from non-public technology companies obtained as part of the loan origination process. The Corporate Development Department is responsible for the warrant valuation process, which includes reviewing all significant inputs for reasonableness, and for providing valuation results to senior management. Increases in any of these inputs in isolation, with the exception of exercise price, would result in a higher fair value. Increases in exercise price in isolation would result in a lower fair value. The Corporation classifies warrants accounted for as derivatives as Level 3. Nonmarketable equity securities The Corporation has a portfolio of indirect (through funds) private equity and venture capital investments with a carrying value of $6 million and unfunded commitments of less than $1 million , at December 31, 2017 . These funds generally cannot be redeemed and the majority is not readily marketable. Distributions from these funds are received by the Corporation as a result of the liquidation of underlying investments of the funds and/or as income distributions. The investments are accounted for either on the cost or equity method and are individually reviewed for impairment on a quarterly basis by comparing the carrying value to the estimated fair value. These investments may be carried at fair value on a nonrecurring basis when they are deemed to be impaired and written down to fair value. Where there is not a readily determinable fair value, the Corporation estimates fair value for indirect private equity and venture capital investments based on the net asset value, as reported by the fund. On a quarterly basis, the Corporate Development Department is responsible, with appropriate oversight and approval provided by senior management, for performing the valuation procedures and updating significant inputs, as are primarily provided by the underlying fund's management. The Corporation also holds restricted equity investments, primarily Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock. Restricted equity securities are not readily marketable and are recorded at cost (par value) in "accrued income and other assets" on the consolidated balance sheets and evaluated for impairment based on the ultimate recoverability of the par value. No significant observable market data for these instruments is available. The Corporation considers the profitability and asset quality of the issuer, dividend payment history and recent redemption experience and believes its investments in FHLB and FRB stock are ultimately recoverable at par. Therefore, the carrying amount for these restricted equity investments approximates fair value. The Corporation classifies the estimated fair value of such investments as Level 1. The Corporation’s investment in FHLB stock totaled $122 million at both December 31, 2017 and 2016 , and its investment in FRB stock totaled $85 million at both December 31, 2017 and 2016 . Other real estate Other real estate is included in “accrued income and other assets” on the consolidated balance sheets and includes primarily foreclosed property. Foreclosed property is initially recorded at fair value, less costs to sell, at the date of legal title transfer to the Corporation, establishing a new cost basis. Subsequently, foreclosed property is carried at the lower of cost or fair value, less costs to sell. Other real estate may be carried at fair value on a nonrecurring basis when fair value is less than cost. Fair value is based upon independent market prices, appraised value or management's estimate of the value of the property. The Special Assets Group obtains updated independent market prices and appraised values, as required by state regulation or deemed necessary based on market conditions, and determines if additional write-downs are necessary. On a quarterly basis, senior management reviews all other real estate and determines whether the carrying values are reasonable, based on the length of time elapsed since receipt of independent market price or appraised value and current market conditions. When management determines that the fair value of other real estate requires additional adjustments, either as a result of a non-current appraisal or when there is no observable market price, the Corporation classifies the other real estate as Level 3. Deposit liabilities The estimated fair value of checking, savings and certain money market deposit accounts is represented by the amounts payable on demand. The estimated fair value of term deposits is calculated by discounting the scheduled cash flows using the period-end rates offered on these instruments. As such, the Corporation classifies the estimated fair value of deposit liabilities as Level 2. Short-term borrowings The carrying amount of federal funds purchased, securities sold under agreements to repurchase and other short-term borrowings approximates the estimated fair value. As such, the Corporation classifies the estimated fair value of short-term borrowings as Level 1. Medium- and long-term debt The estimated fair value of the Corporation's medium- and long-term debt is based on quoted market values when available. If quoted market values are not available, the estimated fair value is based on the market values of debt with similar characteristics. The Corporation classifies the estimated fair value of medium- and long-term debt as Level 2. Credit-related financial instruments Credit-related financial instruments include unused commitments to extend credit and letters of credit. These instruments generate ongoing fees which are recognized over the term of the commitment. In situations where credit losses are probable, the Corporation records an allowance. The carrying value of these instruments included in "accrued expenses and other liabilities" on the consolidated balance sheets, which includes the carrying value of the deferred fees plus the related allowance, approximates the estimated fair value. The Corporation classifies the estimated fair value of credit-related financial instruments as Level 3. For further information about fair value measurements refer to Note 2 . Other Short-Term Investments Other short-term investments include trading securities and loans held-for-sale. Trading securities are carried at fair value. Realized and unrealized gains or losses on trading securities are included in “other noninterest income” on the consolidated statements of income. Loans held-for-sale, typically residential mortgages originated with the intent to sell and occasionally may include other loans transferred to held-for-sale, are carried at the lower of cost or fair value. Fair value is determined in the aggregate for each portfolio. Changes in fair value and gains or losses upon sale are included in “other noninterest income” on the consolidated statements of income. Investment Securities Securities not held for trading purposes are classified as available-for-sale or held-to-maturity. Debt securities for which management has the intent and ability to hold to maturity are classified as held-to-maturity and recorded at amortized cost. Securities available-for-sale are recorded at fair value, with unrealized gains and losses, net of income taxes, reported as a separate component of other comprehensive income (OCI). Securities transferred from available-for-sale to held-to-maturity are reclassified at fair value on the date of transfer. The net unrealized gain (loss) at the date of transfer is included in historical cost and amortized over the remaining life of the related securities as a yield adjustment consistent with the amortization of the net unrealized gain (loss) included in accumulated other comprehensive loss on the same securities, resulting in no impact to net income. Investment securities are reviewed quarterly for possible other-than-temporary impairment (OTTI). In determining whether OTTI exists for debt securities in an unrealized loss position, the Corporation assesses the likelihood of selling the security prior to the recovery of its amortized cost basis. If the Corporation intends to sell the debt security or it is more likely than not that the Corporation will be required to sell the debt security prior to the recovery of its amortized cost basis, the debt security is written down to fair value, and the full amount of any impairment charge is recorded as a loss in “net securities gains” in the consolidated statements of income. If the Corporation does not intend to sell the debt security and it is more likely than not that the Corporation will not be required to sell the debt security prior to recovery of its amortized cost basis, only the credit component of any impairment of a debt security is recognized as a loss in “net securities losses” on the consolidated statements of income, with the remaining impairment recorded in OCI. The OTTI review for equity securities includes an analysis of the facts and circumstances of each individual investment and focuses on the severity of loss, the length of time the fair value has been below cost, the expectation for that security’s performance, the financial condition and near-term prospects of the issuer, and management’s intent and ability to hold the security to recovery. A decline in value of an equity security that is considered to be other-than-temporary is recorded as a loss in “net securities losses” on the consolidated statements of income. Gains or losses on the sale of securities are computed based on the adjusted cost of the specific security sold. For further information on investment securities, refer to Note 3 . Loans Loans and leases originated and held for investment are recorded at the principal balance outstanding, net of unearned income, charge-offs and unamortized deferred fees and costs. Interest income is recognized on loans and leases using the interest method. The Corporation assesses all loan modifications to determine whether a restructuring constitutes a troubled debt restructuring (TDR). A restructuring is considered a TDR when a borrower is experiencing financial difficulty and the Corporation grants a concession to the borrower. TDRs on accrual status at the original contractual rate of interest are considered performing. Nonperforming TDRs include TDRs on nonaccrual status and loans which have been renegotiated to less than the original contractual rates (reduced-rate loans). All TDRs are considered impaired loans. Loan Origination Fees and Costs Substantially all loan origination fees and costs are deferred and amortized to net interest income over the life of the related loan or over the commitment period as a yield adjustment. Net deferred income on originated loans, including unearned income and unamortized costs, fees, premiums and discounts, totaled $113 million and $147 million at December 31, 2017 and 2016 , respectively. Loan fees on unused commitments and net origination fees related to loans sold are recognized in noninterest income. Allowance for Credit Losses The allowance for credit losses includes both the allowance for loan losses and the allowance for credit losses on lending-related commitments. The Corporation disaggregates the loan portfolio into segments for purposes of determining the allowance for credit losses. These segments are based on the level at which the Corporation develops, documents and applies a systematic methodology to determine the allowance for credit losses. The Corporation's portfolio segments are business loans and retail loans. Business loans include the commercial, real estate construction, commercial mortgage, lease financing and international loan portfolios. Retail loans consist of traditional residential mortgage, home equity and other consumer loans. For further information on the Allowance for Credit Losses, refer to Note 4 . Allowance for Loan Losses The allowance for loan losses represents management’s assessment of probable, estimable losses inherent in the Corporation’s loan portfolio. The allowance for loan losses includes specific allowances, based on individual evaluations of certain loans, and allowances for homogeneous pools of loans with similar risk characteristics. The Corporation individually evaluates certain impaired loans on a quarterly basis and establishes specific allowances for such loans, if required. A loan is considered impaired when it is probable that interest or principal payments will not be made in accordance with the contractual terms of the loan agreement. Consistent with this definition, all loans for which the accrual of interest has been discontinued (nonaccrual loans) are considered impaired. The Corporation individually evaluates nonaccrual loans with book balances of $2 million or more and accruing loans whose terms have been modified in a TDR. The threshold for individual evaluation is revised on an infrequent basis, generally when economic circumstances change significantly. Specific allowances for impaired loans are estimated using one of several methods, including the estimated fair value of underlying collateral, observable market value of similar debt or discounted expected future cash flows. Collateral values supporting individually evaluated impaired loans are evaluated quarterly. Either appraisals are obtained or appraisal assumptions are updated at least annually unless conditions dictate increased frequency. The Corporation may reduce the collateral value based upon the age of the appraisal and adverse developments in market conditions. Loans which do not meet the criteria to be evaluated individually are evaluated in homogeneous pools of loans with similar risk characteristics. Business loans are assigned to pools based on the Corporation's internal risk rating system. Internal risk ratings are assigned to each business loan at the time of approval and are subjected to subsequent periodic reviews by the Corporation’s senior management, generally at least annually or more frequently upon the occurrence of a circumstance that affects the credit risk of the loan. For business loans not individually evaluated, losses inherent to the pool are estimated by applying standard reserve factors to outstanding principal balances. Standard reserve factors are based on estimated probabilities of default for each internal risk rating, set to a default horizon based on an estimated loss emergence period, and loss given default. These factors are evaluated quarterly and updated annually, unless economic conditions necessitate a ch

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Note 1 contains information about the fair value hierarchy, descriptions of the valuation methodologies and key inputs used to measure financial assets and liabilities recorded at fair value, as well as a description of the methods and significant assumptions used to estimate fair value disclosures for financial instruments not recorded at fair value in their entirety on a recurring basis. ASSETS AND LIABLILITIES RECORDED AT FAIR VALUE ON A RECURRING BASIS The following tables present the recorded amount of assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 and 2016 . (in millions) Total Level 1 Level 2 Level 3 December 31, 2017 Trading securities: Deferred compensation plan assets $ 92 $ 92 $ — $ — Investment securities available-for-sale: U.S. Treasury and other U.S. government agency securities 2,727 2,727 — — Residential mortgage-backed securities (a) 8,124 — 8,124 — State and municipal securities 5 — — 5 (b) Equity and other non-debt securities 82 38 — 44 (b) Total investment securities available-for-sale 10,938 2,765 8,124 49 Derivative assets: Interest rate contracts 57 — 43 14 Energy derivative contracts 93 — 93 — Foreign exchange contracts 42 — 42 — Warrants 2 — — 2 Total derivative assets 194 — 178 16 Total assets at fair value $ 11,224 $ 2,857 $ 8,302 $ 65 Derivative liabilities: Interest rate contracts $ 59 $ — $ 59 $ — Energy derivative contracts 91 — 91 — Foreign exchange contracts 40 — 40 — Total derivative liabilities 190 — 190 — Deferred compensation plan liabilities 92 92 — — Total liabilities at fair value $ 282 $ 92 $ 190 $ — (a) Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (b) Auction-rate securities. (in millions) Total Level 1 Level 2 Level 3 December 31, 2016 Trading securities: Deferred compensation plan assets $ 87 $ 87 $ — $ — Equity and other non-debt securities 1 1 — — Total trading securities 88 88 — — Investment securities available-for-sale: U.S. Treasury and other U.S. government agency securities 2,779 2,779 — — Residential mortgage-backed securities (a) 7,872 — 7,872 — State and municipal securities 7 — — 7 (b) Equity and other non-debt securities 129 82 — 47 (b) Total investment securities available-for-sale 10,787 2,861 7,872 54 Derivative assets: Interest rate contracts 223 — 212 11 Energy derivative contracts 146 — 146 — Foreign exchange contracts 38 — 38 — Warrants 3 — — 3 Total derivative assets 410 — 396 14 Total assets at fair value $ 11,285 $ 2,949 $ 8,268 $ 68 Derivative liabilities: Interest rate contracts $ 81 $ — $ 81 $ — Energy derivative contracts 144 — 144 — Foreign exchange contracts 29 — 29 — Total derivative liabilities 254 — 254 — Deferred compensation plan liabilities 87 87 — — Total liabilities at fair value $ 341 $ 87 $ 254 $ — (a) Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (b) Auction-rate securities. There were no transfers of assets or liabilities recorded at fair value on a recurring basis into or out of Level 1, Level 2 and Level 3 fair value measurements during the years ended December 31, 2017 and 2016 . The following table summarizes the changes in Level 3 assets measured at fair value on a recurring basis for the years ended December 31, 2017 and 2016 . Net Realized/Unrealized Gains (Losses) (Pretax) Balance at Beginning of Period Recorded in Earnings Recorded in Other Comprehensive Income Balance at End of Period (in millions) Realized Unrealized Redemptions Sales Year Ended December 31, 2017 Investment securities available-for-sale: State and municipal securities (a) $ 7 $ — $ — $ — $ (2 ) $ — $ 5 Equity and other non-debt securities (a) 47 — — (2 ) (b) (1 ) — 44 Total investment securities 54 — — (2 ) (b) (3 ) — 49 Derivative assets: Interest rate contracts 11 — 3 (c) — — — 14 Warrants 3 6 (c) (1 ) (c) — — (6 ) 2 Year Ended December 31, 2016 Investment securities available-for-sale: State and municipal securities (a) $ 9 $ — $ — $ — $ (2 ) $ — $ 7 Corporate debt securities (a) 1 — — — (1 ) — — Equity and other non-debt securities (a) 67 — — (1 ) (b) (19 ) — 47 Total investment securities 77 — — (1 ) (b) (22 ) — 54 Derivative assets: Interest rate contracts 9 — 2 (c) — — — 11 Warrants 2 6 (c) 1 (c) — — (6 ) 3 (a) Auction-rate securities. (b) Recorded in "net unrealized holding losses arising during the period" in other comprehensive income (loss). (c) Realized and unrealized gains and losses due to changes in fair value recorded in "other noninterest income" on the consolidated statements of income. ASSETS AND LIABILITIES RECORDED AT FAIR VALUE ON A NONRECURRING BASIS The Corporation may be required, from time to time, to record certain assets and liabilities at fair value on a nonrecurring basis. These include assets that are recorded at the lower of cost or fair value, and were recognized at fair value since it was less than cost at the end of the period. The following table presents assets recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 . No liabilities were recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 . (in millions) Level 3 December 31, 2017 Loans: Commercial $ 111 Commercial mortgage 5 Total assets at fair value $ 116 December 31, 2016 Loans: Commercial $ 256 Commercial mortgage 15 International 11 Total loans 282 Other real estate 1 Total assets at fair value $ 283 Level 3 assets recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 included loans for which a specific allowance was established based on the fair value of collateral and other real estate for which fair value of the properties was less than the cost basis. For both asset classes, the unobservable inputs were the additional adjustments applied by management to the appraised values to reflect such factors as non-current appraisals and revisions to estimated time to sell. These adjustments are determined based on qualitative judgments made by management on a case-by-case basis and are not quantifiable inputs, although they are used in the determination of fair value. ESTIMATED FAIR VALUES OF FINANCIAL INSTRUMENTS NOT RECORDED AT FAIR VALUE ON A RECURRING BASIS The Corporation typically holds the majority of its financial instruments until maturity and thus does not expect to realize many of the estimated fair value amounts disclosed. The disclosures also do not include estimated fair value amounts for items that are not defined as financial instruments, but which have significant value. These include such items as core deposit intangibles, the future earnings potential of significant customer relationships and the value of trust operations and other fee generating businesses. The Corporation believes the imprecision of an estimate could be significant. The carrying amount and estimated fair value of financial instruments not recorded at fair value in their entirety on a recurring basis on the Corporation’s consolidated balance sheets are as follows: Carrying Amount Estimated Fair Value (in millions) Total Level 1 Level 2 Level 3 December 31, 2017 Assets Cash and due from banks $ 1,438 $ 1,438 $ 1,438 $ — $ — Interest-bearing deposits with banks 4,407 4,407 4,407 — — Investment securities held-to-maturity 1,266 1,246 — 1,246 — Loans held-for-sale 4 4 — 4 — Total loans, net of allowance for loan losses (a) 48,461 48,153 — — 48,153 Customers’ liability on acceptances outstanding 2 2 2 — — Restricted equity investments 207 207 207 — — Nonmarketable equity securities (b) 6 9 Liabilities Demand deposits (noninterest-bearing) 32,071 32,071 — 32,071 — Interest-bearing deposits 23,667 23,667 — 23,667 — Customer certificates of deposit 2,165 2,142 — 2,142 — Total deposits 57,903 57,880 — 57,880 — Short-term borrowings 10 10 10 — — Acceptances outstanding 2 2 2 — — Medium- and long-term debt 4,622 4,636 — 4,636 — Credit-related financial instruments (67 ) (67 ) — — (67 ) December 31, 2016 Assets Cash and due from banks $ 1,249 $ 1,249 $ 1,249 $ — $ — Interest-bearing deposits with banks 5,969 5,969 5,969 — — Investment securities held-to-maturity 1,582 1,576 — 1,576 — Loans held-for-sale 4 4 — 4 — Total loans, net of allowance for loan losses (a) 48,358 48,250 — — 48,250 Customers’ liability on acceptances outstanding 5 5 5 — — Restricted equity investments 207 207 207 — — Nonmarketable equity securities (b) 11 16 Liabilities Demand deposits (noninterest-bearing) 31,540 31,540 — 31,540 — Interest-bearing deposits 24,639 24,639 — 24,639 — Customer certificates of deposit 2,806 2,731 — 2,731 — Total deposits 58,985 58,910 — 58,910 — Short-term borrowings 25 25 25 — — Acceptances outstanding 5 5 5 — — Medium- and long-term debt 5,160 5,132 — 5,132 — Credit-related financial instruments (73 ) (73 ) — — (73 ) (a) Included $116 million and $282 million of impaired loans recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 , respectively. (b) Certain investments that are measured at fair value using the net asset value have not been classified in the fair value hierarchy. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets.

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investment Securities	INVESTMENT SECURITIES A summary of the Corporation’s investment securities follows: (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value December 31, 2017 Investment securities available-for-sale: U.S. Treasury and other U.S. government agency securities $ 2,743 $ — $ 16 $ 2,727 Residential mortgage-backed securities (a) 8,230 22 128 8,124 State and municipal securities 5 — — 5 Equity and other non-debt securities 83 1 2 82 Total investment securities available-for-sale (b) $ 11,061 $ 23 $ 146 $ 10,938 Investment securities held-to-maturity (c): Residential mortgage-backed securities (a) $ 1,266 $ — $ 20 $ 1,246 December 31, 2016 Investment securities available-for-sale: U.S. Treasury and other U.S. government agency securities $ 2,772 $ 8 $ 1 $ 2,779 Residential mortgage-backed securities (a) 7,921 48 97 7,872 State and municipal securities 7 — — 7 Equity and other non-debt securities 129 1 1 129 Total investment securities available-for-sale (b) $ 10,829 $ 57 $ 99 $ 10,787 Investment securities held-to-maturity (c): Residential mortgage-backed securities (a) $ 1,582 $ 1 $ 7 $ 1,576 (a) Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (b) Included auction-rate securities at amortized cost and fair value of $51 million and $49 million , respectively, as of December 31, 2017 and $55 million and $54 million , respectively, as of December 31, 2016 . (c) The amortized cost of investment securities held-to-maturity included the unamortized balance of net unrealized losses as of the transfer date of $9 million and $12 million at December 31, 2017 and 2016 , respectively, related to securities transferred from available-for-sale, which is included in accumulated other comprehensive loss. A summary of the Corporation’s investment securities in an unrealized loss position as of December 31, 2017 and 2016 follows: Temporarily Impaired Less than 12 Months 12 Months or more Total (in millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses December 31, 2017 U.S. Treasury and other U.S. government agency securities $ 2,727 $ 16 $ — $ — $ 2,727 $ 16 Residential mortgage-backed securities (a) 3,845 32 4,003 125 7,848 157 State and municipal securities (b) — — 5 — (c) 5 — (c) Equity and other non-debt securities (b) — — 44 2 44 2 Total impaired securities $ 6,572 $ 48 $ 4,052 $ 127 $ 10,624 $ 175 December 31, 2016 U.S. Treasury and other U.S. government agency securities $ 527 $ 1 $ — $ — $ 527 $ 1 Residential mortgage-backed securities (a) 4,992 87 1,177 32 6,169 119 State and municipal securities (b) — — 7 — (c) 7 — (c) Equity and other non-debt securities (b) 36 — (c) 11 — (c) 47 — (c) Total impaired securities $ 5,555 $ 88 $ 1,195 $ 32 $ 6,750 $ 120 (a) Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (b) Primarily auction-rate securities. (c) Unrealized losses less than $0.5 million. At December 31, 2017 , the Corporation had 354 securities in an unrealized loss position with no credit impairment, including 29 U.S. Treasury securities, 284 residential mortgage-backed securities, 13 state and municipal auction-rate securities, and 28 equity and other non-debt auction-rate preferred securities. The unrealized losses for these securities resulted from changes in market interest rates and liquidity, not changes in credit quality. The Corporation ultimately expects full collection of the carrying amount of these securities, does not intend to sell the securities in an unrealized loss position, and it is not more-likely-than-not that the Corporation will be required to sell the securities in an unrealized loss position prior to recovery of amortized cost. The Corporation does not consider these securities to be other-than-temporarily impaired at December 31, 2017 . Sales, calls and write-downs of investment securities available-for-sale resulted in the following gains and losses recorded in “net securities losses” on the consolidated statements of income, computed based on the adjusted cost of the specific security. (in millions) Years Ended December 31 2017 2016 2015 Securities gains $ 2 $ — $ — Securities losses (5 ) (5 ) (2 ) Net securities losses (a) $ (3 ) $ (5 ) $ (2 ) (a) Primarily charges related to a derivative contract tied to the conversion rate of Visa Class B shares. The following table summarizes the amortized cost and fair values of debt securities by contractual maturity. Securities with multiple maturity dates are classified in the period of final maturity. 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. (in millions) Available-for-sale Held-to-maturity December 31, 2017 Amortized Cost Fair Value Amortized Cost Fair Value Contractual maturity After one year through five years $ 2,956 $ 2,939 $ — $ — After five years through ten years 1,690 1,697 17 17 After ten years 6,332 6,220 1,249 1,229 Subtotal 10,978 10,856 1,266 1,246 Equity and other non-debt securities 83 82 — — Total investment securities $ 11,061 $ 10,938 $ 1,266 $ 1,246 Included in the contractual maturity distribution in the table above were residential mortgage-backed securities available-for-sale with a total amortized cost of $8.2 billion and a fair value of $8.1 billion , and residential mortgage-backed securities held-to-maturity with a total amortized cost of $1.3 billion and a fair value of $1.2 billion . The actual cash flows of mortgage-backed securities may differ from contractual maturity as the borrowers of the underlying loans may exercise prepayment options. At December 31, 2017 , investment securities with a carrying value of $770 million were pledged where permitted or required by law to secure $484 million of liabilities, primarily public and other deposits of state and local government agencies and derivative instruments.

Credit Quality And Allowance Fo

Credit Quality And Allowance For Credit Losses	12 Months Ended
	Dec. 31, 2017
Credit Quality And Allowance For Credit Losses [Abstract]
Credit Quality And Allowance For Credit Losses	CREDIT QUALITY AND ALLOWANCE FOR CREDIT LOSSES The following table presents an aging analysis of the recorded balance of loans. Loans Past Due and Still Accruing (in millions) 30-59 Days 60-89 Days 90 Days or More Total Nonaccrual Loans Current Loans Total Loans December 31, 2017 Business loans: Commercial $ 79 $ 134 $ 12 $ 225 $ 309 $ 30,526 $ 31,060 Real estate construction: Commercial Real Estate business line (a) 3 — — 3 — 2,627 2,630 Other business lines (b) 4 — — 4 — 327 331 Total real estate construction 7 — — 7 — 2,954 2,961 Commercial mortgage: Commercial Real Estate business line (a) 14 — — 14 9 1,808 1,831 Other business lines (b) 27 6 22 55 22 7,251 7,328 Total commercial mortgage 41 6 22 69 31 9,059 9,159 Lease financing — — — — 4 464 468 International 13 — — 13 6 964 983 Total business loans 140 140 34 314 350 43,967 44,631 Retail loans: Residential mortgage 10 2 — 12 31 1,945 1,988 Consumer: Home equity 5 1 — 6 21 1,789 1,816 Other consumer 4 — 1 5 — 733 738 Total consumer 9 1 1 11 21 2,522 2,554 Total retail loans 19 3 1 23 52 4,467 4,542 Total loans $ 159 $ 143 $ 35 $ 337 $ 402 $ 48,434 $ 49,173 December 31, 2016 Business loans: Commercial $ 30 $ 12 $ 14 $ 56 $ 445 $ 30,493 $ 30,994 Real estate construction: Commercial Real Estate business line (a) — — — — — 2,485 2,485 Other business lines (b) — — — — — 384 384 Total real estate construction — — — — — 2,869 2,869 Commercial mortgage: Commercial Real Estate business line (a) 5 — — 5 9 2,004 2,018 Other business lines (b) 58 5 5 68 37 6,808 6,913 Total commercial mortgage 63 5 5 73 46 8,812 8,931 Lease financing — — — — 6 566 572 International 1 — — 1 14 1,243 1,258 Total business loans 94 17 19 130 511 43,983 44,624 Retail loans: Residential mortgage 7 3 — 10 39 1,893 1,942 Consumer: Home equity 4 3 — 7 28 1,765 1,800 Other consumer 1 — — 1 4 717 722 Total consumer 5 3 — 8 32 2,482 2,522 Total retail loans 12 6 — 18 71 4,375 4,464 Total loans $ 106 $ 23 $ 19 $ 148 $ 582 $ 48,358 $ 49,088 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate. The following table presents loans by credit quality indicator, based on internal risk ratings assigned to each business loan at the time of approval and subjected to subsequent reviews, generally at least annually, and to pools of retail loans with similar risk characteristics. Internally Assigned Rating (in millions) Pass (a) Special Mention (b) Substandard (c) Nonaccrual (d) Total December 31, 2017 Business loans: Commercial $ 29,263 $ 591 $ 897 $ 309 $ 31,060 Real estate construction: Commercial Real Estate business line (e) 2,630 — — — 2,630 Other business lines (f) 327 4 — — 331 Total real estate construction 2,957 4 — — 2,961 Commercial mortgage: Commercial Real Estate business line (e) 1,759 20 43 9 1,831 Other business lines (f) 7,099 115 92 22 7,328 Total commercial mortgage 8,858 135 135 31 9,159 Lease financing 440 23 1 4 468 International 946 11 20 6 983 Total business loans 42,464 764 1,053 350 44,631 Retail loans: Residential mortgage 1,955 2 — 31 1,988 Consumer: Home equity 1,786 1 8 21 1,816 Other consumer 737 1 — — 738 Total consumer 2,523 2 8 21 2,554 Total retail loans 4,478 4 8 52 4,542 Total loans $ 46,942 $ 768 $ 1,061 $ 402 $ 49,173 December 31, 2016 Business loans: Commercial $ 28,616 $ 944 $ 989 $ 445 $ 30,994 Real estate construction: Commercial Real Estate business line (e) 2,485 — — — 2,485 Other business lines (f) 381 — 3 — 384 Total real estate construction 2,866 — 3 — 2,869 Commercial mortgage: Commercial Real Estate business line (e) 1,970 19 20 9 2,018 Other business lines (f) 6,645 109 122 37 6,913 Total commercial mortgage 8,615 128 142 46 8,931 Lease financing 550 11 5 6 572 International 1,200 22 22 14 1,258 Total business loans 41,847 1,105 1,161 511 44,624 Retail loans: Residential mortgage 1,900 3 — 39 1,942 Consumer: Home equity 1,767 1 4 28 1,800 Other consumer 718 — — 4 722 Total consumer 2,485 1 4 32 2,522 Total retail loans 4,385 4 4 71 4,464 Total loans $ 46,232 $ 1,109 $ 1,165 $ 582 $ 49,088 (a) Includes all loans not included in the categories of special mention, substandard or nonaccrual. (b) Special mention loans are accruing loans that have potential credit weaknesses that deserve management’s close attention, such as loans to borrowers who may be experiencing financial difficulties that may result in deterioration of repayment prospects from the borrower at some future date. This category is generally consistent with the "special mention" category as defined by regulatory authorities. (c) Substandard loans are accruing loans that have a well-defined weakness, or weaknesses, such as loans to borrowers who may be experiencing losses from operations or inadequate liquidity of a degree and duration that jeopardizes the orderly repayment of the loan. Substandard loans also are distinguished by the distinct possibility of loss in the future if these weaknesses are not corrected. This category is generally consistent with the "substandard" category as defined by regulatory authorities. (d) Nonaccrual loans are loans for which the accrual of interest has been discontinued. For further information regarding nonaccrual loans, refer to the Nonperforming Assets subheading in Note 1 - Basis of Presentation and Accounting Policies. A significant majority of nonaccrual loans are generally consistent with the "substandard" category and the remainder are generally consistent with the "doubtful" category as defined by regulatory authorities. (e) Primarily loans to real estate developers. (f) Primarily loans secured by owner-occupied real estate. The following table summarizes nonperforming assets. (in millions) December 31, 2017 December 31, 2016 Nonaccrual loans $ 402 $ 582 Reduced-rate loans (a) 8 8 Total nonperforming loans 410 590 Foreclosed property (b) 5 17 Total nonperforming assets $ 415 $ 607 (a) There were no reduced-rate business loans at both December 31, 2017 and 2016 . Reduced-rate retail loans totaled $8 million at both December 31, 2017 and 2016 . (b) Included foreclosed residential real estate properties of $4 million and $3 million at December 31, 2017 and 2016 , respectively. There were no retail loans secured by residential real estate properties in process of foreclosure included in nonaccrual loans at both December 31, 2017 and 2016 . Allowance for Credit Losses The following table details the changes in the allowance for loan losses and related loan amounts. 2017 2016 2015 (in millions) Business Loans Retail Loans Total Business Loans Retail Loans Total Business Loans Retail Loans Total Years Ended December 31 Allowance for loan losses: Balance at beginning of period $ 682 $ 48 $ 730 $ 579 $ 55 $ 634 $ 534 $ 60 $ 594 Loan charge-offs (143 ) (6 ) (149 ) (207 ) (7 ) (214 ) (157 ) (11 ) (168 ) Recoveries on loans previously charged-off 50 7 57 63 5 68 55 13 68 Net loan (charge-offs) recoveries (93 ) 1 (92 ) (144 ) (2 ) (146 ) (102 ) 2 (100 ) Provision for loan losses 71 2 73 246 (5 ) 241 149 (7 ) 142 Foreign currency translation adjustment 1 — 1 1 — 1 (2 ) — (2 ) Balance at end of period $ 661 $ 51 $ 712 $ 682 $ 48 $ 730 $ 579 $ 55 $ 634 As a percentage of total loans 1.48 % 1.12 % 1.45 % 1.53 % 1.08 % 1.49 % 1.30 % 1.26 % 1.29 % December 31 Allowance for loan losses: Individually evaluated for impairment $ 67 $ — $ 67 $ 86 $ 3 $ 89 $ 53 $ — $ 53 Collectively evaluated for impairment 594 51 645 596 45 641 526 55 581 Total allowance for loan losses $ 661 $ 51 $ 712 $ 682 $ 48 $ 730 $ 579 $ 55 $ 634 Loans: Individually evaluated for impairment $ 443 $ 34 $ 477 $ 566 $ 48 $ 614 $ 393 $ 31 $ 424 Collectively evaluated for impairment 44,188 4,508 48,696 44,058 4,416 48,474 44,336 4,324 48,660 Total loans evaluated for impairment $ 44,631 $ 4,542 $ 49,173 $ 44,624 $ 4,464 $ 49,088 $ 44,729 $ 4,355 $ 49,084 Changes in the allowance for credit losses on lending-related commitments, included in "accrued expenses and other liabilities" on the consolidated balance sheets, are summarized in the following table. (in millions) Years Ended December 31 2017 2016 2015 Balance at beginning of period $ 41 $ 45 $ 41 Charge-offs on lending-related commitments (a) — (11 ) (1 ) Provision for credit losses on lending-related commitments 1 7 5 Balance at end of period $ 42 $ 41 $ 45 (a) Charge-offs result from the sale of unfunded lending-related commitments. Individually Evaluated Impaired Loans The following table presents additional information regarding individually evaluated impaired loans. Recorded Investment In: (in millions) Impaired Loans with No Related Allowance Impaired Loans with Related Allowance Total Impaired Loans Unpaid Principal Balance Related Allowance for Loan Losses December 31, 2017 Business loans: Commercial $ 105 $ 267 $ 372 $ 460 $ 63 Commercial mortgage: Commercial Real Estate business line (a) 39 1 40 49 — Other business lines (b) 3 22 25 29 3 Total commercial mortgage 42 23 65 78 3 International — 6 6 17 1 Total business loans 147 296 443 555 67 Retail loans: Residential mortgage 14 8 22 22 — Consumer: Home equity 11 — 11 14 — Other consumer 1 — 1 2 — Total consumer 12 — 12 16 — Total retail loans (c) 26 8 34 38 — Total individually evaluated impaired loans $ 173 $ 304 $ 477 $ 593 $ 67 December 31, 2016 Business loans: Commercial $ 90 $ 423 $ 513 $ 608 $ 80 Commercial mortgage: Commercial Real Estate business line (a) — 7 7 15 1 Other business lines (b) 2 30 32 40 3 Total commercial mortgage 2 37 39 55 4 International 3 11 14 20 2 Total business loans 95 471 566 683 86 Retail loans: Residential mortgage 19 9 28 30 2 Consumer: Home equity 15 — 15 19 — Other consumer 2 3 5 6 1 Total consumer 17 3 20 25 1 Total retail loans (c) 36 12 48 55 3 Total individually evaluated impaired loans $ 131 $ 483 $ 614 $ 738 $ 89 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate. (c) Individually evaluated retail loans generally have no related allowance for loan losses, primarily due to policy which results in direct write-downs of most restructured retail loans. The following table presents information regarding average individually evaluated impaired loans and the related interest recognized. Interest income recognized for the period primarily related to reduced-rate loans. Individually Evaluated Impaired Loans 2017 2016 2015 (in millions) Average Balance for the Period Interest Income Recognized for the Period Average Balance for the Period Interest Income Recognized for the Period Average Balance for the Period Interest Income Recognized for the Period Years Ended December 31 Business loans: Commercial $ 451 $ 8 $ 550 $ 10 $ 206 $ 5 Commercial mortgage: Commercial Real Estate business line (a) 21 2 9 — 16 — Other business lines (b) 31 — 31 1 39 1 Total commercial mortgage 52 2 40 1 55 1 International 8 — 18 — 6 — Total business loans 511 10 608 11 267 6 Retail loans: Residential mortgage 24 — 15 — 21 — Consumer: Home equity 13 — 13 — 12 — Other consumer 3 — 4 — 6 — Total consumer 16 — 17 — 18 — Total retail loans 40 — 32 — 39 — Total individually evaluated impaired loans $ 551 $ 10 $ 640 $ 11 $ 306 $ 6 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate. Troubled Debt Restructurings The following tables detail the recorded balance at December 31, 2017 and 2016 of loans considered to be TDRs that were restructured during the years ended December 31, 2017 and 2016 , by type of modification. In cases of loans with more than one type of modification, the loans were categorized based on the most significant modification. 2017 2016 Type of Modification Type of Modification (in millions) Principal Deferrals (a) Interest Rate (b) AB Note Restructures (c) Total Modifications Principal Deferrals (a) Interest Rate (b) AB Note Restructures (c) Total Modifications Years Ended December 31 Business loans: Commercial $ 77 $ 18 $ 21 $ 116 $ 140 $ — $ 48 $ 188 Commercial mortgage: Commercial Real Estate business line (d) 37 — — 37 — — — — Other business lines (e) 3 — — 3 5 — — 5 Total commercial mortgage 40 — — 40 5 — — 5 International — — — — — — 3 3 Total business loans 117 18 21 156 145 — 51 196 Retail loans: Residential mortgage — — — — — 2 — 2 Consumer: Home equity (f) 1 2 — 3 2 1 — 3 Total retail loans 1 2 — 3 2 3 — 5 Total loans $ 118 $ 20 $ 21 $ 159 $ 147 $ 3 $ 51 $ 201 (a) Primarily represents loan balances where terms were extended 90 days or more at or above contractual interest rates. (b) Loan restructurings whereby interest rates were either reduced or were not at market rates. (c) Loan restructurings whereby the original loan is restructured into two notes: an "A" note, which generally reflects the portion of the modified loan which is expected to be collected; and a "B" note, which is either fully charged off or exchanged for an equity interest. (d) Primarily loans to real estate developers. (e) Primarily loans secured by owner-occupied real estate. (f) Includes bankruptcy loans for which the court has discharged the borrower's obligation and the borrower has not reaffirmed the debt. At December 31, 2017 and 2016 , commitments to lend additional funds to borrowers whose terms have been modified in TDRs totaled $31 million and $24 million , respectively. The majority of the modifications considered to be TDRs that occurred during the years ended December 31, 2017 and 2016 were principal deferrals. The Corporation charges interest on principal balances outstanding during deferral periods. Additionally, none of the modifications involved forgiveness of principal. As a result, the current and future financial effects of the recorded balance of loans considered to be TDRs that were restructured during the years ended December 31, 2017 and 2016 were insignificant. On an ongoing basis, the Corporation monitors the performance of modified loans to their restructured terms. The allowance for loan losses continues to be reassessed on the basis of an individual evaluation of the loan. The following table presents information regarding the recorded balance at December 31, 2017 and 2016 of loans modified by principal deferral during the years ended December 31, 2017 and 2016 , and those principal deferrals which experienced a subsequent default during the same periods. For principal deferrals, incremental deterioration in the credit quality of the loan, represented by a downgrade in the risk rating of the loan, for example, due to missed interest payments or a reduction of collateral value, is considered a subsequent default. 2017 2016 (in millions) Balance at December 31 Subsequent Default in the Year Ended December 31 Balance at December 31 Subsequent Default in the Year Ended December 31 Principal deferrals: Business loans: Commercial $ 77 $ 3 $ 140 $ 13 Commercial mortgage: Commercial Real Estate business line (a) 37 — — — Other business lines (b) 3 — 5 1 Total commercial mortgage 40 — 5 1 International — — — — Total business loans 117 3 145 14 Retail loans: Consumer: Home equity (c) 1 — 2 — Total principal deferrals $ 118 $ 3 $ 147 $ 14 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate. (c) Includes bankruptcy loans for which the court has discharged the borrower's obligation and the borrower has not reaffirmed the debt. For interest rate and loans restructured into two notes (AB note restructures), a subsequent payment default is defined in terms of delinquency, when a principal or interest payment is 90 days past due. There were no subsequent payment defaults of interest rate loans or AB note restructures during the year ended December 31, 2017 and 2016 .

Significant Group Concentration

Significant Group Concentrations of Credit Risk	12 Months Ended
	Dec. 31, 2017
Significant Group Concentrations of Credit Risk [Abstract]
Significant Group Concentrations of Credit Risk	SIGNIFICANT GROUP CONCENTRATIONS OF CREDIT RISK Concentrations of credit risk may exist when a number of borrowers are engaged in similar activities, or activities in the same geographic region, and have similar economic characteristics that would cause them to be similarly impacted by changes in economic or other conditions. Concentrations of both on-balance sheet and off-balance sheet credit risk are controlled and monitored as part of credit policies. The Corporation is a regional financial services holding company with a geographic concentration of its on-balance-sheet and off-balance-sheet activities in Michigan, California and Texas. As outlined below, the Corporation has a concentration of credit risk with the automotive industry. Loans to automotive dealers and to borrowers involved with automotive production are reported as automotive, as management believes these loans have similar economic characteristics that might cause them to react similarly to changes in economic conditions. This aggregation involves the exercise of judgment. Included in automotive production are: (a) original equipment manufacturers and Tier 1 and Tier 2 suppliers that produce components used in vehicles and whose primary revenue source is automotive-related (“primary” defined as greater than 50%) and (b) other manufacturers that produce components used in vehicles and whose primary revenue source is automotive-related. Loans less than $1 million and loans recorded in the Small Business loan portfolio were excluded from the definition. Outstanding loans, included in "commercial loans" on the consolidated balance sheets, and total exposure (outstanding loans, unused commitments and standby letters of credit) to companies related to the automotive industry were as follows: (in millions) December 31 2017 2016 Automotive loans: Production $ 1,344 $ 1,326 Dealer 7,592 7,123 Total automotive loans $ 8,936 $ 8,449 Total automotive exposure: Production $ 2,439 $ 2,534 Dealer 9,405 8,730 Total automotive exposure $ 11,844 $ 11,264 Further, the Corporation’s portfolio of commercial real estate loans, which includes real estate construction and commercial mortgage loans, was as follows. (in millions) December 31 2017 2016 Real estate construction loans: Commercial Real Estate business line (a) $ 2,630 $ 2,485 Other business lines (b) 331 384 Total real estate construction loans 2,961 2,869 Commercial mortgage loans: Commercial Real Estate business line (a) 1,831 2,018 Other business lines (b) 7,328 6,913 Total commercial mortgage loans 9,159 8,931 Total commercial real estate loans $ 12,120 $ 11,800 Total unused commitments on commercial real estate loans $ 3,018 $ 3,046 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate.

