KeyCorp (KEY) 10-K 26 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 20, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	KEYCORP /NEW/
Trading Symbol	KEY
Entity Central Index Key	91,576
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		1,060,687,384
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 20,477,922,563

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and due from banks		$ 671	$ 677
Short-term investments		4,447	2,775
Trading account assets		836	867
Securities available for sale		18,139	20,212
Held-to-maturity securities (fair value: $11,565 and $10,007)		11,830	10,232
Other investments		726	738
Loans, net of unearned income of $736 and $826		86,405	86,038
Allowance for loan and lease losses		(877)	(858)
Net loans		85,528	85,180
Loans held for sale	[1]	1,107	1,104
Premises and equipment		930	978
Operating lease assets		821	540
Goodwill		2,538	2,446
Other intangible assets		416	384
Corporate-owned life insurance		4,132	4,068
Derivative assets		669	803
Accrued income and other assets		3,568	3,864
Discontinued assets		1,340	1,585
Total assets		137,698	136,453
Deposits in domestic offices:
NOW and money market deposit accounts		53,627	54,590
Savings deposits		6,296	6,491
Certificates of deposit ($100,000 or more)		6,849	5,483
Other time deposits		4,798	4,698
Total interest-bearing deposits		71,570	71,262
Noninterest-bearing deposits		33,665	32,825
Total deposits		105,235	104,087
Federal funds purchased and securities sold under repurchase agreements		377	1,502
Bank notes and other short-term borrowings		634	808
Derivative liabilities		291	636
Accrued expense and other liabilities		1,803	1,796
Long-term debt		14,333	12,384
Total liabilities		122,673	121,213
EQUITY
Preferred stock		1,025	1,665
Common Shares, $1 par value; authorized 1,400,000,000 shares; issued 1,256,702,081 and 1,256,702,081 shares		1,257	1,257
Capital surplus		6,335	6,385
Retained earnings	[2]	10,335	9,378
Treasury stock, at cost (187,617,832 and 177,388,429 shares)		(3,150)	(2,904)
Accumulated other comprehensive income (loss)	[2]	(779)	(541)
Key shareholders’ equity		15,023	15,240
Noncontrolling interests		2	0
Total equity		15,025	15,240
Total liabilities and equity		$ 137,698	$ 136,453
[1]	Total loans held for sale include Real estate — residential mortgage loans held for sale at fair value of $71 million at December 31, 2017, and $62 million at December 31, 2016
[2]	These figures for December 31, 2017, have been revised from what has previously been disclosed in our earnings release on January 18, 2018, as a result of updated guidance from the FASB. See Note 1 (“Summary of Significant Accounting Policies”) for more information.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Held-to-maturity securities, fair value	$ 11,565,000,000	$ 10,007,000,000
Unearned income on loans	736,000,000	826,000,000
Aggregate amount of certificates of deposit, denominations	$ 100,000	$ 100,000
Common shares, par value (in dollars per share)	$ 1	$ 1
Common shares, shares authorized (in shares)	1,400,000,000	1,400,000,000
Common shares, shares issued (in shares)	1,256,702,081	1,256,702,081
Treasury stock (in shares)	187,617,832	177,388,429
Loans held for sale	$ 0	$ 0
Residential Mortgage [Member]
Loans held for sale	$ 71,000,000	$ 62,000,000