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises and Equipment	PREMISES AND EQUIPMENT A summary of premises and equipment by major category follows: (in millions) December 31 2017 2016 Land $ 85 $ 86 Buildings and improvements 813 831 Furniture and equipment 484 499 Total cost 1,382 1,416 Less: Accumulated depreciation and amortization (916 ) (915 ) Net book value $ 466 $ 501 The Corporation conducts a portion of its business from leased facilities and leases certain equipment. Rental expense for leased properties and equipment amounted to $78 million , $80 million and $79 million in 2017 , 2016 and 2015 , respectively. As of December 31, 2017 , future minimum rental payments under operating leases were as follows: (in millions) Years Ending December 31 2018 $ 68 2019 61 2020 52 2021 43 2022 32 Thereafter 135 Total $ 391

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Core Deposit Intangibles	GOODWILL AND CORE DEPOSIT INTANGIBLES The following table summarizes the carrying value of goodwill by reporting unit for the years ended December 31, 2017 and 2016 . (in millions) December 31 2017 2016 Business Bank $ 380 $ 380 Retail Bank 194 194 Wealth Management 61 61 Total $ 635 $ 635 The Corporation performs its annual evaluation of goodwill impairment in the third quarter of each year and on an interim basis if events or changes in circumstances between annual tests indicate goodwill might be impaired. In 2017 and 2016 , the annual test of goodwill impairment was performed as of the beginning of the third quarter. At the conclusion of the first step of the annual and interim goodwill impairment tests performed in 2017 and 2016 the estimated fair values of all reporting units exceeded their carrying amounts, including goodwill, indicating that goodwill was not impaired. There have been no events since the annual test performed in the third quarter 2017 that would indicate that it was more likely than not that goodwill had become impaired. A summary of core deposit intangible carrying value and related accumulated amortization follows: (in millions) December 31 2017 2016 Gross carrying amount $ 34 $ 34 Accumulated amortization (28 ) (26 ) Net carrying amount $ 6 $ 8 The Corporation recorded amortization expense related to the core deposit intangible of $2 million for each of the years ended December 31, 2017 and 2016 , and $3 million for 2015 . At December 31, 2017 , estimated future amortization expense was as follows: (in millions) Years Ending December 31 2018 $ 2 2019 2 2020 1 2021 1 Total $ 6

Derivative And Credit-Related F

Derivative And Credit-Related Financial Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative And Credit-Related Financial Instruments	DERIVATIVE AND CREDIT-RELATED FINANCIAL INSTRUMENTS In the normal course of business, the Corporation enters into various transactions involving derivative and credit-related financial instruments to manage exposure to fluctuations in interest rate, foreign currency and other market risks and to meet the financing needs of customers (customer-initiated derivatives). These financial instruments involve, to varying degrees, elements of market and credit risk. Market and credit risk are included in the determination of fair value. Market risk is the potential loss that may result from movements in interest rates, foreign currency exchange rates or energy commodity prices that cause an unfavorable change in the value of a financial instrument. The Corporation manages this risk by establishing monetary exposure limits and monitoring compliance with those limits. Market risk inherent in interest rate and energy contracts entered into on behalf of customers is mitigated by taking offsetting positions, except in those circumstances when the amount, tenor and/or contract rate level results in negligible economic risk, whereby the cost of purchasing an offsetting contract is not economically justifiable. The Corporation mitigates most of the inherent market risk in foreign exchange contracts entered into on behalf of customers by taking offsetting positions and manages the remainder through individual foreign currency position limits and aggregate value-at-risk limits. These limits are established annually and positions are monitored quarterly. Market risk inherent in derivative instruments held or issued for risk management purposes is typically offset by changes in the fair value of the assets or liabilities being hedged. Credit risk is the possible loss that may occur in the event of nonperformance by the counterparty to a financial instrument. The Corporation attempts to minimize credit risk arising from customer-initiated derivatives by evaluating the creditworthiness of each customer, adhering to the same credit approval process used for traditional lending activities and obtaining collateral as deemed necessary. Derivatives with dealer counterparties are either cleared through a clearinghouse or settled directly with a single counterparty. For derivatives settled directly with dealer counterparties, the Corporation utilizes counterparty risk limits and monitoring procedures, as well as master netting arrangements and bilateral collateral agreements to facilitate the management of credit risk. Master netting arrangements effectively reduce credit risk by permitting settlement of positive and negative positions and offset cash collateral held with the same counterparty on a net basis. Bilateral collateral agreements require daily exchange of cash or highly rated securities issued by the U.S. Treasury or other U.S. government entities to collateralize amounts due to either party beyond certain risk limits. At December 31, 2017 , counterparties with bilateral collateral agreements had pledged $3 million of marketable investment securities and deposited $1 million of cash with the Corporation to secure the fair value of contracts in an unrealized gain position, and the Corporation had pledged $25 million of investment securities and posted $40 million of cash as collateral for contracts in an unrealized loss position. For those counterparties not covered under bilateral collateral agreements, collateral is obtained, if deemed necessary, based on the results of management’s credit evaluation of the counterparty. Collateral varies, but may include cash, investment securities, accounts receivable, equipment or real estate. Included in the fair value of derivative instruments are credit valuation adjustments reflecting counterparty credit risk. These adjustments are determined by applying a credit spread for the counterparty or the Corporation, as appropriate, to the total expected exposure of the derivative. There were no derivative instruments with credit-risk-related contingent features that were in a liability position at December 31, 2017 . Derivative Instruments Derivative instruments utilized by the Corporation are negotiated over-the-counter and primarily include swaps, caps and floors, forward contracts and options, each of which may relate to interest rates, energy commodity prices or foreign currency exchange rates. Swaps are agreements in which two parties periodically exchange cash payments based on specified indices applied to a specified notional amount until a stated maturity. Caps and floors are agreements which entitle the buyer to receive cash payments based on the difference between a specified reference rate or price and an agreed strike rate or price, applied to a specified notional amount until a stated maturity. Forward contracts are over-the-counter agreements to buy or sell an asset at a specified future date and price. Options are similar to forward contracts except the purchaser has the right, but not the obligation, to buy or sell the asset during a specified period or at a specified future date. Over-the-counter contracts are tailored to meet the needs of the counterparties involved and, therefore, contain a greater degree of credit risk and liquidity risk than exchange-traded contracts, which have standardized terms and readily available price information. The Corporation reduces exposure to market and liquidity risks from over-the-counter derivative instruments entered into for risk management purposes, and transactions entered into to mitigate the market risk associated with customer-initiated transactions, by conducting hedging transactions with investment grade domestic and foreign financial institutions and subjecting counterparties to credit approvals, limits and collateral monitoring procedures similar to those used in making other extensions of credit. In addition, certain derivative contracts executed bilaterally with a dealer counterparty in the over-the-counter market are cleared through a clearinghouse, whereby the clearinghouse becomes the counterparty to the transaction. The following table presents the composition of the Corporation’s derivative instruments held or issued for risk management purposes or in connection with customer-initiated and other activities at December 31, 2017 and 2016 . The table excludes commitments and warrants accounted for as derivatives. December 31, 2017 December 31, 2016 Fair Value Fair Value (in millions) Notional/ Contract Amount (a) Gross Derivative Assets Gross Derivative Liabilities Notional/ Contract Amount (a) Gross Derivative Assets Gross Derivative Liabilities Risk management purposes Derivatives designated as hedging instruments Interest rate contracts: Swaps - fair value - receive fixed/pay floating (b) $ 1,775 $ — $ 2 $ 2,275 $ 92 $ 4 Derivatives used as economic hedges Foreign exchange contracts: Spot, forwards and swaps 650 — 2 717 2 2 Total risk management purposes 2,425 — 4 2,992 94 6 Customer-initiated and other activities Interest rate contracts: Caps and floors written 635 — — 436 — 1 Caps and floors purchased 635 — — 436 1 — Swaps (b) 13,119 57 57 12,451 130 76 Total interest rate contracts 14,389 57 57 13,323 131 77 Energy contracts: Caps and floors written 164 — 11 419 1 31 Caps and floors purchased 164 11 — 419 31 1 Swaps 1,519 82 80 1,389 114 112 Total energy contracts 1,847 93 91 2,227 146 144 Foreign exchange contracts: Spot, forwards, options and swaps 1,884 42 38 1,509 36 27 Total customer-initiated and other activities 18,120 192 186 17,059 313 248 Total gross derivatives $ 20,545 192 190 $ 20,051 407 254 Amounts offset in the consolidated balance sheets: Netting adjustment - Offsetting derivative assets/liabilities (49 ) (49 ) (84 ) (84 ) Netting adjustment - Cash collateral received/posted (1 ) (39 ) (47 ) (45 ) Net derivatives included in the consolidated balance sheets (c) 142 102 276 125 Amounts not offset in the consolidated balance sheets: Marketable securities received/pledged under bilateral collateral agreements (3 ) (24 ) (19 ) (8 ) Net derivatives after deducting amounts not offset in the consolidated balance sheets $ 139 $ 78 $ 257 $ 117 (a) Notional or contractual amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets. (b) Due to clearinghouse rule changes, beginning January 1, 2017, variation margin payments are treated as settlements of derivative exposure rather than as collateral. As a result, these payments are now considered in determining the fair value of centrally cleared derivatives, resulting in centrally cleared derivatives having a fair value of approximately zero. (c) Net derivative assets are included in “accrued income and other assets” and net derivative liabilities are included in “accrued expenses and other liabilities” on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and credit risk of the Corporation. The fair value of net derivative assets included credit valuation adjustments for counterparty credit risk of $4 million and $5 million at December 31, 2017 and 2016 , respectively. Risk Management The Corporation's derivative instruments used for managing interest rate risk currently comprise swaps converting fixed rate long-term debt to variable rates. These instruments reduced interest expense by $32 million and $60 million for the years ended December 31 2017 and 2016 , respectively. These hedges have been highly effective, with ineffectiveness net gains of $1 million for 2017 and net losses of $2 million for 2016 included in "other noninterest income" in the consolidated statements. The following table summarizes the expected weighted average remaining maturity of the notional amount of risk management interest rate swaps and the weighted average interest rates associated with amounts expected to be received or paid on interest rate swap agreements as of December 31, 2017 and 2016 . Weighted Average (dollar amounts in millions) Notional Amount Remaining Maturity (in years) Receive Rate Pay Rate (a) December 31, 2017 Swaps - fair value - receive fixed/pay floating rate Medium- and long-term debt designation $ 1,775 4.6 3.26 % 2.35 % December 31, 2016 Swaps - fair value - receive fixed/pay floating rate Medium- and long-term debt designation 2,275 4.5 3.69 1.80 (a) Variable rates paid on receive fixed swaps are based on six-month LIBOR rates in effect at December 31, 2017 and 2016 . Foreign exchange rate risk arises from changes in the value of certain assets and liabilities denominated in foreign currencies. The Corporation employs spot and forward contracts in addition to swap contracts to manage exposure to these and other risks. These instruments are used as economic hedges and net gains or losses are included in "other noninterest income" in the consolidated statements of comprehensive income. Customer-Initiated and Other The Corporation enters into derivative transactions at the request of customers and generally takes offsetting positions with dealer counterparties to mitigate the inherent market risk. Income primarily results from the spread between the customer derivative and the offsetting dealer position. For customer-initiated foreign exchange contracts where offsetting positions have not been taken, the Corporation manages the remaining inherent market risk through individual foreign currency position limits and aggregate value-at-risk limits. These limits are established annually and reviewed quarterly. For those customer-initiated derivative contracts which were not offset or where the Corporation holds a position within the limits described above, the Corporation recognized an insignificant amount net losses and $1 million of net gains in “other noninterest income” in the consolidated statements of income for the years ended December 31 2017 and 2016 , respectively. Fair values of customer-initiated and other derivative instruments represent the net unrealized gains or losses on such contracts and are recorded in the consolidated balance sheets. Changes in fair value are recognized in the consolidated statements of income. The net gains recognized in income on customer-initiated derivative instruments, net of the impact of offsetting positions, were as follows: (in millions) Years Ended December 31 Location of Gain 2017 2016 Interest rate contracts Other noninterest income $ 24 $ 25 Energy contracts Other noninterest income 2 2 Foreign exchange contracts Foreign exchange income 45 41 Total $ 71 $ 68 Credit-Related Financial Instruments The Corporation issues off-balance sheet financial instruments in connection with commercial and consumer lending activities. The Corporation’s credit risk associated with these instruments is represented by the contractual amounts indicated in the following table. (in millions) December 31 2017 2016 Unused commitments to extend credit: Commercial and other $ 22,636 $ 24,333 Bankcard, revolving check credit and home equity loan commitments 2,833 2,658 Total unused commitments to extend credit $ 25,469 $ 26,991 Standby letters of credit $ 3,228 $ 3,623 Commercial letters of credit 39 46 The Corporation maintains an allowance to cover probable credit losses inherent in lending-related commitments, including unused commitments to extend credit, letters of credit and financial guarantees. At December 31, 2017 and 2016 , the allowance for credit losses on lending-related commitments, included in “accrued expenses and other liabilities” on the consolidated balance sheets, was $42 million and $41 million , respectively. Unused Commitments to Extend Credit Commitments to extend credit are legally binding agreements to lend to a customer, provided there is no violation of any condition established in the contract. These commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Commitments may expire without being drawn upon; therefore, the total contractual amount of commitments does not necessarily represent future cash requirements of the Corporation. Commercial and other unused commitments are primarily variable rate commitments. The allowance for credit losses on lending-related commitments included $27 million and $29 million at December 31, 2017 and 2016 , respectively, for probable credit losses inherent in the Corporation’s unused commitments to extend credit. Standby and Commercial Letters of Credit Standby letters of credit represent conditional obligations of the Corporation which guarantee the performance of a customer to a third party. Standby letters of credit are primarily issued to support public and private borrowing arrangements, including commercial paper, bond financing and similar transactions. Commercial letters of credit are issued to finance foreign or domestic trade transactions. These contracts expire in decreasing amounts through the year 2023 . The Corporation may enter into participation arrangements with third parties that effectively reduce the maximum amount of future payments which may be required under standby and commercial letters of credit. These risk participations covered $127 million and $255 million at December 31, 2017 and 2016 , respectively, of the $3.3 billion and $3.7 billion of standby and commercial letters of credit outstanding at December 31, 2017 and 2016 , respectively. The carrying value of the Corporation’s standby and commercial letters of credit, included in “accrued expenses and other liabilities” on the consolidated balance sheets, totaled $40 million at December 31, 2017 , including $25 million in deferred fees and $15 million in the allowance for credit losses on lending-related commitments. At December 31, 2016 , the comparable amounts were $44 million , $32 million and $12 million , respectively. The following table presents a summary of criticized standby and commercial letters of credit at December 31, 2017 and December 31, 2016 . The Corporation's criticized list is consistent with the Special Mention, Substandard and Doubtful categories defined by regulatory authorities. The Corporation manages credit risk through underwriting, periodically reviewing and approving its credit exposures using Board committee approved credit policies and guidelines. (dollar amounts in millions) December 31, 2017 December 31, 2016 Total criticized standby and commercial letters of credit $ 88 $ 135 As a percentage of total outstanding standby and commercial letters of credit 2.7 % 3.7 % Other Credit-Related Financial Instruments The Corporation enters into credit risk participation agreements, under which the Corporation assumes credit exposure associated with a borrower’s performance related to certain interest rate derivative contracts. The Corporation is not a party to the interest rate derivative contracts and only enters into these credit risk participation agreements in instances in which the Corporation is also a party to the related loan participation agreement for such borrowers. The Corporation manages its credit risk on the credit risk participation agreements by monitoring the creditworthiness of the borrowers, which is based on the normal credit review process had it entered into the derivative instruments directly with the borrower. The notional amount of such credit risk participation agreement reflects the pro-rata share of the derivative instrument, consistent with its share of the related participated loan. As of December 31, 2017 and 2016 , the total notional amount of the credit risk participation agreements was approximately $549 million and $458 million , respectively, and the fair value, included in customer-initiated interest rate contracts recorded in "accrued expenses and other liabilities" on the consolidated balance sheets, was insignificant for each period. The maximum estimated exposure to these agreements, as measured by projecting a maximum value of the guaranteed derivative instruments, assuming 100 percent default by all obligors on the maximum values, was insignificant at December 31, 2017 and $3 million at December 31, 2016 , respectively. In the event of default, the lead bank has the ability to liquidate the assets of the borrower, in which case the lead bank would be required to return a percentage of the recouped assets to the participating banks. As of December 31, 2017 , the weighted average remaining maturity of outstanding credit risk participation agreements was 2.6 years.

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Deposits	DEPOSITS At December 31, 2017 , the scheduled maturities of certificates of deposit and other deposits with a stated maturity were as follows: (in millions) Years Ending December 31 2018 $ 1,855 2019 200 2020 66 2021 28 2022 16 Thereafter 15 Total $ 2,180 A maturity distribution of domestic certificates of deposit of $100,000 and over follows: (in millions) December 31 2017 2016 Three months or less $ 355 $ 510 Over three months to six months 207 322 Over six months to twelve months 319 449 Over twelve months 130 230 Total $ 1,011 $ 1,511 The aggregate amount of domestic certificates of deposit that meet or exceed the current FDIC insurance limit of $250,000 was $462 million and $882 million at December 31, 2017 and 2016 , respectively. All foreign office time deposits of $15 million and $19 million at December 31, 2017 and 2016 , respectively, were in denominations of $250,000 or more.

Net Income Per Common Share

Net Income Per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Income Per Common Share	NET INCOME PER COMMON SHARE Basic and diluted net income per common share are presented in the following table. (in millions, except per share data) Years Ended December 31 2017 2016 2015 Basic and diluted Net income $ 743 $ 477 $ 521 Less income allocated to participating securities 5 4 6 Net income attributable to common shares $ 738 $ 473 $ 515 Basic average common shares 174 172 176 Basic net income per common share $ 4.23 $ 2.74 $ 2.93 Basic average common shares 174 172 176 Dilutive common stock equivalents: Net effect of the assumed exercise of stock options 3 2 2 Net effect of the assumed exercise of warrants 1 3 3 Diluted average common shares 178 177 181 Diluted net income per common share $ 4.14 $ 2.68 $ 2.84 The following average shares related to outstanding options to purchase shares of common stock were not included in the computation of diluted net income per common share because the options were anti-dilutive for the period. There were no anti-dilutive options for the year ended December 31, 2017. (shares in millions) Years Ended December 31 2016 2015 Average outstanding options 3.3 5.1 Range of exercise prices $37.26 - $59.86 $46.68 - $60.82

Variable Interest Entities (VIE

Variable Interest Entities (VIEs)	12 Months Ended
	Dec. 31, 2017
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Variable Interest Entities (VIEs)	VARIABLE INTEREST ENTITIES (VIEs) The Corporation evaluates its interest in certain entities to determine if these entities meet the definition of a VIE and whether the Corporation is the primary beneficiary and should consolidate the entity based on the variable interests it held both at inception and when there is a change in circumstances that requires a reconsideration. The Corporation holds ownership interests in funds in the form of limited partnerships or limited liability companies (LLCs) investing in affordable housing projects that qualify for the LIHTC. The Corporation also directly invests in limited partnerships and LLCs which invest in community development projects which generate similar tax credits to investors. As an investor, the Corporation obtains income tax credits and deductions from the operating losses of these tax credit entities. These tax credit entities meet the definition of a VIE; however, the Corporation is not the primary beneficiary of the entities, as the general partner or the managing member has both the power to direct the activities that most significantly impact the economic performance of the entities and the obligation to absorb losses or the right to receive benefits that could be significant to the entities. The Corporation accounts for its interests in LIHTC entities using the proportional amortization method. Exposure to loss as a result of the Corporation’s involvement with LIHTC entities at December 31, 2017 was limited to approximately $422 million . Ownership interests in other community development projects which generate similar tax credits to investors (other tax credit entities) are accounted for under either the cost or equity method. Exposure to loss as a result of the Corporation's involvement in other tax credit entities at December 31, 2017 was limited to approximately $7 million . The Corporation evaluated these investments for impairment after the enactment of the Tax Cuts and Jobs act and recorded an insignificant impairment. Investment balances, including all legally binding commitments to fund future investments, are included in “accrued income and other assets” on the consolidated balance sheets. A liability is recognized in “accrued expenses and other liabilities” on the consolidated balance sheets for all legally binding unfunded commitments to fund tax credit entities ( $165 million at December 31, 2017 ). Amortization and other write-downs of LIHTC investments are presented on a net basis as a component of the "provision for income taxes" on the consolidated statements of income, while amortization and write-downs of other tax credit investments are recorded in “other noninterest income." The income tax credits and deductions are recorded as a reduction of income tax expense and a reduction of federal income taxes payable. The Corporation provided no financial or other support that was not contractually required to any of the above VIEs during the years ended December 31, 2017 , 2016 and 2015 . The following table summarizes the impact of these tax credit entities on line items on the Corporation’s consolidated statements of income. (in millions) Years Ended December 31 2017 2016 2015 Other noninterest income: Amortization of other tax credit investments $ 2 $ (1 ) $ 1 Provision for income taxes: Amortization of LIHTC Investments 67 66 62 Low income housing tax credits (63 ) (62 ) (61 ) Other tax benefits related to tax credit entities (24 ) (26 ) (22 ) Total provision for income taxes $ (20 ) $ (22 ) $ (21 ) For further information on the Corporation’s consolidation policy, see Note 1.

Short-term Borrowings

Short-term Borrowings	12 Months Ended
	Dec. 31, 2017
Short-term Debt [Abstract]
Short-term Borrowings	SHORT-TERM BORROWINGS Federal funds purchased and securities sold under agreements to repurchase generally mature within one to four days from the transaction date. Other short-term borrowings, which may consist of borrowed securities and short-term notes, generally mature within one to 120 days from the transaction date. At December 31, 2017 , Comerica Bank (the Bank), a wholly-owned subsidiary of the Corporation, had pledged loans totaling $21.3 billion which provided for up to $17.2 billion of available collateralized borrowing with the FRB. The following table provides a summary of short-term borrowings. (dollar amounts in millions) Federal Funds Purchased and Securities Sold Under Agreements to Repurchase Other Short-term Borrowings December 31, 2017 Amount outstanding at year-end $ 10 $ — Weighted average interest rate at year-end 1.43 % — % Maximum month-end balance during the year $ 41 $ 1,024 Average balance outstanding during the year 20 257 Weighted average interest rate during the year 1.02 % 1.15 % December 31, 2016 Amount outstanding at year-end $ 25 $ — Weighted average interest rate at year-end 0.54 % — % Maximum month-end balance during the year $ 25 $ 501 Average balance outstanding during the year 15 123 Weighted average interest rate during the year 0.47 % 0.45 % December 31, 2015 Amount outstanding at year-end $ 23 $ — Weighted average interest rate at year-end 0.38 % — % Maximum month-end balance during the year $ 109 $ — Average balance outstanding during the year 93 — Weighted average interest rate during the year 0.05 % — %

Medium- And Long-Term Debt

Medium- And Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Medium- And Long-Term Debt	MEDIUM- AND LONG-TERM DEBT Medium- and long-term debt is summarized as follows: (in millions) December 31 2017 2016 Parent company Subordinated notes: 3.80% subordinated notes due 2026 (a) $ 255 $ 256 Medium-term notes: 2.125% notes due 2019 (a) 347 348 Total parent company 602 604 Subsidiaries Subordinated notes: 5.20% subordinated notes due 2017 (a) — 511 4.00% subordinated notes due 2025 (a) 347 347 7.875% subordinated notes due 2026 (a) 208 215 Total subordinated notes 555 1,073 Medium-term notes: 2.50% notes due 2020 (a) 665 667 FHLB advances: Floating-rate based on FHLB auction rate due 2026 2,800 2,800 Other notes: 6.0% - 6.4% fixed-rate notes due 2018 to 2020 — 16 Total subsidiaries 4,020 4,556 Total medium- and long-term debt $ 4,622 $ 5,160 (a) The fixed interest rates on these notes have been swapped to a variable rate and designated in a hedging relationship. Accordingly, carrying value has been adjusted to reflect the change in the fair value of the debt as a result of changes in the benchmark rate. Subordinated notes with remaining maturities greater than one year qualify as Tier 2 capital. The Bank is a member of the FHLB, which provides short- and long-term funding to its members through advances collateralized by real-estate related assets. The interest rate on each FHLB advance resets every four weeks, based on the FHLB auction rate, with the reset date of each note scheduled at one-week intervals. At December 31, 2017 the weighted-average rate on these advances was 1.41% . Each note may be prepaid in full, without penalty, at each scheduled reset date. Borrowing capacity is contingent upon the amount of collateral available to be pledged to the FHLB. At December 31, 2017 , $15.6 billion of real estate-related loans were pledged to the FHLB as blanket collateral for current and potential future borrowings of approximately $5.2 billion . Unamortized debt issuance costs deducted from the carrying amount of medium- and long-term debt totaled $5 million and $7 million at December 31, 2017 and 2016 , respectively. At December 31, 2017 , the principal maturities of medium- and long-term debt were as follows: (in millions) Years Ending December 31 2018 $ — 2019 350 2020 675 2021 — 2022 — Thereafter 3,550 Total $ 4,575

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Stockholders' Equity	SHAREHOLDERS’ EQUITY The Federal Reserve completed its 2017 Comprehensive Capital Analysis and Review (CCAR) in June 2017 and did not object to the Corporation's 2017/2018 capital plan and capital distributions contemplated in the plan for the period ending June 30, 2018. The plan includes equity repurchases of up to $605 million for the four-quarter period commencing in the third quarter 2017 and ending in the second quarter 2018. During the year ended December 31, 2017 , the Corporation had repurchased $531 million under the equity repurchase program. Repurchases of common stock under the equity repurchase program authorized in 2010 by the Board of Directors of the Corporation totaled 7.3 million shares at an average price paid of $72.44 in 2017 , 6.6 million shares at an average price paid of $46.09 per share in 2016 and 5.1 million shares at an average price paid of $45.65 per share in 2015 . The Corporation also repurchased 500,000 warrants at an average price paid of $20.70 in 2015. There is no expiration date for the Corporation's equity repurchase program. At December 31, 2017 , the Corporation had 1.0 million warrants outstanding to purchase 906,000 common shares at a weighted-average exercise price of $29.42 . Outstanding warrants were exercisable at the date of grant and expire in 2018 . Approximately 1.8 million , 2.3 million and 934,000 shares of common stock were issued upon exercise of warrants in 2017 , 2016 and 2015 , respectively. At December 31, 2017 , the Corporation had 906,000 shares of common stock reserved for warrant exercises, 5.1 million shares of common stock reserved for stock option exercises and restricted stock unit vesting and 1.2 million shares of restricted stock outstanding to employees and directors under share-based compensation plans.

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 LOSS The following table presents a reconciliation of the changes in the components of accumulated other comprehensive loss and details the components of other comprehensive income (loss) for the year ended December 31, 2017 , 2016 and 2015 , including the amount of income tax expense (benefit) allocated to each component of other comprehensive income (loss). (in millions) Years Ended December 31 2017 2016 2015 Accumulated net unrealized (losses) gains on investment securities: Balance at beginning of period, net of tax $ (33 ) $ 9 $ 37 Net unrealized holding losses arising during the period (81 ) (70 ) (55 ) Less: Benefit for income taxes (27 ) (26 ) (21 ) Net unrealized holding losses arising during the period, net of tax (54 ) (44 ) (34 ) Less: Net realized losses included in net securities losses — — (2 ) Less: Benefit for income taxes — — (1 ) Reclassification adjustment for net securities losses included in net income, net of tax — — (1 ) Less: Net losses realized as a yield adjustment in interest on investment securities (3 ) (3 ) (8 ) Less: Benefit for income taxes (1 ) (1 ) (3 ) Reclassification adjustment for net losses realized as a yield adjustment included in net income, net of tax (2 ) (2 ) (5 ) Change in net unrealized losses on investment securities, net of tax (52 ) (42 ) (28 ) Reclassification of certain deferred tax effects (a) (16 ) — — Balance at end of period, net of tax $ (101 ) $ (33 ) $ 9 Accumulated defined benefit pension and other postretirement plans adjustment: Balance at beginning of period, net of tax $ (350 ) $ (438 ) $ (449 ) Actuarial gain (loss) arising during the period 72 (134 ) (57 ) Prior service credit arising during the period — 234 3 Net defined benefit pension and other postretirement adjustment arising during the period 72 100 (54 ) Less: Provision (benefit) for income taxes 17 37 (19 ) Net defined benefit pension and other postretirement adjustment arising during the period, net of tax 55 63 (35 ) Amounts recognized in salaries and benefits expense: Amortization of actuarial net loss 51 46 70 Amortization of prior service (credit) cost (27 ) (7 ) 1 Total amounts recognized in salaries and benefits expense 24 39 71 Less: Provision for income taxes 8 14 25 Adjustment for amounts recognized as components of net periodic benefit cost during the period, net of tax 16 25 46 Change in defined benefit pension and other postretirement plans adjustment, net of tax 71 88 11 Reclassification of certain deferred tax effects (a) (71 ) — — Balance at end of period, net of tax $ (350 ) $ (350 ) $ (438 ) Total accumulated other comprehensive loss at end of period, net of tax $ (451 ) $ (383 ) $ (429 ) (a) Amounts reclassified to retained earnings due to early adoption of ASU 2018-02 . For further information, refer to Note 1.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2017
Share-based Compensation [Abstract]
Share-based Compensation	SHARE-BASED COMPENSATION Share-based compensation expense is charged to “salaries and benefits” expense on the consolidated statements of income. The components of share-based compensation expense for all share-based compensation plans and related tax benefits are as follows: (in millions) Years Ended December 31 2017 2016 2015 Total share-based compensation expense $ 39 $ 34 $ 38 Related tax benefits recognized in net income $ 14 $ 13 $ 14 The following table summarizes unrecognized compensation expense for all share-based plans. (dollar amounts in millions) December 31, 2017 Total unrecognized share-based compensation expense $ 40 Weighted-average expected recognition period (in years) 2.8 The Corporation has share-based compensation plans under which it awards shares of restricted stock and restricted stock units to executive officers, directors and key personnel, and stock options to executive officers and key personnel of the Corporation and its subsidiaries. Restricted stock and restricted stock units vest over periods ranging from one year to five years, and stock options vest over periods ranging from one year to four years. The maturity of each option is determined at the date of grant; however, no options may be exercised later than ten years from the date of grant. The options may have restrictions regarding exercisability. The plans originally provided for a grant of up to 19.4 million common shares, plus shares under certain plans that are forfeited, expire or are canceled, which become available for re-grant. At December 31, 2017 , 9.5 million shares were available for grant. The Corporation used a binomial model to value stock options granted in the periods presented. Option valuation models require several inputs, including the expected stock price volatility, and changes in input assumptions can materially affect the fair value estimates. The model used may not necessarily provide a reliable single measure of the fair value of employee and director stock options. The risk-free interest rate assumption used in the binomial option-pricing model as outlined in the table below was based on the federal ten-year treasury interest rate. The expected dividend yield was based on the historical and projected long-term dividend yield patterns of the Corporation’s common shares. Expected volatility assumptions considered both the historical volatility of the Corporation’s common stock over a ten-year period and implied volatility based on actively traded options on the Corporation’s common stock with pricing terms and trade dates similar to the stock options granted. Expected option life was based on historical exercise activity over the contractual term of the option grant (10 years), excluding certain forced transactions. The estimated weighted-average grant-date fair value per option and the underlying binomial option-pricing model assumptions are summarized in the following table: Years Ended December 31 2017 2016 2015 Weighted-average grant-date fair value per option $ 19.61 $ 9.94 $ 11.31 Weighted-average assumptions: Risk-free interest rates 2.47 % 2.01 % 1.83 % Expected dividend yield 3.00 3.00 3.00 Expected volatility factors of the market price of Comerica common stock 34 38 33 Expected option life (in years) 7.0 6.9 6.9 A summary of the Corporation’s stock option activity and related information for the year ended December 31, 2017 follows: Weighted-Average Number of Options (in thousands) Exercise Price per Share Remaining Contractual Term (in years) Aggregate Intrinsic Value (in millions) Outstanding-January 1, 2017 6,892 $ 37.24 Granted 430 67.67 Forfeited or expired (57 ) 48.74 Exercised (3,092 ) 37.45 Outstanding-December 31, 2017 4,173 40.06 5.9 $ 195 Exercisable-December 31, 2017 2,347 $ 36.27 4.3 $ 119 The aggregate intrinsic value of outstanding options shown in the table above represents the total pretax intrinsic value at December 31, 2017 , based on the Corporation’s closing stock price of $86.81 at December 31, 2017 . The total intrinsic value of stock options exercised was $104 million , $46 million and $12 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. A summary of the Corporation’s restricted stock activity and related information for the year ended December 31, 2017 follows: Number of Shares (in thousands) Weighted-Average Grant-Date Fair Value per Share Outstanding-January 1, 2017 1,591 $ 37.20 Granted 237 67.83 Forfeited (59 ) 42.53 Vested (526 ) 35.28 Outstanding-December 31, 2017 1,243 $ 43.59 The total fair value of restricted stock awards that fully vested was $19 million , $22 million and $18 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. A summary of the Corporation's restricted stock unit activity and related information for the year ended December 31, 2017 follows: Service-Based Units Performance-Based Units Number of Units (in thousands) Weighted-Average Grant-Date Fair Value per Share Number of Units (in thousands) Weighted-Average Grant-Date Fair Value per Share Outstanding-January 1, 2017 180 $ 39.61 781 $ 39.47 Granted 19 75.06 149 66.07 Vested — — (212 ) 48.32 Outstanding-December 31, 2017 199 43.00 718 42.39 The total fair value of restricted stock units that fully vested was $10 million and $11 million for the years ended December 31, 2017 and 2016 , respectively. There were no restricted stock units that vested in 2015 . The Corporation expects to satisfy the exercise of stock options, the vesting of restricted stock units and future grants of restricted stock by issuing shares of common stock out of treasury. At December 31, 2017 , the Corporation held 55.3 million shares in treasury. For further information on the Corporation’s share-based compensation plans, refer to Note 1 .

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS Defined Benefit Pension and Postretirement Benefit Plans The Corporation has a qualified and non-qualified defined benefit pension plan. Prior to January 1, 2017, the plans were in effect for substantially all salaried employees hired before January 1, 2007. In October 2016, the Corporation modified its defined benefit pension plans to freeze final average pay benefits as of December 31, 2016, other than for participants who were age 60 or older as of December 31, 2016, and added a cash balance plan provision effective January 1, 2017. Active pension plan participants 60 years or older as of December 31, 2016 receive the greater of the final average pay formula or the frozen final average pay benefit as of December 31, 2016 plus the cash balance benefit earned after January 1, 2017. Employees participating in the retirement account plan as of December 31, 2016 were eligible to participate in the cash balance pension plan effective January 1, 2017. Benefits earned under the cash balance pension formula, in the form of an account balance, include contribution credits based on eligible pay earned each month, age and years of service and monthly interest credits based on the 30-year Treasury rate. Salaries and benefits expense included defined benefit pension income of $18 million for the year ended December 31, 2017 and expense of $6 million and $47 million in the years ended December 31, 2016 and 2015 , respectively, for the plans. The Corporation’s postretirement benefit plan continues to provide postretirement health care and life insurance benefits for retirees as of December 31, 1992. The plan also provides certain postretirement health care and life insurance benefits for a limited number of retirees who retired prior to January 1, 2000. For all other employees hired prior to January 1, 2000, a nominal benefit is provided. Employees hired on or after January 1, 2000 and prior to January 1, 2007 are eligible to participate in the plan on a full contributory basis until Medicare-eligible based on age and service. Employees hired on or after January 1, 2007 are not eligible to participate in the plan. The Corporation funds the pre-1992 retiree plan benefits with bank-owned life insurance. Employee benefits expense included no postretirement benefit expense for each of the years ended December 31, 2017 and 2016 , and $1 million for the year ended December 31, 2015 . The following table sets forth reconciliations of plan assets and the projected benefit obligation, the weighted-average assumptions used to determine year-end benefit obligations, and the amounts recognized in accumulated other comprehensive income (loss) for the Corporation’s defined benefit pension plans and postretirement benefit plan at December 31, 2017 and 2016 . The Corporation used a measurement date of December 31, 2017 for these plans. Defined Benefit Pension Plans Qualified Non-Qualified Postretirement Benefit Plan (dollar amounts in millions) 2017 2016 2017 2016 2017 2016 Change in fair value of plan assets: Fair value of plan assets at January 1 $ 2,453 $ 2,346 $ — $ — $ 62 $ 61 Actual return on plan assets 396 200 — — 2 2 Employer contributions — — — — 1 4 Benefits paid (102 ) (93 ) — — (5 ) (5 ) Fair value of plan assets at December 31 $ 2,747 $ 2,453 $ — $ — $ 60 $ 62 Change in projected benefit obligation: Projected benefit obligation at January 1 $ 1,902 $ 1,916 $ 201 $ 222 $ 55 $ 59 Service cost 29 31 2 3 — — Interest cost 78 87 8 10 2 3 Actuarial loss (gain) 154 161 12 11 (1 ) (2 ) Benefits paid (102 ) (93 ) (11 ) (11 ) (5 ) (5 ) Plan change — (200 ) — (34 ) — — Projected benefit obligation at December 31 $ 2,061 $ 1,902 $ 212 $ 201 $ 51 $ 55 Accumulated benefit obligation $ 2,052 $ 1,894 $ 209 $ 198 $ 51 $ 55 Funded status at December 31 (a) (b) $ 686 $ 551 $ (212 ) $ (201 ) $ 9 $ 7 Weighted-average assumptions used: Discount rate 3.74 % 4.23 % 3.74 % 4.23 % 3.55 % 3.92 % Rate of compensation increase 3.75 3.50 3.75 3.50 n/a n/a Healthcare cost trend rate: Cost trend rate assumed for next year n/a n/a n/a n/a 6.50 6.50 Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) n/a n/a n/a n/a 4.50 5.00 Year when rate reaches the ultimate trend rate n/a n/a n/a n/a 2027 2027 Amounts recognized in accumulated other comprehensive income (loss) before income taxes: Net actuarial loss $ (548 ) $ (673 ) $ (85 ) $ (82 ) $ (19 ) $ (20 ) Prior service credit 159 178 42 50 1 1 Balance at December 31 $ (389 ) $ (495 ) $ (43 ) $ (32 ) $ (18 ) $ (19 ) (a) Based on projected benefit obligation for defined benefit pension plans and accumulated benefit obligation for postretirement benefit plan. (b) The Corporation recognizes the overfunded and underfunded status of the plans in “accrued income and other assets” and “accrued expenses and other liabilities,” respectively, on the consolidated balance sheets. n/a - not applicable Because the non-qualified defined benefit pension plan has no assets, the accumulated benefit obligation exceeded the fair value of plan assets at December 31, 2017 and December 31, 2016 . The following table details the changes in plan assets and benefit obligations recognized in other comprehensive income (loss) for the year ended December 31, 2017 . Defined Benefit Pension Plans (in millions) Qualified Non-Qualified Postretirement Benefit Plan Total Actuarial gain (loss) arising during the period $ 82 $ (11 ) $ 1 $ 72 Amortization of net actuarial loss 43 8 — 51 Amortization of prior service credit (19 ) (8 ) — (27 ) Total recognized in other comprehensive income (loss) $ 106 $ (11 ) $ 1 $ 96 Components of net periodic defined benefit cost and postretirement benefit cost, the actual return on plan assets and the weighted-average assumptions used were as follows: Defined Benefit Pension Plans (dollar amounts in millions) Qualified Non-Qualified Years Ended December 31 2017 2016 2015 2017 2016 2015 Service cost $ 29 $ 31 $ 35 $ 2 $ 3 $ 4 Interest cost 78 87 88 8 10 10 Expected return on plan assets (159 ) (163 ) (159 ) — — — Amortization of prior service (credit) cost (19 ) (2 ) 4 (8 ) (5 ) (4 ) Amortization of net loss 43 38 59 8 7 10 Net periodic defined benefit (credit) cost $ (28 ) $ (9 ) $ 27 $ 10 $ 15 $ 20 Actual return on plan assets $ 396 $ 200 $ (73 ) n/a n/a n/a Actual rate of return on plan assets 16.48 % 8.66 % (2.95 )% n/a n/a n/a Weighted-average assumptions used: Discount rate 4.23 % 4.53 % 4.28 % 4.23 % 4.53 % 4.28 % Expected long-term return on plan assets 6.50 6.75 6.75 n/a n/a n/a Rate of compensation increase 3.50 3.75 3.75 3.50 3.75 3.75 n/a - not applicable (dollar amounts in millions) Postretirement Benefit Plan Years Ended December 31 2017 2016 2015 Interest cost $ 2 $ 3 $ 3 Expected return on plan assets (3 ) (4 ) (4 ) Amortization of prior service cost — — 1 Amortization of net loss 1 1 1 Net periodic postretirement benefit cost $ — $ — $ 1 Actual return on plan assets $ 2 $ 2 $ — Actual rate of return on plan assets 3.52 % 2.83 % (0.53 )% Weighted-average assumptions used: Discount rate 3.92 % 4.53 % 3.99 % Expected long-term return on plan assets 5.00 5.00 5.00 Healthcare cost trend rate: Cost trend rate assumed 6.50 7.00 7.00 Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 4.50 5.00 5.00 Year that the rate reaches the ultimate trend rate 2027 2027 2026 The expected long-term rate of return of plan assets is the average rate of return expected to be realized on funds invested or expected to be invested over the life of the plan, which has an estimated duration of approximately 12 years as of December 31, 2017 . The expected long-term rate of return on plan assets is set after considering both long-term returns in the general market and long-term returns experienced by the assets in the plan. The returns on the various asset categories are blended to derive one long-term rate of return. The Corporation reviews its pension plan assumptions on an annual basis with its actuarial consultants to determine if assumptions are reasonable and adjusts the assumptions to reflect changes in future expectations. The estimated portion of balances remaining in accumulated other comprehensive income (loss) that are expected to be recognized as a component of net periodic benefit cost in the year ended December 31, 2018 are as follows: Defined Benefit Pension Plans (in millions) Qualified Non-Qualified Postretirement Benefit Plan Total Net loss $ 51 $ 8 $ 1 $ 60 Prior service credit (19 ) (8 ) — (27 ) Assumed healthcare cost trend rates have a significant effect on the amounts reported for the postretirement benefit plan. A one-percentage-point change in 2017 assumed healthcare and prescription drug cost trend rates would have the following effects. One-Percentage-Point (in millions) Increase Decrease Effect on postretirement benefit obligation $ 3 $ (2 ) Effect on total service and interest cost — — Plan Assets The Corporation’s overall investment goals for the qualified defined benefit pension plan are to maintain a portfolio of assets of appropriate liquidity and diversification; to generate investment returns (net of operating costs) that are reasonably anticipated to maintain the plan’s fully funded status or to reduce a funding deficit, after taking into account various factors, including reasonably anticipated future contributions and expense and the interest rate sensitivity of the plan’s assets relative to that of the plan’s liabilities; and to generate investment returns (net of operating costs) that meet or exceed a customized benchmark as defined in the plan investment policy. Derivative instruments are permissible for hedging and transactional efficiency, but only to the extent that the derivative use enhances the efficient execution of the plan’s investment policy. The plan does not directly invest in securities issued by the Corporation and its subsidiaries. The Corporation’s target allocations for plan investments are 45 percent to 55 percent for both equity securities and fixed income, including cash. Equity securities include collective investment and mutual funds and common stock. Fixed income securities include U.S. Treasury and other U.S. government agency securities, mortgage-backed securities, corporate bonds and notes, municipal bonds, collateralized mortgage obligations and money market funds. Fair Value Measurements The Corporation’s qualified defined benefit pension plan utilizes fair value measurements to record fair value adjustments and to determine fair value disclosures. The Corporation’s qualified benefit pension plan categorizes investments recorded at fair value into a three-level hierarchy, based on the markets in which the investment are traded and the reliability of the assumptions used to determine fair value. Refer to Note 1 for a description of the three-level hierarchy. Following is a description of the valuation methodologies and key inputs used to measure the fair value of the Corporation’s qualified defined benefit pension plan investments, including an indication of the level of the fair value hierarchy in which the investments are classified. Mutual funds Fair value measurement is based upon the net asset value (NAV) provided by the administrator of the fund. Mutual fund NAVs are quoted in an active market exchange, such as the New York Stock Exchange, and are included in Level 1 of the fair value hierarchy. Commercial paper Fair value measurement is based on benchmark yields and quotes from market makers and other broker/dealers recognized to be market participants. Commercial paper is included in Level 2 of the fair value hierarchy. Common stock Fair value measurement is based upon the closing price quoted in an active market exchange, such as the New York Stock Exchange. Level 1 common stock includes domestic and foreign stock and real estate investment trusts. U.S. Treasury and other U.S. government agency securities Level 1 securities include U.S. Treasury securities that are traded by dealers or brokers in active over-the-counter markets. Fair value measurement is based upon quoted prices in an active market exchange, such as the New York Stock Exchange. Level 2 securities include debt securities issued by U.S. government agencies and U.S. government-sponsored entities. The fair value of Level 2 securities is determined using quoted prices of securities with similar characteristics, or pricing models based on observable market data inputs, primarily interest rates and spreads. Corporate and municipal bonds and notes Fair value measurement is based upon quoted prices of securities with similar characteristics or pricing models based on observable market data inputs, primarily interest rates, spreads and prepayment information. Level 2 securities include corporate bonds, municipal bonds, foreign bonds and foreign notes. Mortgage-backed securities Fair value measurement is based upon independent pricing models or other model-based valuation techniques such as the present value of future cash flows, adjusted for the security's credit rating, prepayment assumptions and other factors, such as credit loss and liquidity assumptions, and are included in Level 2 of the fair value hierarchy. Private placements Fair value is measured using the NAV provided by fund management as quoted prices in active markets are not available. Management considers additional discounts to the provided NAV for market and credit risk. Private placements are included in Level 3 of the fair value hierarchy. Collective investment funds Fair value measurement is based upon the NAV provided by the administrator of the fund as a practical expedient to estimate fair value. There are no unfunded commitments or redemption restrictions on the collective investment funds. The investments are redeemable daily. Fair Values The fair values of the Corporation’s qualified defined benefit pension plan investments measured at fair value on a recurring basis at December 31, 2017 and 2016 , by asset category and level within the fair value hierarchy, are detailed in the table below. (in millions) Total Level 1 Level 2 Level 3 December 31, 2017 Equity securities: Mutual funds $ 1 $ 1 $ — $ — Common stock 961 961 — — Fixed income securities: U.S. Treasury and other U.S. government agency securities 456 451 5 — Corporate and municipal bonds and notes 765 — 765 — Mortgage-backed securities 25 — 25 — Private placements 80 — — 80 Total investments in the fair value hierarchy 2,288 $ 1,413 $ 795 $ 80 Investments measured at net asset value: Collective investment funds 455 Total investments at fair value $ 2,743 December 31, 2016 Cash equivalent securities: Commercial paper $ 2 $ — $ 2 $ — Common stock 850 850 — — Fixed income securities: U.S. Treasury and other U.S. government agency securities 377 366 11 — Corporate and municipal bonds and notes 710 — 710 — Mortgage-backed securities 23 — 23 — Private placements 71 — — 71 Total investments in the fair value hierarchy 2,033 $ 1,216 $ 746 $ 71 Investments measured at net asset value: Collective investment funds 415 Total investments at fair value $ 2,448 The table below provides a summary of changes in the Corporation’s qualified defined benefit pension plan’s Level 3 investments measured at fair value on a recurring basis for the years ended December 31, 2017 and 2016 . Balance at Beginning of Period Balance at End of Period Net Gains (Losses) (in millions) Realized Unrealized Purchases Sales Year Ended December 31, 2017 Private placements $ 71 $ 2 $ 3 $ 77 $ (73 ) $ 80 Year Ended December 31, 2016 Private placements $ 105 $ 1 $ 3 $ 64 $ (102 ) $ 71 There were no assets in the non-qualified defined benefit pension plan at December 31, 2017 and 2016 . The postretirement benefit plan is fully invested in bank-owned life insurance policies. The fair value of bank-owned life insurance policies is based on the cash surrender values of the policies as reported by the insurance companies and is classified in Level 2 of the fair value hierarchy. Cash Flows The Corporation currently expects to make no employer contributions to the qualified and non-qualified defined benefit pension plans and postretirement benefit plan for the year ended December 31, 2018 . Estimated Future Benefit Payments (in millions) Years Ended December 31 Qualified Defined Benefit Pension Plan Non-Qualified Defined Benefit Pension Plan Postretirement Benefit Plan (a) 2018 $ 120 $ 11 $ 6 2019 123 12 5 2020 125 13 5 2021 127 13 5 2022 130 13 5 2023 - 2027 665 66 19 (a) Estimated benefit payments in the postretirement benefit plan are net of estimated Medicare subsidies. Defined Contribution Plans Substantially all of the Corporation’s employees are eligible to participate in the Corporation’s principal defined contribution plan (a 401(k) plan). Under this plan, the Corporation makes core matching cash contributions of 100 percent of the first 4 percent of qualified earnings contributed by employees (up to the current IRS compensation limit), invested based on employee investment elections. Employee benefits expense included expense for the plan of $21 million for the year ended December 31, 2017 and $22 million for each of the years ended December 31, 2016 and 2015 . Through December 31, 2016, the Corporation also provided a retirement account plan for the benefit of substantially all employees who worked at least 1,000 hours in a plan year and were not accruing a benefit in the defined benefit pension plan. Under the retirement account plan, the Corporation made an annual discretionary allocation to the individual account of each eligible employee ranging from 3 percent to 8 percent of annual compensation, determined based on combined age and years of service. The allocations were invested based on employee investment elections. Employees participating in the retirement account plan as of December 31, 2016 were eligible to participate in the cash balance pension plan effective January 1, 2017. Final retirement account plan balances were transferred to the Corporation's 401(k) plan in the first quarter of 2017. Contributions to the retirement account plan ceased for periods beginning after December 31, 2016. The Corporation recognized $10 million of employee benefits expense in both of the years ended December 31, 2016 and 2015 . Deferred Compensation Plans The Corporation offers optional deferred compensation plans under which certain employees may make an irrevocable election to defer incentive compensation and/or a portion of base salary until retirement or separation from the Corporation. The employee may direct deferred compensation into one or more deemed investment options. Although not required to do so, the Corporation invests actual funds into the deemed investments as directed by employees, resulting in a deferred compensation asset, recorded in “other short-term investments” on the consolidated balance sheets that offsets the liability to employees under the plan, recorded in “accrued expenses and other liabilities.” The earnings from the deferred compensation asset are recorded in “interest on short-term investments” and “other noninterest income” and the related change in the liability to employees under the plan is recorded in “salaries” expense on the consolidated statements of income.

Income Taxes And Tax-Related It

Income Taxes And Tax-Related Items	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes and Tax-Related Items	INCOME TAXES AND TAX-RELATED ITEMS The provision for income taxes is calculated as the sum of income taxes due for the current year and deferred taxes. Income taxes due for the current year is computed by applying federal and state tax statutes to current year taxable income. Deferred taxes arise from temporary differences between the income tax basis and financial accounting basis of assets and liabilities. Tax-related interest and penalties and foreign taxes are then added to the tax provision. The current and deferred components of the provision for income taxes were as follows: (in millions) December 31 2017 2016 2015 Current: Federal $ 371 $ 224 $ 275 Foreign 5 5 5 State and local 36 15 20 Total current 412 244 300 Deferred: Federal (26 ) (49 ) (68 ) State and local (2 ) (2 ) (3 ) Remeasurement of deferred taxes 107 — — Total deferred 79 (51 ) (71 ) Total $ 491 $ 193 $ 229 Income before income taxes of $1.2 billion for the year ended December 31, 2017 included $24 million of foreign-source income. The provision for income taxes for the year ended December 31, 2017 included a $107 million charge to adjust deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act. Refer to Note 1 for further details. The income tax provision on securities transactions for the years ended December 31, 2017 , 2016 and 2015 were benefits of $1 million , $2 million and $1 million , respectively. The provision for income taxes does not reflect the tax effects of unrealized gains and losses on investment securities available-for-sale or the change in defined benefit pension and other postretirement plans adjustment included in accumulated other comprehensive loss. Refer to Note 14 for additional information on accumulated other comprehensive loss. The provision for income taxes for 2017 included a benefit of $35 million related to employee stock transactions as a result of new accounting guidance for stock compensation. For the years ended December 31, 2016 and 2015, tax effects of employee stock transactions of $4 million and $3 million , respectively, were recorded in shareholders' equity. A reconciliation of expected income tax expense at the federal statutory rate to the Corporation’s provision for income taxes and effective tax rate follows: (dollar amounts in millions) 2017 2016 2015 Years Ended December 31 Amount Rate Amount Rate Amount Rate Tax based on federal statutory rate $ 432 35.0 % $ 235 35.0 % $ 262 35.0 % Remeasurement of deferred taxes 107 8.7 — — — — State income taxes 22 1.8 8 1.2 10 1.3 Employee stock transactions (35 ) (2.8 ) — — — — Affordable housing and historic credits (21 ) (1.7 ) (22 ) (3.3 ) (22 ) (2.9 ) Bank-owned life insurance (16 ) (1.3 ) (15 ) (2.3 ) (15 ) (2.0 ) Lease termination transactions (2 ) (0.2 ) (15 ) (2.2 ) (5 ) (0.7 ) Tax-related interest and penalties 4 0.3 3 0.5 1 0.1 Other — — (1 ) (0.1 ) (2 ) (0.3 ) Provision for income taxes $ 491 39.8 % $ 193 28.8 % $ 229 30.5 % The liability for tax-related interest and penalties included in “accrued expenses and other liabilities” on the consolidated balance sheets was $10 million and $7 million at December 31, 2017 and 2016 , respectively. In the ordinary course of business, the Corporation enters into certain transactions that have tax consequences. From time to time, the Internal Revenue Service (IRS) may review and/or challenge specific interpretive tax positions taken by the Corporation with respect to those transactions. The Corporation believes that its tax returns were filed based upon applicable statutes, regulations and case law in effect at the time of the transactions. The IRS, an administrative authority or a court, if presented with the transactions, could disagree with the Corporation’s interpretation of the tax law. A reconciliation of the beginning and ending amount of net unrecognized tax benefits follows: (in millions) 2017 2016 2015 Balance at January 1 $ 15 $ 22 $ 14 Increase as a result of tax positions taken during a prior period 4 — 8 Decrease related to settlements with tax authorities (8 ) (7 ) — Other (1 ) — — Balance at December 31 $ 10 $ 15 $ 22 The Corporation anticipates that it is reasonably possible that settlements with tax authorities will result in a $1 million decrease in net unrecognized tax benefits within the next twelve months. After consideration of the effect of the federal tax benefit available on unrecognized state tax benefits, the total amount of unrecognized tax benefits that, if recognized, would affect the Corporation’s effective tax rate was approximately $8 million and $4 million at December 31, 2017 and 2016 , respectively. The following tax years for significant jurisdictions remain subject to examination as of December 31, 2017 : Jurisdiction Tax Years Federal 2014-2016 California 2005-2016 Based on current knowledge and probability assessment of various potential outcomes, the Corporation believes that current tax reserves are adequate, and the amount of any potential incremental liability arising is not expected to have a material adverse effect on the Corporation’s consolidated financial condition or results of operations. Probabilities and outcomes are reviewed as events unfold, and adjustments to the reserves are made when necessary. The principal components of deferred tax assets and liabilities were as follows: (in millions) December 31 2017 2016 Deferred tax assets: Allowance for loan losses $ 150 $ 256 Deferred compensation 49 91 Deferred loan origination fees and costs 6 20 Net unrealized losses on investment securities available-for-sale 31 20 Other temporary differences, net 57 76 Total deferred tax asset before valuation allowance 293 463 Valuation allowance (3 ) (3 ) Total deferred tax assets 290 460 Deferred tax liabilities: Lease financing transactions (76 ) (150 ) Defined benefit plans (72 ) (82 ) Allowance for depreciation (1 ) (11 ) Total deferred tax liabilities (149 ) (243 ) Net deferred tax asset $ 141 $ 217 Deferred tax assets included state net operating loss carryforwards of $4 million at both December 31, 2017 and December 31, 2016 . The carryforwards expire between 2018 and 2027 . The Corporation believes it is more likely than not that the benefit from certain of these state net operating loss carryforwards will not be realized and, accordingly, maintained a valuation allowance of $3 million at both December 31, 2017 and December 31, 2016 . For further information on the Corporation’s valuation policy for deferred tax assets, refer to Note 1 .

Transactions with Related Parti

Transactions with Related Parties	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Transactions with Related Parties	TRANSACTIONS WITH RELATED PARTIES The Corporation’s banking subsidiaries had, and expect to have in the future, transactions with the Corporation’s directors and executive officers, companies with which these individuals are associated, and certain related individuals. Such transactions were made in the ordinary course of business and included extensions of credit, leases and professional services. With respect to extensions of credit, all were made on substantially the same terms, including interest rates and collateral, as those prevailing at the same time for comparable transactions with other customers and did not, in management’s opinion, involve more than normal risk of collectibility or present other unfavorable features. The aggregate amount of loans attributable to persons who were related parties at December 31, 2017 , totaled $108 million at the beginning of 2017 and $66 million at the end of 2017 . During 2017 , new loans to related parties aggregated $637 million and repayments totaled $679 million .

Regulatory Capital and Reserve

Regulatory Capital and Reserve Requirements	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Regulatory Capital and Reserve Requirements	REGULATORY CAPITAL AND RESERVE REQUIREMENTS Reserves required to be maintained and/or deposited with the FRB are classified in interest-bearing deposits with banks. These reserve balances vary, depending on the level of customer deposits in the Corporation’s banking subsidiaries. The average required reserve balances were $572 million and $518 million for the years ended December 31, 2017 and 2016 , respectively. Banking regulations limit the transfer of assets in the form of dividends, loans or advances from the bank subsidiaries to the parent company. Under the most restrictive of these regulations, the aggregate amount of dividends which can be paid to the parent company, with prior approval from bank regulatory agencies, approximated $7 million at January 1, 2018 , plus 2018 net profits. Substantially all the assets of the Corporation’s banking subsidiaries are restricted from transfer to the parent company of the Corporation in the form of loans or advances. The Corporation’s subsidiary banks declared dividends of $907 million , $545 million and $437 million in 2017 , 2016 and 2015 , respectively. The Corporation and its U.S. banking subsidiaries are subject to various regulatory capital requirements administered by federal and state banking agencies. The U.S. adoption of the Basel III regulatory capital framework (Basel III) became effective for the Corporation on January 1, 2015. Basel III sets forth two comprehensive methodologies for calculating risk-weighted assets (RWA), a standardized approach and an advanced approach. The Corporation and its U.S. banking subsidiaries are subject to the standardized approach under the rules. Under the standardized approach, RWA is generally based on supervisory risk-weightings which vary by counterparty type and asset class. Under the Basel III standardized approach, capital is required for credit risk RWA, to cover the risk of unexpected losses due to failure of a customer or counterparty to meet its financial obligations in accordance with contractual terms; and if trading assets and liabilities exceed certain thresholds, capital is also required for market risk RWA, to cover the risk of losses due to adverse market movements or from position-specific factors. Under Basel III, there are three categories of risk-based capital: CET1 capital, Tier 1 capital and Tier 2 capital. CET1 capital predominantly includes common shareholders' equity, less certain deductions for goodwill, intangible assets and deferred tax assets that arise from net operating losses and tax credit carry-forwards. Additionally, the Corporation has elected to permanently exclude capital in accumulated other comprehensive income related to debt and equity securities classified as available-for-sale as well as for defined benefit postretirement plans from CET1, an option available to standardized approach entities under Basel III. Tier 1 capital incrementally includes noncumulative perpetual preferred stock. Tier 2 capital includes Tier 1 capital as well as subordinated debt qualifying as Tier 2 and qualifying allowance for credit losses. Total capital is Tier 1 capital plus Tier 2 capital. In addition to the minimum risk-based capital requirements, the Corporation is required to maintain a minimum capital conservation buffer, in the form of common equity, in order to avoid restrictions on capital distributions and discretionary bonuses. The required amount of the capital conservation buffer is being phased in and ultimately increasing to 2.5% on January 1, 2019. Quantitative measures established by regulation to ensure capital adequacy require the maintenance of minimum amounts and ratios of CET1, Tier 1 and total capital (as defined in the regulations) to average and/or risk-weighted assets. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Corporation’s financial statements. At December 31, 2017 and 2016 , the Corporation and its U.S. banking subsidiaries exceeded the ratios required for an institution to be considered “well capitalized” For U.S. banking subsidiaries, those requirements were total risk-based capital, Tier 1 risk-based capital, CET1 risk-based capital and leverage ratios greater than 10 percent , 8 percent , 6.5 percent and 5 percent , respectively, at December 31, 2017 and 2016 . For the Corporation, requirements to be considered "well capitalized" were total risk-based capital and Tier 1 risk-based capital ratios greater than 10 percent and 6 percent , respectively, at December 31, 2017 and 2016 . There have been no conditions or events since December 31, 2017 that management believes have changed the capital adequacy classification of the Corporation or its U.S. banking subsidiaries. The following is a summary of the capital position of the Corporation and Comerica Bank, its principal banking subsidiary. (dollar amounts in millions) Comerica Incorporated (Consolidated) Comerica Bank December 31, 2017 CET1 capital (minimum $3.0 billion (Consolidated)) $ 7,773 $ 7,121 Tier 1 capital (minimum-$4.0 billion (Consolidated)) 7,773 7,121 Total capital (minimum-$5.3 billion (Consolidated)) 9,211 8,378 Risk-weighted assets 66,575 66,447 Average assets (fourth quarter) 71,372 71,181 CET1 capital to risk-weighted assets (minimum-4.5%) 11.68 % 10.72 % Tier 1 capital to risk-weighted assets (minimum-6.0%) 11.68 10.72 Total capital to risk-weighted assets (minimum-8.0%) 13.84 12.61 Tier 1 capital to average assets (minimum-4.0%) 10.89 10.00 Capital conservation buffer 5.68 4.61 December 31, 2016 CET1 capital (minimum $3.1 billion (Consolidated)) $ 7,540 $ 7,120 Tier 1 capital (minimum-$4.1 billion (Consolidated)) 7,540 7,120 Total capital (minimum-$5.4 billion (Consolidated)) 9,018 8,397 Risk-weighted assets 67,966 67,739 Average assets (fourth quarter) 74,086 73,804 CET1 capital to risk-weighted assets (minimum-4.5%) 11.09 % 10.51 % Tier 1 capital to risk-weighted assets (minimum-6.0%) 11.09 10.51 Total capital to risk-weighted assets (minimum-8.0%) 13.27 12.40 Tier 1 capital to average assets (minimum-4.0%) 10.18 9.65 Capital conservation buffer 5.09 4.40

Contingent Liabilities

Contingent Liabilities	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Contingent Liabilities	CONTINGENT LIABILITIES Legal Proceedings Comerica Bank, a wholly owned subsidiary of the Corporation, was named in November 2011 as a third-party defendant in Butte Local Development v. Masters Group v. Comerica Bank (“the case”), for lender liability. The case was tried in January 2014, in the Montana Second District Judicial Court for Silver Bow County in Butte, Montana. On January 17, 2014 , a jury awarded Masters $52 million against the Bank. On July 1, 2015, after an appeal filed by the Corporation, the Montana Supreme Court reversed the judgment against the Corporation and remanded the case for a new trial with instructions that Michigan contract law should apply and dismissing all other claims. The case was retried in the same district court, without a jury, in January 2017, and the Corporation awaits a ruling. Management believes that current reserves related to this case are adequate in the event of a negative outcome. The Corporation and certain of its subsidiaries are subject to various other pending or threatened legal proceedings arising out of the normal course of business or operations. The Corporation believes it has meritorious defenses to the claims asserted against it in its other currently outstanding legal proceedings and, with respect to such legal proceedings, intends to continue to defend itself vigorously, litigating or settling cases according to management’s judgment as to what is in the best interests of the Corporation and its shareholders. Settlement may result from the Corporation's determination that it may be more prudent financially to settle, rather than litigate, and should not be regarded as an admission of liability. On at least a quarterly basis, the Corporation assesses its potential liabilities and contingencies in connection with outstanding legal proceedings utilizing the latest information available. On a case-by-case basis, reserves are established for those legal claims for which it is probable that a loss will be incurred either as a result of a settlement or judgment, and the amount of such loss can be reasonably estimated. The actual costs of resolving these claims may be substantially higher or lower than the amounts reserved. Based on current knowledge, and after consultation with legal counsel, management believes that current reserves are adequate, and the amount of any incremental liability arising from these matters is not expected to have a material adverse effect on the Corporation’s consolidated financial condition, consolidated results of operations or consolidated cash flows. Legal fees of $15 million , $19 million and $21 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, were included in "other noninterest expenses" on the consolidated statements of income. For matters where a loss is not probable, the Corporation has not established legal reserves. The Corporation believes the estimate of the aggregate range of reasonably possible losses, in excess of reserves established, for all legal proceedings in which it is involved is from zero to approximately $29 million at December 31, 2017 . This estimated aggregate range of reasonably possible losses is based upon currently available information for those proceedings in which the Corporation is involved, taking into account the Corporation’s best estimate of such losses for those cases for which such estimate can be made. For certain cases, the Corporation does not believe that an estimate can currently be made. The Corporation’s estimate involves significant judgment, given the varying stages of the proceedings (including the fact that many are currently in preliminary stages), the existence in certain proceedings of multiple defendants (including the Corporation) whose share of liability has yet to be determined, the numerous yet-unresolved issues in many of the proceedings (including issues regarding class certification and the scope of many of the claims) and the attendant uncertainty of the various potential outcomes of such proceedings. Accordingly, the Corporation’s estimate will change from time to time, and actual losses may be more or less than the current estimate. In the event of unexpected future developments, it is possible that the ultimate resolution of these matters, if unfavorable, may be material to the Corporation's consolidated financial condition, consolidated results of operations or consolidated cash flows. For information regarding income tax contingencies, refer to Note 18 .

Restructuring Charges Restructu

Restructuring Charges Restructuring Charges	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring Charges	RESTRUCTURING CHARGES The Corporation launched an initiative in the second quarter 2016 designed to reduce overhead and increase revenue (the "GEAR Up" initiative). The actions in the initiative include, but are not limited to, a reduction in workforce, a new retirement program, streamlining operational processes, real estate optimization including consolidating 38 banking centers as well as reducing office and operations space, selective outsourcing of technology functions, reduction of technology system applications, enhanced sales tools and training, expanded product offerings and improved customer analytics to drive opportunities. Certain actions associated with the GEAR Up initiative result in restructuring charges. Generally, costs associated with or incurred to generate revenue as part of the initiative are recorded according to the nature of the cost and are not included in restructuring charges. The Corporation considers the following costs associated with the initiative to be restructuring charges: • Employee costs: Primarily severance costs in accordance with the Corporation’s severance plan. • Facilities costs: Costs pertaining to consolidating banking centers and other facilities, such as lease termination costs and decommissioning costs. Also includes accelerated depreciation and impairment of owned property to be sold. • Technology costs: Impairment and other costs associated with optimizing technology infrastructure and reducing the number of applications. • Other costs: Includes primarily professional fees, as well as other contract termination fees and legal fees incurred in the execution of the initiative. Restructuring charges are recorded as a component of noninterest expenses on the consolidated statements of income. The following table presents changes in restructuring reserves, cumulative charges incurred to date and total expected restructuring charges: (in millions) Employee Costs Facilities Costs Technology Costs Other Costs Total Year Ended December 31, 2017 Balance at beginning of period $ 10 $ 4 $ — $ 4 $ 18 Restructuring charges 10 2 26 7 45 Payments (12 ) (6 ) (15 ) (10 ) (43 ) Adjustments for non-cash charges (a) — — (5 ) — (5 ) Balance at end of period $ 8 $ — $ 6 $ 1 $ 15 Year Ended December 31, 2016 Balance at beginning of period $ — $ — $ — $ — $ — Restructuring charges 52 15 — 26 93 Payments (44 ) (6 ) — (22 ) (72 ) Adjustments for non-cash charges (a) 2 (5 ) — — (3 ) Balance at end of period $ 10 $ 4 $ — $ 4 $ 18 Total restructuring charges incurred to date $ 62 $ 17 $ 26 $ 33 $ 138 Total expected restructuring charges (b) 70 20 - 25 60 - 65 35 185 - 195 (a) Adjustments for non-cash charges primarily include the benefit from forfeitures of nonvested stock compensation in Employee Costs, accelerated depreciation expense in Facilities Costs and impairments of previously capitalized software costs in Technology Costs. (b) Restructuring activities are expected to be substantially completed by 12/31/2018 . Restructuring charges directly attributable to a business segment are assigned to that business segment. Restructuring charges incurred by areas whose services support the overall Corporation are allocated based on the methodology described in Note 23 to the consolidated financial statements. Total restructuring charges assigned to the Business Bank, Retail Bank and Wealth Management were $24 million , $15 million and $6 million , respectively, for the year ended December 31, 2017 and $43 million , $38 million and $12 million , respectively, for the year ended December 31, 2016 . Remaining expected restructuring charges will be assigned to the business segments using the same methodology. Facilities costs pertaining to the consolidation of banking centers are expected to impact primarily the Retail Bank.

Business Segment Information

Business Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Business Segment Information	BUSINESS SEGMENT INFORMATION The Corporation has strategically aligned its operations into three major business segments: the Business Bank, the Retail Bank and Wealth Management. These business segments are differentiated based on the type of customer and the related products and services provided. In addition to the three major business segments, the Finance Division is also reported as a segment. Business segment results are produced by the Corporation’s internal management accounting system. This system measures financial results based on the internal business unit structure of the Corporation. The performance of the business segments is not comparable with the Corporation's consolidated results and is not necessarily comparable with similar information for any other financial institution. Additionally, because of the interrelationships of the various segments, the information presented is not indicative of how the segments would perform if they operated as independent entities. The management accounting system assigns balance sheet and income statement items to each business segment using certain methodologies, which are regularly reviewed and refined. From time to time, the Corporation may make reclassifications among the segments to more appropriately reflect management's current view of the segments, and methodologies may be modified as the management accounting system is enhanced and changes occur in the organizational structure and/or product lines. For comparability purposes, amounts in all periods are based on business unit structure and methodologies in effect at December 31, 2017 . Net interest income for each business segment is the total of interest income generated by earning assets less interest expense on interest-bearing liabilities plus the net impact from associated internal funds transfer pricing (FTP) funding credits and charges. The FTP methodology provides the business segments credits for deposits and other funds provided and charges the business segments for loans and other assets utilizing funds. This credit or charge is based on matching stated or implied maturities for these assets and liabilities. The FTP credit provided for deposits reflects the long-term value of deposits generated based on their implied maturity. The FTP charge for funding assets reflects a matched cost of funds based on the pricing and term characteristics of the assets. For acquired loans and deposits, matched maturity funding is determined based on origination date. Accordingly, the FTP process reflects the transfer of interest rate risk exposures to the Corporate Treasury department within the Finance segment, where such exposures are centrally managed. Effective January 1, 2016, in conjunction with the effective date for regulatory Liquidity Coverage Ratio (LCR) requirements, the Corporation prospectively implemented an additional FTP charge, primarily for the cost of maintaining liquid assets to support potential draws on unfunded loan commitments and for the long-term economic cost of holding collateral for secured deposits. The allowance for loan losses is allocated to the business segments based on the methodology used to estimate the consolidated allowance for loan losses described in Note 1. The related provision for loan losses is assigned based on the amount necessary to maintain an allowance for loan losses appropriate for each business segment. Noninterest income and expenses directly attributable to a line of business are assigned to that business segment. Direct expenses incurred by areas whose services support the overall Corporation are allocated to the business segments as follows: product processing expenditures are allocated based on standard unit costs applied to actual volume measurements; administrative expenses are allocated based on estimated time expended; and corporate overhead is assigned 50 percent based on the ratio of the business segment’s noninterest expenses to total noninterest expenses incurred by all business segments and 50 percent based on the ratio of the business segment’s attributed equity to total attributed equity of all business segments. Equity is attributed based on credit, operational and interest rate risks. Most of the equity attributed relates to credit risk, which is determined based on the credit score and expected remaining life of each loan, letter of credit and unused commitment recorded in the business segments. Operational risk is allocated based on loans and letters of credit, deposit balances, non-earning assets, trust assets under management, certain noninterest income items, and the nature and extent of expenses incurred by business units. Virtually all interest rate risk is assigned to Finance, as are the Corporation’s hedging activities. The following discussion provides information about the activities of each business segment. A discussion of the financial results and the factors impacting 2017 performance can be found in the section entitled "Business Segments" in the financial review. The Business Bank meets the needs of middle market businesses, multinational corporations and governmental entities by offering various products and services, including commercial loans and lines of credit, deposits, cash management, capital market products, international trade finance, letters of credit, foreign exchange management services and loan syndication services. The Retail Bank includes small business banking and personal financial services, consisting of consumer lending, consumer deposit gathering and mortgage loan origination. In addition to a full range of financial services provided to small business customers, this business segment offers a variety of consumer products, including deposit accounts, installment loans, credit cards, student loans, home equity lines of credit and residential mortgage loans. Wealth Management offers products and services consisting of fiduciary services, private banking, retirement services, investment management and advisory services, investment banking and brokerage services. This business segment also offers the sale of annuity products, as well as life, disability and long-term care insurance products. The Finance segment includes the Corporation’s securities portfolio and asset and liability management activities. This segment is responsible for managing the Corporation’s funding, liquidity and capital needs, performing interest sensitivity analysis and executing various strategies to manage the Corporation’s exposure to liquidity, interest rate risk and foreign exchange risk. The Other category includes the income and expense impact of equity and cash, tax benefits not assigned to specific business segments, charges of an unusual or infrequent nature that are not reflective of the normal operations of the business segments and miscellaneous other expenses of a corporate nature. Business segment financial results are as follows: (dollar amounts in millions) Business Bank Retail Bank Wealth Management Finance Other Total Year Ended December 31, 2017 Earnings summary: Net interest income (expense) $ 1,372 $ 658 $ 170 $ (175 ) $ 36 $ 2,061 Provision for credit losses 58 13 1 — 2 74 Noninterest income 601 193 255 48 10 1,107 Noninterest expenses 802 731 285 (4 ) 46 1,860 Provision (benefit) for income taxes 389 39 51 (58 ) 70 (a) 491 Net income (loss) $ 724 $ 68 $ 88 $ (65 ) $ (72 ) $ 743 Net credit-related charge-offs (recoveries) $ 82 $ 15 $ (5 ) $ — $ — $ 92 Selected average balances: Assets $ 38,801 $ 6,478 $ 5,401 $ 13,954 $ 6,818 $ 71,452 Loans 37,445 5,857 5,256 — — 48,558 Deposits 28,803 23,971 4,081 241 162 57,258 Statistical data: Return on average assets (b) 1.87 % 0.28 % 1.63 % N/M N/M 1.04 % Efficiency ratio (c) 40.61 85.54 66.84 N/M N/M 58.57 (dollar amounts in millions) Business Bank Retail Bank Wealth Management Finance Other Total Year Ended December 31, 2016 Earnings summary: Net interest income (expense) $ 1,417 $ 618 $ 167 $ (428 ) $ 23 $ 1,797 Provision for credit losses 217 35 (4 ) — — 248 Noninterest income 572 189 243 43 4 1,051 Noninterest expenses 839 767 301 (4 ) 27 1,930 Provision (benefit) for income taxes 295 1 39 (142 ) — 193 Net income (loss) $ 638 $ 4 $ 74 $ (239 ) $ — $ 477 Net credit-related charge-offs $ 145 $ 12 $ — $ — $ — $ 157 Selected average balances: Assets $ 39,497 $ 6,551 $ 5,232 $ 13,993 $ 6,470 $ 71,743 Loans 38,067 5,881 5,048 — — 48,996 Deposits 29,704 23,558 4,126 88 265 57,741 Statistical data: Return on average assets (b) 1.61 % 0.02 % 1.42 % N/M N/M 0.67 % Efficiency ratio (c) 42.11 94.35 73.48 N/M N/M 67.53 (Table continues on following page) (dollar amounts in millions) Business Bank Retail Bank Wealth Management Finance Other Total Year Ended December 31, 2015 Earnings summary: Net interest income (expense) $ 1,497 $ 623 $ 177 $ (623 ) $ 15 $ 1,689 Provision for credit losses 158 8 (20 ) — 1 147 Noninterest income 571 185 235 44 — 1,035 Noninterest expenses 778 734 305 (4 ) 14 1,827 Provision (benefit) for income taxes 371 21 43 (206 ) — 229 Net income (loss) $ 761 $ 45 $ 84 $ (369 ) $ — $ 521 Net credit-related charge-offs (recoveries) $ 89 $ 29 $ (17 ) $ — $ — $ 101 Selected average balances: Assets $ 39,501 $ 6,474 $ 5,153 $ 11,764 $ 7,355 $ 70,247 Loans 37,889 5,792 4,953 — (6 ) 48,628 Deposits 30,894 22,876 4,151 138 267 58,326 Statistical data: Return on average assets (b) 1.93 % 0.19 % 1.62 % N/M N/M 0.74 % Efficiency ratio (c) 37.59 90.64 73.68 N/M N/M 66.93 (a) Included a $107 million charge to adjust deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act and a $35 million tax benefit from employee stock transactions. (b) Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity. (c) Noninterest expenses as a percentage of the sum of net interest income (fully taxable equivalent basis) and noninterest income excluding net securities gains. N/M – not meaningful The Corporation operates in three primary markets - Texas, California, and Michigan, as well as in Arizona and Florida, with select businesses operating in several other states, and in Canada and Mexico. The Corporation produces market segment results for the Corporation’s three primary geographic markets as well as Other Markets. Other Markets includes Florida, Arizona, the International Finance division and businesses with a national perspective. The Finance & Other category includes the Finance segment and the Other category as previously described. Market segment results are provided as supplemental information to the business segment results and may not meet all operating segment criteria as set forth in GAAP. For comparability purposes, amounts in all periods are based on market segments and methodologies in effect at December 31, 2017 . A discussion of the financial results and the factors impacting performance can be found in the section entitled "Market Segments" in the financial review. Market segment financial results are as follows: (dollar amounts in millions) Michigan California Texas Other Markets Finance & Other Total Year Ended December 31, 2017 Earnings summary: Net interest income (expense) $ 685 $ 719 $ 465 $ 331 $ (139 ) $ 2,061 Provision for credit losses 8 100 (72 ) 36 2 74 Noninterest income 324 171 131 423 58 1,107 Noninterest expenses 590 404 375 449 42 1,860 Provision (benefit) for income taxes 147 148 109 75 12 (a) 491 Net income (loss) $ 264 $ 238 $ 184 $ 194 $ (137 ) $ 743 Net credit-related (recoveries) charge-offs $ (1 ) $ 33 $ 46 $ 14 $ — $ 92 Selected average balances: Assets $ 13,395 $ 18,269 $ 10,443 $ 8,573 $ 20,772 $ 71,452 Loans 12,677 18,008 9,969 7,904 — 48,558 Deposits 21,823 17,533 9,625 7,874 403 57,258 Statistical data: Return on average assets (b) 1.17 % 1.29 % 1.69 % 2.25 % N/M 1.04 % Efficiency ratio (c) 58.30 45.26 62.80 59.57 N/M 58.57 (Table continues on following page) (dollar amounts in millions) Michigan California Texas Other Markets Finance & Other Total Year Ended December 31, 2016 Earnings summary: Net interest income (expense) $ 666 $ 716 $ 470 $ 350 $ (405 ) $ 1,797 Provision for credit losses 9 21 225 (7 ) — 248 Noninterest income 320 162 129 393 47 1,051 Noninterest expenses 620 434 408 445 23 1,930 Provision (benefit) for income taxes 114 152 (12 ) 81 (142 ) 193 Net income (loss) $ 243 $ 271 $ (22 ) $ 224 $ (239 ) $ 477 Net credit-related charge-offs $ 9 $ 26 $ 118 $ 4 $ — $ 157 Selected average balances: Assets $ 13,105 $ 18,012 $ 11,101 $ 9,062 $ 20,463 $ 71,743 Loans 12,457 17,731 10,637 8,171 — 48,996 Deposits 21,777 17,438 10,168 8,005 353 57,741 Statistical data: Return on average assets (b) 1.08 % 1.46 % (0.18 )% 2.47 % N/M 0.67 % Efficiency ratio (c) 62.33 49.55 67.94 59.86 N/M 67.53 (dollar amounts in millions) Michigan California Texas Other Markets Finance & Other Total Year Ended December 31, 2015 Earnings summary: Net interest income (expense) $ 708 $ 735 $ 518 $ 336 $ (608 ) $ 1,689 Provision for credit losses (27 ) 17 131 25 1 147 Noninterest income 329 150 131 381 44 1,035 Noninterest expenses 594 405 387 431 10 1,827 Provision (benefit) for income taxes 151 166 54 64 (206 ) 229 Net income (loss) $ 319 $ 297 $ 77 $ 197 $ (369 ) $ 521 Net credit-related charge-offs $ 8 $ 18 $ 46 $ 29 $ — $ 101 Selected average balances: Assets $ 13,598 $ 17,044 $ 11,778 $ 8,708 $ 19,119 $ 70,247 Loans 13,016 16,778 11,168 7,673 (7 ) 48,628 Deposits 21,848 17,788 10,882 7,403 405 58,326 Statistical data: Return on average assets (b) 1.40 % 1.57 % 0.62 % 2.26 % N/M 0.74 % Efficiency ratio (c) 56.93 45.88 59.63 59.92 N/M 66.93 (a) Included a $107 million charge to adjust deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act and a $35 million tax benefit from employee stock transactions. (b) Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity. (c) Noninterest expenses as a percentage of the sum of net interest income (fully taxable equivalent basis) and noninterest income excluding net securities gains. N/M – not meaningful

Parent Company FInancial Statem

Parent Company FInancial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Parent Company Financial Statments	PARENT COMPANY FINANCIAL STATEMENTS BALANCE SHEETS - COMERICA INCORPORATED (in millions, except share data) December 31 2017 2016 Assets Cash and due from subsidiary bank $ 1,059 $ 761 Other short-term investments 92 87 Investment in subsidiaries, principally banks 7,467 7,561 Premises and equipment 2 2 Other assets 127 150 Total assets $ 8,747 $ 8,561 Liabilities and Shareholders’ Equity Medium- and long-term debt $ 602 $ 604 Other liabilities 182 161 Total liabilities 784 765 Common stock - $5 par value: Authorized - 325,000,000 shares Issued - 228,164,824 shares 1,141 1,141 Capital surplus 2,122 2,135 Accumulated other comprehensive loss (451 ) (383 ) Retained earnings 7,887 7,331 Less cost of common stock in treasury - 55,306,483 shares at 12/31/17 and 52,851,156 shares at 12/31/16 (2,736 ) (2,428 ) Total shareholders’ equity 7,963 7,796 Total liabilities and shareholders’ equity $ 8,747 $ 8,561 STATEMENTS OF INCOME - COMERICA INCORPORATED (in millions) Years Ended December 31 2017 2016 2015 Income Income from subsidiaries: Dividends from subsidiaries $ 915 $ 549 $ 441 Other interest income 3 1 1 Intercompany management fees 136 138 123 Other noninterest income 8 3 1 Total income 1,062 691 566 Expenses Interest on medium- and long-term debt 13 10 14 Salaries and benefits expense 127 114 112 Net occupancy expense 5 5 5 Equipment expense 1 1 1 Restructuring charges 6 33 — Other noninterest expenses 80 72 70 Total expenses 232 235 202 Income before benefit for income taxes and equity in undistributed earnings of subsidiaries 830 456 364 Benefit for income taxes (26 ) (28 ) (27 ) Income before equity in undistributed earnings of subsidiaries 856 484 391 Equity in undistributed earnings of subsidiaries, principally banks (113 ) (7 ) 130 Net income 743 477 521 Less income allocated to participating securities 5 4 6 Net income attributable to common shares $ 738 $ 473 $ 515 STATEMENTS OF CASH FLOWS - COMERICA INCORPORATED (in millions) Years Ended December 31 2017 2016 2015 Operating Activities Net income $ 743 $ 477 $ 521 Adjustments to reconcile net income to net cash provided by operating activities: Undistributed earnings of subsidiaries, principally banks 113 7 (130 ) Depreciation and amortization 1 1 1 Net periodic defined benefit (credit) cost (2 ) 1 5 Share-based compensation expense 16 14 14 Benefit for deferred income taxes (10 ) (3 ) — Other, net 59 6 5 Net cash provided by operating activities 920 503 416 Investing Activities Net change in premises and equipment — — (1 ) Net cash used in investing activities — — (1 ) Financing Activities Medium- and long-term debt: Maturities and redemptions — — (600 ) Common Stock: Repurchases (552 ) (315 ) (240 ) Cash dividends paid (180 ) (152 ) (147 ) Issuances of common stock under employee stock plans 110 152 22 Purchase and retirement of warrants — — (10 ) Net cash used in financing activities (622 ) (315 ) (975 ) Net increase (decrease) in cash and cash equivalents 298 188 (560 ) Cash and cash equivalents at beginning of period 761 573 1,133 Cash and cash equivalents at end of period $ 1,059 $ 761 $ 573 Interest paid $ 12 $ 9 $ 16 Income taxes recovered $ (331 ) $ (139 ) $ (62 )

Summary of Quarterly Financial

Summary of Quarterly Financial Statements (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Statements (Unaudited)	SUMMARY OF QUARTERLY FINANCIAL STATEMENTS (UNAUDITED) The following quarterly information is unaudited. However, in the opinion of management, the information reflects all adjustments, which are necessary for the fair presentation of the results of operations, for the periods presented. 2017 (in millions, except per share data) Fourth Quarter Third Quarter Second Quarter First Quarter Interest income $ 578 $ 579 $ 529 $ 496 Interest expense 33 33 29 26 Net interest income 545 546 500 470 Provision for credit losses 17 24 17 16 Net securities losses — (1 ) (2 ) — Noninterest income excluding net securities losses 285 276 278 271 Noninterest expenses 483 463 457 457 Provision for income taxes 218 108 99 66 Net income 112 226 203 202 Less income allocated to participating securities — 2 1 2 Net income attributable to common shares $ 112 $ 224 $ 202 $ 200 Earnings per common share: Basic $ 0.65 $ 1.29 $ 1.15 $ 1.15 Diluted 0.63 1.26 1.13 1.11 Comprehensive income 107 228 221 206 2016 (in millions, except per share data) Fourth Quarter Third Quarter Second Quarter First Quarter Interest income $ 484 $ 480 $ 473 $ 472 Interest expense 29 30 28 25 Net interest income 455 450 445 447 Provision for credit losses 35 16 49 148 Net securities losses (2 ) — (1 ) (2 ) Noninterest income excluding net securities losses 269 272 269 246 Noninterest expenses 461 493 518 458 Provision for income taxes 62 64 42 25 Net income 164 149 104 60 Less income allocated to participating securities 1 1 1 1 Net income attributable to common shares $ 163 $ 148 $ 103 $ 59 Earnings per common share: Basic $ 0.95 $ 0.87 $ 0.60 $ 0.34 Diluted 0.92 0.84 0.58 0.34 Comprehensive income 73 152 137 161