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INTEREST INCOME
Loans		$ 3,677	$ 2,773	$ 2,149
Loans held for sale		52	34	37
Securities available for sale		369	329	293
Held-to-maturity securities		222	122	96
Trading account assets		27	23	21
Short-term investments		26	22	8
Other investments		17	16	18
Total interest income		4,390	3,319	2,622
INTEREST EXPENSE
Deposits		278	171	105
Federal funds purchased and securities sold under repurchase agreements		1	1	0
Bank notes and other short-term borrowings		15	10	9
Long-term debt		319	218	160
Total interest expense		613	400	274
NET INTEREST INCOME		3,777	2,919	2,348
Provision for credit losses		229	266	166
Net interest income after provision for credit losses		3,548	2,653	2,182
NONINTEREST INCOME
Trust and investment services income		535	464	433
Investment banking and debt placement fees		603	482	445
Service charges on deposit accounts		357	302	256
Operating lease income and other leasing gains		96	62	73
Corporate services income		219	215	198
Cards and payments income		287	233	183
Corporate-owned life insurance income		131	125	127
Consumer mortgage income		26	17	12
Mortgage servicing fees		71	57	48
Net gains (losses) from principal investing		7	20	51
Other income	[1]	146	94	54
Total noninterest income		2,478	2,071	1,880
NONINTEREST EXPENSE
Personnel		2,273	2,073	1,652
Net occupancy		331	305	255
Computer processing		225	255	164
Business services and professional fees		192	235	159
Equipment		114	98	88
Operating lease expense		92	59	47
Marketing		120	101	57
FDIC assessment		82	61	32
Intangible asset amortization		95	55	36
OREO expense, net		11	9	6
Other expense		563	505	344
Total noninterest expense		4,098	3,756	2,840
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		1,928	968	1,222
Income taxes		637	179	303
INCOME (LOSS) FROM CONTINUING OPERATIONS		1,291	789	919
Income (loss) from discontinued operations		7	1	1
NET INCOME (LOSS)		1,298	790	920
Less: Net income (loss) attributable to noncontrolling interests		2	(1)	4
NET INCOME (LOSS) ATTRIBUTABLE TO KEY		1,296	791	916
Income (loss) from continuing operations attributable to Key common shareholders		1,219	753	892
Net income (loss) attributable to Key common shareholders		$ 1,226	$ 754	$ 893
Per Common Share:
Income (loss) from continuing operations attributable to Key common shareholders (in dollars per share)		$ 1.13	$ 0.81	$ 1.06
Income (loss) from discontinued operations, net of taxes (in dollars per share)		0.01	0	0
Net income (loss) attributable to Key common shareholders (in dollars per share)	[2]	1.14	0.81	1.06
Per Common Share — assuming dilution:
Income (loss) from continuing operations attributable to Key common shareholders (in dollars per share)		1.12	0.80	1.05
Income (loss) from discontinued operations, net of taxes (in dollars per share)		0.01	0	0
Net income (loss) attributable to Key common shareholders (in dollars per share)	[2]	1.13	0.80	1.05
Cash dividends declared per common share (in dollars per share)		$ 0.38	$ 0.33	$ 0.290
Weighted-average common shares outstanding (000) (in shares)		1,072,078	927,816	836,846
Effect of convertible preferred stock (in shares)		0	0	0
Effect of common share options and other stock awards (in shares)		16,515	10,720	7,643
Weighted-average common shares and potential common shares outstanding (000) (in shares)	[3]	1,088,593	938,536	844,489
[1]	Net securities gains (losses) totaled less than $1 million for each of the years ended December 31, 2017, 2016, and 2015. For 2017, 2016, and 2015, we did not have any impairment losses related to securities.
[2]	EPS may not foot due to rounding.
[3]	Assumes conversion of Common Share options and other stock awards and/or convertible preferred stock, as applicable.

Consolidated Statements of Inc5

Consolidated Statements of Income (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net securities gains (losses) (less than)	$ 1,000,000	$ 0	$ 0
Impairment losses related to securities	0	0	0
Other Noninterest Income [Member]
Net securities gains (losses) (less than)	$ 1,000,000	$ 1,000,000	$ 1,000,000

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 (loss)	$ 1,298	$ 790	$ 920
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of $13, ($76), and ($32)	(126)	(127)	(54)
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of ($19), ($19), and $17	(72)	(34)	28
Foreign currency translation adjustments, net of income taxes of $9, ($1), and ($14)	12	(1)	(24)
Net pension and postretirement benefit costs, net of income taxes of $80, $19, and ($2)	(52)	26	1
Total other comprehensive income (loss), net of tax	(238)	(136)	(49)
Comprehensive income (loss)	1,060	654	871
Less: Comprehensive income attributable to noncontrolling interests	2	(1)	4
Comprehensive income (loss) attributable to Key	$ 1,058	$ 655	$ 867