Basis of Presentation and Acc34

Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Corporation and the accounts of those subsidiaries that are majority owned and in which the Corporation has a controlling financial interest. The Corporation consolidates entities not determined to be variable interest entities (VIEs) when it holds a controlling financial interest and uses the cost or equity method when it holds less than a controlling financial interest. In consolidation, all significant intercompany accounts and transactions are eliminated. The results of operations of companies acquired are included from the date of acquisition. The Corporation holds investments in certain legal entities that are considered VIEs. In general, a VIE is an entity that either (1) has an insufficient amount of equity to carry out its principal activities without additional subordinated financial support, (2) has a group of equity owners that are unable to make significant decisions about its activities, or (3) has a group of equity owners that do not have the obligation to absorb losses or the right to receive returns generated by its operations. If any of these characteristics are present, the entity is subject to a variable interests consolidation model, and consolidation is based on variable interests, not on voting interests. Variable interests are defined as contractual ownership or other money interests in an entity that change with fluctuations in the entity’s net asset value. The primary beneficiary is required to consolidate the VIE. The primary beneficiary is defined as the party that has both the power to direct the activities of the VIE that most significantly impact the entity’s economic performance and the obligation to absorb losses or the right to receive benefits that could be significant to the VIE. The maximum potential exposure to losses relative to investments in VIEs is generally limited to the sum of the outstanding book basis and unfunded commitments for future investments. The Corporation evaluates its investments in VIEs, both at inception and when there is a change in circumstances that requires reconsideration, to determine if the Corporation is the primary beneficiary and consolidation is required. The Corporation accounts for unconsolidated VIEs using either the proportional, cost or equity method. These investments comprise investments in community development projects which generate tax credits to their investors and are included in "accrued income and other assets" on the consolidated balance sheets. The proportional method is used for investments in affordable housing projects that qualify for the low-income housing tax credit (LIHTC). The equity method is used for other investments where the Corporation has the ability to exercise significant influence over the entity’s operation and financial policies. Other unconsolidated equity investments that do not meet the criteria to be accounted for under the equity method are accounted for under the cost method. Amortization and other write-downs of LIHTC investments are presented on a net basis as a component of the "provision for income taxes," while income, amortization and write-downs from cost and equity method investments are recorded in “other noninterest income” on the consolidated statements of income. Assets held in an agency or fiduciary capacity are not assets of the Corporation and are not included in the consolidated financial statements.
Fair Value Measurements	Fair Value Measurements The Corporation utilizes fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures. The determination of fair values of financial instruments often requires the use of estimates. In cases where quoted market values in an active market are not available, the Corporation uses present value techniques and other valuation methods to estimate the fair values of its financial instruments. These valuation methods require considerable judgment and the resulting estimates of fair value can be significantly affected by the assumptions made and methods used. Fair value is an estimate of the exchange price that would be received to sell an asset or paid to transfer a liability in an orderly transaction (i.e., not a forced transaction, such as a liquidation or distressed sale) between market participants at the measurement date. Fair value is based on the assumptions market participants would use when pricing an asset or liability. Trading securities, investment securities available-for-sale, derivatives and deferred compensation plans are recorded at fair value on a recurring basis. Additionally, from time to time, the Corporation may be required to record other assets and liabilities at fair value on a nonrecurring basis, such as impaired loans, other real estate (primarily foreclosed property), nonmarketable equity securities and certain other assets and liabilities. These nonrecurring fair value adjustments typically involve write-downs of individual assets or application of lower of cost or fair value accounting. Fair value measurements and disclosures guidance establishes a three-level fair value hierarchy based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. The fair value hierarchy gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data. Fair value measurements are separately disclosed by level within the fair value hierarchy. For assets and liabilities recorded at fair value, it is the Corporation’s policy to maximize the use of observable inputs and minimize the use of unobservable inputs when developing fair value measurements. Level 1 Valuation is based upon quoted prices for identical instruments traded in active markets. Level 2 Valuation is based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are less active, and model-based valuation techniques for which all significant assumptions are observable in the market. Level 3 Valuation is generated from model-based techniques that use at least one significant assumption not observable in the market. These unobservable assumptions reflect estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques include use of option pricing models, discounted cash flow models and similar techniques. The Corporation generally utilizes third-party pricing services to value Level 1 and Level 2 trading and investment securities, as well as certain derivatives designated as fair value hedges. Management reviews the methodologies and assumptions used by the third-party pricing services and evaluates the values provided, principally by comparison with other available market quotes for similar instruments and/or analysis based on internal models using available third-party market data. The Corporation may occasionally adjust certain values provided by the third-party pricing service when management believes, as the result of its review, that the adjusted price most appropriately reflects the fair value of the particular security. Fair value measurements for assets and liabilities where limited or no observable market data exists are based primarily upon estimates, often calculated based on the economic and competitive environment, the characteristics of the asset or liability and other factors. Therefore, the results cannot be determined with precision and may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there may be inherent weaknesses in any calculation technique, and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the results of current or future values. Following are descriptions of the valuation methodologies and key inputs used to measure financial assets and liabilities recorded at fair value, as well as a description of the methods and significant assumptions used to estimate fair value disclosures for financial instruments not recorded at fair value in their entirety on a recurring basis. The descriptions include an indication of the level of the fair value hierarchy in which the assets or liabilities are classified. Transfers of assets or liabilities between levels of the fair value hierarchy are recognized at the beginning of the reporting period, when applicable. Cash and due from banks, federal funds sold and interest-bearing deposits with banks Due to their short-term nature, the carrying amount of these instruments approximates the estimated fair value. As such, the Corporation classifies the estimated fair value of these instruments as Level 1. Trading securities and associated deferred compensation plan liabilities Trading securities include securities held for trading purposes as well as assets held related to employee deferred compensation plans. Trading securities and associated deferred compensation plan liabilities are recorded at fair value on a recurring basis and included in “other short-term investments” and “accrued expenses and other liabilities,” respectively, on the consolidated balance sheets. Level 1 trading securities include assets related to employee deferred compensation plans, which are invested in mutual funds, U.S. Treasury securities that are traded by dealers or brokers in active over-the-counter markets and other securities traded on an active exchange, such as the New York Stock Exchange. Deferred compensation plan liabilities represent the fair value of the obligation to the employee, which corresponds to the fair value of the invested assets. Level 2 trading securities include municipal bonds and residential mortgage-backed securities issued by U.S. government-sponsored entities and corporate debt securities. The methods used to value trading securities are the same as the methods used to value investment securities, discussed below. Investment securities Investment securities available-for-sale are recorded at fair value on a recurring basis. The Corporation discloses estimated fair values of investment securities held-to-maturity, which is determined in the same manner as investment securities available-for-sale. Level 1 securities include those traded on an active exchange, such as the New York Stock Exchange, U.S. Treasury securities that are traded by dealers or brokers in active over-the-counter markets and money market funds. Level 2 securities include residential mortgage-backed securities issued by U.S. government agencies and U.S. government-sponsored entities and corporate debt securities. The fair value of Level 2 securities is determined using quoted prices of securities with similar characteristics, or pricing models based on observable market data inputs, primarily interest rates, spreads and prepayment information. Securities classified as Level 3 represent securities in less liquid markets requiring significant management assumptions when determining fair value. Auction-rate securities comprise Level 3 investment securities available-for-sale. The Corporate Treasury department, with appropriate oversight and approval provided by senior management, is responsible for the valuation of auction-rate securities. Valuation results, including an analysis of changes to the valuation methodology, are provided to senior management for review on a quarterly basis. Loans held-for-sale Loans held-for-sale, included in “other short-term investments” on the consolidated balance sheets, are recorded at the lower of cost or fair value. Loans held-for-sale may be carried at fair value on a nonrecurring basis when fair value is less than cost. The fair value is based on what secondary markets are currently offering for portfolios with similar characteristics. As such, the Corporation classifies both loans held-for-sale subjected to nonrecurring fair value adjustments and the estimated fair value of loans held-for sale as Level 2. Loans The Corporation does not record loans at fair value on a recurring basis. However, the Corporation may establish a specific allowance for an impaired loan based on the fair value of the underlying collateral. Such loan values are reported as nonrecurring fair value measurements. Collateral values supporting individually evaluated impaired loans are evaluated quarterly. When management determines that the fair value of the collateral requires additional adjustments, either as a result of non-current appraisal value or when there is no observable market price, the Corporation classifies the impaired loan as Level 3. The Special Assets Group is responsible for performing quarterly credit quality reviews for all impaired loans as part of the quarterly allowance for loan losses process overseen by the Chief Credit Officer, during which valuation adjustments to updated collateral values are determined. The Corporation discloses fair value estimates for loans. The estimated fair value is determined based on characteristics such as loan category, repricing features and remaining maturity, and includes prepayment and credit loss estimates. For variable rate business loans that reprice frequently, the estimated fair value is based on carrying values adjusted for estimated credit losses inherent in the portfolio at the balance sheet date. For other business loans and retail loans, fair values are estimated using a discounted cash flow model that employs a discount rate that reflects the Corporation's current pricing for loans with similar characteristics and remaining maturity, adjusted by an amount for estimated credit losses inherent in the portfolio at the balance sheet date. The rates take into account the expected yield curve, as well as an adjustment for prepayment risk, when applicable. The Corporation classifies the estimated fair value of loans held for investment as Level 3. Customers’ liability on acceptances outstanding and acceptances outstanding Customers' liability on acceptances outstanding is included in "accrued income and other assets" and acceptances outstanding are included in "accrued expenses and other liabilities" on the consolidated balance sheets. Due to their short-term nature, the carrying amount of these instruments approximates the estimated fair value. As such, the Corporation classifies the estimated fair value of these instruments as Level 1. Derivative assets and derivative liabilities Derivative instruments held or issued for risk management or customer-initiated activities are traded in over-the-counter markets where quoted market prices are not readily available. Fair value for over-the-counter derivative instruments is measured on a recurring basis using internally developed models that use primarily market observable inputs, such as yield curves and option volatilities. Fair value for certain derivatives designated as fair value hedges is determined using third-party pricing services. The Corporation manages credit risk on its derivative positions based on whether the derivatives are being settled through a clearinghouse or bilaterally with each counterparty. For derivative positions settled on a counterparty-by-counterparty basis, the Corporation calculates credit valuation adjustments, included in the fair value of these instruments, on the basis of its relationships at the counterparty portfolio/master netting agreement level. These credit valuation adjustments are determined by applying a credit spread for the counterparty or the Corporation, as appropriate, to the total expected exposure of the derivative after considering collateral and other master netting arrangements. These adjustments, which are considered Level 3 inputs, are based on estimates of current credit spreads to evaluate the likelihood of default. When credit valuation adjustments are significant to the overall fair value of a derivative, the Corporation classifies the over-the-counter derivative valuation in Level 3 of the fair value hierarchy; otherwise, over-the-counter derivative valuations are classified in Level 2. Warrants which contain a net exercise provision or a non-contingent put right embedded in the warrant agreement are accounted for as derivatives and recorded at fair value on a recurring basis using a Black-Scholes valuation model. The Black-Scholes valuation model utilizes five inputs: risk-free rate, expected life, volatility, exercise price, and the per share market value of the underlying company. The Corporation holds a portfolio of warrants for generally nonmarketable equity securities with a fair value of $2 million at December 31, 2017 , included in "accrued income and other assets" on the consolidated balance sheets. These warrants are primarily from non-public technology companies obtained as part of the loan origination process. The Corporate Development Department is responsible for the warrant valuation process, which includes reviewing all significant inputs for reasonableness, and for providing valuation results to senior management. Increases in any of these inputs in isolation, with the exception of exercise price, would result in a higher fair value. Increases in exercise price in isolation would result in a lower fair value. The Corporation classifies warrants accounted for as derivatives as Level 3. Nonmarketable equity securities The Corporation has a portfolio of indirect (through funds) private equity and venture capital investments with a carrying value of $6 million and unfunded commitments of less than $1 million , at December 31, 2017 . These funds generally cannot be redeemed and the majority is not readily marketable. Distributions from these funds are received by the Corporation as a result of the liquidation of underlying investments of the funds and/or as income distributions. The investments are accounted for either on the cost or equity method and are individually reviewed for impairment on a quarterly basis by comparing the carrying value to the estimated fair value. These investments may be carried at fair value on a nonrecurring basis when they are deemed to be impaired and written down to fair value. Where there is not a readily determinable fair value, the Corporation estimates fair value for indirect private equity and venture capital investments based on the net asset value, as reported by the fund. On a quarterly basis, the Corporate Development Department is responsible, with appropriate oversight and approval provided by senior management, for performing the valuation procedures and updating significant inputs, as are primarily provided by the underlying fund's management. The Corporation also holds restricted equity investments, primarily Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock. Restricted equity securities are not readily marketable and are recorded at cost (par value) in "accrued income and other assets" on the consolidated balance sheets and evaluated for impairment based on the ultimate recoverability of the par value. No significant observable market data for these instruments is available. The Corporation considers the profitability and asset quality of the issuer, dividend payment history and recent redemption experience and believes its investments in FHLB and FRB stock are ultimately recoverable at par. Therefore, the carrying amount for these restricted equity investments approximates fair value. The Corporation classifies the estimated fair value of such investments as Level 1. The Corporation’s investment in FHLB stock totaled $122 million at both December 31, 2017 and 2016 , and its investment in FRB stock totaled $85 million at both December 31, 2017 and 2016 . Other real estate Other real estate is included in “accrued income and other assets” on the consolidated balance sheets and includes primarily foreclosed property. Foreclosed property is initially recorded at fair value, less costs to sell, at the date of legal title transfer to the Corporation, establishing a new cost basis. Subsequently, foreclosed property is carried at the lower of cost or fair value, less costs to sell. Other real estate may be carried at fair value on a nonrecurring basis when fair value is less than cost. Fair value is based upon independent market prices, appraised value or management's estimate of the value of the property. The Special Assets Group obtains updated independent market prices and appraised values, as required by state regulation or deemed necessary based on market conditions, and determines if additional write-downs are necessary. On a quarterly basis, senior management reviews all other real estate and determines whether the carrying values are reasonable, based on the length of time elapsed since receipt of independent market price or appraised value and current market conditions. When management determines that the fair value of other real estate requires additional adjustments, either as a result of a non-current appraisal or when there is no observable market price, the Corporation classifies the other real estate as Level 3. Deposit liabilities The estimated fair value of checking, savings and certain money market deposit accounts is represented by the amounts payable on demand. The estimated fair value of term deposits is calculated by discounting the scheduled cash flows using the period-end rates offered on these instruments. As such, the Corporation classifies the estimated fair value of deposit liabilities as Level 2. Short-term borrowings The carrying amount of federal funds purchased, securities sold under agreements to repurchase and other short-term borrowings approximates the estimated fair value. As such, the Corporation classifies the estimated fair value of short-term borrowings as Level 1. Medium- and long-term debt The estimated fair value of the Corporation's medium- and long-term debt is based on quoted market values when available. If quoted market values are not available, the estimated fair value is based on the market values of debt with similar characteristics. The Corporation classifies the estimated fair value of medium- and long-term debt as Level 2. Credit-related financial instruments Credit-related financial instruments include unused commitments to extend credit and letters of credit. These instruments generate ongoing fees which are recognized over the term of the commitment. In situations where credit losses are probable, the Corporation records an allowance. The carrying value of these instruments included in "accrued expenses and other liabilities" on the consolidated balance sheets, which includes the carrying value of the deferred fees plus the related allowance, approximates the estimated fair value. The Corporation classifies the estimated fair value of credit-related financial instruments as Level 3.
Other Short-Term Investments	Other Short-Term Investments Other short-term investments include trading securities and loans held-for-sale. Trading securities are carried at fair value. Realized and unrealized gains or losses on trading securities are included in “other noninterest income” on the consolidated statements of income. Loans held-for-sale, typically residential mortgages originated with the intent to sell and occasionally may include other loans transferred to held-for-sale, are carried at the lower of cost or fair value. Fair value is determined in the aggregate for each portfolio. Changes in fair value and gains or losses upon sale are included in “other noninterest income” on the consolidated statements of income.
Investment Securities	Investment Securities Securities not held for trading purposes are classified as available-for-sale or held-to-maturity. Debt securities for which management has the intent and ability to hold to maturity are classified as held-to-maturity and recorded at amortized cost. Securities available-for-sale are recorded at fair value, with unrealized gains and losses, net of income taxes, reported as a separate component of other comprehensive income (OCI). Securities transferred from available-for-sale to held-to-maturity are reclassified at fair value on the date of transfer. The net unrealized gain (loss) at the date of transfer is included in historical cost and amortized over the remaining life of the related securities as a yield adjustment consistent with the amortization of the net unrealized gain (loss) included in accumulated other comprehensive loss on the same securities, resulting in no impact to net income. Investment securities are reviewed quarterly for possible other-than-temporary impairment (OTTI). In determining whether OTTI exists for debt securities in an unrealized loss position, the Corporation assesses the likelihood of selling the security prior to the recovery of its amortized cost basis. If the Corporation intends to sell the debt security or it is more likely than not that the Corporation will be required to sell the debt security prior to the recovery of its amortized cost basis, the debt security is written down to fair value, and the full amount of any impairment charge is recorded as a loss in “net securities gains” in the consolidated statements of income. If the Corporation does not intend to sell the debt security and it is more likely than not that the Corporation will not be required to sell the debt security prior to recovery of its amortized cost basis, only the credit component of any impairment of a debt security is recognized as a loss in “net securities losses” on the consolidated statements of income, with the remaining impairment recorded in OCI. The OTTI review for equity securities includes an analysis of the facts and circumstances of each individual investment and focuses on the severity of loss, the length of time the fair value has been below cost, the expectation for that security’s performance, the financial condition and near-term prospects of the issuer, and management’s intent and ability to hold the security to recovery. A decline in value of an equity security that is considered to be other-than-temporary is recorded as a loss in “net securities losses” on the consolidated statements of income. Gains or losses on the sale of securities are computed based on the adjusted cost of the specific security sold.
Loans	Loans Loans and leases originated and held for investment are recorded at the principal balance outstanding, net of unearned income, charge-offs and unamortized deferred fees and costs. Interest income is recognized on loans and leases using the interest method.
Loans, Troubled Debt Restructuring	The Corporation assesses all loan modifications to determine whether a restructuring constitutes a troubled debt restructuring (TDR). A restructuring is considered a TDR when a borrower is experiencing financial difficulty and the Corporation grants a concession to the borrower. TDRs on accrual status at the original contractual rate of interest are considered performing. Nonperforming TDRs include TDRs on nonaccrual status and loans which have been renegotiated to less than the original contractual rates (reduced-rate loans). All TDRs are considered impaired loans.
Loan Origination Fees and Costs	Loan Origination Fees and Costs Substantially all loan origination fees and costs are deferred and amortized to net interest income over the life of the related loan or over the commitment period as a yield adjustment. Net deferred income on originated loans, including unearned income and unamortized costs, fees, premiums and discounts, totaled $113 million and $147 million at December 31, 2017 and 2016 , respectively. Loan fees on unused commitments and net origination fees related to loans sold are recognized in noninterest income.
Allowance for Credit Losses	Allowance for Credit Losses The allowance for credit losses includes both the allowance for loan losses and the allowance for credit losses on lending-related commitments. The Corporation disaggregates the loan portfolio into segments for purposes of determining the allowance for credit losses. These segments are based on the level at which the Corporation develops, documents and applies a systematic methodology to determine the allowance for credit losses. The Corporation's portfolio segments are business loans and retail loans. Business loans include the commercial, real estate construction, commercial mortgage, lease financing and international loan portfolios. Retail loans consist of traditional residential mortgage, home equity and other consumer loans.
Allowance for Loan Losses	Allowance for Loan Losses The allowance for loan losses represents management’s assessment of probable, estimable losses inherent in the Corporation’s loan portfolio. The allowance for loan losses includes specific allowances, based on individual evaluations of certain loans, and allowances for homogeneous pools of loans with similar risk characteristics. The Corporation individually evaluates certain impaired loans on a quarterly basis and establishes specific allowances for such loans, if required. A loan is considered impaired when it is probable that interest or principal payments will not be made in accordance with the contractual terms of the loan agreement. Consistent with this definition, all loans for which the accrual of interest has been discontinued (nonaccrual loans) are considered impaired. The Corporation individually evaluates nonaccrual loans with book balances of $2 million or more and accruing loans whose terms have been modified in a TDR. The threshold for individual evaluation is revised on an infrequent basis, generally when economic circumstances change significantly. Specific allowances for impaired loans are estimated using one of several methods, including the estimated fair value of underlying collateral, observable market value of similar debt or discounted expected future cash flows. Collateral values supporting individually evaluated impaired loans are evaluated quarterly. Either appraisals are obtained or appraisal assumptions are updated at least annually unless conditions dictate increased frequency. The Corporation may reduce the collateral value based upon the age of the appraisal and adverse developments in market conditions. Loans which do not meet the criteria to be evaluated individually are evaluated in homogeneous pools of loans with similar risk characteristics. Business loans are assigned to pools based on the Corporation's internal risk rating system. Internal risk ratings are assigned to each business loan at the time of approval and are subjected to subsequent periodic reviews by the Corporation’s senior management, generally at least annually or more frequently upon the occurrence of a circumstance that affects the credit risk of the loan. For business loans not individually evaluated, losses inherent to the pool are estimated by applying standard reserve factors to outstanding principal balances. Standard reserve factors are based on estimated probabilities of default for each internal risk rating, set to a default horizon based on an estimated loss emergence period, and loss given default. These factors are evaluated quarterly and updated annually, unless economic conditions necessitate a change, giving consideration to count-based borrower risk rating migration experience and trends, recent charge-off experience, current economic conditions and trends, changes in collateral values of properties securing loans, and trends with respect to past due and nonaccrual amounts. The allowance for business loans not individually evaluated also includes qualitative adjustments to bring the allowance to the level management believes is appropriate based on factors that have not otherwise been fully accounted for, including adjustments for (i) risk factors that have not been fully addressed in internal risk ratings, (ii) imprecision in the risk rating system resulting from inaccuracy in assigning and/or entering risk ratings in the loan accounting system, (iii) market conditions and (iv) model imprecision. Risk factors that have not been fully addressed in internal risk ratings may include portfolios where recent historical losses exceed expected losses or known recent events are expected to alter risk ratings once evidence is acquired, portfolios where a certain level of concentration introduces added risk, or changes in the level and quality of experience held by lending management. An additional allowance for risk rating errors is calculated based on the results of risk rating accuracy assessments performed on samples of business loans conducted by the Corporation's asset quality review function, a function independent of the lending and credit groups responsible for assigning the initial internal risk rating at the time of approval. Qualitative adjustments for market conditions are determined based on an established framework. The determination of the appropriate adjustment is based on management's analysis of observable macroeconomic metrics, including consideration of regional metrics within the Corporation's footprint, internal credit risk movement and a qualitative assessment of the lending environment, including underwriting standards, current economic and political conditions, and other factors affecting credit quality. Management recognizes the sensitivity of various assumptions made in the quantitative modeling of expected losses and may adjust reserves depending upon the level of uncertainty that currently exists in one or more assumption. The allowance for retail loans not individually evaluated is determined by applying estimated loss rates to various pools of loans within the portfolios with similar risk characteristics. Estimated loss rates for all pools are updated quarterly, incorporating quantitative and qualitative factors such as recent charge-off experience, current economic conditions and trends, changes in collateral values of properties securing loans (using index-based estimates), and trends with respect to past due and nonaccrual amounts. The total allowance for loan losses is sufficient to absorb incurred losses inherent in the total portfolio. Unanticipated economic events, including political, economic and regulatory instability in countries where the Corporation has loans, could cause changes in the credit characteristics of the portfolio and result in an unanticipated increase in the allowance. Significant increases in current portfolio exposures, as well as the inclusion of additional industry-specific portfolio exposures in the allowance, could also increase the amount of the allowance. Any of these events, or some combination thereof, may result in the need for additional provision for credit losses in order to maintain an allowance that complies with credit risk and accounting policies. Loans deemed uncollectible are charged off and deducted from the allowance. Recoveries on loans previously charged off are added to the allowance.
Allowance for Credit Losses on Lending-Related Commitments	Allowance for Credit Losses on Lending-Related Commitments The allowance for credit losses on lending-related commitments provides for probable losses inherent in lending-related commitments, including unused commitments to extend credit and letters of credit. The allowance for credit losses on lending-related commitments includes allowances based on homogeneous pools of letters of credit and unused commitments to extend credit within each internal risk rating. A probability of draw estimate is applied to the commitment amount, and the result is multiplied by standard reserve factors consistent with business loans. In general, the probability of draw for letters of credit is considered certain for all letters of credit supporting loans and for letters of credit assigned an internal risk rating generally consistent with regulatory defined substandard or doubtful. Other letters of credit and all unfunded commitments have a lower probability of draw. The allowance for credit losses on lending-related commitments is included in “accrued expenses and other liabilities” on the consolidated balance sheets, with the corresponding charge reflected in the “provision for credit losses” on the consolidated statements of income.
Nonperforming Loans	A loan is considered past due when the contractually required principal or interest payment is not received by the specified due date or, for certain loans, when a scheduled monthly payment is past due and unpaid for 30 days or more. Business loans are generally placed on nonaccrual status when management determines full collection of principal or interest is unlikely or when principal or interest payments are 90 days past due, unless the loan is fully collateralized and in the process of collection. The past-due status of a business loan is one of many indicative factors considered in determining the collectibility of the credit. The primary driver of when the principal amount of a business loan should be fully or partially charged-off is based on a qualitative assessment of the recoverability of the principal amount from collateral and other cash flow sources. Residential mortgage and home equity loans are generally placed on nonaccrual status once they become 90 days past due and are charged off to current appraised values less costs to sell no later than 180 days past due. In addition, junior lien home equity loans less than 90 days past due are placed on nonaccrual status if they have underlying risk characteristics that place full collection of the loan in doubt, such as when the related senior lien position is identified as seriously delinquent. Residential mortgage and consumer loans in bankruptcy for which the court has discharged the borrower's obligation and the borrower has not reaffirmed the debt are placed on nonaccrual status and written down to estimated collateral value, without regard to the actual payment status of the loan, and are classified as TDRs. All other consumer loans are generally placed on nonaccrual status at 90 days past due and are charged off at no later than 120 days past due, earlier if deemed uncollectible. At the time a loan is placed on nonaccrual status, interest previously accrued but not collected is charged against current income. Principal and interest payments received on such loans are generally first applied as a reduction of principal. Income on nonaccrual loans is then recognized only to the extent that cash is received after principal has been fully repaid or future collection of principal is probable. Generally, a loan may be returned to accrual status when all delinquent principal and interest have been received and the Corporation expects repayment of the remaining contractual principal and interest, or when the loan or debt security is both well secured and in the process of collection.
Foreclosed Assets	Foreclosed property (primarily real estate) is initially recorded at fair value, less costs to sell, at the date of legal title transfer to the Corporation and subsequently carried at the lower of cost or fair value, less estimated costs to sell. Loans are reclassified to foreclosed property upon obtaining legal title to the collateral. Independent appraisals are obtained to substantiate the fair value of foreclosed property at the time of foreclosure and updated at least annually or upon evidence of deterioration in the property’s value. At the time of foreclosure, the adjustment for the difference between the related loan balance and fair value (less estimated costs to sell) of the property acquired is charged or credited to the allowance for loan losses. Subsequent write-downs, operating expenses and losses upon sale, if any, are charged to noninterest expenses. Foreclosed property is included in “accrued income and other assets” on the consolidated balance sheets.
Premises and Equipment	Premises and Equipment Premises and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation, computed using the straight-line method, is charged to operations over the estimated useful lives of the assets. Estimated useful lives are generally 3 years to 33 years for premises that the Corporation owns and 3 years to 8 years for furniture and equipment. Leasehold improvements are generally amortized over the terms of their respective leases or 10 years, whichever is shorter.
Software	Software Capitalized software is stated at cost, less accumulated amortization. Capitalized software includes purchased software, capitalizable application development costs associated with internally-developed software and cloud computing arrangements, including an in-substance software license. Amortization, computed on the straight-line method, is charged to operations over the estimated useful life of the software, generally 5 years. Capitalized software is included in “accrued income and other assets” on the consolidated balance sheets.
Goodwill	Goodwill, included in "accrued income and other assets" on the consolidated balance sheets, is initially recorded as the excess of the purchase price over the fair value of net assets acquired in a business combination and is subsequently evaluated at least annually for impairment. Goodwill impairment testing is performed at the reporting unit level, equivalent to a business segment or one level below. The Corporation has three reporting units: the Business Bank, the Retail Bank and Wealth Management. The Corporation performs its annual evaluation of goodwill impairment in the third quarter of each year and on an interim basis if events or changes in circumstances between annual tests suggest additional testing may be warranted to determine if goodwill might be impaired. The goodwill impairment test is a two-step test. The first step of the goodwill impairment test compares the estimated fair value of identified reporting units with their carrying amount, including goodwill. If the estimated fair value of the reporting unit is less than the carrying value, the second step must be performed to determine the implied fair value of the reporting unit's goodwill and the amount of goodwill impairment, if any. The implied fair value of goodwill is determined as if the reporting unit were being acquired in a business combination. If the implied fair value of goodwill exceeds the goodwill assigned to the reporting unit, there is no impairment. If the goodwill assigned to a reporting unit exceeds the implied fair value of goodwill, an impairment charge would be recorded for the excess. The Corporation may choose to perform a qualitative assessment to determine whether the first step of the impairment test should be performed in future periods if certain factors indicate that impairment is unlikely. Factors which could be considered in the assessment of the likelihood of impairment include macroeconomic conditions, industry and market considerations, stock performance of the Corporation and its peers, financial performance, events affecting the Corporation as a whole or its reporting units individually and previous results of goodwill impairment tests.
Core Deposit Intangibles	Core deposit intangibles are amortized on an accelerated basis, based on the estimated period the economic benefits are expected to be received. Core deposit intangibles are reviewed for impairment when events or changes in circumstances indicate that their carrying amounts may not be recoverable. Impairment for a finite-lived intangible asset exists if the sum of the undiscounted cash flows expected to result from the use of the asset exceeds its carrying value.
Nonmarketable Equity Securities	Nonmarketable Equity Securities The Corporation has certain investments that are not readily marketable. These investments include a portfolio of investments in indirect private equity and venture capital funds and restricted equity investments, which are securities the Corporation is required to hold for various reasons, primarily Federal Home Loan Bank of Dallas (FHLB) and Federal Reserve Bank (FRB) stock. These investments are accounted for on the cost or equity method and are included in “accrued income and other assets” on the consolidated balance sheets. The investments are individually reviewed for impairment on a quarterly basis. Indirect private equity and venture capital funds are evaluated by comparing the carrying value to the estimated fair value. The amount by which the carrying value exceeds the fair value that is determined to be other-than-temporary impairment is charged to current earnings and the carrying value of the investment is written down accordingly. FHLB and FRB stock are recorded at cost (par value) and evaluated for impairment based on the ultimate recoverability of the par value. If the Corporation does not expect to recover the full par value, the amount by which the par value exceeds the ultimately recoverable value would be charged to current earnings and the carrying value of the investment would be written down accordingly.
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities Derivative instruments are carried at fair value in either “accrued income and other assets” or “accrued expenses and other liabilities” on the consolidated balance sheets. The accounting for changes in the fair value (i.e., gains or losses) of a derivative instrument is determined by whether it has been designated and qualifies as part of a hedging relationship and, further, by the type of hedging relationship. The Corporation presents derivative instruments at fair value in the consolidated balance sheets on a net basis when a right of offset exists, based on transactions with a single counterparty and any cash collateral paid to and/or received from that counterparty for derivative contracts that are subject to legally enforceable master netting arrangements. For derivative instruments designated and qualifying as fair value hedges (i.e., hedging the exposure to changes in the fair value of an asset or a liability or an identified portion thereof that is attributable to a particular risk), the gain or loss on the derivative instrument, as well as the offsetting loss or gain on the hedged item attributable to the hedged risk, are recognized in current earnings during the period of the change in fair values. For derivative instruments that are designated and qualify as cash flow hedges (i.e., hedging the exposure to variability in expected future cash flows that is attributable to a particular risk), the effective portion of the gain or loss on the derivative instrument is reported as a component of other comprehensive income and reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. The remaining gain or loss on the derivative instrument in excess of the cumulative change in the present value of future cash flows of the hedged item (i.e., the ineffective portion), if any, is recognized in current earnings during the period of change. For derivative instruments not designated as hedging instruments, the gain or loss is recognized in current earnings during the period of change. To qualify for the use of hedge accounting, a derivative must be effective at inception and expected to be continuously effective in offsetting the risk being hedged. For derivatives designated as hedging instruments at inception, the Corporation uses either the short-cut method or applies statistical regression analysis to assess effectiveness. The short-cut method is used for $150 million notional of fair value hedges of medium and long-term debt issued prior to 2006. This method allows for the assumption of zero hedge ineffectiveness and eliminates the requirement to further assess hedge effectiveness on these transactions. For hedge relationships to which the Corporation does not apply the short-cut method, statistical regression analysis is used at inception and for each reporting period thereafter to assess whether the derivative used has been and is expected to be highly effective in offsetting changes in the fair value or cash flows of the hedged item. All components of each derivative instrument’s gain or loss are included in the assessment of hedge effectiveness. Net hedge ineffectiveness is recorded in “other noninterest income” on the consolidated statements of income.
Derivative Instruments Fair Value Amounts Offset	The Corporation presents derivative instruments at fair value in the consolidated balance sheets on a net basis when a right of offset exists, based on transactions with a single counterparty and any cash collateral paid to and/or received from that counterparty for derivative contracts that are subject to legally enforceable master netting arrangements.
Short-Term Borrowings	Short-Term Borrowings Securities sold under agreements to repurchase are treated as collateralized borrowings and are recorded at amounts equal to the cash received. The contractual terms of the agreements to repurchase may require the Corporation to provide additional collateral if the fair value of the securities underlying the borrowings declines during the term of the agreement.
Financial Guarantees	Financial Guarantees Certain guarantee contracts or indemnification agreements that contingently require the Corporation, as guarantor, to make payments to the guaranteed party are initially measured at fair value and included in “accrued expenses and other liabilities” on the consolidated balance sheets. The subsequent accounting for the liability depends on the nature of the underlying guarantee. The release from risk is accounted for under a particular guarantee when the guarantee expires or is settled, or by a systematic and rational amortization method.
Share-Based Compensation	Share-Based Compensation The Corporation recognizes share-based compensation expense using the straight-line method over the requisite service period for all stock awards, including those with graded vesting. The requisite service period is the period an employee is required to provide service in order to vest in the award, which cannot extend beyond the date at which the employee is no longer required to perform any service to receive the share-based compensation (the retirement-eligible date). The Corporation adopted Accounting Standards Update (ASU) No. 2016-09, "Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payments Accounting" (ASU 2016-09), effective January 1, 2017. Upon adoption, the Corporation elected to account for compensation cost based on forfeitures as they occur. Prior to the adoption, compensation cost was accounted for based on an estimate of the number of awards that were expected to vest. The prior period effect of this policy election as of the beginning of the year was reported as "cumulative effect of change in accounting principle" in the accompanying Consolidated Statements of Changes in Shareholders’ Equity. Certain awards are contingent upon performance and/or market conditions, which affect the number of shares ultimately issued. The Corporation periodically evaluates the probable outcome of the performance conditions and makes cumulative adjustments to compensation expense as appropriate. Market conditions are included in the determination of the fair value of the award on the date of grant. Subsequent to the grant date, market conditions have no impact on the amount of compensation expense the Corporation will recognize over the life of the award.
Revenue Recognition	Revenue Recognition The following summarizes the Corporation’s revenue recognition policies as they relate to certain noninterest income line items in the consolidated statements of income. Card fees includes primarily bankcard interchange revenue which is recorded as revenue when earned. For certain products where the Corporation bears the risks and rewards of providing the service at the program level, interchange revenue is presented gross of network costs, which are included within "outside processing fee expense" in noninterest income. Service charges on deposit accounts include fees for banking services provided, overdrafts and non-sufficient funds. Revenue is generally recognized in accordance with published deposit account agreements for retail accounts or when fixed and determinable per contractual agreements for commercial accounts. Fiduciary income includes fees and commissions from asset management, custody, recordkeeping, investment advisory and other services provided to personal and institutional trust customers. Revenue is recognized on an accrual basis at the time the services are performed and are based on either the market value of the assets managed or the services provided. Commercial lending fees primarily include fees assessed on the unused portion of commercial lines of credit (unused commitment fees) and syndication agent fees. Unused commitment fees are recognized when earned. Syndication agent fees are generally recognized when the transaction is complete.
Defined Benefit Pension and Other Postretirement Costs	Defined Benefit Pension and Other Postretirement Costs Defined benefit pension costs are included in “salaries and benefits expense" on the consolidated statements of income and are funded consistent with the requirements of federal laws and regulations. Inherent in the determination of defined benefit pension costs are assumptions concerning future events that will affect the amount and timing of required benefit payments under the plans. These assumptions include demographic assumptions such as retirement age and mortality, a compensation rate increase, a discount rate used to determine the current benefit obligation, form of payment election and a long-term expected rate of return on plan assets. Net periodic defined benefit pension expense includes service cost, interest cost based on the assumed discount rate, an expected return on plan assets based on an actuarially derived market-related value of assets, amortization of prior service cost or credit and amortization of net actuarial gains or losses. The market-related value of plan assets is determined by amortizing the current year’s investment gains and losses (the actual investment return net of the expected investment return) over 5 years. The amortization adjustment cannot exceed 10 percent of the fair value of assets. Prior service costs or credits include the impact of plan amendments on the liabilities and are amortized over the future service periods of active employees expected to receive benefits under the plan. Actuarial gains and losses result from experience different from that assumed and from changes in assumptions (excluding asset gains and losses not yet reflected in market-related value). Amortization of actuarial gains and losses is included as a component of net periodic defined benefit pension cost for a year if the actuarial net gain or loss exceeds 10 percent of the greater of the projected benefit obligation or the market-related value of plan assets. If amortization is required, the excess is amortized over the average remaining service period of participating employees expected to receive benefits under the plan. Postretirement benefits are recognized in “salaries and benefits expense" on the consolidated statements of income during the average remaining service period of participating employees expected to receive benefits under the plan or the average remaining future lifetime of retired participants currently receiving benefits under the plan.
Income Taxes	Income Taxes The provision for income taxes is the sum of income taxes due for the current year and deferred taxes. The Corporation classifies interest and penalties on income tax liabilities and, beginning January 1, 2017, excess tax benefits and deficiencies resulting from employee stock awards in the “provision for income taxes” on the consolidated statements of income. Deferred taxes arise from temporary differences between the income tax basis and financial accounting basis of assets and liabilities. Deferred tax assets are evaluated for realization based on available evidence of projected future reversals of existing taxable temporary differences, assumptions made regarding future events and, when applicable, state loss carryback capacity. A valuation allowance is provided when it is more likely than not that some portion of the deferred tax asset will not be realized. The Tax Cuts and Jobs Act (the "Act"), enacted on December 22, 2017, reduced the U.S. federal corporate tax rate from 35 percent to 21 percent. Also on December 22, 2017, the Securities and Exchange Commission issued Staff Accounting Bulletin No. 118 (SAB 118), which provides guidance on accounting for tax effects of the Act. SAB 118 provides a measurement period of up to one year from the enactment date to complete the accounting. Based on the information available and current interpretation of the rules, the Corporation has made reasonable estimates of the impact of the reduction in the corporate tax rate and remeasurement of certain deferred tax assets and liabilities based on the rate at which they are expected to reverse in the future, generally 21 percent. The provisional amount recorded related to the remeasurement of the Corporation's deferred tax balance was $107 million . The final impact of the Act may differ from these estimates as a result of changes in management’s interpretations and assumptions, as well as new guidance that may be issued by the Internal Revenue Service (IRS).
Earnings Per Share	Earnings Per Share Basic net income per common share is calculated using the two-class method. The two-class method is an earnings allocation formula that determines earnings per share for each share of common stock and participating securities according to dividends declared (distributed earnings) and participation rights in undistributed earnings. Distributed and undistributed earnings are allocated between common and participating security shareholders based on their respective rights to receive dividends. Nonvested share-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents are considered participating securities (e.g., nonvested restricted stock and service-based restricted stock units). Undistributed net losses are not allocated to nonvested restricted shareholders, as these shareholders do not have a contractual obligation to fund the losses incurred by the Corporation. Net income attributable to common shares is then divided by the weighted-average number of common shares outstanding during the period. Diluted net income per common share is calculated using the more dilutive of either the treasury method or the two-class method. The dilutive calculation considers common stock issuable under the assumed exercise of stock options and performance-based restricted stock units granted under the Corporation’s stock plans and warrants using the treasury stock method, if dilutive. Net income attributable to common shares is then divided by the total of weighted-average number of common shares and common stock equivalents outstanding during the period.
Statements Of Cash Flows	Statements of Cash Flows Cash and cash equivalents are defined as those amounts included in “cash and due from banks”, “federal funds sold” and “interest-bearing deposits with banks” on the consolidated balance sheets. As a result of the adoption of ASU 2016-09, the Corporation retrospectively applied certain changes to the statement of cash flows to classify excess tax benefits as an operating activity and cash paid to a tax authority when withholding shares from an employee's award for tax-withholding purposes as a financing activity. Accordingly, net cash provided by operating activities increased by $9 million and $3 million for 2016 and 2015, respectively, and net cash provided by financing activities decreased by the corresponding amounts.
Comprehensive Income (Loss)	Comprehensive Income (Loss) The Corporation presents on an annual basis the components of net income and other comprehensive income in two separate, but consecutive statements and presents on an interim basis the components of net income and a total for comprehensive income in one continuous consolidated statement of comprehensive income. The Corporation early adopted ASU No. 2018-02 , “Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” ( ASU 2018-02 ) in the fourth quarter 2017. ASU 2018-02 , issued in February 2018, provides for the reclassification of the effect of remeasuring deferred tax balances related to items within accumulated other comprehensive income (AOCI) to retained earnings resulting from the Tax Cuts and Jobs Act of 2017. As a result, the Corporation reclassified $87 million from AOCI to retained earnings.
Pending Accounting Pronouncements	Pending Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606),” (ASU 2014-09), which is intended to improve and converge the financial reporting requirements for revenue contracts with customers. Previous GAAP comprised broad revenue recognition concepts along with numerous industry-specific requirements. The new guidance establishes a five-step model which entities must follow to recognize revenue and removes inconsistencies in existing guidance. The guidance under ASU 2014-09 is effective for annual and interim periods beginning after December 15, 2017, and must be retrospectively applied. The Corporation will adopt ASU 2014-09 in the first quarter of 2018 using the modified retrospective approach, which includes presenting the cumulative effect of initial application along with supplementary disclosures. The revenue streams within the scope of Topic 606 were less than 30 percent of total revenues. Under the new guidance, card fee revenue from certain products will generally be presented net of network costs (including interchange costs, surcharge fees and assessment fees), as opposed to the current presentation of associated network costs in "outside processing fees." Network costs impacted by the new guidance were approximately $115 million for the year ended December 31, 2017. There were similar adjustments made for other revenue streams that resulted in additional net decreases of $5 million each to noninterest income and noninterest expense. These changes in presentation will not impact net income. The Corporation currently defers recognition of certain treasury management fees in "service charges on deposit accounts" in the consolidated statements of comprehensive income until the amount of compensation is considered fixed and determinable. Under the new guidance, a portion of these fees will be recognized as services are rendered. As a result of this earlier recognition, the Corporation will record a receivable of approximately $17 million with a corresponding adjustment to retained earnings and deferred tax liability upon adoption of ASU 2014-09. The annual amount of treasury management fees reflected in the Corporation's results of operations is not expected to significantly change. There were similar adjustments made for other revenue streams that resulted in an incremental cumulative adjustment to retained earnings of $2 million . In January 2016, the FASB issued ASU No. 2016-01, "Financial Instruments - Overall (Subtopic 825-10): Recognition of Financial Assets and Financial Liabilities," (ASU 2016-01), which makes targeted amendments to the guidance for recognition, measurement, presentation and disclosure of financial instruments. The Corporation will adopt ASU 2016-01 in the first quarter of 2018. The guidance under ASU 2016-01 requires equity investments, other than equity method investments, to be measured at fair value with changes in fair value recognized in net income. As of December 31, 2017, the Corporation classified approximately $82 million of securities as available-for-sale equity securities. At adoption, the cumulative net unrealized loss ( $1 million , pretax) of these securities previously recognized in AOCI was recorded as an adjustment to the opening balance of retained earnings. Any further changes to the fair value of equity securities, other than equity method investments, will be recorded in net income. ASU 2016-01 also emphasizes the existing requirement to use exit prices to measure fair value for disclosure purposes and clarifies that entities should not make use of a practicability exception in determining the fair value of loans. Accordingly, the Corporation will refine the calculation used to determine the disclosed fair value of its held-for-investment loan portfolio as part of adopting the standard. In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842),” (ASU 2016-02), to increase the transparency and comparability of lease recognition and disclosure. The update requires lessees to recognize lease contracts with a term greater than one year on the balance sheet, while recognizing expenses on the income statement in a manner similar to current guidance. For lessors, the update makes targeted changes to the classification criteria and the lessor accounting model to align the guidance with the new lessee model and revenue guidance. ASU 2016-02 is effective for the Corporation on January 1, 2019 and must be applied using the modified retrospective approach. Early adoption is permitted. The Corporation is currently in the process of gathering a complete inventory of leases and migrating identified lease data onto a new system platform. Based on preliminary evaluation, the right-of-use asset and the corresponding lease liability is expected to be less than one percent of the Corporation’s total assets at adoption. The Corporation will continue to evaluate for other impacts of adoption, including potential additional regulatory costs, but does not anticipate these to be significant. In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments," (ASU 2016-13), which addresses concerns regarding the perceived delay in recognition of credit losses under the existing incurred loss model. The amendment introduces a new, single model for recognizing credit losses on all financial instruments presented on cost basis. Under the new model, entities must estimate current expected credit losses by considering all available relevant information, including historical and current information, as well as reasonable and supportable forecasts of future events. The update also requires additional qualitative and quantitative information to allow users to better understand the credit risk within the portfolio and the methodologies for determining the allowance for credit losses. ASU 2016-13 is effective for the Corporation on January 1, 2020 and must be applied using the modified retrospective approach with limited exceptions. Early adoption is permitted. The Corporation is currently evaluating the impact of adopting ASU 2016-13. In August 2016, the FASB issued ASU No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments,” (ASU 2016-15), which reduces diversity in the presentation of several categories of transactions in the cash flow statement. Among other things, the update clarifies the appropriate classification for proceeds from settlement of bank-owned life insurance (BOLI) policies. The Corporation will adopt ASU 2016-15 in the first quarter 2018 and retrospectively change the classification of proceeds from settlement of BOLI policies from operating activities to investing activities. Proceeds from settlement of BOLI policies totaled $18 million and $16 million for the years ended December 31, 2017 and 2016, respectively. Other changes in classification resulting from this update are not significant. In January 2017, the FASB issued ASU No. 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” (ASU 2017-04), which intends to simplify goodwill impairment testing by eliminating the second step of the analysis under which the implied fair value of goodwill is determined as if the reporting unit were being acquired in a business combination. The update instead requires entities to compare the fair value of a reporting unit with its carrying amount and recognize an impairment charge for any amount by which the carrying amount exceeds the reporting unit’s fair value, to the extent that the loss recognized does not exceed the amount of goodwill allocated to that reporting unit. ASU 2017-04 must be applied prospectively and is effective for the Corporation on January 1, 2020. Early adoption is permitted. The Corporation does not expect the new guidance to have a material impact on its financial condition or results of operation. In March 2017, the FASB issued ASU No. 2017-07, “Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost” (ASU 2017-07), which requires employers to retrospectively report service cost as part of compensation expense and the other components of net benefit cost separately from service cost on the statement of income. Further, only the service cost component will be eligible for capitalization in deferred loan costs. The Corporation currently includes all components of net benefit cost in "salaries and benefits expense" in the consolidated statements of comprehensive income. Upon adoption of ASU 2017-07 in the first quarter 2018, only service cost will remain in salaries and benefits expense, and the other components (interest cost, expected return on assets, amortization of prior service cost or credit and amortization of net actuarial gains or losses) will be included in "other noninterest expenses." The other components of net benefit cost were a benefit of $50 million and $28 million for the years ended December 31, 2017 and 2016, respectively. In August 2017, the FASB issued ASU No. 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities” (ASU 2017-12), which better aligns the accounting and reporting of hedging relationships with the economics of risk management activities. ASU 2017-12 provides administrative reliefs to simplify the application of hedge accounting. The amendment is effective for the Corporation on January 1, 2019 and early adoption is permitted. The Corporation will early adopt in the first quarter of 2018 and record an adjustment of approximately $1 million to opening retained earnings for the cumulative effect of changes to the measurement methodology on the basis of hedged items at transition. As permitted under the transition rules, upon adoption, the Corporation will reclassify its portfolio of held-to-maturity securities to available-for-sale, as the securities are eligible to be hedged under the new guidance. The Corporation’s derivative instruments used for risk management predominately comprise swaps converting fixed-rate long-term debt to variable rates. An ineffectiveness net gain of $1 million and net loss of $2 million were included in “other noninterest income” in the consolidated statements of income for the years ended December 31, 2017 and 2016, respectively. Under the amendment, gains or losses relating to hedge ineffectiveness will prospectively be included in “net interest income” rather than “other noninterest income."

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Assets And Liabilities Recorded At Fair Value On A Recurring Basis	The following tables present the recorded amount of assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 and 2016 . (in millions) Total Level 1 Level 2 Level 3 December 31, 2017 Trading securities: Deferred compensation plan assets $ 92 $ 92 $ — $ — Investment securities available-for-sale: U.S. Treasury and other U.S. government agency securities 2,727 2,727 — — Residential mortgage-backed securities (a) 8,124 — 8,124 — State and municipal securities 5 — — 5 (b) Equity and other non-debt securities 82 38 — 44 (b) Total investment securities available-for-sale 10,938 2,765 8,124 49 Derivative assets: Interest rate contracts 57 — 43 14 Energy derivative contracts 93 — 93 — Foreign exchange contracts 42 — 42 — Warrants 2 — — 2 Total derivative assets 194 — 178 16 Total assets at fair value $ 11,224 $ 2,857 $ 8,302 $ 65 Derivative liabilities: Interest rate contracts $ 59 $ — $ 59 $ — Energy derivative contracts 91 — 91 — Foreign exchange contracts 40 — 40 — Total derivative liabilities 190 — 190 — Deferred compensation plan liabilities 92 92 — — Total liabilities at fair value $ 282 $ 92 $ 190 $ — (a) Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (b) Auction-rate securities. (in millions) Total Level 1 Level 2 Level 3 December 31, 2016 Trading securities: Deferred compensation plan assets $ 87 $ 87 $ — $ — Equity and other non-debt securities 1 1 — — Total trading securities 88 88 — — Investment securities available-for-sale: U.S. Treasury and other U.S. government agency securities 2,779 2,779 — — Residential mortgage-backed securities (a) 7,872 — 7,872 — State and municipal securities 7 — — 7 (b) Equity and other non-debt securities 129 82 — 47 (b) Total investment securities available-for-sale 10,787 2,861 7,872 54 Derivative assets: Interest rate contracts 223 — 212 11 Energy derivative contracts 146 — 146 — Foreign exchange contracts 38 — 38 — Warrants 3 — — 3 Total derivative assets 410 — 396 14 Total assets at fair value $ 11,285 $ 2,949 $ 8,268 $ 68 Derivative liabilities: Interest rate contracts $ 81 $ — $ 81 $ — Energy derivative contracts 144 — 144 — Foreign exchange contracts 29 — 29 — Total derivative liabilities 254 — 254 — Deferred compensation plan liabilities 87 87 — — Total liabilities at fair value $ 341 $ 87 $ 254 $ — (a) Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (b) Auction-rate securities.
Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis	The following table summarizes the changes in Level 3 assets measured at fair value on a recurring basis for the years ended December 31, 2017 and 2016 . Net Realized/Unrealized Gains (Losses) (Pretax) Balance at Beginning of Period Recorded in Earnings Recorded in Other Comprehensive Income Balance at End of Period (in millions) Realized Unrealized Redemptions Sales Year Ended December 31, 2017 Investment securities available-for-sale: State and municipal securities (a) $ 7 $ — $ — $ — $ (2 ) $ — $ 5 Equity and other non-debt securities (a) 47 — — (2 ) (b) (1 ) — 44 Total investment securities 54 — — (2 ) (b) (3 ) — 49 Derivative assets: Interest rate contracts 11 — 3 (c) — — — 14 Warrants 3 6 (c) (1 ) (c) — — (6 ) 2 Year Ended December 31, 2016 Investment securities available-for-sale: State and municipal securities (a) $ 9 $ — $ — $ — $ (2 ) $ — $ 7 Corporate debt securities (a) 1 — — — (1 ) — — Equity and other non-debt securities (a) 67 — — (1 ) (b) (19 ) — 47 Total investment securities 77 — — (1 ) (b) (22 ) — 54 Derivative assets: Interest rate contracts 9 — 2 (c) — — — 11 Warrants 2 6 (c) 1 (c) — — (6 ) 3 (a) Auction-rate securities. (b) Recorded in "net unrealized holding losses arising during the period" in other comprehensive income (loss). (c) Realized and unrealized gains and losses due to changes in fair value recorded in "other noninterest income" on the consolidated statements of income.
Assets And Liabilities Recorded At Fair Value On A Nonrecurring Basis	The following table presents assets recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 . No liabilities were recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 . (in millions) Level 3 December 31, 2017 Loans: Commercial $ 111 Commercial mortgage 5 Total assets at fair value $ 116 December 31, 2016 Loans: Commercial $ 256 Commercial mortgage 15 International 11 Total loans 282 Other real estate 1 Total assets at fair value $ 283
Estimated Fair Values Of Financial Instruments Not Recorded At Fair Value In Their Entirety On A Recurring Basis	The carrying amount and estimated fair value of financial instruments not recorded at fair value in their entirety on a recurring basis on the Corporation’s consolidated balance sheets are as follows: Carrying Amount Estimated Fair Value (in millions) Total Level 1 Level 2 Level 3 December 31, 2017 Assets Cash and due from banks $ 1,438 $ 1,438 $ 1,438 $ — $ — Interest-bearing deposits with banks 4,407 4,407 4,407 — — Investment securities held-to-maturity 1,266 1,246 — 1,246 — Loans held-for-sale 4 4 — 4 — Total loans, net of allowance for loan losses (a) 48,461 48,153 — — 48,153 Customers’ liability on acceptances outstanding 2 2 2 — — Restricted equity investments 207 207 207 — — Nonmarketable equity securities (b) 6 9 Liabilities Demand deposits (noninterest-bearing) 32,071 32,071 — 32,071 — Interest-bearing deposits 23,667 23,667 — 23,667 — Customer certificates of deposit 2,165 2,142 — 2,142 — Total deposits 57,903 57,880 — 57,880 — Short-term borrowings 10 10 10 — — Acceptances outstanding 2 2 2 — — Medium- and long-term debt 4,622 4,636 — 4,636 — Credit-related financial instruments (67 ) (67 ) — — (67 ) December 31, 2016 Assets Cash and due from banks $ 1,249 $ 1,249 $ 1,249 $ — $ — Interest-bearing deposits with banks 5,969 5,969 5,969 — — Investment securities held-to-maturity 1,582 1,576 — 1,576 — Loans held-for-sale 4 4 — 4 — Total loans, net of allowance for loan losses (a) 48,358 48,250 — — 48,250 Customers’ liability on acceptances outstanding 5 5 5 — — Restricted equity investments 207 207 207 — — Nonmarketable equity securities (b) 11 16 Liabilities Demand deposits (noninterest-bearing) 31,540 31,540 — 31,540 — Interest-bearing deposits 24,639 24,639 — 24,639 — Customer certificates of deposit 2,806 2,731 — 2,731 — Total deposits 58,985 58,910 — 58,910 — Short-term borrowings 25 25 25 — — Acceptances outstanding 5 5 5 — — Medium- and long-term debt 5,160 5,132 — 5,132 — Credit-related financial instruments (73 ) (73 ) — — (73 ) (a) Included $116 million and $282 million of impaired loans recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 , respectively. (b) Certain investments that are measured at fair value using the net asset value have not been classified in the fair value hierarchy. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets.

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Summary Of Investment Securities	A summary of the Corporation’s investment securities follows: (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value December 31, 2017 Investment securities available-for-sale: U.S. Treasury and other U.S. government agency securities $ 2,743 $ — $ 16 $ 2,727 Residential mortgage-backed securities (a) 8,230 22 128 8,124 State and municipal securities 5 — — 5 Equity and other non-debt securities 83 1 2 82 Total investment securities available-for-sale (b) $ 11,061 $ 23 $ 146 $ 10,938 Investment securities held-to-maturity (c): Residential mortgage-backed securities (a) $ 1,266 $ — $ 20 $ 1,246 December 31, 2016 Investment securities available-for-sale: U.S. Treasury and other U.S. government agency securities $ 2,772 $ 8 $ 1 $ 2,779 Residential mortgage-backed securities (a) 7,921 48 97 7,872 State and municipal securities 7 — — 7 Equity and other non-debt securities 129 1 1 129 Total investment securities available-for-sale (b) $ 10,829 $ 57 $ 99 $ 10,787 Investment securities held-to-maturity (c): Residential mortgage-backed securities (a) $ 1,582 $ 1 $ 7 $ 1,576 (a) Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (b) Included auction-rate securities at amortized cost and fair value of $51 million and $49 million , respectively, as of December 31, 2017 and $55 million and $54 million , respectively, as of December 31, 2016 . (c) The amortized cost of investment securities held-to-maturity included the unamortized balance of net unrealized losses as of the transfer date of $9 million and $12 million at December 31, 2017 and 2016 , respectively, related to securities transferred from available-for-sale, which is included in accumulated other comprehensive loss.
Summary Of Investment Securities In Unrealized Loss Positions	A summary of the Corporation’s investment securities in an unrealized loss position as of December 31, 2017 and 2016 follows: Temporarily Impaired Less than 12 Months 12 Months or more Total (in millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses December 31, 2017 U.S. Treasury and other U.S. government agency securities $ 2,727 $ 16 $ — $ — $ 2,727 $ 16 Residential mortgage-backed securities (a) 3,845 32 4,003 125 7,848 157 State and municipal securities (b) — — 5 — (c) 5 — (c) Equity and other non-debt securities (b) — — 44 2 44 2 Total impaired securities $ 6,572 $ 48 $ 4,052 $ 127 $ 10,624 $ 175 December 31, 2016 U.S. Treasury and other U.S. government agency securities $ 527 $ 1 $ — $ — $ 527 $ 1 Residential mortgage-backed securities (a) 4,992 87 1,177 32 6,169 119 State and municipal securities (b) — — 7 — (c) 7 — (c) Equity and other non-debt securities (b) 36 — (c) 11 — (c) 47 — (c) Total impaired securities $ 5,555 $ 88 $ 1,195 $ 32 $ 6,750 $ 120 (a) Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (b) Primarily auction-rate securities. (c) Unrealized losses less than $0.5 million.
Summary of Net Securities Gains (Losses)	Sales, calls and write-downs of investment securities available-for-sale resulted in the following gains and losses recorded in “net securities losses” on the consolidated statements of income, computed based on the adjusted cost of the specific security. (in millions) Years Ended December 31 2017 2016 2015 Securities gains $ 2 $ — $ — Securities losses (5 ) (5 ) (2 ) Net securities losses (a) $ (3 ) $ (5 ) $ (2 ) (a) Primarily charges related to a derivative contract tied to the conversion rate of Visa Class B shares.
Contractual Maturity Distribution Of Debt Securities	The following table summarizes the amortized cost and fair values of debt securities by contractual maturity. Securities with multiple maturity dates are classified in the period of final maturity. 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. (in millions) Available-for-sale Held-to-maturity December 31, 2017 Amortized Cost Fair Value Amortized Cost Fair Value Contractual maturity After one year through five years $ 2,956 $ 2,939 $ — $ — After five years through ten years 1,690 1,697 17 17 After ten years 6,332 6,220 1,249 1,229 Subtotal 10,978 10,856 1,266 1,246 Equity and other non-debt securities 83 82 — — Total investment securities $ 11,061 $ 10,938 $ 1,266 $ 1,246

Credit Quality And Allowance 37

Credit Quality And Allowance For Credit Losses (Tables)	12 Months Ended
	Dec. 31, 2017
Credit Quality And Allowance For Credit Losses [Abstract]
Aging Analysis Of Loans	The following table presents an aging analysis of the recorded balance of loans. Loans Past Due and Still Accruing (in millions) 30-59 Days 60-89 Days 90 Days or More Total Nonaccrual Loans Current Loans Total Loans December 31, 2017 Business loans: Commercial $ 79 $ 134 $ 12 $ 225 $ 309 $ 30,526 $ 31,060 Real estate construction: Commercial Real Estate business line (a) 3 — — 3 — 2,627 2,630 Other business lines (b) 4 — — 4 — 327 331 Total real estate construction 7 — — 7 — 2,954 2,961 Commercial mortgage: Commercial Real Estate business line (a) 14 — — 14 9 1,808 1,831 Other business lines (b) 27 6 22 55 22 7,251 7,328 Total commercial mortgage 41 6 22 69 31 9,059 9,159 Lease financing — — — — 4 464 468 International 13 — — 13 6 964 983 Total business loans 140 140 34 314 350 43,967 44,631 Retail loans: Residential mortgage 10 2 — 12 31 1,945 1,988 Consumer: Home equity 5 1 — 6 21 1,789 1,816 Other consumer 4 — 1 5 — 733 738 Total consumer 9 1 1 11 21 2,522 2,554 Total retail loans 19 3 1 23 52 4,467 4,542 Total loans $ 159 $ 143 $ 35 $ 337 $ 402 $ 48,434 $ 49,173 December 31, 2016 Business loans: Commercial $ 30 $ 12 $ 14 $ 56 $ 445 $ 30,493 $ 30,994 Real estate construction: Commercial Real Estate business line (a) — — — — — 2,485 2,485 Other business lines (b) — — — — — 384 384 Total real estate construction — — — — — 2,869 2,869 Commercial mortgage: Commercial Real Estate business line (a) 5 — — 5 9 2,004 2,018 Other business lines (b) 58 5 5 68 37 6,808 6,913 Total commercial mortgage 63 5 5 73 46 8,812 8,931 Lease financing — — — — 6 566 572 International 1 — — 1 14 1,243 1,258 Total business loans 94 17 19 130 511 43,983 44,624 Retail loans: Residential mortgage 7 3 — 10 39 1,893 1,942 Consumer: Home equity 4 3 — 7 28 1,765 1,800 Other consumer 1 — — 1 4 717 722 Total consumer 5 3 — 8 32 2,482 2,522 Total retail loans 12 6 — 18 71 4,375 4,464 Total loans $ 106 $ 23 $ 19 $ 148 $ 582 $ 48,358 $ 49,088 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate.
Loans By Credit Quality Indicator	The following table presents loans by credit quality indicator, based on internal risk ratings assigned to each business loan at the time of approval and subjected to subsequent reviews, generally at least annually, and to pools of retail loans with similar risk characteristics. Internally Assigned Rating (in millions) Pass (a) Special Mention (b) Substandard (c) Nonaccrual (d) Total December 31, 2017 Business loans: Commercial $ 29,263 $ 591 $ 897 $ 309 $ 31,060 Real estate construction: Commercial Real Estate business line (e) 2,630 — — — 2,630 Other business lines (f) 327 4 — — 331 Total real estate construction 2,957 4 — — 2,961 Commercial mortgage: Commercial Real Estate business line (e) 1,759 20 43 9 1,831 Other business lines (f) 7,099 115 92 22 7,328 Total commercial mortgage 8,858 135 135 31 9,159 Lease financing 440 23 1 4 468 International 946 11 20 6 983 Total business loans 42,464 764 1,053 350 44,631 Retail loans: Residential mortgage 1,955 2 — 31 1,988 Consumer: Home equity 1,786 1 8 21 1,816 Other consumer 737 1 — — 738 Total consumer 2,523 2 8 21 2,554 Total retail loans 4,478 4 8 52 4,542 Total loans $ 46,942 $ 768 $ 1,061 $ 402 $ 49,173 December 31, 2016 Business loans: Commercial $ 28,616 $ 944 $ 989 $ 445 $ 30,994 Real estate construction: Commercial Real Estate business line (e) 2,485 — — — 2,485 Other business lines (f) 381 — 3 — 384 Total real estate construction 2,866 — 3 — 2,869 Commercial mortgage: Commercial Real Estate business line (e) 1,970 19 20 9 2,018 Other business lines (f) 6,645 109 122 37 6,913 Total commercial mortgage 8,615 128 142 46 8,931 Lease financing 550 11 5 6 572 International 1,200 22 22 14 1,258 Total business loans 41,847 1,105 1,161 511 44,624 Retail loans: Residential mortgage 1,900 3 — 39 1,942 Consumer: Home equity 1,767 1 4 28 1,800 Other consumer 718 — — 4 722 Total consumer 2,485 1 4 32 2,522 Total retail loans 4,385 4 4 71 4,464 Total loans $ 46,232 $ 1,109 $ 1,165 $ 582 $ 49,088 (a) Includes all loans not included in the categories of special mention, substandard or nonaccrual. (b) Special mention loans are accruing loans that have potential credit weaknesses that deserve management’s close attention, such as loans to borrowers who may be experiencing financial difficulties that may result in deterioration of repayment prospects from the borrower at some future date. This category is generally consistent with the "special mention" category as defined by regulatory authorities. (c) Substandard loans are accruing loans that have a well-defined weakness, or weaknesses, such as loans to borrowers who may be experiencing losses from operations or inadequate liquidity of a degree and duration that jeopardizes the orderly repayment of the loan. Substandard loans also are distinguished by the distinct possibility of loss in the future if these weaknesses are not corrected. This category is generally consistent with the "substandard" category as defined by regulatory authorities. (d) Nonaccrual loans are loans for which the accrual of interest has been discontinued. For further information regarding nonaccrual loans, refer to the Nonperforming Assets subheading in Note 1 - Basis of Presentation and Accounting Policies. A significant majority of nonaccrual loans are generally consistent with the "substandard" category and the remainder are generally consistent with the "doubtful" category as defined by regulatory authorities. (e) Primarily loans to real estate developers. (f) Primarily loans secured by owner-occupied real estate.
Schedule Of Nonaccrual, Reduced-Rate Loans And Foreclosed Property	The following table summarizes nonperforming assets. (in millions) December 31, 2017 December 31, 2016 Nonaccrual loans $ 402 $ 582 Reduced-rate loans (a) 8 8 Total nonperforming loans 410 590 Foreclosed property (b) 5 17 Total nonperforming assets $ 415 $ 607 (a) There were no reduced-rate business loans at both December 31, 2017 and 2016 . Reduced-rate retail loans totaled $8 million at both December 31, 2017 and 2016 . (b) Included foreclosed residential real estate properties of $4 million and $3 million at December 31, 2017 and 2016 , respectively.
Changes In The Allowance For Loan Losses And Related Loan Amounts	The following table details the changes in the allowance for loan losses and related loan amounts. 2017 2016 2015 (in millions) Business Loans Retail Loans Total Business Loans Retail Loans Total Business Loans Retail Loans Total Years Ended December 31 Allowance for loan losses: Balance at beginning of period $ 682 $ 48 $ 730 $ 579 $ 55 $ 634 $ 534 $ 60 $ 594 Loan charge-offs (143 ) (6 ) (149 ) (207 ) (7 ) (214 ) (157 ) (11 ) (168 ) Recoveries on loans previously charged-off 50 7 57 63 5 68 55 13 68 Net loan (charge-offs) recoveries (93 ) 1 (92 ) (144 ) (2 ) (146 ) (102 ) 2 (100 ) Provision for loan losses 71 2 73 246 (5 ) 241 149 (7 ) 142 Foreign currency translation adjustment 1 — 1 1 — 1 (2 ) — (2 ) Balance at end of period $ 661 $ 51 $ 712 $ 682 $ 48 $ 730 $ 579 $ 55 $ 634 As a percentage of total loans 1.48 % 1.12 % 1.45 % 1.53 % 1.08 % 1.49 % 1.30 % 1.26 % 1.29 % December 31 Allowance for loan losses: Individually evaluated for impairment $ 67 $ — $ 67 $ 86 $ 3 $ 89 $ 53 $ — $ 53 Collectively evaluated for impairment 594 51 645 596 45 641 526 55 581 Total allowance for loan losses $ 661 $ 51 $ 712 $ 682 $ 48 $ 730 $ 579 $ 55 $ 634 Loans: Individually evaluated for impairment $ 443 $ 34 $ 477 $ 566 $ 48 $ 614 $ 393 $ 31 $ 424 Collectively evaluated for impairment 44,188 4,508 48,696 44,058 4,416 48,474 44,336 4,324 48,660 Total loans evaluated for impairment $ 44,631 $ 4,542 $ 49,173 $ 44,624 $ 4,464 $ 49,088 $ 44,729 $ 4,355 $ 49,084
Changes In the Allowance For Credit Losses On Lending-Related Commitments	Changes in the allowance for credit losses on lending-related commitments, included in "accrued expenses and other liabilities" on the consolidated balance sheets, are summarized in the following table. (in millions) Years Ended December 31 2017 2016 2015 Balance at beginning of period $ 41 $ 45 $ 41 Charge-offs on lending-related commitments (a) — (11 ) (1 ) Provision for credit losses on lending-related commitments 1 7 5 Balance at end of period $ 42 $ 41 $ 45 (a) Charge-offs result from the sale of unfunded lending-related commitments.
Individually Evaluated Impaired Loans	The following table presents additional information regarding individually evaluated impaired loans. Recorded Investment In: (in millions) Impaired Loans with No Related Allowance Impaired Loans with Related Allowance Total Impaired Loans Unpaid Principal Balance Related Allowance for Loan Losses December 31, 2017 Business loans: Commercial $ 105 $ 267 $ 372 $ 460 $ 63 Commercial mortgage: Commercial Real Estate business line (a) 39 1 40 49 — Other business lines (b) 3 22 25 29 3 Total commercial mortgage 42 23 65 78 3 International — 6 6 17 1 Total business loans 147 296 443 555 67 Retail loans: Residential mortgage 14 8 22 22 — Consumer: Home equity 11 — 11 14 — Other consumer 1 — 1 2 — Total consumer 12 — 12 16 — Total retail loans (c) 26 8 34 38 — Total individually evaluated impaired loans $ 173 $ 304 $ 477 $ 593 $ 67 December 31, 2016 Business loans: Commercial $ 90 $ 423 $ 513 $ 608 $ 80 Commercial mortgage: Commercial Real Estate business line (a) — 7 7 15 1 Other business lines (b) 2 30 32 40 3 Total commercial mortgage 2 37 39 55 4 International 3 11 14 20 2 Total business loans 95 471 566 683 86 Retail loans: Residential mortgage 19 9 28 30 2 Consumer: Home equity 15 — 15 19 — Other consumer 2 3 5 6 1 Total consumer 17 3 20 25 1 Total retail loans (c) 36 12 48 55 3 Total individually evaluated impaired loans $ 131 $ 483 $ 614 $ 738 $ 89 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate. (c) Individually evaluated retail loans generally have no related allowance for loan losses, primarily due to policy which results in direct write-downs of most restructured retail loans.
Average Individually Evaluated Impaired Loans And Related Interest Recognized	The following table presents information regarding average individually evaluated impaired loans and the related interest recognized. Interest income recognized for the period primarily related to reduced-rate loans. Individually Evaluated Impaired Loans 2017 2016 2015 (in millions) Average Balance for the Period Interest Income Recognized for the Period Average Balance for the Period Interest Income Recognized for the Period Average Balance for the Period Interest Income Recognized for the Period Years Ended December 31 Business loans: Commercial $ 451 $ 8 $ 550 $ 10 $ 206 $ 5 Commercial mortgage: Commercial Real Estate business line (a) 21 2 9 — 16 — Other business lines (b) 31 — 31 1 39 1 Total commercial mortgage 52 2 40 1 55 1 International 8 — 18 — 6 — Total business loans 511 10 608 11 267 6 Retail loans: Residential mortgage 24 — 15 — 21 — Consumer: Home equity 13 — 13 — 12 — Other consumer 3 — 4 — 6 — Total consumer 16 — 17 — 18 — Total retail loans 40 — 32 — 39 — Total individually evaluated impaired loans $ 551 $ 10 $ 640 $ 11 $ 306 $ 6 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate.
Troubled Debt Restructurings By Type Of Modification	The following tables detail the recorded balance at December 31, 2017 and 2016 of loans considered to be TDRs that were restructured during the years ended December 31, 2017 and 2016 , by type of modification. In cases of loans with more than one type of modification, the loans were categorized based on the most significant modification. 2017 2016 Type of Modification Type of Modification (in millions) Principal Deferrals (a) Interest Rate (b) AB Note Restructures (c) Total Modifications Principal Deferrals (a) Interest Rate (b) AB Note Restructures (c) Total Modifications Years Ended December 31 Business loans: Commercial $ 77 $ 18 $ 21 $ 116 $ 140 $ — $ 48 $ 188 Commercial mortgage: Commercial Real Estate business line (d) 37 — — 37 — — — — Other business lines (e) 3 — — 3 5 — — 5 Total commercial mortgage 40 — — 40 5 — — 5 International — — — — — — 3 3 Total business loans 117 18 21 156 145 — 51 196 Retail loans: Residential mortgage — — — — — 2 — 2 Consumer: Home equity (f) 1 2 — 3 2 1 — 3 Total retail loans 1 2 — 3 2 3 — 5 Total loans $ 118 $ 20 $ 21 $ 159 $ 147 $ 3 $ 51 $ 201 (a) Primarily represents loan balances where terms were extended 90 days or more at or above contractual interest rates. (b) Loan restructurings whereby interest rates were either reduced or were not at market rates. (c) Loan restructurings whereby the original loan is restructured into two notes: an "A" note, which generally reflects the portion of the modified loan which is expected to be collected; and a "B" note, which is either fully charged off or exchanged for an equity interest. (d) Primarily loans to real estate developers. (e) Primarily loans secured by owner-occupied real estate. (f) Includes bankruptcy loans for which the court has discharged the borrower's obligation and the borrower has not reaffirmed the debt.
Troubled Debt Restructuring Subsequent Default	The following table presents information regarding the recorded balance at December 31, 2017 and 2016 of loans modified by principal deferral during the years ended December 31, 2017 and 2016 , and those principal deferrals which experienced a subsequent default during the same periods. For principal deferrals, incremental deterioration in the credit quality of the loan, represented by a downgrade in the risk rating of the loan, for example, due to missed interest payments or a reduction of collateral value, is considered a subsequent default. 2017 2016 (in millions) Balance at December 31 Subsequent Default in the Year Ended December 31 Balance at December 31 Subsequent Default in the Year Ended December 31 Principal deferrals: Business loans: Commercial $ 77 $ 3 $ 140 $ 13 Commercial mortgage: Commercial Real Estate business line (a) 37 — — — Other business lines (b) 3 — 5 1 Total commercial mortgage 40 — 5 1 International — — — — Total business loans 117 3 145 14 Retail loans: Consumer: Home equity (c) 1 — 2 — Total principal deferrals $ 118 $ 3 $ 147 $ 14 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate. (c) Includes bankruptcy loans for which the court has discharged the borrower's obligation and the borrower has not reaffirmed the debt.

Significant Group Concentrati38

Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Tables)	12 Months Ended
	Dec. 31, 2017
Significant Group Concentrations of Credit Risk [Abstract]
Schedule of Automotive Industry Outstanding Loans and Total Exposure	Outstanding loans, included in "commercial loans" on the consolidated balance sheets, and total exposure (outstanding loans, unused commitments and standby letters of credit) to companies related to the automotive industry were as follows: (in millions) December 31 2017 2016 Automotive loans: Production $ 1,344 $ 1,326 Dealer 7,592 7,123 Total automotive loans $ 8,936 $ 8,449 Total automotive exposure: Production $ 2,439 $ 2,534 Dealer 9,405 8,730 Total automotive exposure $ 11,844 $ 11,264
Schedule of Commercial Real Estate Loans and Unused Commitments	Further, the Corporation’s portfolio of commercial real estate loans, which includes real estate construction and commercial mortgage loans, was as follows. (in millions) December 31 2017 2016 Real estate construction loans: Commercial Real Estate business line (a) $ 2,630 $ 2,485 Other business lines (b) 331 384 Total real estate construction loans 2,961 2,869 Commercial mortgage loans: Commercial Real Estate business line (a) 1,831 2,018 Other business lines (b) 7,328 6,913 Total commercial mortgage loans 9,159 8,931 Total commercial real estate loans $ 12,120 $ 11,800 Total unused commitments on commercial real estate loans $ 3,018 $ 3,046 (a) Primarily loans to real estate developers. (b) Primarily loans secured by owner-occupied real estate.

Premises and Equipment Premises

Premises and Equipment 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 by major category follows: (in millions) December 31 2017 2016 Land $ 85 $ 86 Buildings and improvements 813 831 Furniture and equipment 484 499 Total cost 1,382 1,416 Less: Accumulated depreciation and amortization (916 ) (915 ) Net book value $ 466 $ 501
Schedule of Future Minimum Lease Payments	As of December 31, 2017 , future minimum rental payments under operating leases were as follows: (in millions) Years Ending December 31 2018 $ 68 2019 61 2020 52 2021 43 2022 32 Thereafter 135 Total $ 391

Goodwill and Intangible Assets

Goodwill and Intangible Assets Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Changes in Carrying Value of Goodwill	The following table summarizes the carrying value of goodwill by reporting unit for the years ended December 31, 2017 and 2016 . (in millions) December 31 2017 2016 Business Bank $ 380 $ 380 Retail Bank 194 194 Wealth Management 61 61 Total $ 635 $ 635
Summary of Core Deposit Intangible Carrying Value and Amortization	A summary of core deposit intangible carrying value and related accumulated amortization follows: (in millions) December 31 2017 2016 Gross carrying amount $ 34 $ 34 Accumulated amortization (28 ) (26 ) Net carrying amount $ 6 $ 8
Schedule of Core Deposit Intangible Estimated Future Amortization Expense	At December 31, 2017 , estimated future amortization expense was as follows: (in millions) Years Ending December 31 2018 $ 2 2019 2 2020 1 2021 1 Total $ 6

Derivative And Credit-Related41

Derivative And Credit-Related Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule Of Derivative Instruments	The following table presents the composition of the Corporation’s derivative instruments held or issued for risk management purposes or in connection with customer-initiated and other activities at December 31, 2017 and 2016 . The table excludes commitments and warrants accounted for as derivatives. December 31, 2017 December 31, 2016 Fair Value Fair Value (in millions) Notional/ Contract Amount (a) Gross Derivative Assets Gross Derivative Liabilities Notional/ Contract Amount (a) Gross Derivative Assets Gross Derivative Liabilities Risk management purposes Derivatives designated as hedging instruments Interest rate contracts: Swaps - fair value - receive fixed/pay floating (b) $ 1,775 $ — $ 2 $ 2,275 $ 92 $ 4 Derivatives used as economic hedges Foreign exchange contracts: Spot, forwards and swaps 650 — 2 717 2 2 Total risk management purposes 2,425 — 4 2,992 94 6 Customer-initiated and other activities Interest rate contracts: Caps and floors written 635 — — 436 — 1 Caps and floors purchased 635 — — 436 1 — Swaps (b) 13,119 57 57 12,451 130 76 Total interest rate contracts 14,389 57 57 13,323 131 77 Energy contracts: Caps and floors written 164 — 11 419 1 31 Caps and floors purchased 164 11 — 419 31 1 Swaps 1,519 82 80 1,389 114 112 Total energy contracts 1,847 93 91 2,227 146 144 Foreign exchange contracts: Spot, forwards, options and swaps 1,884 42 38 1,509 36 27 Total customer-initiated and other activities 18,120 192 186 17,059 313 248 Total gross derivatives $ 20,545 192 190 $ 20,051 407 254 Amounts offset in the consolidated balance sheets: Netting adjustment - Offsetting derivative assets/liabilities (49 ) (49 ) (84 ) (84 ) Netting adjustment - Cash collateral received/posted (1 ) (39 ) (47 ) (45 ) Net derivatives included in the consolidated balance sheets (c) 142 102 276 125 Amounts not offset in the consolidated balance sheets: Marketable securities received/pledged under bilateral collateral agreements (3 ) (24 ) (19 ) (8 ) Net derivatives after deducting amounts not offset in the consolidated balance sheets $ 139 $ 78 $ 257 $ 117 (a) Notional or contractual amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets. (b) Due to clearinghouse rule changes, beginning January 1, 2017, variation margin payments are treated as settlements of derivative exposure rather than as collateral. As a result, these payments are now considered in determining the fair value of centrally cleared derivatives, resulting in centrally cleared derivatives having a fair value of approximately zero. (c) Net derivative assets are included in “accrued income and other assets” and net derivative liabilities are included in “accrued expenses and other liabilities” on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and credit risk of the Corporation. The fair value of net derivative assets included credit valuation adjustments for counterparty credit risk of $4 million and $5 million at December 31, 2017 and 2016 , respectively.
Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps	The following table summarizes the expected weighted average remaining maturity of the notional amount of risk management interest rate swaps and the weighted average interest rates associated with amounts expected to be received or paid on interest rate swap agreements as of December 31, 2017 and 2016 . Weighted Average (dollar amounts in millions) Notional Amount Remaining Maturity (in years) Receive Rate Pay Rate (a) December 31, 2017 Swaps - fair value - receive fixed/pay floating rate Medium- and long-term debt designation $ 1,775 4.6 3.26 % 2.35 % December 31, 2016 Swaps - fair value - receive fixed/pay floating rate Medium- and long-term debt designation 2,275 4.5 3.69 1.80 (a) Variable rates paid on receive fixed swaps are based on six-month LIBOR rates in effect at December 31, 2017 and 2016 .
Schedule Of Net Gains Recognized In Income On Customer-Initiated Derivatives	The net gains recognized in income on customer-initiated derivative instruments, net of the impact of offsetting positions, were as follows: (in millions) Years Ended December 31 Location of Gain 2017 2016 Interest rate contracts Other noninterest income $ 24 $ 25 Energy contracts Other noninterest income 2 2 Foreign exchange contracts Foreign exchange income 45 41 Total $ 71 $ 68
Schedule Of Financial Instruments With Off-Balance Sheet Credit Risk	The Corporation’s credit risk associated with these instruments is represented by the contractual amounts indicated in the following table. (in millions) December 31 2017 2016 Unused commitments to extend credit: Commercial and other $ 22,636 $ 24,333 Bankcard, revolving check credit and home equity loan commitments 2,833 2,658 Total unused commitments to extend credit $ 25,469 $ 26,991 Standby letters of credit $ 3,228 $ 3,623 Commercial letters of credit 39 46
Summary Of Criticized Letters Of Credit	The following table presents a summary of criticized standby and commercial letters of credit at December 31, 2017 and December 31, 2016 . The Corporation's criticized list is consistent with the Special Mention, Substandard and Doubtful categories defined by regulatory authorities. The Corporation manages credit risk through underwriting, periodically reviewing and approving its credit exposures using Board committee approved credit policies and guidelines. (dollar amounts in millions) December 31, 2017 December 31, 2016 Total criticized standby and commercial letters of credit $ 88 $ 135 As a percentage of total outstanding standby and commercial letters of credit 2.7 % 3.7 %

Deposits Deposits (Tables)

Deposits Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Schedule Of Maturities Of Certificates of Deposit and Other Deposits with a Stated Maturity	At December 31, 2017 , the scheduled maturities of certificates of deposit and other deposits with a stated maturity were as follows: (in millions) Years Ending December 31 2018 $ 1,855 2019 200 2020 66 2021 28 2022 16 Thereafter 15 Total $ 2,180
Schedule Of Maturities Of Domestic Deposits Of $100,000 Or More	A maturity distribution of domestic certificates of deposit of $100,000 and over follows: (in millions) December 31 2017 2016 Three months or less $ 355 $ 510 Over three months to six months 207 322 Over six months to twelve months 319 449 Over twelve months 130 230 Total $ 1,011 $ 1,511

Net Income Per Common Share (Ta

Net Income Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Basic And Diluted Net Income Per Common Share	Basic and diluted net income per common share are presented in the following table. (in millions, except per share data) Years Ended December 31 2017 2016 2015 Basic and diluted Net income $ 743 $ 477 $ 521 Less income allocated to participating securities 5 4 6 Net income attributable to common shares $ 738 $ 473 $ 515 Basic average common shares 174 172 176 Basic net income per common share $ 4.23 $ 2.74 $ 2.93 Basic average common shares 174 172 176 Dilutive common stock equivalents: Net effect of the assumed exercise of stock options 3 2 2 Net effect of the assumed exercise of warrants 1 3 3 Diluted average common shares 178 177 181 Diluted net income per common share $ 4.14 $ 2.68 $ 2.84
Schedule of Average Shares Excluded From Diluted Net Income Per Common Share Computation	The following average shares related to outstanding options to purchase shares of common stock were not included in the computation of diluted net income per common share because the options were anti-dilutive for the period. There were no anti-dilutive options for the year ended December 31, 2017. (shares in millions) Years Ended December 31 2016 2015 Average outstanding options 3.3 5.1 Range of exercise prices $37.26 - $59.86 $46.68 - $60.82

Variable Interest Entities (V44

Variable Interest Entities (VIEs) (Tables)	12 Months Ended
	Dec. 31, 2017
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Impact of VIEs on the Consolidated Statements of Income	The following table summarizes the impact of these tax credit entities on line items on the Corporation’s consolidated statements of income. (in millions) Years Ended December 31 2017 2016 2015 Other noninterest income: Amortization of other tax credit investments $ 2 $ (1 ) $ 1 Provision for income taxes: Amortization of LIHTC Investments 67 66 62 Low income housing tax credits (63 ) (62 ) (61 ) Other tax benefits related to tax credit entities (24 ) (26 ) (22 ) Total provision for income taxes $ (20 ) $ (22 ) $ (21 )

Short-term Borrowings Short-ter

Short-term Borrowings Short-term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Short-term Debt [Abstract]
Summary of Short-term Borrowings	The following table provides a summary of short-term borrowings. (dollar amounts in millions) Federal Funds Purchased and Securities Sold Under Agreements to Repurchase Other Short-term Borrowings December 31, 2017 Amount outstanding at year-end $ 10 $ — Weighted average interest rate at year-end 1.43 % — % Maximum month-end balance during the year $ 41 $ 1,024 Average balance outstanding during the year 20 257 Weighted average interest rate during the year 1.02 % 1.15 % December 31, 2016 Amount outstanding at year-end $ 25 $ — Weighted average interest rate at year-end 0.54 % — % Maximum month-end balance during the year $ 25 $ 501 Average balance outstanding during the year 15 123 Weighted average interest rate during the year 0.47 % 0.45 % December 31, 2015 Amount outstanding at year-end $ 23 $ — Weighted average interest rate at year-end 0.38 % — % Maximum month-end balance during the year $ 109 $ — Average balance outstanding during the year 93 — Weighted average interest rate during the year 0.05 % — %

Medium- And Long-Term Debt (Tab

Medium- And Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule Of Medium- And Long-Term Debt	Medium- and long-term debt is summarized as follows: (in millions) December 31 2017 2016 Parent company Subordinated notes: 3.80% subordinated notes due 2026 (a) $ 255 $ 256 Medium-term notes: 2.125% notes due 2019 (a) 347 348 Total parent company 602 604 Subsidiaries Subordinated notes: 5.20% subordinated notes due 2017 (a) — 511 4.00% subordinated notes due 2025 (a) 347 347 7.875% subordinated notes due 2026 (a) 208 215 Total subordinated notes 555 1,073 Medium-term notes: 2.50% notes due 2020 (a) 665 667 FHLB advances: Floating-rate based on FHLB auction rate due 2026 2,800 2,800 Other notes: 6.0% - 6.4% fixed-rate notes due 2018 to 2020 — 16 Total subsidiaries 4,020 4,556 Total medium- and long-term debt $ 4,622 $ 5,160 (a) The fixed interest rates on these notes have been swapped to a variable rate and designated in a hedging relationship. Accordingly, carrying value has been adjusted to reflect the change in the fair value of the debt as a result of changes in the benchmark rate.
Schedule of Maturities of Medium- and Long-term Debt	At December 31, 2017 , the principal maturities of medium- and long-term debt were as follows: (in millions) Years Ending December 31 2018 $ — 2019 350 2020 675 2021 — 2022 — Thereafter 3,550 Total $ 4,575

Accumulated Other Comprehensi47

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule Of Accumulated Other Comprehensive Income (Loss)	The following table presents a reconciliation of the changes in the components of accumulated other comprehensive loss and details the components of other comprehensive income (loss) for the year ended December 31, 2017 , 2016 and 2015 , including the amount of income tax expense (benefit) allocated to each component of other comprehensive income (loss). (in millions) Years Ended December 31 2017 2016 2015 Accumulated net unrealized (losses) gains on investment securities: Balance at beginning of period, net of tax $ (33 ) $ 9 $ 37 Net unrealized holding losses arising during the period (81 ) (70 ) (55 ) Less: Benefit for income taxes (27 ) (26 ) (21 ) Net unrealized holding losses arising during the period, net of tax (54 ) (44 ) (34 ) Less: Net realized losses included in net securities losses — — (2 ) Less: Benefit for income taxes — — (1 ) Reclassification adjustment for net securities losses included in net income, net of tax — — (1 ) Less: Net losses realized as a yield adjustment in interest on investment securities (3 ) (3 ) (8 ) Less: Benefit for income taxes (1 ) (1 ) (3 ) Reclassification adjustment for net losses realized as a yield adjustment included in net income, net of tax (2 ) (2 ) (5 ) Change in net unrealized losses on investment securities, net of tax (52 ) (42 ) (28 ) Reclassification of certain deferred tax effects (a) (16 ) — — Balance at end of period, net of tax $ (101 ) $ (33 ) $ 9 Accumulated defined benefit pension and other postretirement plans adjustment: Balance at beginning of period, net of tax $ (350 ) $ (438 ) $ (449 ) Actuarial gain (loss) arising during the period 72 (134 ) (57 ) Prior service credit arising during the period — 234 3 Net defined benefit pension and other postretirement adjustment arising during the period 72 100 (54 ) Less: Provision (benefit) for income taxes 17 37 (19 ) Net defined benefit pension and other postretirement adjustment arising during the period, net of tax 55 63 (35 ) Amounts recognized in salaries and benefits expense: Amortization of actuarial net loss 51 46 70 Amortization of prior service (credit) cost (27 ) (7 ) 1 Total amounts recognized in salaries and benefits expense 24 39 71 Less: Provision for income taxes 8 14 25 Adjustment for amounts recognized as components of net periodic benefit cost during the period, net of tax 16 25 46 Change in defined benefit pension and other postretirement plans adjustment, net of tax 71 88 11 Reclassification of certain deferred tax effects (a) (71 ) — — Balance at end of period, net of tax $ (350 ) $ (350 ) $ (438 ) Total accumulated other comprehensive loss at end of period, net of tax $ (451 ) $ (383 ) $ (429 ) (a) Amounts reclassified to retained earnings due to early adoption of ASU 2018-02 . For further information, refer to Note 1.

Share-Based Compensation Share-

Share-Based Compensation Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Share-based Compensation [Abstract]
Summary of Components of Share-Based Compensation Expense	The components of share-based compensation expense for all share-based compensation plans and related tax benefits are as follows: (in millions) Years Ended December 31 2017 2016 2015 Total share-based compensation expense $ 39 $ 34 $ 38 Related tax benefits recognized in net income $ 14 $ 13 $ 14
Schedule of Unrecognized Compensation Expense	The following table summarizes unrecognized compensation expense for all share-based plans. (dollar amounts in millions) December 31, 2017 Total unrecognized share-based compensation expense $ 40 Weighted-average expected recognition period (in years) 2.8
Estimated Weighted-Average Grant-Date Fair Value per Option and the Underlying Model Assumptions	The estimated weighted-average grant-date fair value per option and the underlying binomial option-pricing model assumptions are summarized in the following table: Years Ended December 31 2017 2016 2015 Weighted-average grant-date fair value per option $ 19.61 $ 9.94 $ 11.31 Weighted-average assumptions: Risk-free interest rates 2.47 % 2.01 % 1.83 % Expected dividend yield 3.00 3.00 3.00 Expected volatility factors of the market price of Comerica common stock 34 38 33 Expected option life (in years) 7.0 6.9 6.9
Summary of Stock Option Activity and Related Information	A summary of the Corporation’s stock option activity and related information for the year ended December 31, 2017 follows: Weighted-Average Number of Options (in thousands) Exercise Price per Share Remaining Contractual Term (in years) Aggregate Intrinsic Value (in millions) Outstanding-January 1, 2017 6,892 $ 37.24 Granted 430 67.67 Forfeited or expired (57 ) 48.74 Exercised (3,092 ) 37.45 Outstanding-December 31, 2017 4,173 40.06 5.9 $ 195 Exercisable-December 31, 2017 2,347 $ 36.27 4.3 $ 119
Summary of Restricted Stock Activity and Related Information	A summary of the Corporation’s restricted stock activity and related information for the year ended December 31, 2017 follows: Number of Shares (in thousands) Weighted-Average Grant-Date Fair Value per Share Outstanding-January 1, 2017 1,591 $ 37.20 Granted 237 67.83 Forfeited (59 ) 42.53 Vested (526 ) 35.28 Outstanding-December 31, 2017 1,243 $ 43.59
Summary of Restricted Stock Unit Activity and Related Information	A summary of the Corporation's restricted stock unit activity and related information for the year ended December 31, 2017 follows: Service-Based Units Performance-Based Units Number of Units (in thousands) Weighted-Average Grant-Date Fair Value per Share Number of Units (in thousands) Weighted-Average Grant-Date Fair Value per Share Outstanding-January 1, 2017 180 $ 39.61 781 $ 39.47 Granted 19 75.06 149 66.07 Vested — — (212 ) 48.32 Outstanding-December 31, 2017 199 43.00 718 42.39

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Schedule of Defined Benefit Plans Disclosures	The following table sets forth reconciliations of plan assets and the projected benefit obligation, the weighted-average assumptions used to determine year-end benefit obligations, and the amounts recognized in accumulated other comprehensive income (loss) for the Corporation’s defined benefit pension plans and postretirement benefit plan at December 31, 2017 and 2016 . The Corporation used a measurement date of December 31, 2017 for these plans. Defined Benefit Pension Plans Qualified Non-Qualified Postretirement Benefit Plan (dollar amounts in millions) 2017 2016 2017 2016 2017 2016 Change in fair value of plan assets: Fair value of plan assets at January 1 $ 2,453 $ 2,346 $ — $ — $ 62 $ 61 Actual return on plan assets 396 200 — — 2 2 Employer contributions — — — — 1 4 Benefits paid (102 ) (93 ) — — (5 ) (5 ) Fair value of plan assets at December 31 $ 2,747 $ 2,453 $ — $ — $ 60 $ 62 Change in projected benefit obligation: Projected benefit obligation at January 1 $ 1,902 $ 1,916 $ 201 $ 222 $ 55 $ 59 Service cost 29 31 2 3 — — Interest cost 78 87 8 10 2 3 Actuarial loss (gain) 154 161 12 11 (1 ) (2 ) Benefits paid (102 ) (93 ) (11 ) (11 ) (5 ) (5 ) Plan change — (200 ) — (34 ) — — Projected benefit obligation at December 31 $ 2,061 $ 1,902 $ 212 $ 201 $ 51 $ 55 Accumulated benefit obligation $ 2,052 $ 1,894 $ 209 $ 198 $ 51 $ 55 Funded status at December 31 (a) (b) $ 686 $ 551 $ (212 ) $ (201 ) $ 9 $ 7 Weighted-average assumptions used: Discount rate 3.74 % 4.23 % 3.74 % 4.23 % 3.55 % 3.92 % Rate of compensation increase 3.75 3.50 3.75 3.50 n/a n/a Healthcare cost trend rate: Cost trend rate assumed for next year n/a n/a n/a n/a 6.50 6.50 Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) n/a n/a n/a n/a 4.50 5.00 Year when rate reaches the ultimate trend rate n/a n/a n/a n/a 2027 2027 Amounts recognized in accumulated other comprehensive income (loss) before income taxes: Net actuarial loss $ (548 ) $ (673 ) $ (85 ) $ (82 ) $ (19 ) $ (20 ) Prior service credit 159 178 42 50 1 1 Balance at December 31 $ (389 ) $ (495 ) $ (43 ) $ (32 ) $ (18 ) $ (19 ) (a) Based on projected benefit obligation for defined benefit pension plans and accumulated benefit obligation for postretirement benefit plan. (b) The Corporation recognizes the overfunded and underfunded status of the plans in “accrued income and other assets” and “accrued expenses and other liabilities,” respectively, on the consolidated balance sheets. n/a - not applicable
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss)	The following table details the changes in plan assets and benefit obligations recognized in other comprehensive income (loss) for the year ended December 31, 2017 . Defined Benefit Pension Plans (in millions) Qualified Non-Qualified Postretirement Benefit Plan Total Actuarial gain (loss) arising during the period $ 82 $ (11 ) $ 1 $ 72 Amortization of net actuarial loss 43 8 — 51 Amortization of prior service credit (19 ) (8 ) — (27 ) Total recognized in other comprehensive income (loss) $ 106 $ (11 ) $ 1 $ 96
Components of Net Periodic Defined Benefit Cost	Components of net periodic defined benefit cost and postretirement benefit cost, the actual return on plan assets and the weighted-average assumptions used were as follows: Defined Benefit Pension Plans (dollar amounts in millions) Qualified Non-Qualified Years Ended December 31 2017 2016 2015 2017 2016 2015 Service cost $ 29 $ 31 $ 35 $ 2 $ 3 $ 4 Interest cost 78 87 88 8 10 10 Expected return on plan assets (159 ) (163 ) (159 ) — — — Amortization of prior service (credit) cost (19 ) (2 ) 4 (8 ) (5 ) (4 ) Amortization of net loss 43 38 59 8 7 10 Net periodic defined benefit (credit) cost $ (28 ) $ (9 ) $ 27 $ 10 $ 15 $ 20 Actual return on plan assets $ 396 $ 200 $ (73 ) n/a n/a n/a Actual rate of return on plan assets 16.48 % 8.66 % (2.95 )% n/a n/a n/a Weighted-average assumptions used: Discount rate 4.23 % 4.53 % 4.28 % 4.23 % 4.53 % 4.28 % Expected long-term return on plan assets 6.50 6.75 6.75 n/a n/a n/a Rate of compensation increase 3.50 3.75 3.75 3.50 3.75 3.75 n/a - not applicable (dollar amounts in millions) Postretirement Benefit Plan Years Ended December 31 2017 2016 2015 Interest cost $ 2 $ 3 $ 3 Expected return on plan assets (3 ) (4 ) (4 ) Amortization of prior service cost — — 1 Amortization of net loss 1 1 1 Net periodic postretirement benefit cost $ — $ — $ 1 Actual return on plan assets $ 2 $ 2 $ — Actual rate of return on plan assets 3.52 % 2.83 % (0.53 )% Weighted-average assumptions used: Discount rate 3.92 % 4.53 % 3.99 % Expected long-term return on plan assets 5.00 5.00 5.00 Healthcare cost trend rate: Cost trend rate assumed 6.50 7.00 7.00 Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 4.50 5.00 5.00 Year that the rate reaches the ultimate trend rate 2027 2027 2026
Balances Remaining in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year	The estimated portion of balances remaining in accumulated other comprehensive income (loss) that are expected to be recognized as a component of net periodic benefit cost in the year ended December 31, 2018 are as follows: Defined Benefit Pension Plans (in millions) Qualified Non-Qualified Postretirement Benefit Plan Total Net loss $ 51 $ 8 $ 1 $ 60 Prior service credit (19 ) (8 ) — (27 )
Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	Assumed healthcare cost trend rates have a significant effect on the amounts reported for the postretirement benefit plan. A one-percentage-point change in 2017 assumed healthcare and prescription drug cost trend rates would have the following effects. One-Percentage-Point (in millions) Increase Decrease Effect on postretirement benefit obligation $ 3 $ (2 ) Effect on total service and interest cost — —
Fair Value of Defined Benefit Plan Investments	The fair values of the Corporation’s qualified defined benefit pension plan investments measured at fair value on a recurring basis at December 31, 2017 and 2016 , by asset category and level within the fair value hierarchy, are detailed in the table below. (in millions) Total Level 1 Level 2 Level 3 December 31, 2017 Equity securities: Mutual funds $ 1 $ 1 $ — $ — Common stock 961 961 — — Fixed income securities: U.S. Treasury and other U.S. government agency securities 456 451 5 — Corporate and municipal bonds and notes 765 — 765 — Mortgage-backed securities 25 — 25 — Private placements 80 — — 80 Total investments in the fair value hierarchy 2,288 $ 1,413 $ 795 $ 80 Investments measured at net asset value: Collective investment funds 455 Total investments at fair value $ 2,743 December 31, 2016 Cash equivalent securities: Commercial paper $ 2 $ — $ 2 $ — Common stock 850 850 — — Fixed income securities: U.S. Treasury and other U.S. government agency securities 377 366 11 — Corporate and municipal bonds and notes 710 — 710 — Mortgage-backed securities 23 — 23 — Private placements 71 — — 71 Total investments in the fair value hierarchy 2,033 $ 1,216 $ 746 $ 71 Investments measured at net asset value: Collective investment funds 415 Total investments at fair value $ 2,448
Changes in Level 3 Defined Benefit Plan Investments	The table below provides a summary of changes in the Corporation’s qualified defined benefit pension plan’s Level 3 investments measured at fair value on a recurring basis for the years ended December 31, 2017 and 2016 . Balance at Beginning of Period Balance at End of Period Net Gains (Losses) (in millions) Realized Unrealized Purchases Sales Year Ended December 31, 2017 Private placements $ 71 $ 2 $ 3 $ 77 $ (73 ) $ 80 Year Ended December 31, 2016 Private placements $ 105 $ 1 $ 3 $ 64 $ (102 ) $ 71
Estimated Future Benefit Payments	The Corporation currently expects to make no employer contributions to the qualified and non-qualified defined benefit pension plans and postretirement benefit plan for the year ended December 31, 2018 . Estimated Future Benefit Payments (in millions) Years Ended December 31 Qualified Defined Benefit Pension Plan Non-Qualified Defined Benefit Pension Plan Postretirement Benefit Plan (a) 2018 $ 120 $ 11 $ 6 2019 123 12 5 2020 125 13 5 2021 127 13 5 2022 130 13 5 2023 - 2027 665 66 19 (a) Estimated benefit payments in the postretirement benefit plan are net of estimated Medicare subsidies.