Consolidated Statements of Com7

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Income taxes effect on net unrealized (losses) gains on securities available for sale	$ 13	$ (76)	$ (32)
Income taxes effect net unrealized (losses) gains on derivative financial instruments	(19)	(19)	17
Income taxes effect on foreign currency translation adjustments	9	(1)	(14)
Income taxes effect on net pension and postretirement benefit costs	$ 80	$ 19	$ (2)

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Total	Series A Preferred Stock [Member]	Series D Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]Series A Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member]Series A Preferred Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Retained Earnings [Member]Series A Preferred Stock [Member]	Retained Earnings [Member]Series C Preferred Stock [Member]	Retained Earnings [Member]Series D Preferred Stock [Member]	Retained Earnings [Member]Series E Preferred Stock [Member]	Treasury Stock, at Cost [Member]	Treasury Stock, at Cost [Member]Series A Preferred Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
Beginning Balance, Preferred Shares (in shares) at Dec. 31, 2014				2,905,000
Beginning Balance, Common Shares (in shares) at Dec. 31, 2014						859,403,000
Beginning Balance at Dec. 31, 2014				$ 291		$ 1,017		$ 3,986	$ 8,273					$ (2,681)		$ (356)	$ 12
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 920								916								4
Other comprehensive income (loss):	(49)															(49)
Deferred compensation								11
Dividends, Cash [Abstract]
Cash dividends declared on common shares									(244)
Cash dividends declared on Noncumulative Series A Preferred Stock									(23)
Common Shares repurchased (in shares)						(31,267,000)
Common Shares repurchased														(448)
Series A Preferred Stock exchanged for common shares (in shares)					5,000		(33,000)
Issuance of Preferred Stock					$ (1)										$ 1
Redemption of Series C Preferred Stock	0
Common shares reissued (returned) for stock options and other employee benefit plans (in shares)						7,582,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(75)						128
Net contribution from (distribution to) noncontrolling interests																	(3)
Ending Balance, Preferred Shares (in shares) at Dec. 31, 2015				2,900,000
Ending Balance, Common Shares (in shares) at Dec. 31, 2015						835,751,000
Ending Balance at Dec. 31, 2015				$ 290		$ 1,017		3,922	8,922					(3,000)		(405)	13
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	790								791								(1)
Other comprehensive income (loss):	(136)															(136)
Deferred compensation								(4)
Dividends, Cash [Abstract]
Cash dividends declared on common shares									(298)
Cash dividends declared on Noncumulative Series A Preferred Stock										$ (22)	$ (8)	$ (7)
Common Shares issued for the acquisition of FNFG (in shares)						239,732,000
Common Shares issued for the acquisition of FNFG						$ 240		2,591
Common Shares repurchased (in shares)						(10,502,000)
Common Shares repurchased														(140)
Issuance of Preferred Stock (in shares)				14,521,000
Shares issued				$ 1,375				(16)
Redemption of Series C Preferred Stock	0
Common shares reissued (returned) for stock options and other employee benefit plans (in shares)						14,333,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(108)						236
Net contribution from (distribution to) noncontrolling interests																	(12)
Ending Balance, Preferred Shares (in shares) at Dec. 31, 2016		2,900,234		17,421,000
Ending Balance, Common Shares (in shares) at Dec. 31, 2016						1,079,314,000
Ending Balance at Dec. 31, 2016	15,240			$ 1,665		$ 1,257		6,385	9,378					(2,904)		(541)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,298								1,296								2
Other comprehensive income (loss):	(238)															(238)
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	141								141							(141)
Deferred compensation								16
Dividends, Cash [Abstract]
Cash dividends declared on common shares									(410)
Cash dividends declared on Noncumulative Series A Preferred Stock										$ (6)	$ (7)	$ (26)	$ (31)
Common Shares repurchased (in shares)						(36,140,000)
Common Shares repurchased														(665)
Series A Preferred Stock exchanged for common shares (in shares)				2,900,000		20,568,000
Issuance of Preferred Stock				$ (290)				(49)						338
Employee equity compensation program common share repurchases (in shares)						3,520,000
Employee equity compensation program Common Share repurchases														(65)
Redemption of Preferred Stock Series C (in shares)				(14,000,000)
Redemption of Series C Preferred Stock	350			$ (350)
Common shares reissued (returned) for stock options and other employee benefit plans (in shares)						8,862,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(17)						146
Net contribution from (distribution to) noncontrolling interests																	0
Ending Balance, Preferred Shares (in shares) at Dec. 31, 2017			21,000	521,000
Ending Balance, Common Shares (in shares) at Dec. 31, 2017						1,069,084,000
Ending Balance at Dec. 31, 2017	$ 15,025			$ 1,025		$ 1,257		$ 6,335	$ 10,335					$ (3,150)		$ (779)	$ 2