Income Taxes And Tax-Related 50

Income Taxes And Tax-Related Items Income Taxes And Tax-Related Items (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current and Deferred Components of the Provision for Income Taxes	The current and deferred components of the provision for income taxes were as follows: (in millions) December 31 2017 2016 2015 Current: Federal $ 371 $ 224 $ 275 Foreign 5 5 5 State and local 36 15 20 Total current 412 244 300 Deferred: Federal (26 ) (49 ) (68 ) State and local (2 ) (2 ) (3 ) Remeasurement of deferred taxes 107 — — Total deferred 79 (51 ) (71 ) Total $ 491 $ 193 $ 229
Reconciliation of Expected Income Tax Expense at the Federal Statutory Rate to the Provision for Income Taxes	A reconciliation of expected income tax expense at the federal statutory rate to the Corporation’s provision for income taxes and effective tax rate follows: (dollar amounts in millions) 2017 2016 2015 Years Ended December 31 Amount Rate Amount Rate Amount Rate Tax based on federal statutory rate $ 432 35.0 % $ 235 35.0 % $ 262 35.0 % Remeasurement of deferred taxes 107 8.7 — — — — State income taxes 22 1.8 8 1.2 10 1.3 Employee stock transactions (35 ) (2.8 ) — — — — Affordable housing and historic credits (21 ) (1.7 ) (22 ) (3.3 ) (22 ) (2.9 ) Bank-owned life insurance (16 ) (1.3 ) (15 ) (2.3 ) (15 ) (2.0 ) Lease termination transactions (2 ) (0.2 ) (15 ) (2.2 ) (5 ) (0.7 ) Tax-related interest and penalties 4 0.3 3 0.5 1 0.1 Other — — (1 ) (0.1 ) (2 ) (0.3 ) Provision for income taxes $ 491 39.8 % $ 193 28.8 % $ 229 30.5 %
Reconciliation of Beginning and Ending Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of net unrecognized tax benefits follows: (in millions) 2017 2016 2015 Balance at January 1 $ 15 $ 22 $ 14 Increase as a result of tax positions taken during a prior period 4 — 8 Decrease related to settlements with tax authorities (8 ) (7 ) — Other (1 ) — — Balance at December 31 $ 10 $ 15 $ 22
Tax Years Remaining Open for Examination for Significant Tax Jurisdictions	The following tax years for significant jurisdictions remain subject to examination as of December 31, 2017 : Jurisdiction Tax Years Federal 2014-2016 California 2005-2016
Principal Components of Deferred Tax Assets and Liabilities	The principal components of deferred tax assets and liabilities were as follows: (in millions) December 31 2017 2016 Deferred tax assets: Allowance for loan losses $ 150 $ 256 Deferred compensation 49 91 Deferred loan origination fees and costs 6 20 Net unrealized losses on investment securities available-for-sale 31 20 Other temporary differences, net 57 76 Total deferred tax asset before valuation allowance 293 463 Valuation allowance (3 ) (3 ) Total deferred tax assets 290 460 Deferred tax liabilities: Lease financing transactions (76 ) (150 ) Defined benefit plans (72 ) (82 ) Allowance for depreciation (1 ) (11 ) Total deferred tax liabilities (149 ) (243 ) Net deferred tax asset $ 141 $ 217

Regulatory Capital and Reserv51

Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Tables)	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Summary of Capital Position	The following is a summary of the capital position of the Corporation and Comerica Bank, its principal banking subsidiary. (dollar amounts in millions) Comerica Incorporated (Consolidated) Comerica Bank December 31, 2017 CET1 capital (minimum $3.0 billion (Consolidated)) $ 7,773 $ 7,121 Tier 1 capital (minimum-$4.0 billion (Consolidated)) 7,773 7,121 Total capital (minimum-$5.3 billion (Consolidated)) 9,211 8,378 Risk-weighted assets 66,575 66,447 Average assets (fourth quarter) 71,372 71,181 CET1 capital to risk-weighted assets (minimum-4.5%) 11.68 % 10.72 % Tier 1 capital to risk-weighted assets (minimum-6.0%) 11.68 10.72 Total capital to risk-weighted assets (minimum-8.0%) 13.84 12.61 Tier 1 capital to average assets (minimum-4.0%) 10.89 10.00 Capital conservation buffer 5.68 4.61 December 31, 2016 CET1 capital (minimum $3.1 billion (Consolidated)) $ 7,540 $ 7,120 Tier 1 capital (minimum-$4.1 billion (Consolidated)) 7,540 7,120 Total capital (minimum-$5.4 billion (Consolidated)) 9,018 8,397 Risk-weighted assets 67,966 67,739 Average assets (fourth quarter) 74,086 73,804 CET1 capital to risk-weighted assets (minimum-4.5%) 11.09 % 10.51 % Tier 1 capital to risk-weighted assets (minimum-6.0%) 11.09 10.51 Total capital to risk-weighted assets (minimum-8.0%) 13.27 12.40 Tier 1 capital to average assets (minimum-4.0%) 10.18 9.65 Capital conservation buffer 5.09 4.40

Restructuring Charges Restruc52

Restructuring Charges Restructuring Charges (Tables)	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs	The following table presents changes in restructuring reserves, cumulative charges incurred to date and total expected restructuring charges: (in millions) Employee Costs Facilities Costs Technology Costs Other Costs Total Year Ended December 31, 2017 Balance at beginning of period $ 10 $ 4 $ — $ 4 $ 18 Restructuring charges 10 2 26 7 45 Payments (12 ) (6 ) (15 ) (10 ) (43 ) Adjustments for non-cash charges (a) — — (5 ) — (5 ) Balance at end of period $ 8 $ — $ 6 $ 1 $ 15 Year Ended December 31, 2016 Balance at beginning of period $ — $ — $ — $ — $ — Restructuring charges 52 15 — 26 93 Payments (44 ) (6 ) — (22 ) (72 ) Adjustments for non-cash charges (a) 2 (5 ) — — (3 ) Balance at end of period $ 10 $ 4 $ — $ 4 $ 18 Total restructuring charges incurred to date $ 62 $ 17 $ 26 $ 33 $ 138 Total expected restructuring charges (b) 70 20 - 25 60 - 65 35 185 - 195 (a) Adjustments for non-cash charges primarily include the benefit from forfeitures of nonvested stock compensation in Employee Costs, accelerated depreciation expense in Facilities Costs and impairments of previously capitalized software costs in Technology Costs. (b) Restructuring activities are expected to be substantially completed by 12/31/2018 .

Business Segment Information (T

Business Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Business Segment Financial Results	Business segment financial results are as follows: (dollar amounts in millions) Business Bank Retail Bank Wealth Management Finance Other Total Year Ended December 31, 2017 Earnings summary: Net interest income (expense) $ 1,372 $ 658 $ 170 $ (175 ) $ 36 $ 2,061 Provision for credit losses 58 13 1 — 2 74 Noninterest income 601 193 255 48 10 1,107 Noninterest expenses 802 731 285 (4 ) 46 1,860 Provision (benefit) for income taxes 389 39 51 (58 ) 70 (a) 491 Net income (loss) $ 724 $ 68 $ 88 $ (65 ) $ (72 ) $ 743 Net credit-related charge-offs (recoveries) $ 82 $ 15 $ (5 ) $ — $ — $ 92 Selected average balances: Assets $ 38,801 $ 6,478 $ 5,401 $ 13,954 $ 6,818 $ 71,452 Loans 37,445 5,857 5,256 — — 48,558 Deposits 28,803 23,971 4,081 241 162 57,258 Statistical data: Return on average assets (b) 1.87 % 0.28 % 1.63 % N/M N/M 1.04 % Efficiency ratio (c) 40.61 85.54 66.84 N/M N/M 58.57 (dollar amounts in millions) Business Bank Retail Bank Wealth Management Finance Other Total Year Ended December 31, 2016 Earnings summary: Net interest income (expense) $ 1,417 $ 618 $ 167 $ (428 ) $ 23 $ 1,797 Provision for credit losses 217 35 (4 ) — — 248 Noninterest income 572 189 243 43 4 1,051 Noninterest expenses 839 767 301 (4 ) 27 1,930 Provision (benefit) for income taxes 295 1 39 (142 ) — 193 Net income (loss) $ 638 $ 4 $ 74 $ (239 ) $ — $ 477 Net credit-related charge-offs $ 145 $ 12 $ — $ — $ — $ 157 Selected average balances: Assets $ 39,497 $ 6,551 $ 5,232 $ 13,993 $ 6,470 $ 71,743 Loans 38,067 5,881 5,048 — — 48,996 Deposits 29,704 23,558 4,126 88 265 57,741 Statistical data: Return on average assets (b) 1.61 % 0.02 % 1.42 % N/M N/M 0.67 % Efficiency ratio (c) 42.11 94.35 73.48 N/M N/M 67.53 (Table continues on following page) (dollar amounts in millions) Business Bank Retail Bank Wealth Management Finance Other Total Year Ended December 31, 2015 Earnings summary: Net interest income (expense) $ 1,497 $ 623 $ 177 $ (623 ) $ 15 $ 1,689 Provision for credit losses 158 8 (20 ) — 1 147 Noninterest income 571 185 235 44 — 1,035 Noninterest expenses 778 734 305 (4 ) 14 1,827 Provision (benefit) for income taxes 371 21 43 (206 ) — 229 Net income (loss) $ 761 $ 45 $ 84 $ (369 ) $ — $ 521 Net credit-related charge-offs (recoveries) $ 89 $ 29 $ (17 ) $ — $ — $ 101 Selected average balances: Assets $ 39,501 $ 6,474 $ 5,153 $ 11,764 $ 7,355 $ 70,247 Loans 37,889 5,792 4,953 — (6 ) 48,628 Deposits 30,894 22,876 4,151 138 267 58,326 Statistical data: Return on average assets (b) 1.93 % 0.19 % 1.62 % N/M N/M 0.74 % Efficiency ratio (c) 37.59 90.64 73.68 N/M N/M 66.93 (a) Included a $107 million charge to adjust deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act and a $35 million tax benefit from employee stock transactions. (b) Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity. (c) Noninterest expenses as a percentage of the sum of net interest income (fully taxable equivalent basis) and noninterest income excluding net securities gains. N/M – not meaningful
Market Segment Financial Results	Market segment financial results are as follows: (dollar amounts in millions) Michigan California Texas Other Markets Finance & Other Total Year Ended December 31, 2017 Earnings summary: Net interest income (expense) $ 685 $ 719 $ 465 $ 331 $ (139 ) $ 2,061 Provision for credit losses 8 100 (72 ) 36 2 74 Noninterest income 324 171 131 423 58 1,107 Noninterest expenses 590 404 375 449 42 1,860 Provision (benefit) for income taxes 147 148 109 75 12 (a) 491 Net income (loss) $ 264 $ 238 $ 184 $ 194 $ (137 ) $ 743 Net credit-related (recoveries) charge-offs $ (1 ) $ 33 $ 46 $ 14 $ — $ 92 Selected average balances: Assets $ 13,395 $ 18,269 $ 10,443 $ 8,573 $ 20,772 $ 71,452 Loans 12,677 18,008 9,969 7,904 — 48,558 Deposits 21,823 17,533 9,625 7,874 403 57,258 Statistical data: Return on average assets (b) 1.17 % 1.29 % 1.69 % 2.25 % N/M 1.04 % Efficiency ratio (c) 58.30 45.26 62.80 59.57 N/M 58.57 (Table continues on following page) (dollar amounts in millions) Michigan California Texas Other Markets Finance & Other Total Year Ended December 31, 2016 Earnings summary: Net interest income (expense) $ 666 $ 716 $ 470 $ 350 $ (405 ) $ 1,797 Provision for credit losses 9 21 225 (7 ) — 248 Noninterest income 320 162 129 393 47 1,051 Noninterest expenses 620 434 408 445 23 1,930 Provision (benefit) for income taxes 114 152 (12 ) 81 (142 ) 193 Net income (loss) $ 243 $ 271 $ (22 ) $ 224 $ (239 ) $ 477 Net credit-related charge-offs $ 9 $ 26 $ 118 $ 4 $ — $ 157 Selected average balances: Assets $ 13,105 $ 18,012 $ 11,101 $ 9,062 $ 20,463 $ 71,743 Loans 12,457 17,731 10,637 8,171 — 48,996 Deposits 21,777 17,438 10,168 8,005 353 57,741 Statistical data: Return on average assets (b) 1.08 % 1.46 % (0.18 )% 2.47 % N/M 0.67 % Efficiency ratio (c) 62.33 49.55 67.94 59.86 N/M 67.53 (dollar amounts in millions) Michigan California Texas Other Markets Finance & Other Total Year Ended December 31, 2015 Earnings summary: Net interest income (expense) $ 708 $ 735 $ 518 $ 336 $ (608 ) $ 1,689 Provision for credit losses (27 ) 17 131 25 1 147 Noninterest income 329 150 131 381 44 1,035 Noninterest expenses 594 405 387 431 10 1,827 Provision (benefit) for income taxes 151 166 54 64 (206 ) 229 Net income (loss) $ 319 $ 297 $ 77 $ 197 $ (369 ) $ 521 Net credit-related charge-offs $ 8 $ 18 $ 46 $ 29 $ — $ 101 Selected average balances: Assets $ 13,598 $ 17,044 $ 11,778 $ 8,708 $ 19,119 $ 70,247 Loans 13,016 16,778 11,168 7,673 (7 ) 48,628 Deposits 21,848 17,788 10,882 7,403 405 58,326 Statistical data: Return on average assets (b) 1.40 % 1.57 % 0.62 % 2.26 % N/M 0.74 % Efficiency ratio (c) 56.93 45.88 59.63 59.92 N/M 66.93 (a) Included a $107 million charge to adjust deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act and a $35 million tax benefit from employee stock transactions. (b) Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity. (c) Noninterest expenses as a percentage of the sum of net interest income (fully taxable equivalent basis) and noninterest income excluding net securities gains. N/M – not meaningful

Parent Company FInancial Stat54

Parent Company FInancial Statements Parent Company Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Balance Sheets - Comerica Incorporated	BALANCE SHEETS - COMERICA INCORPORATED (in millions, except share data) December 31 2017 2016 Assets Cash and due from subsidiary bank $ 1,059 $ 761 Other short-term investments 92 87 Investment in subsidiaries, principally banks 7,467 7,561 Premises and equipment 2 2 Other assets 127 150 Total assets $ 8,747 $ 8,561 Liabilities and Shareholders’ Equity Medium- and long-term debt $ 602 $ 604 Other liabilities 182 161 Total liabilities 784 765 Common stock - $5 par value: Authorized - 325,000,000 shares Issued - 228,164,824 shares 1,141 1,141 Capital surplus 2,122 2,135 Accumulated other comprehensive loss (451 ) (383 ) Retained earnings 7,887 7,331 Less cost of common stock in treasury - 55,306,483 shares at 12/31/17 and 52,851,156 shares at 12/31/16 (2,736 ) (2,428 ) Total shareholders’ equity 7,963 7,796 Total liabilities and shareholders’ equity $ 8,747 $ 8,561
Statements of Income - Comerica Incorporated	STATEMENTS OF INCOME - COMERICA INCORPORATED (in millions) Years Ended December 31 2017 2016 2015 Income Income from subsidiaries: Dividends from subsidiaries $ 915 $ 549 $ 441 Other interest income 3 1 1 Intercompany management fees 136 138 123 Other noninterest income 8 3 1 Total income 1,062 691 566 Expenses Interest on medium- and long-term debt 13 10 14 Salaries and benefits expense 127 114 112 Net occupancy expense 5 5 5 Equipment expense 1 1 1 Restructuring charges 6 33 — Other noninterest expenses 80 72 70 Total expenses 232 235 202 Income before benefit for income taxes and equity in undistributed earnings of subsidiaries 830 456 364 Benefit for income taxes (26 ) (28 ) (27 ) Income before equity in undistributed earnings of subsidiaries 856 484 391 Equity in undistributed earnings of subsidiaries, principally banks (113 ) (7 ) 130 Net income 743 477 521 Less income allocated to participating securities 5 4 6 Net income attributable to common shares $ 738 $ 473 $ 515
Statements of Cash Flows - Comerica Incorporated	STATEMENTS OF CASH FLOWS - COMERICA INCORPORATED (in millions) Years Ended December 31 2017 2016 2015 Operating Activities Net income $ 743 $ 477 $ 521 Adjustments to reconcile net income to net cash provided by operating activities: Undistributed earnings of subsidiaries, principally banks 113 7 (130 ) Depreciation and amortization 1 1 1 Net periodic defined benefit (credit) cost (2 ) 1 5 Share-based compensation expense 16 14 14 Benefit for deferred income taxes (10 ) (3 ) — Other, net 59 6 5 Net cash provided by operating activities 920 503 416 Investing Activities Net change in premises and equipment — — (1 ) Net cash used in investing activities — — (1 ) Financing Activities Medium- and long-term debt: Maturities and redemptions — — (600 ) Common Stock: Repurchases (552 ) (315 ) (240 ) Cash dividends paid (180 ) (152 ) (147 ) Issuances of common stock under employee stock plans 110 152 22 Purchase and retirement of warrants — — (10 ) Net cash used in financing activities (622 ) (315 ) (975 ) Net increase (decrease) in cash and cash equivalents 298 188 (560 ) Cash and cash equivalents at beginning of period 761 573 1,133 Cash and cash equivalents at end of period $ 1,059 $ 761 $ 573 Interest paid $ 12 $ 9 $ 16 Income taxes recovered $ (331 ) $ (139 ) $ (62 )

Summary of Quarterly Financia55

Summary of Quarterly Financial Statements (Unaudited) Summary of Quarterly Financial Statements (Unaudited ) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Statements	The following quarterly information is unaudited. However, in the opinion of management, the information reflects all adjustments, which are necessary for the fair presentation of the results of operations, for the periods presented. 2017 (in millions, except per share data) Fourth Quarter Third Quarter Second Quarter First Quarter Interest income $ 578 $ 579 $ 529 $ 496 Interest expense 33 33 29 26 Net interest income 545 546 500 470 Provision for credit losses 17 24 17 16 Net securities losses — (1 ) (2 ) — Noninterest income excluding net securities losses 285 276 278 271 Noninterest expenses 483 463 457 457 Provision for income taxes 218 108 99 66 Net income 112 226 203 202 Less income allocated to participating securities — 2 1 2 Net income attributable to common shares $ 112 $ 224 $ 202 $ 200 Earnings per common share: Basic $ 0.65 $ 1.29 $ 1.15 $ 1.15 Diluted 0.63 1.26 1.13 1.11 Comprehensive income 107 228 221 206 2016 (in millions, except per share data) Fourth Quarter Third Quarter Second Quarter First Quarter Interest income $ 484 $ 480 $ 473 $ 472 Interest expense 29 30 28 25 Net interest income 455 450 445 447 Provision for credit losses 35 16 49 148 Net securities losses (2 ) — (1 ) (2 ) Noninterest income excluding net securities losses 269 272 269 246 Noninterest expenses 461 493 518 458 Provision for income taxes 62 64 42 25 Net income 164 149 104 60 Less income allocated to participating securities 1 1 1 1 Net income attributable to common shares $ 163 $ 148 $ 103 $ 59 Earnings per common share: Basic $ 0.95 $ 0.87 $ 0.60 $ 0.34 Diluted 0.92 0.84 0.58 0.34 Comprehensive income 73 152 137 161

Basis of Presentation and Acc56

Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Narrative) (Details) $ in Millions		12 Months Ended
		Dec. 31, 2017USD ($)markets	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jan. 01, 2018USD ($)	Dec. 31, 2014USD ($)
Number of Primary Geographic Markets | markets		3
Derivative assets		$ 192	$ 407
Commitments to fund additional investments in nonmarketable equity securities		1
Federal Home Loan Bank Stock		122	122
Federal Reserve Bank Stock		85	85
Net Deferred Income on Originated Loans		113	147
Allowance for Credit Losses, Threshold for Individual Evaluation, Nonaccrual Loans		$ 2
Delinquency Status, Period of Unpaid Scheduled Monthly Payment		30 days
Number of Reporting Units		3
Notional Amount	[1]	$ 20,545	20,051
Defined Benefit Plan Market-related Value Plan Assets, Amortization Period		5 years
Defined Benefit Plan Investment Gain Loss Amortization Adjustment, Allowable Percentage		10.00%
Defined Benefit Plan Actuarial Gain Loss Amortization Adjustment, Allowable Percentage		10.00%
Remeasurement of the Corporation's Deferred Tax Balance		$ (107)	0	$ 0
Reclassification of the effect of remeasuring deferred tax balances related to items within accumulated other comprehensive income to retained earnings		0
Network costs to be presented net of card fee revenue		333	303	276
Net decreases to noninterest income due to adjustments to other revenue streams		111	102	102
Net decreases to noninterest expense due to adjustments to other revenue streams		135	135	160
Cumulative effect of changes to retained earnings as a result of adoption of ASU		7,963	7,796	7,560		$ 7,402
Ineffectiveness net gain		$ 1	(2)
Premises the Corporation owns | Minimum
Premises and Equipment, Useful Life		3 years
Premises the Corporation owns | Maximum
Premises and Equipment, Useful Life		33 years
Furniture and equipment | Minimum
Premises and Equipment, Useful Life		3 years
Furniture and equipment | Maximum
Premises and Equipment, Useful Life		8 years
Leasehold improvements | Maximum
Premises and Equipment, Useful Life		10 years
Software
Premises and Equipment, Useful Life		5 years
Recurring
Derivative assets		$ 194	410
Carrying Amount
Nonmarketable equity securities	[2]	$ 6	11
Retail loans | Real estate mortgage
Past Due Period Residential Mortgage And Home Equity Loans Placed On Nonaccrual Status		90 days
Past Due Threshold For Charge-Off		180 days
Warrants | Recurring
Derivative assets		$ 2	3
Short-Cut Method | Designated as Hedging Instrument | Interest Rate Swaps | Fair Value Hedging
Notional Amount		$ 150
Commercial borrower | Business loans
Past Due Period Business Loans Placed On Nonaccrual Status		90 days
Consumer borrower | Retail loans | Home equity
Maximum Past Due Status Junior Lien Home Equity Placed On Nonaccrual Status		90 days
Consumer borrower | Retail loans | Other consumer
Past Due Threshold For Charge-Off		120 days
Threshold, Days Past Due, Other Consumer Placed On Nonaccrual Status		90 days
Accounting Standards Update 2016-09
Net excess tax benefit and cash paid to tax authority reclassified to operating activities from financing activities			9	3
Accounting Standards Update 2018-01
Reclassification of the effect of remeasuring deferred tax balances related to items within accumulated other comprehensive income to retained earnings		$ 87
Accounting Standards Update 2014-09
Network costs to be presented net of card fee revenue		115
Net decreases to noninterest income due to adjustments to other revenue streams		5
Net decreases to noninterest expense due to adjustments to other revenue streams		5
Treasury management fee receivable		17
Cumulative effect of changes to retained earnings as a result of adoption of ASU		2
Accounting Standards Update 2016-01
Auction-rate securities reclassified as available for sale equity securities		82
Cumulative net unrealized loss recognized in AOCI reclassified to retained earnings		(1)
Accounting Standards Update 2016-15
Proceeds from settlements of bank owned life insurance policies		18	16
Accounting Standards Update 2017-07
Other components of net benefit cost to be reclassified		50	28
Accounting Standards Update 2017-12
Ineffectiveness net gain		1	2
Retained Earnings
Cumulative effect of changes to retained earnings as a result of adoption of ASU		7,887	$ 7,331	$ 7,084		$ 6,744
Retained Earnings | Accounting Standards Update 2018-01
Reclassification of the effect of remeasuring deferred tax balances related to items within accumulated other comprehensive income to retained earnings		$ 87
Adoption effective January 1, 2018 | Retained Earnings | Accounting Standards Update 2017-12
Cumulative effect of changes to retained earnings as a result of adoption of ASU					$ 1
[1]	Notional or contractual amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets.
[2]	Certain investments that are measured at fair value using the net asset value have not been classified in the fair value hierarchy. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets.

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Recurring
Transfers into or out of Level 1 or Level 2 or Level 3	$ 0	$ 0
Total liabilities at fair value	282	341
Nonrecurring
Total liabilities at fair value	$ 0	$ 0

Fair Value Measurements (Assets

Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale	[1]	$ 10,938	$ 10,787
Derivative assets		192	407
Derivative liabilities	[2]	102	125
Equity and other non-debt securities
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		82	129
U.S. Treasury and other U.S. government agency securities
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		2,727	2,779
Residential mortgage-backed securities
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale	[3]	8,124	7,872
Recurring
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities			88
Investment securities available-for-sale		10,938	10,787
Derivative assets		194	410
Total assets at fair value		11,224	11,285
Derivative liabilities		190	254
Deferred compensation plan liabilities		92	87
Total liabilities at fair value		282	341
Recurring | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities			88
Investment securities available-for-sale		2,765	2,861
Derivative assets		0	0
Total assets at fair value		2,857	2,949
Derivative liabilities		0	0
Deferred compensation plan liabilities		92	87
Total liabilities at fair value		92	87
Recurring | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities			0
Investment securities available-for-sale		8,124	7,872
Derivative assets		178	396
Total assets at fair value		8,302	8,268
Derivative liabilities		190	254
Deferred compensation plan liabilities		0	0
Total liabilities at fair value		190	254
Recurring | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities			0
Investment securities available-for-sale		49	54
Derivative assets		16	14
Total assets at fair value		65	68
Derivative liabilities		0	0
Deferred compensation plan liabilities		0	0
Total liabilities at fair value		0	0
Recurring | Interest rate contracts
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		57	223
Derivative liabilities		59	81
Recurring | Interest rate contracts | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Recurring | Interest rate contracts | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		43	212
Derivative liabilities		59	81
Recurring | Interest rate contracts | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		14	11
Derivative liabilities		0	0
Recurring | Energy derivative contracts
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		93	146
Derivative liabilities		91	144
Recurring | Energy derivative contracts | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Recurring | Energy derivative contracts | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		93	146
Derivative liabilities		91	144
Recurring | Energy derivative contracts | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Recurring | Foreign exchange contracts
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		42	38
Derivative liabilities		40	29
Recurring | Foreign exchange contracts | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Recurring | Foreign exchange contracts | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		42	38
Derivative liabilities		40	29
Recurring | Foreign exchange contracts | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Recurring | Warrants
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		2	3
Recurring | Warrants | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		0	0
Recurring | Warrants | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		0	0
Recurring | Warrants | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets		2	3
Recurring | Deferred compensation plan assets
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities		92	87
Recurring | Deferred compensation plan assets | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities		92	87
Recurring | Deferred compensation plan assets | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities		0	0
Recurring | Deferred compensation plan assets | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities		0	0
Recurring | Equity and other non-debt securities
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities			1
Investment securities available-for-sale		82	129
Recurring | Equity and other non-debt securities | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities			1
Investment securities available-for-sale		38	82
Recurring | Equity and other non-debt securities | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities			0
Investment securities available-for-sale		0	0
Recurring | Equity and other non-debt securities | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Trading securities			0
Investment securities available-for-sale	[4]	44	47
Recurring | U.S. Treasury and other U.S. government agency securities
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		2,727	2,779
Recurring | U.S. Treasury and other U.S. government agency securities | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		2,727	2,779
Recurring | U.S. Treasury and other U.S. government agency securities | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		0	0
Recurring | U.S. Treasury and other U.S. government agency securities | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		0	0
Recurring | Residential mortgage-backed securities
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale	[5]	8,124	7,872
Recurring | Residential mortgage-backed securities | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale	[5]	0	0
Recurring | Residential mortgage-backed securities | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale	[5]	8,124	7,872
Recurring | Residential mortgage-backed securities | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale	[5]	0	0
Recurring | State and municipal securities
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		5	7
Recurring | State and municipal securities | Level 1
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		0	0
Recurring | State and municipal securities | Level 2
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale		0	0
Recurring | State and municipal securities | Level 3
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Investment securities available-for-sale	[4]	$ 5	$ 7
[1]	Included auction-rate securities at amortized cost and fair value of $51 million and $49 million, respectively, as of December 31, 2017 and $55 million and $54 million, respectively, as of December 31, 2016.
[2]	Net derivative assets are included in “accrued income and other assets” and net derivative liabilities are included in “accrued expenses and other liabilities” on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and credit risk of the Corporation. The fair value of net derivative assets included credit valuation adjustments for counterparty credit risk of $4 million and $5 million at December 31, 2017 and 2016, respectively.
[3]	Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.
[4]	Auction-rate securities.
[5]	Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.

Fair Value Measurements (Change

Fair Value Measurements (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Interest rate contracts
Balance at beginning of period		$ 11	$ 9
Realized gains (losses) recorded in earnings		0	0
Unrealized gains (losses) recorded in earnings	[1]	3	2
Gains (losses) recorded in other comprehensive income (loss)		0	0
Redemptions		0	0
Sales		0	0
Balance at end of period		14	11
Warrants
Balance at beginning of period		3	2
Realized gains (losses) recorded in earnings	[1]	6	6
Unrealized gains (losses) recorded in earnings	[1]	(1)	1
Gains (losses) recorded in other comprehensive income (loss)		0	0
Redemptions		0	0
Sales		(6)	(6)
Balance at end of period		2	3
Investment securities available-for-sale
Balance at beginning of period		54	77
Realized gains (losses) recorded in earnings		0	0
Unrealized gains (losses) recorded in earnings		0	0
Gains (losses) recorded in other comprehensive income (loss)	[2]	(2)	(1)
Redemptions		(3)	(22)
Sales		0	0
Balance at end of period		49	54
State and municipal securities | Investment securities available-for-sale
Balance at beginning of period	[3]	7	9
Realized gains (losses) recorded in earnings	[3]	0	0
Unrealized gains (losses) recorded in earnings	[3]	0	0
Gains (losses) recorded in other comprehensive income (loss)	[3]	0	0
Redemptions	[3]	(2)	(2)
Sales	[3]	0	0
Balance at end of period	[3]	5	7
Corporate debt securities | Investment securities available-for-sale
Balance at beginning of period	[3]	0	1
Realized gains (losses) recorded in earnings	[3]		0
Unrealized gains (losses) recorded in earnings	[3]		0
Gains (losses) recorded in other comprehensive income (loss)	[3]		0
Redemptions	[3]		1
Sales	[3]		0
Balance at end of period	[3]		0
Equity and other non-debt securities | Investment securities available-for-sale
Balance at beginning of period	[3]	47	67
Realized gains (losses) recorded in earnings	[3]	0	0
Unrealized gains (losses) recorded in earnings	[3]	0	0
Gains (losses) recorded in other comprehensive income (loss)	[2],[3]	(2)	(1)
Redemptions	[3]	(1)	(19)
Sales	[3]	0	0
Balance at end of period	[3]	$ 44	$ 47
[1]	Realized and unrealized gains and losses due to changes in fair value recorded in "other noninterest income" on the consolidated statements of income.
[2]	Recorded in "net unrealized holding losses arising during the period" in other comprehensive income (loss).
[3]	Auction-rate securities.

Fair Value Measurements (Asse60

Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Nonrecurring Basis) (Details) - Nonrecurring - Level 3 - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Line Items]
Loans		$ 282
Other real estate		1
Total assets at fair value	$ 116	283
Commercial borrower | Domestic loans
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Line Items]
Loans	111	256
Commercial borrower | International loans
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Line Items]
Loans		11
Commercial borrower | Commercial mortgage loans | Domestic loans
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Line Items]
Loans	$ 5	$ 15

Fair Value Measurements (Estima

Fair Value Measurements (Estimated Fair Values Of Financial Instruments Not Recorded At Fair Value In Their Entirety On A Recurring Basis) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Cash and due from banks		$ 1,438	$ 1,249
Interest-bearing deposits with banks		4,407	5,969
Investment securities held-to-maturity		1,266	1,582
Total loans, net of allowance for loan losses		48,461	48,358
Demand deposits (noninterest-bearing)		32,071	31,540
Customer certificates of deposit		2,165	2,806
Total deposits		57,903	58,985
Short-term borrowings		10	25
Medium- and long-term debt		4,622	5,160
Carrying Amount
Cash and due from banks		1,438	1,249
Interest-bearing deposits with banks		4,407	5,969
Investment securities held-to-maturity		1,266	1,582
Loans held-for-sale		4	4
Total loans, net of allowance for loan losses	[1]	48,461	48,358
Customers' liability on acceptances outstanding		2	5
Restricted equity investments		207	207
Nonmarketable equity securities	[2]	6	11
Demand deposits (noninterest-bearing)		32,071	31,540
Interest-bearing deposits		23,667	24,639
Customer certificates of deposit		2,165	2,806
Total deposits		57,903	58,985
Short-term borrowings		10	25
Acceptances outstanding		2	5
Medium- and long-term debt		4,622	5,160
Credit-related financial instruments		(67)	(73)
Estimated Fair Value
Cash and due from banks		1,438	1,249
Interest-bearing deposits with banks		4,407	5,969
Investment securities held-to-maturity		1,246	1,576
Loans held-for-sale		4	4
Total loans, net of allowance for loan losses	[1]	48,153	48,250
Customers' liability on acceptances outstanding		2	5
Restricted equity investments		207	207
Nonmarketable equity securities	[2]	9	16
Demand deposits (noninterest-bearing)		32,071	31,540
Interest-bearing deposits		23,667	24,639
Customer certificates of deposit		2,142	2,731
Total deposits		57,880	58,910
Short-term borrowings		10	25
Acceptances outstanding		2	5
Medium- and long-term debt		4,636	5,132
Credit-related financial instruments		(67)	(73)
Level 1 | Estimated Fair Value
Cash and due from banks		1,438	1,249
Interest-bearing deposits with banks		4,407	5,969
Investment securities held-to-maturity		0	0
Loans held-for-sale		0	0
Total loans, net of allowance for loan losses	[1]	0	0
Customers' liability on acceptances outstanding		2	5
Restricted equity investments		207	207
Demand deposits (noninterest-bearing)		0	0
Interest-bearing deposits		0	0
Customer certificates of deposit		0	0
Total deposits		0	0
Short-term borrowings		10	25
Acceptances outstanding		2	5
Medium- and long-term debt		0	0
Credit-related financial instruments		0	0
Level 2 | Estimated Fair Value
Cash and due from banks		0	0
Interest-bearing deposits with banks		0	0
Investment securities held-to-maturity		1,246	1,576
Loans held-for-sale		4	4
Total loans, net of allowance for loan losses	[1]	0	0
Customers' liability on acceptances outstanding		0	0
Restricted equity investments		0	0
Demand deposits (noninterest-bearing)		32,071	31,540
Interest-bearing deposits		23,667	24,639
Customer certificates of deposit		2,142	2,731
Total deposits		57,880	58,910
Short-term borrowings		0	0
Acceptances outstanding		0	0
Medium- and long-term debt		4,636	5,132
Credit-related financial instruments		0	0
Level 3 | Estimated Fair Value
Cash and due from banks		0	0
Interest-bearing deposits with banks		0	0
Investment securities held-to-maturity		0	0
Loans held-for-sale		0	0
Total loans, net of allowance for loan losses	[1]	48,153	48,250
Customers' liability on acceptances outstanding		0	0
Restricted equity investments		0	0
Demand deposits (noninterest-bearing)		0	0
Interest-bearing deposits		0	0
Customer certificates of deposit		0	0
Total deposits		0	0
Short-term borrowings		0	0
Acceptances outstanding		0	0
Medium- and long-term debt		0	0
Credit-related financial instruments		(67)	(73)
Nonrecurring
Total loans, net of allowance for loan losses		$ 116	$ 282
[1]	Included $116 million and $282 million of impaired loans recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016, respectively.
[2]	Certain investments that are measured at fair value using the net asset value have not been classified in the fair value hierarchy. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets.

Investment Securities (Narrativ

Investment Securities (Narrative) (Details) $ in Millions		Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Securities with no credit impairment in unrealized loss position		354
Investment securities available-for-sale, Amortized Cost	[1]	$ 11,061	$ 10,829
Investment securities available-for-sale, Fair Value	[1]	10,938	10,787
Investment securities held-to-maturity, Amortized Cost		1,266	1,582
Investment securities held-to-maturity, Fair Value		1,246
Carrying value of securities pledged		800
Liabilities secured by pledged collateral		$ 500
U.S. Treasury and other U.S. government agency securities
Securities with no credit impairment in unrealized loss position		29
Investment securities available-for-sale, Amortized Cost		$ 2,743	2,772
Investment securities available-for-sale, Fair Value		$ 2,727	2,779
Residential mortgage-backed securities
Securities with no credit impairment in unrealized loss position		284
Investment securities available-for-sale, Amortized Cost	[2]	$ 8,230	7,921
Investment securities available-for-sale, Fair Value	[2]	8,124	7,872
Investment securities held-to-maturity, Amortized Cost	[2],[3]	1,266	1,582
Investment securities held-to-maturity, Fair Value	[2],[3]	$ 1,246	$ 1,576
Auction-rate state and municipal securities
Securities with no credit impairment in unrealized loss position		13
Auction-rate preferred securities
Securities with no credit impairment in unrealized loss position		28
Prepayment options | Residential mortgage-backed securities
Investment securities available-for-sale, Fair Value		$ 8,100
Investment securities held-to-maturity, Fair Value		$ 1,200
[1]	Included auction-rate securities at amortized cost and fair value of $51 million and $49 million, respectively, as of December 31, 2017 and $55 million and $54 million, respectively, as of December 31, 2016.
[2]	Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.
[3]	The amortized cost of investment securities held-to-maturity included the unamortized balance of net unrealized losses as of the transfer date of $9 million and $12 million at December 31, 2017 and 2016, respectively, related to securities transferred from available-for-sale, which is included in accumulated other comprehensive loss.

Investment Securities (Summary

Investment Securities (Summary Of Investment Securities Available-For-Sale) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Investment securities available-for-sale, Amortized Cost	[1]	$ 11,061	$ 10,829
Investment securities available-for-sale, Gross Unrealized Gains	[1]	23	57
Investment securities available-for-sale, Gross Unrealized Losses	[1]	146	99
Investment securities available-for-sale, Fair Value	[1]	10,938	10,787
Investment securities held-to-maturity, Amortized Cost		1,266	1,582
Investment securities held-to-maturity, Fair Value		1,246
Unrealized losses on available-for-sale securities transferred to held-to-maturity		9	12
U.S. Treasury and other U.S. government agency securities
Investment securities available-for-sale, Amortized Cost		2,743	2,772
Investment securities available-for-sale, Gross Unrealized Gains		0	8
Investment securities available-for-sale, Gross Unrealized Losses		16	1
Investment securities available-for-sale, Fair Value		2,727	2,779
Residential mortgage-backed securities
Investment securities available-for-sale, Amortized Cost	[2]	8,230	7,921
Investment securities available-for-sale, Gross Unrealized Gains	[2]	22	48
Investment securities available-for-sale, Gross Unrealized Losses	[2]	128	97
Investment securities available-for-sale, Fair Value	[2]	8,124	7,872
Investment securities held-to-maturity, Amortized Cost	[2],[3]	1,266	1,582
Investment securities held-to-maturity, Gross Unrealized Gains	[2],[3]	0	1
Investment securities held-to-maturity, Gross Unrealized Losses	[2],[3]	20	7
Investment securities held-to-maturity, Fair Value	[2],[3]	1,246	1,576
State and municipal securities
Investment securities available-for-sale, Amortized Cost		5	7
Investment securities available-for-sale, Gross Unrealized Gains		0	0
Investment securities available-for-sale, Gross Unrealized Losses		0	0
Investment securities available-for-sale, Fair Value		5	7
Equity and other non-debt securities
Investment securities available-for-sale, Amortized Cost		83	129
Investment securities available-for-sale, Gross Unrealized Gains		1	1
Investment securities available-for-sale, Gross Unrealized Losses		2	1
Investment securities available-for-sale, Fair Value		82	129
Investment securities held-to-maturity, Amortized Cost		0
Investment securities held-to-maturity, Fair Value		0
Auction-rate securities
Investment securities available-for-sale, Amortized Cost		51	55
Investment securities available-for-sale, Fair Value		$ 49	$ 54
[1]	Included auction-rate securities at amortized cost and fair value of $51 million and $49 million, respectively, as of December 31, 2017 and $55 million and $54 million, respectively, as of December 31, 2016.
[2]	Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.
[3]	The amortized cost of investment securities held-to-maturity included the unamortized balance of net unrealized losses as of the transfer date of $9 million and $12 million at December 31, 2017 and 2016, respectively, related to securities transferred from available-for-sale, which is included in accumulated other comprehensive loss.

Investment Securities (Summar64

Investment Securities (Summary Of Investment Securities Available-For-Sale In Unrealized Loss Positions) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Temporarily Impaired Less than 12 Months, Fair Value		$ 6,572	$ 5,555
Temporarily Impaired, Less than 12 Months, Unrealized Losses		48	88
Temporarily Impaired 12 Months or more, Fair Value		4,052	1,195
Temporarily Impaired, 12 Months or more, Unrealized Losses		127	32
Temporarily Impaired Total, Fair Value		10,624	6,750
Temporarily Impaired Total, Unrealized Losses		175	120
U.S. Treasury and other U.S. government agency securities
Temporarily Impaired Less than 12 Months, Fair Value		2,727	527
Temporarily Impaired, Less than 12 Months, Unrealized Losses		16	1
Temporarily Impaired 12 Months or more, Fair Value		0	0
Temporarily Impaired, 12 Months or more, Unrealized Losses		0	0
Temporarily Impaired Total, Fair Value		2,727	527
Temporarily Impaired Total, Unrealized Losses		16	1
Residential mortgage-backed securities
Temporarily Impaired Less than 12 Months, Fair Value	[1]	3,845	4,992
Temporarily Impaired, Less than 12 Months, Unrealized Losses	[1]	32	87
Temporarily Impaired 12 Months or more, Fair Value	[1]	4,003	1,177
Temporarily Impaired, 12 Months or more, Unrealized Losses	[1]	125	32
Temporarily Impaired Total, Fair Value	[1]	7,848	6,169
Temporarily Impaired Total, Unrealized Losses	[1]	157	119
State and municipal securities
Temporarily Impaired Less than 12 Months, Fair Value	[2]	0	0
Temporarily Impaired, Less than 12 Months, Unrealized Losses	[2]	0	0
Temporarily Impaired 12 Months or more, Fair Value	[2]	5	7
Temporarily Impaired, 12 Months or more, Unrealized Losses	[2],[3]	0	0
Temporarily Impaired Total, Fair Value	[2]	5	7
Temporarily Impaired Total, Unrealized Losses	[2],[3]	0	0
Equity and other non-debt securities
Temporarily Impaired Less than 12 Months, Fair Value	[2]	0	36
Temporarily Impaired, Less than 12 Months, Unrealized Losses	[2]	0	0	[3]
Temporarily Impaired 12 Months or more, Fair Value	[2]	44	11
Temporarily Impaired, 12 Months or more, Unrealized Losses	[2]	2	0	[3]
Temporarily Impaired Total, Fair Value	[2]	44	47
Temporarily Impaired Total, Unrealized Losses	[2]	$ 2	$ 0	[3]
[1]	Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.
[2]	Primarily auction-rate securities.
[3]	Unrealized losses less than $0.5 million.

Investment Securities (Gains An

Investment Securities (Gains And Losses On Available-For-Sale Securities) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Securities gains										$ 2	$ 0	$ 0
Securities losses	[1]									(5)	(5)	(2)
Net securities losses		$ 0	$ (1)	$ (2)	$ 0	$ (2)	$ 0	$ (1)	$ (2)	$ (3)	$ (5)	$ (2)
[1]	Primarily charges related to a derivative contract tied to the conversion rate of Visa Class B shares.

Investment Securities (Contract

Investment Securities (Contractual Maturity Distribution Of Debt Securities) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Available-for-sale, After one year through five years, Amortized Cost		$ 2,956
Available-for-sale, After five years through ten years, Amortized Cost		1,690
Available-for-sale, After ten years, Amortized Cost		6,332
Available-for-sale, Subtotal, Amortized Cost		10,978
Available-for-sale, After one year through five years, Fair Value		2,939
Available-for-sale, After five years through ten years, Fair Value		1,697
Available-for-sale, After ten years, Fair Value		6,220
Available-for-sale, Subtotal, Fair Value		10,856
Investment securities available-for-sale, Amortized Cost	[1]	11,061	$ 10,829
Investment securities available-for-sale, Fair Value	[1]	10,938	10,787
Held-to-maturity, After one year through five years, Net Carrying Amount		0
Held-to-maturity, After five years through ten years, Net Carrying Amount		17
Held-to-maturity, After ten years, Net Carrying Amount		1,249
Investment securities held-to-maturity, Net Carrying Amount		1,266	1,582
Held-to-maturity, After one year through five years, Fair Value		0
Held-to-maturity, After five years through ten years, Fair Value		17
Held-to-maturity, After ten years, Fair Value		1,229
Investment securities held-to-maturity, Fair Value		1,246
Equity and other non-debt securities
Investment securities available-for-sale, Amortized Cost		83	129
Investment securities available-for-sale, Fair Value		82	$ 129
Investment securities held-to-maturity, Net Carrying Amount		0
Investment securities held-to-maturity, Fair Value		$ 0
[1]	Included auction-rate securities at amortized cost and fair value of $51 million and $49 million, respectively, as of December 31, 2017 and $55 million and $54 million, respectively, as of December 31, 2016.

Credit Quality And Allowance 67

Credit Quality And Allowance For Credit Losses (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Retail loans secured by residential real estate in process of foreclosure	$ 0	$ 0
Commitments to lend additional funds to TDR borrowers	$ 31	$ 24
Interest rate reductions
Days past due defined as subsequent default	90 days	90 days
Subsequent default during period	$ 0	$ 0
AB Note Restructures
Days past due defined as subsequent default	90 days	90 days
Subsequent default during period	$ 0	$ 0

Credit Quality And Allowance 68

Credit Quality And Allowance For Credit Losses (Aging Analysis Of Loans) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		$ 337	$ 148
Nonaccrual loans		402	582
Current loans		48,434	48,358
Total loans		49,173	49,088
30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		159	106
60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		143	23
90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		35	19
Real estate construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		2,961	2,869
Real estate mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		9,159	8,931
Business loans | Commercial borrower
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		314	130
Nonaccrual loans		350	511
Current loans		43,967	43,983
Total loans		44,631	44,624
Business loans | Commercial borrower | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		140	94
Business loans | Commercial borrower | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		140	17
Business loans | Commercial borrower | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		34	19
Business loans | Commercial borrower | Domestic loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		225	56
Nonaccrual loans		309	445
Current loans		30,526	30,493
Total loans		31,060	30,994
Business loans | Commercial borrower | Domestic loans | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		79	30
Business loans | Commercial borrower | Domestic loans | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		134	12
Business loans | Commercial borrower | Domestic loans | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		12	14
Business loans | Commercial borrower | International loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		13	1
Nonaccrual loans		6	14
Current loans		964	1,243
Total loans		983	1,258
Business loans | Commercial borrower | International loans | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		13	1
Business loans | Commercial borrower | International loans | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Business loans | Commercial borrower | International loans | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		7	0
Nonaccrual loans		0	0
Current loans		2,954	2,869
Total loans		2,961	2,869
Business loans | Real estate construction | Commercial borrower | Domestic loans | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		7	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[1]	3	0
Nonaccrual loans	[1]	0	0
Current loans	[1]	2,627	2,485
Total loans	[1],[2]	2,630	2,485
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[1]	3	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[1]	0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[1]	0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[3]	4	0
Nonaccrual loans	[3]	0	0
Current loans	[3]	327	384
Total loans	[3],[4]	331	384
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[3]	4	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[3]	0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[3]	0	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		69	73
Nonaccrual loans		31	46
Current loans		9,059	8,812
Total loans		9,159	8,931
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		41	63
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		6	5
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		22	5
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[1]	14	5
Nonaccrual loans	[1]	9	9
Current loans	[1]	1,808	2,004
Total loans	[1],[2]	1,831	2,018
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[1]	14	5
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[1]	0	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[1]	0	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[3]	55	68
Nonaccrual loans	[3]	22	37
Current loans	[3]	7,251	6,808
Total loans	[3],[4]	7,328	6,913
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[3]	27	58
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[3]	6	5
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing	[3]	22	5
Business loans | Lease financing | Commercial borrower | Domestic loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Nonaccrual loans		4	6
Current loans		464	566
Total loans		468	572
Business loans | Lease financing | Commercial borrower | Domestic loans | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Business loans | Lease financing | Commercial borrower | Domestic loans | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Business loans | Lease financing | Commercial borrower | Domestic loans | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Retail loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		23	18
Nonaccrual loans		52	71
Current loans		4,467	4,375
Total loans		4,542	4,464
Retail loans | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		19	12
Retail loans | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		3	6
Retail loans | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		1	0
Retail loans | Consumer borrower
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		11	8
Nonaccrual loans		21	32
Current loans		2,522	2,482
Total loans		2,554	2,522
Retail loans | Consumer borrower | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		9	5
Retail loans | Consumer borrower | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		1	3
Retail loans | Consumer borrower | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		1	0
Retail loans | Real estate mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		12	10
Nonaccrual loans		31	39
Current loans		1,945	1,893
Total loans		1,988	1,942
Retail loans | Real estate mortgage | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		10	7
Retail loans | Real estate mortgage | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		2	3
Retail loans | Real estate mortgage | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Retail loans | Home equity | Consumer borrower
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		6	7
Nonaccrual loans		21	28
Current loans		1,789	1,765
Total loans		1,816	1,800
Retail loans | Home equity | Consumer borrower | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		5	4
Retail loans | Home equity | Consumer borrower | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		1	3
Retail loans | Home equity | Consumer borrower | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Retail loans | Other consumer | Consumer borrower
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		5	1
Nonaccrual loans		0	4
Current loans		733	717
Total loans		738	722
Retail loans | Other consumer | Consumer borrower | 30 to 59 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		4	1
Retail loans | Other consumer | Consumer borrower | 60 to 89 days past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		0	0
Retail loans | Other consumer | Consumer borrower | 90 days or more past due and still accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans past due and still accruing		$ 1	$ 0
[1]	Primarily loans to real estate developers.
[2]	Primarily loans to real estate developers.
[3]	Primarily loans secured by owner-occupied real estate.
[4]	Primarily loans secured by owner-occupied real estate.