Consolidated Statements of Cha9

Consolidated Statements of Changes in Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash dividends declared on common shares, per share (in dollars per share)	$ 0.38	$ 0.33	$ 0.290
Series A Preferred Stock [Member]
Cash dividends declared on Preferred Stock (in dollars per share)	1.9375	7.75	$ 7.75
Series C Preferred Stock [Member]
Cash dividends declared on Preferred Stock (in dollars per share)	0.539063	0.539063
Series D Preferred Stock [Member]
Cash dividends declared on Preferred Stock (in dollars per share)	50	$ 13.33
Series E Preferred Stock [Member]
Cash dividends declared on Preferred Stock (in dollars per share)	$ 1.544012

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 (loss)	$ 1,298	$ 790	$ 920
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Provision for credit losses	229	266	166
Depreciation and amortization expense, net	407	314	247
Accretion of acquired loans	203	116	0
Increase in cash surrender value of corporate-owned life insurance	(119)	(111)	(108)
Stock-based compensation expense	100	99	58
FDIC reimbursement (payments), net of FDIC expense	(3)	13	0
Deferred income taxes (benefit)	303	11	(76)
Proceeds from sales of loans held for sale	11,963	8,572	7,333
Originations of loans held for sale, net of repayments	(11,846)	(8,361)	(7,072)
Net losses (gains) from sale of loans held for sale	(181)	(139)	(103)
Net losses (gains) from principal investing	(7)	(20)	(51)
Net losses (gains) and writedown on OREO	5	4	4
Net losses (gains) on leased equipment	3	7	(6)
Net losses (gains) on sales of fixed assets	24	56	8
Net securities losses (gains)	(1)	0	0
Net decrease (increase) in trading account assets	31	(79)	(38)
Direct acquisition costs	0	(44)	0
Other operating activities, net	(594)	195	(151)
NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES	1,815	1,689	1,131
INVESTING ACTIVITIES
Cash received (used) in acquisitions, net of cash acquired	(144)	(481)	0
Net decrease (increase) in short-term investments, excluding acquisitions	(1,672)	(68)	1,562
Purchases of securities available for sale	(3,002)	(5,718)	(4,090)
Proceeds from sales of securities available for sale	915	4,249	19
Proceeds from prepayments and maturities of securities available for sale	3,999	4,241	3,098
Proceeds from prepayments and maturities of held-to-maturity securities	1,797	1,627	1,102
Purchases of held-to-maturity securities	(3,398)	(6,968)	(988)
Purchases of other investments	(87)	(46)	(32)
Proceeds from sales of other investments	117	243	145
Proceeds from prepayments and maturities of other investments	4	4	8
Net decrease (increase) in loans, excluding acquisitions, sales and transfers	(945)	(3,580)	(2,951)
Proceeds from sales of portfolio loans	183	140	110
Proceeds from corporate-owned life insurance	55	29	46
Purchases of premises, equipment, and software	(112)	(145)	(75)
Proceeds from sales of premises and equipment	0	0	1
Proceeds from sales of OREO	51	16	22
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	(2,239)	(6,457)	(2,023)
FINANCING ACTIVITIES
Net increase (decrease) in deposits, excluding acquisitions	1,148	4,047	(952)
Net increase (decrease) in short-term borrowings	(1,299)	(1,294)	(93)
Net proceeds from issuance of long-term debt	2,852	2,827	3,756
Payments on long-term debt	(748)	(1,308)	(1,172)
Issuance of preferred shares	0	1,009	0
Repurchase of Common Shares	(664)	(140)	(448)
Employee equity compensation program Common Share repurchases	(66)	0	0
Redemption of Preferred Stock Series C	(350)	0	0
Net proceeds from reissuance of Common Shares	25	32	22
Cash dividends paid	(480)	(335)	(267)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	418	4,838	846
NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS	(6)	70	(46)
CASH AND DUE FROM BANKS AT BEGINNING OF YEAR	677	607	653
CASH AND DUE FROM BANKS AT END OF YEAR	671	677	607
Additional disclosures relative to cash flows:
Interest paid	598	429	329
Income taxes paid (refunded)	6	144	281
Noncash items:
Reduction of secured borrowing and related collateral	40	67	160