Credit Quality And Allowance 69

Credit Quality And Allowance For Credit Losses (Loans By Credit Quality Indicator) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans		$ 49,173	$ 49,088
Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	46,942	46,232
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	768	1,109
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	1,061	1,165
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	402	582
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Total loans		2,961	2,869
Real estate mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans		9,159	8,931
Business loans | Commercial borrower
Financing Receivable, Recorded Investment [Line Items]
Total loans		44,631	44,624
Business loans | Commercial borrower | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	42,464	41,847
Business loans | Commercial borrower | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	764	1,105
Business loans | Commercial borrower | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	1,053	1,161
Business loans | Commercial borrower | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	350	511
Business loans | Commercial borrower | Domestic loans
Financing Receivable, Recorded Investment [Line Items]
Total loans		31,060	30,994
Business loans | Commercial borrower | Domestic loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	29,263	28,616
Business loans | Commercial borrower | Domestic loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	591	944
Business loans | Commercial borrower | Domestic loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	897	989
Business loans | Commercial borrower | Domestic loans | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	309	445
Business loans | Commercial borrower | International loans
Financing Receivable, Recorded Investment [Line Items]
Total loans		983	1,258
Business loans | Commercial borrower | International loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	946	1,200
Business loans | Commercial borrower | International loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	11	22
Business loans | Commercial borrower | International loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	20	22
Business loans | Commercial borrower | International loans | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	6	14
Business loans | Real estate construction | Commercial borrower | Domestic loans
Financing Receivable, Recorded Investment [Line Items]
Total loans		2,961	2,869
Business loans | Real estate construction | Commercial borrower | Domestic loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	2,957	2,866
Business loans | Real estate construction | Commercial borrower | Domestic loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	4	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	0	3
Business loans | Real estate construction | Commercial borrower | Domestic loans | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Recorded Investment [Line Items]
Total loans	[5],[6]	2,630	2,485
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1],[6]	2,630	2,485
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2],[6]	0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3],[6]	0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Commercial Real Estate business line | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4],[6]	0	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	[7],[8]	331	384
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1],[8]	327	381
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2],[8]	4	0
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3],[8]	0	3
Business loans | Real estate construction | Commercial borrower | Domestic loans | Other business lines | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4],[8]	0	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Recorded Investment [Line Items]
Total loans		9,159	8,931
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	8,858	8,615
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	135	128
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	135	142
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	31	46
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Recorded Investment [Line Items]
Total loans	[5],[6]	1,831	2,018
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1],[6]	1,759	1,970
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2],[6]	20	19
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3],[6]	43	20
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4],[6]	9	9
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	[7],[8]	7,328	6,913
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1],[8]	7,099	6,645
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2],[8]	115	109
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3],[8]	92	122
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4],[8]	22	37
Business loans | Lease financing | Commercial borrower | Domestic loans
Financing Receivable, Recorded Investment [Line Items]
Total loans		468	572
Business loans | Lease financing | Commercial borrower | Domestic loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	440	550
Business loans | Lease financing | Commercial borrower | Domestic loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	23	11
Business loans | Lease financing | Commercial borrower | Domestic loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	1	5
Business loans | Lease financing | Commercial borrower | Domestic loans | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	4	6
Retail loans
Financing Receivable, Recorded Investment [Line Items]
Total loans		4,542	4,464
Retail loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	4,478	4,385
Retail loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	4	4
Retail loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	8	4
Retail loans | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	52	71
Retail loans | Consumer borrower
Financing Receivable, Recorded Investment [Line Items]
Total loans		2,554	2,522
Retail loans | Consumer borrower | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	2,523	2,485
Retail loans | Consumer borrower | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	2	1
Retail loans | Consumer borrower | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	8	4
Retail loans | Consumer borrower | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	21	32
Retail loans | Real estate mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans		1,988	1,942
Retail loans | Real estate mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	1,955	1,900
Retail loans | Real estate mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	2	3
Retail loans | Real estate mortgage | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	0	0
Retail loans | Real estate mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	31	39
Retail loans | Home equity | Consumer borrower
Financing Receivable, Recorded Investment [Line Items]
Total loans		1,816	1,800
Retail loans | Home equity | Consumer borrower | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	1,786	1,767
Retail loans | Home equity | Consumer borrower | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	1	1
Retail loans | Home equity | Consumer borrower | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	8	4
Retail loans | Home equity | Consumer borrower | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	21	28
Retail loans | Other consumer | Consumer borrower
Financing Receivable, Recorded Investment [Line Items]
Total loans		738	722
Retail loans | Other consumer | Consumer borrower | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	[1]	737	718
Retail loans | Other consumer | Consumer borrower | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	1	0
Retail loans | Other consumer | Consumer borrower | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	[3]	0	0
Retail loans | Other consumer | Consumer borrower | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Total loans	[4]	$ 0	$ 4
[1]	Includes all loans not included in the categories of special mention, substandard or nonaccrual.
[2]	Special mention loans are accruing loans that have potential credit weaknesses that deserve management’s close attention, such as loans to borrowers who may be experiencing financial difficulties that may result in deterioration of repayment prospects from the borrower at some future date. This category is generally consistent with the "special mention" category as defined by regulatory authorities.
[3]	Substandard loans are accruing loans that have a well-defined weakness, or weaknesses, such as loans to borrowers who may be experiencing losses from operations or inadequate liquidity of a degree and duration that jeopardizes the orderly repayment of the loan. Substandard loans also are distinguished by the distinct possibility of loss in the future if these weaknesses are not corrected. This category is generally consistent with the "substandard" category as defined by regulatory authorities.
[4]	Nonaccrual loans are loans for which the accrual of interest has been discontinued. For further information regarding nonaccrual loans, refer to the Nonperforming Assets subheading in Note 1 - Basis of Presentation and Accounting Policies. A significant majority of nonaccrual loans are generally consistent with the "substandard" category and the remainder are generally consistent with the "doubtful" category as defined by regulatory authorities.
[5]	Primarily loans to real estate developers.
[6]	Primarily loans to real estate developers.
[7]	Primarily loans secured by owner-occupied real estate.
[8]	Primarily loans secured by owner-occupied real estate.

Credit Quality And Allowance 70

Credit Quality And Allowance For Credit Losses (Schedule Of Nonaccrual, Reduced-Rate Loans And Foreclosed Property) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Nonaccrual loans		$ 402	$ 582
Reduced-rate loans	[1]	8	8
Total nonperforming loans		410	590
Foreclosed property	[2]	5	17
Total nonperforming assets		415	607
Residential Real Estate
Foreclosed property		4	3
Business loans
Reduced-rate loans		0	0
Retail loans
Nonaccrual loans		52	71
Reduced-rate loans		$ 8	$ 8
[1]	There were no reduced-rate business loans at both December 31, 2017 and 2016. Reduced-rate retail loans totaled $8 million at both December 31, 2017 and 2016.
[2]	Included foreclosed residential real estate properties of $4 million and $3 million at December 31, 2017 and 2016, respectively.

Credit Quality And Allowance 71

Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Loan Losses And Related Loan Amounts) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses	$ 17	$ 24	$ 17	$ 16	$ 35	$ 16	$ 49	$ 148	$ 74	$ 248	$ 147
Total loans												$ 49,173	$ 49,088
Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				730				634	730	634	594
Loan charge-offs									(149)	(214)	(168)
Recoveries on loans previously charged-off									57	68	68
Net loan (charge-offs) recoveries									(92)	(146)	(100)
Provision for loan losses									73	241	142
Foreign currency translation adjustment									1	1	(2)
Balance at end of period	712				730				712	730	634
As a percentage of total loans												1.45%	1.49%	1.29%
Allowance for loan losses individually evaluated for impairment												$ 67	$ 89	$ 53
Allowance for loan losses collectively evaluated for impairment												645	641	581
Total allowance for loan losses	712			730	730			634	730	634	594	712	730	634
Loans individually evaluated for impairment												477	614	424
Loans collectively evaluated for impairment												48,696	48,474	48,660
Total loans												$ 49,173	$ 49,088	$ 49,084
Business loans | Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				682				579	682	579	534
Loan charge-offs									(143)	(207)	(157)
Recoveries on loans previously charged-off									50	63	55
Net loan (charge-offs) recoveries									(93)	(144)	(102)
Provision for loan losses									71	246	149
Foreign currency translation adjustment									1	1	(2)
Balance at end of period	661				682				661	682	579
As a percentage of total loans												1.48%	1.53%	1.30%
Allowance for loan losses individually evaluated for impairment												$ 67	$ 86	$ 53
Allowance for loan losses collectively evaluated for impairment												594	596	526
Total allowance for loan losses	661			682	682			579	682	579	534	661	682	579
Loans individually evaluated for impairment												443	566	393
Loans collectively evaluated for impairment												44,188	44,058	44,336
Total loans												44,631	44,624	$ 44,729
Retail loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans												$ 4,542	$ 4,464
Retail loans | Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				48				55	48	55	60
Loan charge-offs									(6)	(7)	(11)
Recoveries on loans previously charged-off									7	5	13
Net loan (charge-offs) recoveries									1	(2)	2
Provision for loan losses									2	(5)	(7)
Foreign currency translation adjustment									0	0	0
Balance at end of period	51				48				51	48	55
As a percentage of total loans												1.12%	1.08%	1.26%
Allowance for loan losses individually evaluated for impairment												$ 0	$ 3	$ 0
Allowance for loan losses collectively evaluated for impairment												51	45	55
Total allowance for loan losses	$ 51			$ 48	$ 48			$ 55	$ 48	$ 55	$ 60	51	48	55
Loans individually evaluated for impairment												34	48	31
Loans collectively evaluated for impairment												4,508	4,416	4,324
Total loans												$ 4,542	$ 4,464	$ 4,355

Credit Quality And Allowance 72

Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Credit Losses On Lending-Related Commitments) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for credit losses on lending-related commitments		$ 17	$ 24	$ 17	$ 16	$ 35	$ 16	$ 49	$ 148	$ 74	$ 248	$ 147
Lending-related commitments
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period					$ 41				$ 45	41	45	41
Charge-offs on lending related commitments	[1]									0	(11)	(1)
Provision for credit losses on lending-related commitments										1	7	5
Balance at end of period		$ 42				$ 41				$ 42	$ 41	$ 45
[1]	Charge-offs result from the sale of unfunded lending-related commitments.

Credit Quality And Allowance 73

Credit Quality And Allowance For Credit Losses (Individually Evaluated Impaired Loans) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		$ 173	$ 131
Recorded investment in impaired loans with related allowance		304	483
Recorded investment total impaired loans		477	614
Unpaid principal balance		593	738
Related allowance for loan losses		67	89
Business loans | Commercial borrower
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		147	95
Recorded investment in impaired loans with related allowance		296	471
Recorded investment total impaired loans		443	566
Unpaid principal balance		555	683
Related allowance for loan losses		67	86
Business loans | Commercial borrower | Domestic loans
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		105	90
Recorded investment in impaired loans with related allowance		267	423
Recorded investment total impaired loans		372	513
Unpaid principal balance		460	608
Related allowance for loan losses		63	80
Business loans | Commercial borrower | International loans
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		0	3
Recorded investment in impaired loans with related allowance		6	11
Recorded investment total impaired loans		6	14
Unpaid principal balance		17	20
Related allowance for loan losses		1	2
Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		42	2
Recorded investment in impaired loans with related allowance		23	37
Recorded investment total impaired loans		65	39
Unpaid principal balance		78	55
Related allowance for loan losses		3	4
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance	[1]	39	0
Recorded investment in impaired loans with related allowance	[1]	1	7
Recorded investment total impaired loans	[1]	40	7
Unpaid principal balance	[1]	49	15
Related allowance for loan losses	[1]	0	1
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance	[2]	3	2
Recorded investment in impaired loans with related allowance	[2]	22	30
Recorded investment total impaired loans	[2]	25	32
Unpaid principal balance	[2]	29	40
Related allowance for loan losses	[2]	3	3
Retail loans
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance	[3]	26	36
Recorded investment in impaired loans with related allowance	[3]	8	12
Recorded investment total impaired loans	[3]	34	48
Unpaid principal balance	[3]	38	55
Related allowance for loan losses	[3]	0	3
Retail loans | Consumer borrower
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		12	17
Recorded investment in impaired loans with related allowance		0	3
Recorded investment total impaired loans		12	20
Unpaid principal balance		16	25
Related allowance for loan losses		0	1
Retail loans | Real estate mortgage
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		14	19
Recorded investment in impaired loans with related allowance		8	9
Recorded investment total impaired loans		22	28
Unpaid principal balance		22	30
Related allowance for loan losses		0	2
Retail loans | Home equity | Consumer borrower
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		11	15
Recorded investment in impaired loans with related allowance		0	0
Recorded investment total impaired loans		11	15
Unpaid principal balance		14	19
Related allowance for loan losses		0	0
Retail loans | Other consumer | Consumer borrower
Financing Receivable, Impaired [Line Items]
Recorded investment in impaired loans with no related allowance		1	2
Recorded investment in impaired loans with related allowance		0	3
Recorded investment total impaired loans		1	5
Unpaid principal balance		2	6
Related allowance for loan losses		$ 0	$ 1
[1]	Primarily loans to real estate developers.
[2]	Primarily loans secured by owner-occupied real estate.
[3]	Individually evaluated retail loans generally have no related allowance for loan losses, primarily due to policy which results in direct write-downs of most restructured retail loans.

Credit Quality And Allowance 74

Credit Quality And Allowance For Credit Losses (Average Individually Evaluated Impaired Loans And Related Interest Recognized) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		$ 551	$ 640	$ 306
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		10	11	6
Business loans | Commercial borrower
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		511	608	267
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		10	11	6
Business loans | Commercial borrower | Domestic loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		451	550	206
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		8	10	5
Business loans | Commercial borrower | International loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		8	18	6
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		0	0	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		52	40	55
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		2	1	1
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period	[1]	21	9	16
Individually Evaluated Impaired Loans Interest Income Recognized for the Period	[1]	2	0	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period	[2]	31	31	39
Individually Evaluated Impaired Loans Interest Income Recognized for the Period	[2]	0	1	1
Retail loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		40	32	39
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		0	0	0
Retail loans | Consumer borrower
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		16	17	18
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		0	0	0
Retail loans | Real estate mortgage
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		24	15	21
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		0	0	0
Retail loans | Home equity | Consumer borrower
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		13	13	12
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		0	0	0
Retail loans | Other consumer | Consumer borrower
Financing Receivable, Impaired [Line Items]
Individually Evaluated Impaired Loans Average Balance for the Period		3	4	6
Individually Evaluated Impaired Loans Interest Income Recognized for the Period		$ 0	$ 0	$ 0
[1]	Primarily loans to real estate developers.
[2]	Primarily loans secured by owner-occupied real estate.

Credit Quality And Allowance 75

Credit Quality And Allowance For Credit Losses (Troubled Debt Restructurings By Type Of Modification) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period		$ 159	$ 201
Business loans | Commercial borrower
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period		156	196
Business loans | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period		116	188
Business loans | Commercial borrower | International loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period		0	3
Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period		40	5
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[1]	37	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[2]	3	5
Retail loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period		3	5
Retail loans | Real estate mortgage
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period		0	2
Retail loans | Home equity | Consumer borrower
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[3]	3	3
Principal Deferrals
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[4]	$ 118	$ 147
Minimum period loan terms were extended		90 days	90 days
Principal Deferrals | Business loans | Commercial borrower
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[4]	$ 117	$ 145
Principal Deferrals | Business loans | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[4]	77	140
Principal Deferrals | Business loans | Commercial borrower | International loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[4]	0	0
Principal Deferrals | Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[4]	40	5
Principal Deferrals | Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[1],[4]	37	0
Principal Deferrals | Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[2],[4]	3	5
Principal Deferrals | Retail loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[4]	1	2
Principal Deferrals | Retail loans | Real estate mortgage
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[4]	0	0	[1]
Principal Deferrals | Retail loans | Home equity | Consumer borrower
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[3],[4]	1	2
Interest Rate Reductions
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[5]	20	3
Interest Rate Reductions | Business loans | Commercial borrower
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[5]	18	0
Interest Rate Reductions | Business loans | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[5]	18	0
Interest Rate Reductions | Business loans | Commercial borrower | International loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[5]	0	0
Interest Rate Reductions | Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[5]	0	0
Interest Rate Reductions | Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[1],[5]	0	0
Interest Rate Reductions | Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[2],[5]	0	0
Interest Rate Reductions | Retail loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[5]	2	3
Interest Rate Reductions | Retail loans | Real estate mortgage
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[5]	0	2
Interest Rate Reductions | Retail loans | Home equity | Consumer borrower
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[3],[5]	2	1
AB Note Restructures
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[6]	21	51
AB Note Restructures | Business loans | Commercial borrower
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[6]	21	51
AB Note Restructures | Business loans | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[6]	21	48
AB Note Restructures | Business loans | Commercial borrower | International loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[6]	0	3
AB Note Restructures | Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[6]	0	0
AB Note Restructures | Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[1]	0	0
AB Note Restructures | Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[2],[6]	0	0
AB Note Restructures | Retail loans
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[6]	0	0
AB Note Restructures | Retail loans | Real estate mortgage
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[6]	0	0
AB Note Restructures | Retail loans | Home equity | Consumer borrower
Financing Receivable, Modifications [Line Items]
Recorded balance of troubled debt restructuring modified during the period	[3],[6]	$ 0	$ 0
[1]	Primarily loans to real estate developers.
[2]	Primarily loans secured by owner-occupied real estate.
[3]	Includes bankruptcy loans for which the court has discharged the borrower's obligation and the borrower has not reaffirmed the debt.
[4]	Primarily represents loan balances where terms were extended 90 days or more at or above contractual interest rates.
[5]	Loan restructurings whereby interest rates were either reduced or were not at market rates.
[6]	Loan restructurings whereby the original loan is restructured into two notes: an "A" note, which generally reflects the portion of the modified loan which is expected to be collected; and a "B" note, which is either fully charged off or exchanged for an equity interest.

Credit Quality And Allowance 76

Credit Quality And Allowance For Credit Losses Credit Quality And Allowance For Credit Losses (Troubled Debt Restructuring Subsequent Default) (Details) - Principal deferrals - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Balance		$ 118	$ 147
Subsequent default during period		3	14
Business loans | Commercial borrower
Financing Receivable, Modifications [Line Items]
Balance		117	145
Subsequent default during period		3	14
Business loans | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Balance		77	140
Subsequent default during period			13
Business loans | Commercial borrower | International loans
Financing Receivable, Modifications [Line Items]
Balance		0	0
Subsequent default during period		0	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans
Financing Receivable, Modifications [Line Items]
Balance		40	5
Subsequent default during period		0	1
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Commercial Real Estate business line
Financing Receivable, Modifications [Line Items]
Balance	[1]	37	0
Subsequent default during period	[1]	0	0
Business loans | Real estate mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Modifications [Line Items]
Balance	[2]	3	5
Subsequent default during period		0	1	[2]
Retail loans | Home equity | Consumer borrower
Financing Receivable, Modifications [Line Items]
Balance	[3]	1	2
Subsequent default during period		$ 0	$ 0
[1]	Primarily loans to real estate developers.
[2]	Primarily loans secured by owner-occupied real estate.
[3]	Includes bankruptcy loans for which the court has discharged the borrower's obligation and the borrower has not reaffirmed the debt.

Significant Group Concentrati77

Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Schedule of Automotive Industry Outstanding Loans and Total Exposure) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Total automotive loans	$ 8,936	$ 8,449
Total automotive exposure	11,844	11,264
Automotive Production
Concentration Risk [Line Items]
Total automotive loans	1,344	1,326
Total automotive exposure	2,439	2,534
Automotive Dealer
Concentration Risk [Line Items]
Total automotive loans	7,592	7,123
Total automotive exposure	$ 9,405	$ 8,730

Significant Group Concentrati78

Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Commercial Real Estate Exposure) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		$ 49,173	$ 49,088
Real estate construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		2,961	2,869
Commercial mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		9,159	8,931
Total commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		12,120	11,800
Total unused commitments		3,018	3,046
Commercial Real Estate business line | Real estate construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[1]	2,630	2,485
Commercial Real Estate business line | Commercial mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[1]	1,831	2,018
Other business lines | Real estate construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[2]	331	384
Other business lines | Commercial mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[2]	$ 7,328	$ 6,913
[1]	Primarily loans to real estate developers.
[2]	Primarily loans secured by owner-occupied real estate.

Premises and Equipment (Narrati

Premises and Equipment (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Rental expense for leased properties and equipment	$ 78	$ 80	$ 79

Premises and Equipment (Summary

Premises and Equipment (Summary of Premises and Equipment) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land	$ 85	$ 86
Buildings and improvements	813	831
Furniture and equipment	484	499
Total cost	1,382	1,416
Accumulated depreciation and amortization	(916)	(915)
Net book value	$ 466	$ 501

Premises and Equipment (Schedul

Premises and Equipment (Schedule of Future Minimum Lease Payments) (Details) $ in Millions	Dec. 31, 2017USD ($)
Property, Plant and Equipment [Abstract]
2,018	$ 68
2,019	61
2,020	52
2,021	43
2,022	32
Thereafter	135
Total	$ 391

Goodwill and Intangible Asset82

Goodwill and Intangible Assets Goodwill and Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Core deposit intangible
Amortization expense of core deposit intangible	$ 2	$ 2	$ 3

Goodwill and Intangible Asset83

Goodwill and Intangible Assets Goodwill and Intangible Assets (Summary of Changes in Carrying Value of Goodwill) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Balance	$ 635	$ 635
Business Bank
Goodwill [Line Items]
Balance	380	380
Retail Bank
Goodwill [Line Items]
Balance	194	194
Wealth Management
Goodwill [Line Items]
Balance	$ 61	$ 61

Goodwill and Intangible Asset84

Goodwill and Intangible Assets Goodwill and Intangible Assets (Summary of CDI Carrying Value and Amortization) (Details) - Core deposit intangible - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 34	$ 34
Accumulated amortization	(28)	(26)
Net carrying amount	$ 6	$ 8

Goodwill and Intangible Asset85

Goodwill and Intangible Assets Goodwill and Intangible Assets (Schedule of Core Deposit Intangible Estimated Future Amortization Expense (Details) - Core deposit intangible - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
2,018	$ 2
2,019	2
2,020	1
2,021	1
Total	$ 6	$ 8

Derivative And Credit-Related86

Derivative And Credit-Related Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair value of securities received as collateral for derivative assets	$ 3
Cash received as collateral for derivative assets	1
Fair value of securities pledged as collateral for derivative liabilities	25
Cash posted as collateral for derivative liabilities	40
Aggregate fair value of all derivative instruments with credit-risk contingent features that were in a liability position	0
Net interest income generated by risk management fair value interest rate swaps	32	$ 60
Net (loss) gain on interest rate fair value hedge ineffectiveness	1	(2)
Gain (loss) on foreign currency derivatives used as economic hedges	0	0
Net gain on open foreign currency positions	0	1
Allowance for credit losses on lending-related commitments	42	41
Allowance for credit losses on lending-related commitments, unused commitments to extend credit	$ 27	29
Final year of expiration for outstanding letters of credit	2,023
Risk participation agreements covering standby and commercial letters of credit	$ 127	255
Standby and commercial letters of credit outstanding	3,300	3,700
Carrying value of standby and commercial letters of credit included in accrued expenses and other liabilities	40	44
Deferred fees on standby and commercial letters of credit included in accrued expenses and other liabilities	25	32
Allowance for credit losses on lending-related commitments, amount related to standby and commercial letters of credit	15	12
Notional Amount of Derivative Credit Risk Participation Agreements	549	458
Maximum estimated exposure to credit risk participation agreements assuming 100% default	$ 0	$ 3
Weighted average remaining maturity of credit risk participation agreements, in years	2 years 6 months 18 days

Derivative And Credit-Related87

Derivative And Credit-Related Financial Instruments (Schedule Of Derivative Instruments) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	$ 20,545	$ 20,051
Fair Value of Gross Derivative Assets		192	407
Fair Value of Gross Derivative Liabilities		190	254
Derivative assets, Netting adjustment - Offsetting derivative liabilities		(49)	(84)
Derivative liabilities, Netting adjustment - Offsetting derivative assets		(49)	(84)
Derivative assets, Netting adjustment - Cash collateral received		(1)	(47)
Derivative liabilities, Netting adjustment - Cash collateral posted		(39)	(45)
Net derivative assets included in consolidated balance sheets	[2]	142	276
Net derivative liabilities included in the consolidated balance sheet	[2]	102	125
Derivative assets, securities pledged as collateral		(3)	(19)
Derivative liabilities, securities pledged as collateral		(24)	(8)
Net derivative assets after deducting amounts not offset in the consolidated balance sheets		139	257
Net derivative liabilities after deducting amounts not offset in the consolidated balance sheets		78	117
Credit valuation adjustments for counterparty credit risk		4	5
Risk management purposes
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	2,425	2,992
Fair Value of Gross Derivative Assets		0	94
Fair Value of Gross Derivative Liabilities		4	6
Risk management purposes | Derivatives designated as hedging instruments | Fair Value Hedging | Interest rate swap
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1],[3]	1,775	2,275
Fair Value of Gross Derivative Assets	[3]	0	92
Fair Value of Gross Derivative Liabilities	[3]	2	4
Risk management purposes | Derivatives used as economic hedges | Foreign exchange spot, forwards and swaps
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	650	717
Fair Value of Gross Derivative Assets		0	2
Fair Value of Gross Derivative Liabilities		2	2
Customer-initiated and other activities
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	18,120	17,059
Fair Value of Gross Derivative Assets		192	313
Fair Value of Gross Derivative Liabilities		186	248
Customer-initiated and other activities | Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	14,389	13,323
Fair Value of Gross Derivative Assets		57	131
Fair Value of Gross Derivative Liabilities		57	77
Customer-initiated and other activities | Interest rate caps and floors written
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	635	436
Fair Value of Gross Derivative Assets		0	0
Fair Value of Gross Derivative Liabilities		0	1
Customer-initiated and other activities | Interest rate caps and floors purchased
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	635	436
Fair Value of Gross Derivative Assets		0	1
Fair Value of Gross Derivative Liabilities		0	0
Customer-initiated and other activities | Interest rate swap
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1],[3]	13,119	12,451
Fair Value of Gross Derivative Assets	[3]	57	130
Fair Value of Gross Derivative Liabilities	[3]	57	76
Customer-initiated and other activities | Energy contracts
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	1,847	2,227
Fair Value of Gross Derivative Assets		93	146
Fair Value of Gross Derivative Liabilities		91	144
Customer-initiated and other activities | Energy caps and floors written
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	164	419
Fair Value of Gross Derivative Assets		0	1
Fair Value of Gross Derivative Liabilities		11	31
Customer-initiated and other activities | Energy caps and floors purchased
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	164	419
Fair Value of Gross Derivative Assets		11	31
Fair Value of Gross Derivative Liabilities		0	1
Customer-initiated and other activities | Energy swaps
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	1,519	1,389
Fair Value of Gross Derivative Assets		82	114
Fair Value of Gross Derivative Liabilities		80	112
Customer-initiated and other activities | Foreign exchange spot, options and swaps
Derivatives, Fair Value [Line Items]
Notional/Contract Amount	[1]	1,884	1,509
Fair Value of Gross Derivative Assets		42	36
Fair Value of Gross Derivative Liabilities		$ 38	$ 27
[1]	Notional or contractual amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets.
[2]	Net derivative assets are included in “accrued income and other assets” and net derivative liabilities are included in “accrued expenses and other liabilities” on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and credit risk of the Corporation. The fair value of net derivative assets included credit valuation adjustments for counterparty credit risk of $4 million and $5 million at December 31, 2017 and 2016, respectively.
[3]	Due to clearinghouse rule changes, beginning January 1, 2017, variation margin payments are treated as settlements of derivative exposure rather than as collateral. As a result, these payments are now considered in determining the fair value of centrally cleared derivatives, resulting in centrally cleared derivatives having a fair value of approximately zero.

Derivative And Credit-Related88

Derivative And Credit-Related Financial Instruments (Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Notional Amount	[1]	$ 20,545	$ 20,051
Risk management purposes
Notional Amount	[1]	2,425	2,992
Medium- and Long-term Debt | Swaps - fair value - receive fixed/pay floating | Risk management purposes | Interest rate swap
Notional Amount		$ 1,775	$ 2,275
Weighted Average Remaining Maturity		4 years 7 months 17 days	4 years 6 months 12 days
Weighted Average Receive Rate		3.26%	3.69%
Weighted Average Pay Rate	[2]	2.35%	1.80%
[1]	Notional or contractual amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets.
[2]	Variable rates paid on receive fixed swaps are based on six-month LIBOR rates in effect at December 31, 2017 and 2016.

Derivative And Credit-Related89

Derivative And Credit-Related Financial Instruments (Schedule Of Net Gains Recognized In Income On Customer-Initiated Derivatives) (Details) - Customer-initiated and other activities - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Net derivative gain recognized in income	$ 71	$ 68
Interest rate contracts | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Net derivative gain recognized in income	24	25
Energy contracts | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Net derivative gain recognized in income	2	2
Foreign exchange contracts | Foreign exchange income
Derivative Instruments, Gain (Loss) [Line Items]
Net derivative gain recognized in income	$ 45	$ 41

Derivative And Credit-Related90

Derivative And Credit-Related Financial Instruments (Schedule Of Financial Instruments With Off-Balance Sheet Credit Risk) (Details) - Maximum - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Unused Commitments to Extend Credit
Loss contingency, estimate of possible loss, maximum	$ (25,469)	$ (26,991)
Commercial And Other | Unused Commitments to Extend Credit
Loss contingency, estimate of possible loss, maximum	(22,636)	(24,333)
Bankcard, Revolving Check Credit And Home Equity Loan Commitments | Unused Commitments to Extend Credit
Loss contingency, estimate of possible loss, maximum	(2,833)	(2,658)
Standby Letters Of Credit
Loss contingency, estimate of possible loss, maximum	(3,228)	(3,623)
Commercial Letters Of Credit
Loss contingency, estimate of possible loss, maximum	$ (39)	$ (46)

Derivative And Credit-Related91

Derivative And Credit-Related Financial Instruments (Summary Of Criticized Letters Of Credit) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Total criticized standby and commercial letters of credit	$ 88	$ 135
As a percentage of total outstanding standby and commercial letters of credit	2.70%	3.70%

Deposits Deposits (Narrative) (

Deposits Deposits (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deposits [Abstract]
Domestic certificates of deposit of $250,000 or more	$ 462	$ 882
Foreign office time deposits in denominations of $250,000 or more	$ 15	$ 19

Net Income Per Common Share (Ba

Net Income Per Common Share (Basic And Diluted Net Income Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 112	$ 226	$ 203	$ 202	$ 164	$ 149	$ 104	$ 60	$ 743	$ 477	$ 521
Less income allocated to participating securities	0	2	1	2	1	1	1	1	5	4	6
Net income attributable to common shares	$ 112	$ 224	$ 202	$ 200	$ 163	$ 148	$ 103	$ 59	$ 738	$ 473	$ 515
Basic average common shares									174	172	176
Basic net income per common share	$ 0.65	$ 1.29	$ 1.15	$ 1.15	$ 0.95	$ 0.87	$ 0.60	$ 0.34	$ 4.23	$ 2.74	$ 2.93
Basic average common shares									174	172	176
Net effect of the assumed exercise of stock options									3	2	2
Net effect of the assumed exercise of warrants									1	3	3
Diluted average common shares									178	177	181
Diluted net income per common share	$ 0.63	$ 1.26	$ 1.13	$ 1.11	$ 0.92	$ 0.84	$ 0.58	$ 0.34	$ 4.14	$ 2.68	$ 2.84

Variable Interest Entities (V94

Variable Interest Entities (VIEs) (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Unfunded commitments to fund tax credit entities	$ 165
Amount of financial or other support not contractually required provided by the Corporation to VIEs	0	$ 0	$ 0
Low Income Housing Tax Credit Entities
Variable Interest Entity [Line Items]
Exposure to loss as a result of involvement with VIEs	422
Other Tax Credit Entities
Variable Interest Entity [Line Items]
Exposure to loss as a result of involvement with VIEs	$ 7

Deposits Deposits (Schedule of

Deposits Deposits (Schedule of Maturities of Certificates of Deposit and Other Deposits with a Stated Maturity) (Details) $ in Millions	Dec. 31, 2017USD ($)
Deposits [Abstract]
2,018	$ 1,855
2,019	200
2,020	66
2,021	28
2,022	16
Thereafter	15
Total	$ 2,180

Net Income Per Common Share (Sc

Net Income Per Common Share (Schedule of Average Shares Excluded From Diluted Net Income Per Common Share Computation) (Details) - Stock Options - $ / 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]
Average outstanding options	0	3.3	5.1
Minimum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Range of exercise prices	$ 0	$ 37.26	$ 46.68
Maximum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Range of exercise prices	$ 0	$ 59.86	$ 60.82

Variable Interest Entities (V97

Variable Interest Entities (VIEs) (Impact Of VIEs On The Consolidated Statements Of Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Other noninterest income									$ 111	$ 102	$ 102
Provision for income taxes	$ 218	$ 108	$ 99	$ 66	$ 62	$ 64	$ 42	$ 25	491	193	229
Variable Interest Entity
Variable Interest Entity [Line Items]
Other noninterest income									2	(1)	1
Provision for income taxes, amortization of LIHTC investments									67	66	62
Provision for income taxes									(20)	(22)	(21)
Low income housing tax credits | Variable Interest Entity
Variable Interest Entity [Line Items]
Provision for income taxes, affordable housing tax credits and other tax benefits									(63)	(62)	(61)
Other tax benefits related to tax credit entities | Variable Interest Entity
Variable Interest Entity [Line Items]
Provision for income taxes, affordable housing tax credits and other tax benefits									$ (24)	$ (26)	$ (22)

Deposits Deposits (Schedule o98

Deposits Deposits (Schedule of Maturities of Domestic Deposits of One Hundred Thousand or More) (Details) - Domestic certificates of deposit and other deposits - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Three Months or Less	$ 355	$ 510
Over three months to six months	207	322
Over six months to twelve months	319	449
Over twelve months	130	230
Total	$ 1,011	$ 1,511

Short-term Borrowings Short-t99

Short-term Borrowings Short-term Borrowings (Narrative) (Details) $ in Billions	Dec. 31, 2017USD ($)
Short-term Debt [Abstract]
Pledged loans to provide collateralized borrowing with the FRB	$ 21
Available collateralized borrowing with the FRB	$ 17

Short-term Borrowings Short-100

Short-term Borrowings Short-term Borrowings (Summary of Short-term Borrowings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Amount outstanding at year-end	$ 10	$ 25
Federal Funds Purchased and Securities Sold Under Agreements to Repurchase
Short-term Debt [Line Items]
Amount outstanding at year-end	$ 10	$ 25	$ 23
Weighted average interest rate at year-end	1.43%	0.54%	0.38%
Maximum month-end balance during the year	$ 41	$ 25	$ 109
Average balance outstanding during the year	$ 20	$ 15	$ 93
Weighted average interest rate during the year	1.02%	0.47%	0.05%
Other Short-term Borrowings
Short-term Debt [Line Items]
Amount outstanding at year-end	$ 0	$ 0	$ 0
Weighted average interest rate at year-end	0.00%	0.00%	0.00%
Maximum month-end balance during the year	$ 1,024	$ 501	$ 0
Average balance outstanding during the year	$ 257	$ 123	$ 0
Weighted average interest rate during the year	1.15%	0.45%	0.00%

Medium- And Long-Term Debt (Nar

Medium- And Long-Term Debt (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 5	$ 7
Subsidiaries
Debt Instrument [Line Items]
Blanket lien on real-estate related loans securing FHLB advances	16,000
FHLB potential future borrowings	5,000
Floating-rate FHLB advances | Subsidiaries
Debt Instrument [Line Items]
Floating-rate FHLB advances	$ 2,800	$ 2,800
Weighted-average interest rate	1.41%
Minimum | Floating-rate FHLB advances | Subsidiaries
Debt Instrument [Line Items]
Maturity date	Mar. 4, 2026
Maximum | Floating-rate FHLB advances | Subsidiaries
Debt Instrument [Line Items]
Maturity date	May 20, 2026

Medium- And Long-Term Debt (Sch

Medium- And Long-Term Debt (Schedule Of Medium- And Long-Term Debt) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total medium- and long-term debt		$ 4,622	$ 5,160
Parent Company
Debt Instrument [Line Items]
Total medium- and long-term debt		602	604
Subsidiaries
Debt Instrument [Line Items]
Subordinated notes		555	1,073
Total medium- and long-term debt		4,020	4,556
3.80% subordinated notes due 2026 | Parent Company
Debt Instrument [Line Items]
Subordinated notes	[1]	$ 255	$ 256
Stated interest rate		3.80%	3.80%
Maturity date		Jul. 22, 2026	Jul. 22, 2026
2.125% notes due 2019 | Parent Company
Debt Instrument [Line Items]
Medium-term notes	[1]	$ 347	$ 348
Stated interest rate		2.125%	2.125%
Maturity date		May 23, 2019	May 23, 2019
5.75% subordinated notes due 2016 | Subsidiaries
Debt Instrument [Line Items]
Stated interest rate		5.75%	5.75%
Maturity date		Nov. 21, 2016	Nov. 21, 2016
5.20% subordinated notes due 2017 | Subsidiaries
Debt Instrument [Line Items]
Subordinated notes	[1]	$ 0	$ 511
Stated interest rate		5.20%	5.20%
Maturity date		Aug. 22, 2017	Aug. 22, 2017
4.00% subordinated notes due 2025 | Subsidiaries
Debt Instrument [Line Items]
Subordinated notes	[1]	$ 347	$ 347
Stated interest rate		4.00%	4.00%
Maturity date		Jul. 27, 2025	Jul. 27, 2025
7.875% subordinated notes due 2026 | Subsidiaries
Debt Instrument [Line Items]
Subordinated notes	[1]	$ 208	$ 215
Stated interest rate		7.875%	7.875%
Maturity date		Sep. 15, 2026	Sep. 15, 2026
2.50% notes due 2020 | Subsidiaries
Debt Instrument [Line Items]
Medium-term notes	[1]	$ 665	$ 667
Stated interest rate		2.50%	2.50%
Maturity date		Jun. 2, 2020	Jun. 2, 2020
Floating-rate based on FHLB auction rate due 2026 | Subsidiaries
Debt Instrument [Line Items]
Federal Home Loan Bank advances		$ 2,800	$ 2,800
Weighted-average interest rate		1.41%
Floating-rate based on FHLB auction rate due 2026 | Subsidiaries | Minimum
Debt Instrument [Line Items]
Maturity date		Mar. 4, 2026
Floating-rate based on FHLB auction rate due 2026 | Subsidiaries | Maximum
Debt Instrument [Line Items]
Maturity date		May 20, 2026
6.0% - 6.4% fixed-rate notes due 2015 to 2020 | Subsidiaries
Debt Instrument [Line Items]
Other notes		$ 0	$ 16
Maturity date		Jun. 30, 2020	Jun. 30, 2020
6.0% - 6.4% fixed-rate notes due 2015 to 2020 | Subsidiaries | Minimum
Debt Instrument [Line Items]
Stated interest rate		6.00%	6.00%
6.0% - 6.4% fixed-rate notes due 2015 to 2020 | Subsidiaries | Maximum
Debt Instrument [Line Items]
Stated interest rate		6.40%	6.40%
[1]	The fixed interest rates on these notes have been swapped to a variable rate and designated in a hedging relationship. Accordingly, carrying value has been adjusted to reflect the change in the fair value of the debt as a result of changes in the benchmark rate.

Medium- And Long-Term Debt Sche

Medium- And Long-Term Debt Schedule of Maturities of Medium- and Long-term Debt (Details) $ in Millions	Dec. 31, 2017USD ($)
Debt Disclosure [Abstract]
2,018	$ 0
2,019	350
2,020	675
2,021	0
2,022	0
Thereafter	3,550
Total	$ 4,575

Shareholders' Equity Shareholde

Shareholders' Equity Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Repurchases Authorized per Capital Plan	$ 605
Equity Repurchases per Capital Plan	$ 531
Stock Option
Common stock shares reserved for future issuance	5,088,000
Restricted Stock
Shares of non-vested restricted stock outstanding	1,243,000	1,591,000
Common Stock
Shares repurchased under equity repurchase program	7,500,000	6,800,000	5,300,000
Warrants
Number of warrants to purchase common stock outstanding	1,000,000
Number of shares of common stock issuable under outstanding warrants	906,000
Average exercise price for outstanding warrants	$ 29.42
Year of expiration for outstanding warrants	2,018
Shares of common stock issued upon exercise of warrants	1,771,000	2,317,000	934,000
Common stock shares reserved for future issuance	906,000
Equity Repurchase Program | Common Stock
Shares repurchased under equity repurchase program	7,327,000	6,574,000	5,100,000
Average cost per share of shares repurchased under equity repurchase program	$ 72.44	$ 46.09	$ 45.65
Equity Repurchase Program | Warrants
Warrants repurchased under equity repurchase program			500,000
Average cost per warrant repurchased under the equity repurchase program			$ 20.70

Accumulated Other Comprehens105

Accumulated Other Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Investment securities, Balance at beginning of period, net of tax		$ (33)	$ 9	$ 37
Net unrealized holding losses arising during the period		(81)	(70)	(55)
Investment securities, Less: Benefit for income taxes		(27)	(26)	(21)
Investment securities, Net unrealized holding losses arising during period, net of tax		(54)	(44)	(34)
Investment securities, Net realized (losses) gains included in net securities (losses) gains		0	0	(2)
Investment securities, Less: Benefit for income taxes		0	0	(1)
Investment securities, Reclassification adjustment for net securities (losses) gains included in net income, net of tax		0	0	(1)
Investment securities, Net losses realized as a yield adjustment in interest on investment securities		(3)	(3)	(8)
Investment securities, Less: Benefit for income taxes		(1)	(1)	(3)
Investment securities, Reclassification adjustment for net losses realized as a yield adjustment included in net income, net of tax		(2)	(2)	(5)
Investment securities, Change in net unrealized losses on investment securities, net of tax		(52)	(42)	(28)
Investment securities, Reclassification of certain deferred tax effects	[1]	(16)	0	0
Investment securities, Balance at end of period, net of tax		(101)	(33)	9
Benefit plans, Balance at beginning of period, net of tax		(350)	(438)	(449)
Benefit plans, Actuarial loss arising during the period		72	(134)	(57)
Benefit plans, Prior service credit arising during the period		0	234	3
Benefit plans, Net defined benefit pension and other postretirement adjustment arising during the period		72	100	(54)
Benefit plans, Less: Provision (benefit) for income taxes		17	37	(19)
Benefit plans, Net defined benefit pension and other postretirement adjustment arising during the period, net of tax		55	63	(35)
Benefit plans, Amortization of actuarial net loss		51	46	70
Benefit plans, Amortization of prior service (credit) cost		(27)	(7)	1
Benefit plans, Total amounts recognized in employee benefits expense		24	39	71
Benefit plans, Less: Provision for income taxes		8	14	25
Benefit plans, Adjustment for amounts recognized as components of net periodic benefit cost during the period, net of tax		16	25	46
Benefit plans, Change in defined benefit pension and other postretirement plans adjustment, net of tax		71	88	11
Benefit plans, Reclassification of certain deferred tax effects	[1]	(71)	0	0
Benefit plans, Balance at end of period, net of tax		(350)	(350)	(438)
Total accumulated other comprehensive loss at end of period, net of tax		$ (451)	$ (383)	$ (429)
[1]	Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. For further information, refer to Note 1.

Share-Based Compensation Sha106

Share-Based Compensation Share-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of shares originally available for grant	19,400,000
Shares available for grant	9,500,000
Total intrinsic value of stock options exercised	$ 104	$ 46	$ 12
Shares in treasury	55,306,483	52,851,156
Restricted Stock
Total fair value of restricted stock awards that fully vested	$ 19	$ 22	18
Restricted Stock | Minimum
Share-based compensation vesting period	3 years
Restricted Stock | Maximum
Share-based compensation vesting period	5 years
Restricted Stock Units (RSUs)
Total fair value of restricted stock awards that fully vested	$ 10	$ 11	$ 0
Restricted Stock Units (RSUs) | Minimum
Share-based compensation vesting period	1 year
Restricted Stock Units (RSUs) | Maximum
Share-based compensation vesting period	3 years
Stock Options | Minimum
Share-based compensation vesting period	1 year
Stock Options | Maximum
Share-based compensation vesting period	4 years
Comerica Incorporated
Closing stock price per share	$ 86.81

Share-Based Compensation (Summa

Share-Based Compensation (Summary of Components of Share-Based Compensation Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation [Abstract]
Total share-based compensation expense	$ 39	$ 34	$ 38
Related tax benefits recognized in net income	$ 14	$ 13	$ 14

Share-Based Compensation (Unrec

Share-Based Compensation (Unrecognized Compensation Expense) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Share-based Compensation [Abstract]
Total unrecognized share-based compensation expense	$ 40
Weighted-average expected recognition period (in years)	2 years 9 months 18 days

Share-Based Compensation (Estim

Share-Based Compensation (Estimated Weighted-Average Grant-Date Fair Value Per Option Share and the Underlying Binomial Option-Pricing Model Assumptions) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation [Abstract]
Weighted-average grant-date fair value per option	$ 19.61	$ 9.94	$ 11.31
Risk-free interest rates	2.47%	2.01%	1.83%
Expected dividend yield	3.00%	3.00%	3.00%
Expected volatility factors of the market price of Comerica common stock	34.00%	38.00%	33.00%
Expected option life (in years)	7 years	6 years 10 months 24 days	6 years 10 months 24 days

Share-Based Compensation (Su110

Share-Based Compensation (Summary of the Corporation's Stock Option Activity and Related Information) (Details) - Stock Options $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Number of options outstanding at January 1, 2017 | shares	6,892
Options granted | shares	430
Options forfeited or expired | shares	(57)
Options exercised | shares	(3,092)
Number of options outstanding at December 31, 2017 | shares	4,173
Number of options exercisable at December 31, 2017 | shares	2,347
Options outstanding at January 1, 2017 (Weighted-average exercise price) | $ / shares	$ 37.24
Options granted (Weighted-average exercise price) | $ / shares	67.67
Options forfeited or expired (Weighted-average exercise price) | $ / shares	48.74
Options exercised (Weighted-average exercise price) | $ / shares	37.45
Options outstanding at December 31, 2017 (Weighted-average exercise price) | $ / shares	40.06
Options exercisable at December 31, 2017 (Weighted-average exercise price) | $ / shares	$ 36.27
Weighted-average remaining contractual term in years at December 31, 2017	5 years 10 months 24 days
Weighted-average remaining contractual term in years exercisable at December 31, 2017	4 years 3 months 19 days
Aggregate intrinsic value outstanding at December 31, 2017 | $	$ 195
Aggregate intrinsic value exercisable at December 31, 2017 | $	$ 119

Share-Based Compensation (Su111

Share-Based Compensation (Summary of the Corporation's Restricted Stock Activity and Related Information) (Details) - Restricted Stock	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Non-vested shares outstanding at January 1, 2017 | shares	1,591,000
Non-vested shares granted | shares	237,000
Non-vested shares forfeited | shares	(59,000)
Shares vested | shares	(526,000)
Non-vested shares outstanding at December 31, 2017 | shares	1,243,000
Non-vested shares outstanding at January 1, 2017 (Weighted-average grant-date fair value) | $ / shares	$ 37.20
Non-vested shares granted (Weighted-average grant-date fair value) | $ / shares	67.83
Non-vested shares forfeited (Weighted-average grant-date fair value) | $ / shares	42.53
Shares vested (Weighted-average grant-date fair value) | $ / shares	35.28
Non-vested shares outstanding at December 31, 2017 (Weighted-average grant-date fair value) | $ / shares	$ 43.59

Share-Based Compensation Summar

Share-Based Compensation Summary of the Corporation's Restricted Stock Unit Activity and Related Information (Details) - Restricted Stock Units (RSUs) shares in Thousands	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Service-Based Units
Non-vested shares outstanding at January 1, 2017 | shares	180
Non-vested shares granted | shares	19
Shares vested | shares	0
Non-vested shares outstanding at December 31, 2017 | shares	199
Non-vested shares outstanding at January 1, 2017 (Weighted-average grant-date fair value) | $ / shares	$ 39.61
Non-vested shares granted (Weighted-average grant-date fair value) | $ / shares	75.06
Shares vested (Weighted-average grant-date fair value) | $ / shares	0
Non-vested shares outstanding at December 31, 2017 (Weighted-average grant-date fair value) | $ / shares	$ 43
Performance-Based Units
Non-vested shares outstanding at January 1, 2017 | shares	781
Non-vested shares granted | shares	149
Shares vested | shares	(212)
Non-vested shares outstanding at December 31, 2017 | shares	718
Non-vested shares outstanding at January 1, 2017 (Weighted-average grant-date fair value) | $ / shares	$ 39.47
Non-vested shares granted (Weighted-average grant-date fair value) | $ / shares	66.07
Shares vested (Weighted-average grant-date fair value) | $ / shares	48.32
Non-vested shares outstanding at December 31, 2017 (Weighted-average grant-date fair value) | $ / shares	$ 42.39

Employee Benefit Plans (Narrati

Employee Benefit Plans (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit pension expense	$ (18,000,000)	$ 6,000,000	$ 47,000,000
Postretirement benefit expense	(18,000,000)	6,000,000	48,000,000
Fair value of plan assets in defined benefit pension plan	2,743,000,000	2,448,000,000
Estimated employer contributions for defined benefit plans in year 2017	$ 0
Employer core matching cash contribution as percent of employee contribution	100.00%
Percent of qualified earnings contributed by employee matched by the Corporation	4.00%
Defined contribution plan expense	$ 21,000,000	22,000,000	22,000,000
Profit sharing plan annual contribution to the individual account of each eligible employee, minimum percent of annual compensation	3.00%
Profit sharing plan annual contribution to the individual account of each eligible employee, maximum percent of annual compensation	8.00%
Profit sharing plan expense included in employee benefits expense	$ 0	10,000,000	10,000,000
Qualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Postretirement benefit expense	$ (28,000,000)	(9,000,000)	27,000,000
Estimated average life of pension plan in years	12
Fair value of plan assets in defined benefit pension plan	$ 2,747,000,000	2,453,000,000	2,346,000,000
Non-Qualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Postretirement benefit expense	10,000,000	15,000,000	20,000,000
Fair value of plan assets in defined benefit pension plan	0	0
Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Postretirement benefit expense	0	0	1,000,000
Fair value of plan assets in defined benefit pension plan	$ 60,000,000	$ 62,000,000	$ 61,000,000
Minimum | Qualified Plan | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percent	0.45
Minimum | Qualified Plan | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percent	0.45
Maximum | Qualified Plan | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percent	0.55
Maximum | Qualified Plan | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percent	0.55

Employee Benefit Plans (Reconci

Employee Benefit Plans (Reconciliations of Plan assets and the Projected Benefit Obligation, the Weighted-Average Assumptions Used to Determine Year-End Benefit Obligations, and the Amounts Recognized in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair value of plan assets at January 1		$ 2,448,000,000
Fair value of plan assets at December 31		2,743,000,000	$ 2,448,000,000
Qualified Plan
Fair value of plan assets at January 1		2,453,000,000	2,346,000,000
Actual return on plan assets		396,000,000	200,000,000	$ (73,000,000)
Employer contributions		0	0
Benefits paid		102,000,000	93,000,000
Fair value of plan assets at December 31		2,747,000,000	2,453,000,000	2,346,000,000
Projected benefit obligation at January 1		1,902,000,000	1,916,000,000
Service cost		29,000,000	31,000,000	35,000,000
Interest cost		78,000,000	87,000,000	88,000,000
Actuarial (gain) loss		154,000,000	161,000,000
Plan amendment		0	200,000,000
Projected benefit obligation at December 31		2,061,000,000	1,902,000,000	1,916,000,000
Accumulated benefit obligation		2,052,000,000	1,894,000,000
Funded Status at December 31	[1],[2]	$ 686,000,000	$ 551,000,000
Weighted-average assumptions, discount rate, percent		3.74%	4.23%
Weighted-average assumptions, rate of compensation increase, percent		3.75%	3.50%
Accumulated other comprehensive income (loss), net actuarial loss		$ (548,000,000)	$ (673,000,000)
Accumulated other comprehensive income (loss), net prior service (cost) credit		159,000,000	178,000,000
Balance at December 31		(389,000,000)	(495,000,000)
Non-Qualified Plan
Fair value of plan assets at January 1		0
Benefits paid		11,000,000	11,000,000
Fair value of plan assets at December 31		0	0
Projected benefit obligation at January 1		201,000,000	222,000,000
Service cost		2,000,000	3,000,000	4,000,000
Interest cost		8,000,000	10,000,000	10,000,000
Actuarial (gain) loss		12,000,000	11,000,000
Plan amendment		0	34,000,000
Projected benefit obligation at December 31		212,000,000	201,000,000	222,000,000
Accumulated benefit obligation		209,000,000	198,000,000
Funded Status at December 31	[1],[2]	$ (212,000,000)	$ (201,000,000)
Weighted-average assumptions, discount rate, percent		3.74%	4.23%
Weighted-average assumptions, rate of compensation increase, percent		3.75%	3.50%
Accumulated other comprehensive income (loss), net actuarial loss		$ (85,000,000)	$ (82,000,000)
Accumulated other comprehensive income (loss), net prior service (cost) credit		42,000,000	50,000,000
Balance at December 31		(43,000,000)	(32,000,000)
Postretirement Benefit Plan
Fair value of plan assets at January 1		62,000,000	61,000,000
Actual return on plan assets		2,000,000	2,000,000	0
Employer contributions		1,000,000	4,000,000
Benefits paid		5,000,000	5,000,000
Fair value of plan assets at December 31		60,000,000	62,000,000	61,000,000
Projected benefit obligation at January 1		55,000,000	59,000,000
Service cost		0	0
Interest cost		2,000,000	3,000,000	3,000,000
Actuarial (gain) loss		(1,000,000)	(2,000,000)
Plan amendment		0	0
Projected benefit obligation at December 31		51,000,000	55,000,000	$ 59,000,000
Accumulated benefit obligation		51,000,000	55,000,000
Funded Status at December 31	[1],[2]	$ 9,000,000	$ 7,000,000
Weighted-average assumptions, discount rate, percent		3.55%	3.92%
Healthcare cost trend rate assumed for next year		6.50%	6.50%
Rate to which the healthcare cost trend rate is assumed to decline (the ultimate trend rate), percent		4.50%	5.00%	5.00%
Year when healthcare cost trend rate reaches the ultimate trend rate		2,027	2,027
Accumulated other comprehensive income (loss), net actuarial loss		$ (19,000,000)	$ (20,000,000)
Accumulated other comprehensive income (loss), net prior service (cost) credit		1,000,000	1,000,000
Balance at December 31		$ (18,000,000)	$ (19,000,000)
[1]	Based on projected benefit obligation for defined benefit pension plans and accumulated benefit obligation for postretirement benefit plan.
[2]	The Corporation recognizes the overfunded and underfunded status of the plans in “accrued income and other assets” and “accrued expenses and other liabilities,” respectively, on the consolidated balance sheets.

Employee Benefit Plans (Schedul

Employee Benefit Plans (Schedule of Changes, Net of Tax, in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Actuarial gain (loss) arising during the period	$ (72)	$ 134	$ 57
Amortization of actuarial net loss	51	46	70
Amortization of prior service credit	(27)	(7)	1
Total recognized in other comprehensive income (loss)	96	$ 139	$ 17
Qualified Plan
Actuarial gain (loss) arising during the period	(82)
Amortization of actuarial net loss	43
Amortization of prior service credit	(19)
Total recognized in other comprehensive income (loss)	106
Non-Qualified Plan
Actuarial gain (loss) arising during the period	11
Amortization of actuarial net loss	8
Amortization of prior service credit	(8)
Total recognized in other comprehensive income (loss)	(11)
Postretirement Benefit Plan
Actuarial gain (loss) arising during the period	(1)
Amortization of actuarial net loss	0
Amortization of prior service credit	0
Total recognized in other comprehensive income (loss)	$ 1

Employee Benefit Plans Employee

Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	$ (18)	$ 6	$ 48
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	29	31	35
Interest cost	78	87	88
Expected return on plan assets	(159)	(163)	(159)
Amortization of prior service (credit) cost	(19)	(2)	4
Amortization of net loss	43	38	59
Net periodic defined benefit (credit) cost	(28)	(9)	27
Actual return on plan assets	$ 396	$ 200	$ (73)
Actual rate of return on plan assets, percent	16.48%	8.66%	(2.95%)
Weighted-average assumptions, discount rate, percent	4.23%	4.53%	4.28%
Weighted-average assumptions, expected long-term return on plan assets, percent	6.50%	6.75%	6.75%
Weighted-average assumptions, rate of compensation increase, percent	3.50%	3.75%	3.75%
Non-Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 3	$ 4
Interest cost	8	10	10
Expected return on plan assets	0	0	0
Amortization of prior service (credit) cost	(8)	(5)	(4)
Amortization of net loss	8	7	10
Net periodic defined benefit (credit) cost	$ 10	$ 15	$ 20
Weighted-average assumptions, discount rate, percent	4.23%	4.53%	4.28%
Weighted-average assumptions, rate of compensation increase, percent	3.50%	3.75%	3.75%
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0
Interest cost	2	3	$ 3
Expected return on plan assets	(3)	(4)	(4)
Amortization of prior service (credit) cost	0	0	1
Amortization of net loss	1	1	1
Net periodic defined benefit (credit) cost	0	0	1
Actual return on plan assets	$ 2	$ 2	$ 0
Actual rate of return on plan assets, percent	3.52%	2.83%	(0.53%)
Weighted-average assumptions, discount rate, percent	3.92%	4.53%	3.99%
Weighted-average assumptions, expected long-term return on plan assets, percent	5.00%	5.00%	5.00%
Health care cost trend rate assumed	6.50%	7.00%	7.00%
Rate to which the healthcare cost trend rate is assumed to decline (the ultimate trend rate), percent	4.50%	5.00%	5.00%
Defined Benefit Plan Year That Reaches Ultimate Trend Rate In Current Expense	2,027	2,027	2,026

Employee Benefit Plans (The Est

Employee Benefit Plans (The Estimated Portion of Balances Remaining in Accumulated Other Comprehensive Income (Loss) that are Expected to be Recognized as a Component of Net Periodic Benefit Cost) (Details) $ in Millions	Dec. 31, 2017USD ($)
Net loss	$ 60
Prior service credit	(27)
Qualified Plan
Net loss	51
Prior service credit	(19)
Non-Qualified Plan
Net loss	8
Prior service credit	(8)
Postretirement Benefit Plan
Net loss	1
Prior service credit	$ 0

Employee Benefit Plans (Effect

Employee Benefit Plans (Effect of One-Percentage-Point Change in 2014 Assumed Healthcare and Prescription Drug Cost Trend Rates) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Effect on postretirement benefit obligation, Increase	$ 3
Effect on postretirement benefit obligation, Decrease	(2)
Effect on total service and interest cost, Increase	0
Effect on total service and interest cost, Decrease	$ 0

Employee Benefit Plans (Fair Va

Employee Benefit Plans (Fair Values of the Corporation's Qualified Defined Benefit Pension Plan Investments Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair value of plan assets in qualified defined benefit pension plan, Excluding assets valued at net asset value	$ 2,288	$ 2,033
Fair value of plan assets in qualified defined benefit pension plan	2,743	2,448
Cash equivalent securities | Commercial paper
Fair value of plan assets in qualified defined benefit pension plan		2
Equity securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan	1
Equity securities | Common stock
Fair value of plan assets in qualified defined benefit pension plan	961	850
Debt securities | U.S. Treasury and other U.S. government agency securities
Fair value of plan assets in qualified defined benefit pension plan	456	377
Debt securities | Corporate and municipal bonds and notes
Fair value of plan assets in qualified defined benefit pension plan	765	710
Debt securities | Collateralized mortgage obligations
Fair value of plan assets in qualified defined benefit pension plan	25	23
Debt securities | Collective investments funds
Fair value of plan assets in qualified defined benefit pension plan	455	415
Private placements
Fair value of plan assets in qualified defined benefit pension plan	80	71
Level 1
Fair value of plan assets in qualified defined benefit pension plan, Excluding assets valued at net asset value	1,413	1,216
Level 1 | Cash equivalent securities | Commercial paper
Fair value of plan assets in qualified defined benefit pension plan		0
Level 1 | Equity securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan	1
Level 1 | Equity securities | Common stock
Fair value of plan assets in qualified defined benefit pension plan	961	850
Level 1 | Debt securities | U.S. Treasury and other U.S. government agency securities
Fair value of plan assets in qualified defined benefit pension plan	451	366
Level 1 | Debt securities | Corporate and municipal bonds and notes
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 1 | Debt securities | Collateralized mortgage obligations
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 1 | Private placements
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 2
Fair value of plan assets in qualified defined benefit pension plan, Excluding assets valued at net asset value	795	746
Level 2 | Cash equivalent securities | Commercial paper
Fair value of plan assets in qualified defined benefit pension plan		2
Level 2 | Equity securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan	0
Level 2 | Equity securities | Common stock
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 2 | Debt securities | U.S. Treasury and other U.S. government agency securities
Fair value of plan assets in qualified defined benefit pension plan	5	11
Level 2 | Debt securities | Corporate and municipal bonds and notes
Fair value of plan assets in qualified defined benefit pension plan	765	710
Level 2 | Debt securities | Collateralized mortgage obligations
Fair value of plan assets in qualified defined benefit pension plan	25	23
Level 2 | Private placements
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3
Fair value of plan assets in qualified defined benefit pension plan, Excluding assets valued at net asset value	80	71
Level 3 | Cash equivalent securities | Commercial paper
Fair value of plan assets in qualified defined benefit pension plan		0
Level 3 | Equity securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan	0
Level 3 | Equity securities | Common stock
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Debt securities | U.S. Treasury and other U.S. government agency securities
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Debt securities | Corporate and municipal bonds and notes
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Debt securities | Collateralized mortgage obligations
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Private placements
Fair value of plan assets in qualified defined benefit pension plan	$ 80	$ 71

Employee Benefit Plans (Summary

Employee Benefit Plans (Summary of Changes in the Corporation's Qualified Defined Benefit Pension Plan's Level 3 Investments Measured at Fair Value on a Recurring Basis) (Details) - Private placements - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Balance at beginning of period	$ 71	$ 105
Gains (Losses) Realized	2	1
Gains (Losses) Unrealized	3	3
Purchases	77	64
Sales	(73)	(102)
Balance at end of period	$ 80	$ 71

Employee Benefit Plans (Sche121

Employee Benefit Plans (Schedule of Estimated Future Employer Contributions) (Details) $ in Millions	Dec. 31, 2017USD ($)
Qualified Plan
2,017	$ 120
2,018	123
2,019	125
2,020	127
2,021	130
2022 - 2026	665
Non-Qualified Plan
2,017	11
2,018	12
2,019	13
2,020	13
2,021	13
2022 - 2026	66
Postretirement Benefit Plan
2,017	6	[1]
2,018	5	[1]
2,019	5	[1]
2,020	5	[1]
2,021	5	[1]
2022 - 2026	$ 19	[1]
[1]	Estimated benefit payments in the postretirement benefit plan are net of estimated Medicare subsidies.

Income Taxes And Tax-Related122

Income Taxes And Tax-Related Items Income Taxes And Tax-Related Items (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income before income taxes									$ 1,234	$ 670	$ 750
Foreign-source income									24
Remeasurement of deferred taxes									107	0	0
Provision for income taxes	$ 218	$ 108	$ 99	$ 66	$ 62	$ 64	$ 42	$ 25	491	193	229
Income tax benefit related to employee stock transactions									(35)	0	0
Liability for tax-related interest and penalties	10				7				10	7
Reasonably possible change in unrecognized tax benefits in next 12 months	1								1
Unrecognized tax benefits that would impact the effective tax rate	8				4				8	4
State net operating loss carryforwards	4								4
Deferred tax asset valuation allowance	$ 3				$ 3				3	3
Accounting Standards Update 2016-09
Income tax benefit related to employee stock transactions									35	4	3
Available-for-sale Securities
Provision for income taxes									$ 1	$ (2)	$ (1)
Minimum
Years state net operating loss carryforwards expire									Dec. 31, 2018
Maximum
Years state net operating loss carryforwards expire									Dec. 31, 2027

Income Taxes And Tax-Related123

Income Taxes And Tax-Related Items Current and Deferred Components of the Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current federal income tax									$ 371	$ 224	$ 275
Current foreign income tax									5	5	5
Current state and local income tax									36	15	20
Total current income tax									412	244	300
Deferred federal income tax									(26)	(49)	(68)
Deferred state and local income tax									(2)	(2)	(3)
Remeasurement of deferred taxes									107	0	0
Total deferred income tax									79	(51)	(71)
Provision for income taxes	$ 218	$ 108	$ 99	$ 66	$ 62	$ 64	$ 42	$ 25	$ 491	$ 193	$ 229

Income Taxes And Tax-Related124

Income Taxes And Tax-Related Items Reconciliation of Expected Income Tax Expense at the Federal Statutory Rate to the Corporation's Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax based on federal statutory rate, amount									$ 432	$ 235	$ 262
Tax based on federal statutory rate, percent									35.00%	35.00%	35.00%
Remeasurement of deferred taxes, amount									$ 107	$ 0	$ 0
Remearsurement of deferred taxes, percent									8.70%	0.00%	0.00%
State income tax, amount									$ 22	$ 8	$ 10
State income tax, percent									1.80%	1.20%	1.30%
Employee stock transactions, amount									$ (35)	$ 0	$ 0
Employee stock transactions, percent									(2.80%)	0.00%	0.00%
Affordable housing and historic credits, amount									$ (21)	$ (22)	$ (22)
Affordable housing and historic credits, percent									(1.70%)	(3.30%)	(2.90%)
Bank-owned life insurance, amount									$ (16)	$ (15)	$ (15)
Bank-owned life insurance, percent									(1.30%)	(2.30%)	(2.00%)
Lease termination transactions, amount									$ (2)	$ (15)	$ (5)
lease termination transactions, percent									(0.20%)	(2.20%)	(0.70%)
Tax-related interest and penalties, amount									$ 4	$ 3	$ 1
Tax-related interest and penalties, percent									0.30%	0.50%	0.10%
Other, amount									$ 0	$ (1)	$ (2)
Other, percent									0.00%	(0.10%)	(0.30%)
Provision for income taxes, amount	$ 218	$ 108	$ 99	$ 66	$ 62	$ 64	$ 42	$ 25	$ 491	$ 193	$ 229
Provision for income taxes, percent									39.80%	28.80%	30.50%

Income Taxes And Tax-Related125

Income Taxes And Tax-Related Items Reconciliation of the Beginning and Ending Amounts of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at January 1	$ 15	$ 22	$ 14
Increases as a result of tax positions taken during a prior period	4	0	8
Decrease related to settlements with tax authorities	(8)	(7)	0
Decrease related to other tax position changes	(1)	0	0
Balance at December 31	$ 10	$ 15	$ 22

Income Taxes And Tax-Related126

Income Taxes And Tax-Related Items Tax Years for Significant Jurisdictions That Remain Subject to Examination (Details)	12 Months Ended
	Dec. 31, 2017
Federal | Minimum
Open Tax Year	2,013
Federal | Maximum
Open Tax Year	2,015
California | Minimum
Open Tax Year	2,004
California | Maximum
Open Tax Year	2,015

Income Taxes And Tax-Related127

Income Taxes And Tax-Related Items Principal Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Allowance for loan losses	$ 150	$ 256
Deferred compensation	49	91
Deferred loan origination fees and costs	6	20
Net unrealized losses on investment securities available-for-sale	31	20
Other temporary differences, net	57	76
Total deferred tax asset before valuation allowance	293	463
Valuation allowance	(3)	(3)
Total deferred tax assets	290	460
Deferred tax liabilities:
Lease financing transactions	(76)	(150)
Defined benefit plans	(72)	(82)
Allowance for depreciation	(1)	(11)
Total deferred tax liabilities	(149)	(243)
Net deferred tax asset	$ 141	$ 217

Transactions with Related Pa128

Transactions with Related Parties Transactions with Related Parties (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Related Party Transactions [Abstract]
Loans attributed to persons who were related parties at beginning of period	$ 108
New loans to related parties	637
Repayments on loans to related parties	679
Loans attributed to persons who were related parties at end of period	$ 66

Regulatory Capital and Reser129

Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Federal Reserve Bank average reserve requirement	$ 572	$ 518
Dividends available to be paid to parent company without obtaining prior approval from bank regulatory agencies	7
Dividends from bank subsidiaries	$ 907	$ 545	$ 437
Total risk-based capital minimum to be well capitalized	10.00%	10.00%
Tier 1 risk-based capital minimum to be well capitalized	6.00%	6.00%
U.S. Banking Subsidiaries
Total risk-based capital minimum to be well capitalized	10.00%
Tier 1 risk-based capital minimum to be well capitalized	8.00%
Common equity tier 1 risk-based capital minimum to be well capitalized	6.50%
Leverage ratio minimum to be well capitalized	5.00%

Regulatory Capital and Reser130

Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Summary of Capital Position) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Comerica Incorporated
Summary of Capital Position [Line Items]
CET 1 capital	$ 7,773	$ 7,540
Tier 1 capital	7,773	7,540
Total capital	9,211	9,018
Risk-weighted assets	66,575	67,966
Average assets (fourth quarter)	$ 71,372	$ 74,086
CET 1 capital to risk-weighted assets	11.68%	11.09%
Tier 1 capital to risk-weighted assets	11.68%	11.09%
Total capital to risk-weighted assets	13.84%	13.27%
Tier 1 capital to average assets	10.89%	10.18%
Capital conservation buffer	5.68%	5.09%
CET 1 capital - minimum (Consolidated)	$ 3,000	$ 3,100
Tier 1 capital - minimum (Consolidated)	4,000	$ 4,100
Total capital - minimum (Consolidated)	$ 5,300
CET 1 capital to risk-weighted assets - minimum	4.50%	4.50%
Tier 1 capital to risk-weighted assets - minimum	6.00%	6.00%
Total capital to risk-weighted assets - minimum	8.00%	8.00%
Tier 1 capital to average assets - minimum	4.00%
Comerica Bank
Summary of Capital Position [Line Items]
CET 1 capital	$ 7,121	$ 7,120
Tier 1 capital	7,121	7,120
Total capital	8,378	8,397
Risk-weighted assets	66,447	67,739
Average assets (fourth quarter)	$ 71,181	$ 73,804
CET 1 capital to risk-weighted assets	10.72%	10.51%
Tier 1 capital to risk-weighted assets	10.72%	10.51%
Total capital to risk-weighted assets	12.61%	12.40%
Tier 1 capital to average assets	10.00%	9.65%
Capital conservation buffer	4.61%	4.40%
CET 1 capital to risk-weighted assets - minimum	4.50%	4.50%
Tier 1 capital to risk-weighted assets - minimum	6.00%	6.00%
Total capital to risk-weighted assets - minimum	8.00%	8.00%
Tier 1 capital to average assets - minimum	4.00%

Contingent Liabilities (Narrati

Contingent Liabilities (Narrative) (Details) - USD ($)	Jan. 17, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Legal fees		$ 15,000,000	$ 19,000,000	$ 21,000,000
Pending Litigation | Minimum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		0
Pending Litigation | Maximum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		$ 29,000,000
Butte Local Development v. Masters Group v. Comerica Bank
Loss Contingencies [Line Items]
Amount of damages awarded by the jury	$ 52,000,000

Restructuring Charges (Narrativ

Restructuring Charges (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Restructuring Cost and Reserve [Line Items]
Number of banking centers to be consolidated under restructuring plan	38
Restructuring charges	$ 45	$ 93	$ 0
Business Bank
Restructuring Cost and Reserve [Line Items]
Restructuring charges	24	43
Retail Bank
Restructuring Cost and Reserve [Line Items]
Restructuring charges	15	38
Wealth Management
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 6	$ 12

Restructuring Charges (Schedule

Restructuring Charges (Schedule of Changes in Restructuring Reserves) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		$ 18	$ 0
Restructuring charges		45	93	$ 0
Payments		(43)	(72)
Adjustments for non-cash charges	[1]	(5)	(3)
Balance at end of period		15	18	0
Total restructuring charges incurred to date		$ 138
Expected completion date of restructuring activities		Dec. 31, 2018
Employee costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		$ 10	0
Restructuring charges		10	52
Payments		(12)	(44)
Adjustments for non-cash charges	[1]	0	(2)
Balance at end of period		8	10	0
Total restructuring charges incurred to date		62
Facilities costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		4	0
Restructuring charges		2	15
Payments		(6)	(6)
Adjustments for non-cash charges	[1]	0	(5)
Balance at end of period		0	4	0
Total restructuring charges incurred to date		17
Technology costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		0	0
Restructuring charges		26	0
Payments		(15)	0
Adjustments for non-cash charges	[1]	(5)	0
Balance at end of period		6	0	0
Total restructuring charges incurred to date		26
Other costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		4	0
Restructuring charges		7	26
Payments		(10)	(22)
Adjustments for non-cash charges	[1]	0	0
Balance at end of period		1	$ 4	$ 0
Total restructuring charges incurred to date		33
Minimum
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	185
Minimum | Employee costs
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	70
Minimum | Facilities costs
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	20
Minimum | Technology costs
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	60
Minimum | Other costs
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	35
Maximum
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	195
Maximum | Employee costs
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	70
Maximum | Facilities costs
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	25
Maximum | Technology costs
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	65
Maximum | Other costs
Restructuring Cost and Reserve [Line Items]
Total expected restructuring charges	[2]	$ 35
[1]	Adjustments for non-cash charges primarily include the benefit from forfeitures of nonvested stock compensation in Employee Costs, accelerated depreciation expense in Facilities Costs and impairments of previously capitalized software costs in Technology Costs.
[2]	Restructuring activities are expected to be substantially completed by 12/31/2018.

Business Segment Information (N

Business Segment Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017marketssegments
Segment Reporting [Abstract]
Number of Major Business Segments | segments	3
Number of Primary Market Segments | markets	3

Business Segment Information (B

Business Segment Information (Business Segment Financial Results) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Net interest income (expense)		$ 545	$ 546	$ 500	$ 470	$ 455	$ 450	$ 445	$ 447	$ 2,061		$ 1,797	$ 1,689
Provision for credit losses										74		248	147
Noninterest income										1,107		1,051	1,035
Noninterest expenses		483	463	457	457	461	493	518	458	1,860		1,930	1,827
Provision (benefit) for income taxes		(218)	(108)	(99)	(66)	(62)	(64)	(42)	(25)	(491)		(193)	(229)
Net income (loss)		$ 112	$ 226	$ 203	$ 202	$ 164	$ 149	$ 104	$ 60	743		477	521
Net loan charge-offs (recoveries)										92		157	101
Assets, average										71,452		71,743	70,247
Loans, average										48,558		48,996	48,628
Deposits, average										$ 57,258		$ 57,741	$ 58,326
Return on average assets	[1],[2]									1.04%		0.67%	0.74%
Efficiency ratio	[3],[4]									58.57%		67.53%	66.93%
Remeasurement of deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act										$ (107)		$ 0	$ 0
Income tax benefit related to employee stock transactions										(35)		0	0
Business Bank
Net interest income (expense)										1,372		1,417	1,497
Provision for credit losses										58		217	158
Noninterest income										601		572	571
Noninterest expenses										802		839	778
Provision (benefit) for income taxes										(389)		(295)	(371)
Net income (loss)										724		638	761
Net loan charge-offs (recoveries)										82		145	89
Assets, average										38,801		39,497	39,501
Loans, average										37,445		38,067	37,889
Deposits, average										$ 28,803		$ 29,704	$ 30,894
Return on average assets	[1]									1.87%		1.61%	1.93%
Efficiency ratio	[3]									40.61%		42.11%	37.59%
Retail Bank
Net interest income (expense)										$ 658		$ 618	$ 623
Provision for credit losses										13		35	8
Noninterest income										193		189	185
Noninterest expenses										731		767	734
Provision (benefit) for income taxes										(39)		(1)	(21)
Net income (loss)										68		4	45
Net loan charge-offs (recoveries)										15		12	29
Assets, average										6,478		6,551	6,474
Loans, average										5,857		5,881	5,792
Deposits, average										$ 23,971		$ 23,558	$ 22,876
Return on average assets	[1]									0.28%		0.02%	0.19%
Efficiency ratio	[3]									85.54%		94.35%	90.64%
Wealth Management
Net interest income (expense)										$ 170		$ 167	$ 177
Provision for credit losses										1		(4)	(20)
Noninterest income										255		243	235
Noninterest expenses										285		301	305
Provision (benefit) for income taxes										(51)		(39)	(43)
Net income (loss)										88		74	84
Net loan charge-offs (recoveries)										(5)		0	(17)
Assets, average										5,401		5,232	5,153
Loans, average										5,256		5,048	4,953
Deposits, average										$ 4,081		$ 4,126	$ 4,151
Return on average assets	[1]									1.63%		1.42%	1.62%
Efficiency ratio	[3]									66.84%		73.48%	73.68%
Finance
Net interest income (expense)										$ (175)		$ (428)	$ (623)
Provision for credit losses										0		0	0
Noninterest income										48		43	44
Noninterest expenses										(4)		(4)	(4)
Provision (benefit) for income taxes										58		142	206
Net income (loss)										(65)		(239)	(369)
Net loan charge-offs (recoveries)										0		0	0
Assets, average										13,954		13,993	11,764
Loans, average										0		0	0
Deposits, average										241		88	138
Other
Net interest income (expense)										36		23	15
Provision for credit losses										2		0	1
Noninterest income										10		4	0
Noninterest expenses										46		27	14
Provision (benefit) for income taxes										(70)	[5]	0	0
Net income (loss)										(72)		0	0
Net loan charge-offs (recoveries)										0		0	0
Assets, average										6,818		6,470	7,355
Loans, average										0		0	(6)
Deposits, average										162		265	267
Accounting Standards Update 2018-01 | Other
Remeasurement of deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act										(107)
Accounting Standards Update 2016-09
Income tax benefit related to employee stock transactions										35		$ 4	$ 3
Accounting Standards Update 2016-09 | Other
Income tax benefit related to employee stock transactions										$ 35
[1]	Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity.
[2]	Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity.
[3]	Noninterest expenses as a percentage of the sum of net interest income (fully taxable equivalent basis) and noninterest income excluding net securities gains.
[4]	Noninterest expenses as a percentage of the sum of net interest income (fully taxable equivalent basis) and noninterest income excluding net securities gains.
[5]	Included a $107 million charge to adjust deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act and a $35 million tax benefit from employee stock transactions.

Business Segment Information (M

Business Segment Information (Market Segment Financial Results) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Net interest income (expense)		$ 545	$ 546	$ 500	$ 470	$ 455	$ 450	$ 445	$ 447	$ 2,061		$ 1,797	$ 1,689
Provision for credit losses										74		248	147
Noninterest income										1,107		1,051	1,035
Noninterest expenses		483	463	457	457	461	493	518	458	1,860		1,930	1,827
Provision (benefit) for income taxes		(218)	(108)	(99)	(66)	(62)	(64)	(42)	(25)	(491)		(193)	(229)
Net income (loss)		$ 112	$ 226	$ 203	$ 202	$ 164	$ 149	$ 104	$ 60	743		477	521
Net loan charge-offs (recoveries)										92		157	101
Assets, average										71,452		71,743	70,247
Loans, average										48,558		48,996	48,628
Deposits, average										$ 57,258		$ 57,741	$ 58,326
Return on average assets	[1],[2]									1.04%		0.67%	0.74%
Efficiency ratio	[3],[4]									58.57%		67.53%	66.93%
Remeasurement of deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act										$ (107)		$ 0	$ 0
Income tax benefit related to employee stock transactions										(35)		0	0
Michigan
Net interest income (expense)										685		666	708
Provision for credit losses										8		9	(27)
Noninterest income										324		320	329
Noninterest expenses										590		620	594
Provision (benefit) for income taxes										(147)		(114)	(151)
Net income (loss)										264		243	319
Net loan charge-offs (recoveries)										(1)		9	8
Assets, average										13,395		13,105	13,598
Loans, average										12,677		12,457	13,016
Deposits, average										$ 21,823		$ 21,777	$ 21,848
Return on average assets	[2]									1.17%		1.08%	1.40%
Efficiency ratio	[4]									58.30%		62.33%	56.93%
California
Net interest income (expense)										$ 719		$ 716	$ 735
Provision for credit losses										100		21	17
Noninterest income										171		162	150
Noninterest expenses										404		434	405
Provision (benefit) for income taxes										(148)		(152)	(166)
Net income (loss)										238		271	297
Net loan charge-offs (recoveries)										33		26	18
Assets, average										18,269		18,012	17,044
Loans, average										18,008		17,731	16,778
Deposits, average										$ 17,533		$ 17,438	$ 17,788
Return on average assets	[2]									1.29%		1.46%	1.57%
Efficiency ratio	[4]									45.26%		49.55%	45.88%
Texas
Net interest income (expense)										$ 465		$ 470	$ 518
Provision for credit losses										(72)		225	131
Noninterest income										131		129	131
Noninterest expenses										375		408	387
Provision (benefit) for income taxes										(109)		12	(54)
Net income (loss)										184		(22)	77
Net loan charge-offs (recoveries)										46		118	46
Assets, average										10,443		11,101	11,778
Loans, average										9,969		10,637	11,168
Deposits, average										$ 9,625		$ 10,168	$ 10,882
Return on average assets	[2]									1.69%		(0.18%)	0.62%
Efficiency ratio	[4]									62.80%		67.94%	59.63%
Other Markets
Net interest income (expense)										$ 331		$ 350	$ 336
Provision for credit losses										36		(7)	25
Noninterest income										423		393	381
Noninterest expenses										449		445	431
Provision (benefit) for income taxes										(75)		(81)	(64)
Net income (loss)										194		224	197
Net loan charge-offs (recoveries)										14		4	29
Assets, average										8,573		9,062	8,708
Loans, average										7,904		8,171	7,673
Deposits, average										$ 7,874		$ 8,005	$ 7,403
Return on average assets	[2]									2.25%		2.47%	2.26%
Efficiency ratio	[4]									59.57%		59.86%	59.92%
Finance & Other
Net interest income (expense)										$ (139)		$ (405)	$ (608)
Provision for credit losses										2		0	1
Noninterest income										58		47	44
Noninterest expenses										42		23	10
Provision (benefit) for income taxes										(12)	[5]	142	206
Net income (loss)										(137)		(239)	(369)
Net loan charge-offs (recoveries)										0		0	0
Assets, average										20,772		20,463	19,119
Loans, average										0		0	(7)
Deposits, average										403		353	405
Accounting Standards Update 2018-01 | Finance & Other
Remeasurement of deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act										(107)
Accounting Standards Update 2016-09
Income tax benefit related to employee stock transactions										35		$ 4	$ 3
Accounting Standards Update 2016-09 | Finance & Other
Income tax benefit related to employee stock transactions										$ 35
[1]	Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity.
[2]	Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity.
[3]	Noninterest expenses as a percentage of the sum of net interest income (fully taxable equivalent basis) and noninterest income excluding net securities gains.
[4]	Noninterest expenses as a percentage of the sum of net interest income (fully taxable equivalent basis) and noninterest income excluding net securities gains.
[5]	Included a $107 million charge to adjust deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act and a $35 million tax benefit from employee stock transactions.

Parent Company FInancial Sta137

Parent Company FInancial Statements Parent Company Financial Statements (Balance Sheets) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Cash and due from subsidiary bank	$ 1,438	$ 1,249
Other short-term investments	96	92
Premises and equipment	466	501
Accrued income and other assets	4,495	4,440
Total assets	71,567	72,978
Medium- and long-term debt	4,622	5,160
Other liabilities	1,069	1,012
Total liabilities	63,604	65,182
Common stock - $5 par value: Authorized - 325,000,000 shares; Issued - 228,164,824 shares	1,141	1,141
Capital surplus	2,122	2,135
Accumulated other comprehensive loss	(451)	(383)	$ (429)
Retained earnings	7,887	7,331
Less cost of common stock in treasury - 55,306,483 shares at 12/31/17 and 52,851,156 shares at 12/31/16	(2,736)	(2,428)
Total shareholders' equity	7,963	7,796	$ 7,560	$ 7,402
Total liabilities and shareholders' equity	$ 71,567	$ 72,978
Common stock, par value	$ 5	$ 5
Common stock, authorized shares	325,000,000	325,000,000
Common stock, issued shares	228,164,824	228,164,824
Shares in treasury	55,306,483	52,851,156
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash and due from subsidiary bank	$ 1,059	$ 761
Other short-term investments	92	87
Investments in subsidiaries, principally banks	7,467	7,561
Premises and equipment	2	2
Accrued income and other assets	127	150
Total assets	8,747	8,561
Medium- and long-term debt	602	604
Other liabilities	182	161
Total liabilities	784	765
Common stock - $5 par value: Authorized - 325,000,000 shares; Issued - 228,164,824 shares	1,141	1,141
Capital surplus	2,122	2,135
Accumulated other comprehensive loss	(451)	(383)
Retained earnings	7,887	7,331
Less cost of common stock in treasury - 55,306,483 shares at 12/31/17 and 52,851,156 shares at 12/31/16	(2,736)	(2,428)
Total shareholders' equity	7,963	7,796
Total liabilities and shareholders' equity	$ 8,747	$ 8,561

Parent Company FInancial Sta138

Parent Company FInancial Statements Parent Company Financial Statements (Statements of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Other interest income									$ 60	$ 27	$ 17
Other noninterest income									111	102	102
Interest on medium- and long-term debt									76	72	52
Salaries and benefits expense									912	961	1,009
Net occupancy expense									154	157	159
Equipment expense									45	53	53
Restructuring charges									45	93	0
Other noninterest expenses									135	135	160
Benefit for income taxes	$ 218	$ 108	$ 99	$ 66	$ 62	$ 64	$ 42	$ 25	491	193	229
Net Income	112	226	203	202	164	149	104	60	743	477	521
Less income allocated to participating securities	0	2	1	2	1	1	1	1	5	4	6
Net income attributable to common shares	$ 112	$ 224	$ 202	$ 200	$ 163	$ 148	$ 103	$ 59	738	473	515
Parent Company
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries									915	549	441
Other interest income									3	1	1
Intercompany management fees									136	138	123
Other noninterest income									8	3	1
Total income									1,062	691	566
Interest on medium- and long-term debt									13	10	14
Salaries and benefits expense									127	114	112
Net occupancy expense									5	5	5
Equipment expense									1	1	1
Restructuring charges									6	33	0
Other noninterest expenses									80	72	70
Total expenses									232	235	202
Income before benefit for income taxes and equity in undistributed earnings of subsidiaries									830	456	364
Benefit for income taxes									(26)	(28)	(27)
Income before equity in undistributed earnings of subsidiaries									856	484	391
Equity in undistributed earnings of subsidiaries, principally banks									(113)	(7)	130
Net Income									743	477	521
Less income allocated to participating securities									5	4	6
Net income attributable to common shares									$ 738	$ 473	$ 515

Parent Company FInancial Sta139

Parent Company FInancial Statements Parent Company Financial Statements (Statements of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net income	$ 112	$ 226	$ 203	$ 202	$ 164	$ 149	$ 104	$ 60	$ 743	$ 477	$ 521
Depreciation and amortization									121	121	118
Net periodic defined benefit (credit) cost									(18)	6	48
Share-based compensation expense									39	34	38
Benefit for deferred income taxes									79	(51)	(71)
Other, net									57	(350)	105
Net cash provided by operating activities									1,103	502	865
Net change in premises and equipment									(69)	(95)	(119)
Net cash used in investing activities									(138)	(270)	(3,255)
Maturities and redemptions of medium- and long-term debt									(500)	(650)	(606)
Repurchases of common stock									(552)	(315)	(240)
Cash dividends paid on common stock									(180)	(152)	(147)
Issuances of common stock under employee stock plans									110	152	22
Purchase and retirement of warrants									0	0	(10)
Net cash used in financing activities									(2,338)	839	2,466
Net increase (decrease) in cash and cash equivalents									(1,373)	1,071	76
Cash and cash equivalents at beginning of period				7,218				6,147	7,218	6,147	6,071
Cash and cash equivalents at end of period	5,845				7,218				5,845	7,218	6,147
Interest paid									122	111	94
Income taxes recovered									336	151	88
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net income									743	477	521
Undistributed earnings of subsidiaries, principally banks									113	7	(130)
Depreciation and amortization									1	1	1
Net periodic defined benefit (credit) cost									(2)	1	5
Share-based compensation expense									16	14	14
Benefit for deferred income taxes									(10)	(3)	0
Other, net									59	6	5
Net cash provided by operating activities									920	503	416
Net change in premises and equipment									0	0	(1)
Net cash used in investing activities									0	0	(1)
Maturities and redemptions of medium- and long-term debt									0	0	(600)
Repurchases of common stock									(552)	(315)	(240)
Cash dividends paid on common stock									(180)	(152)	(147)
Issuances of common stock under employee stock plans									110	152	22
Purchase and retirement of warrants									0	0	(10)
Net cash used in financing activities									(622)	(315)	(975)
Net increase (decrease) in cash and cash equivalents									298	188	(560)
Cash and cash equivalents at beginning of period				$ 761				$ 573	761	573	1,133
Cash and cash equivalents at end of period	$ 1,059				$ 761				1,059	761	573
Interest paid									12	9	16
Income taxes recovered									$ (331)	$ (139)	$ (62)

Summary of Quarterly Financi140

Summary of Quarterly Financial Statements (Unaudited) Summary of Quarterly Financial Statements (Unaudited) (Summary of Quarterly Financial Statements) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 578	$ 579	$ 529	$ 496	$ 484	$ 480	$ 473	$ 472	$ 2,182	$ 1,909	$ 1,784
Interest expense	33	33	29	26	29	30	28	25	121	112	95
Net interest income	545	546	500	470	455	450	445	447	2,061	1,797	1,689
Provision for credit losses	17	24	17	16	35	16	49	148	74	248	147
Net securities losses	0	(1)	(2)	0	(2)	0	(1)	(2)	(3)	(5)	(2)
Noninterest income excluding net securities losses	285	276	278	271	269	272	269	246
Noninterest expenses	483	463	457	457	461	493	518	458	1,860	1,930	1,827
Provision for income taxes	218	108	99	66	62	64	42	25	491	193	229
Net Income	112	226	203	202	164	149	104	60	743	477	521
Less income allocated to participating securities	0	2	1	2	1	1	1	1	5	4	6
Net income attributable to common shares	$ 112	$ 224	$ 202	$ 200	$ 163	$ 148	$ 103	$ 59	$ 738	$ 473	$ 515
Basic earnings per common share	$ 0.65	$ 1.29	$ 1.15	$ 1.15	$ 0.95	$ 0.87	$ 0.60	$ 0.34	$ 4.23	$ 2.74	$ 2.93
Diluted earnings per common share	$ 0.63	$ 1.26	$ 1.13	$ 1.11	$ 0.92	$ 0.84	$ 0.58	$ 0.34	$ 4.14	$ 2.68	$ 2.84
Comprehensive income	$ 107	$ 228	$ 221	$ 206	$ 73	$ 152	$ 137	$ 161	$ 762	$ 523	$ 504