Loans transferred to portfolio from held for sale	105	10	1
Loans transferred to held for sale from portfolio	42	45	63
Loans transferred to other real estate owned	37	36	20
Reinsurance Retention Policy, Excess Retention, Amount Reinsured	18	0	0
First Niagara assets acquired	0	35,616	0
First Niagara liabilities assumed	0	33,028	0
Preferred Stock [Member]
Noncash items:
Common Shares issued for the acquisition of FNFG	0	350	0
Common Stock [Member]
Noncash items:
Common Shares issued for the acquisition of FNFG	$ 0	$ 2,831	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	1. Summary of Significant Accounting Policies Organization We are one of the nation’s largest bank-based financial services companies, with consolidated total assets of $137.7 billion at December 31, 2017 . We provide deposit, lending, cash management, insurance, and investment services to individuals and small and medium-sized businesses through our subsidiary, KeyBank. We also provide a broad range of sophisticated corporate and investment banking products, such as merger and acquisition advice, public and private debt and equity, syndications, and derivatives to middle market companies in selected industries throughout the United States through our subsidiary, KBCM. As of December 31, 2017 , KeyBank operated 1,197 full-service retail banking branches and 1,572 ATMs in 15 states, as well as additional offices, online and mobile banking capabilities, and a telephone banking call center. Additional information pertaining to our two major business segments, Key Community Bank and Key Corporate Bank, is included in Note 25 (“ Line of Business Results ”). Use of Estimates Our accounting policies conform to GAAP and prevailing practices within the financial services industry. We must make certain estimates and judgments when determining the amounts presented in our consolidated financial statements and the related notes. If these estimates prove to be inaccurate, actual results could differ from those reported. Basis of Presentation The consolidated financial statements include the accounts of KeyCorp and its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. Some previously reported amounts have been reclassified to conform to current reporting practices. The consolidated financial statements include any voting rights entities in which we have a controlling financial interest. In accordance with the applicable accounting guidance for consolidations, we consolidate a VIE if we have: (i) a variable interest in the entity; (ii) the power to direct activities of the VIE that most significantly impact the entity’s economic performance; and (iii) the obligation to absorb losses of the entity or the right to receive benefits from the entity that could potentially be significant to the VIE (i.e., we are considered to be the primary beneficiary). Variable interests can include equity interests, subordinated debt, derivative contracts, leases, service agreements, guarantees, standby letters of credit, loan commitments, and other contracts, agreements and financial instruments. See Note 13 (“ Variable Interest Entities ”) for information on our involvement with VIEs. We use the equity method to account for unconsolidated investments in voting rights entities or VIEs if we have significant influence over the entity’s operating and financing decisions (usually defined as a voting or economic interest of 20% to 50% , but not controlling). Unconsolidated investments in voting rights entities or VIEs in which we have a voting or economic interest of less than 20% generally are carried at cost or fair value. Investments held by our registered broker-dealer and investment company subsidiaries (primarily principal investments) are carried at fair value. In preparing these financial statements, subsequent events were evaluated through the time the financial statements were issued. Financial statements are considered issued when they are widely distributed to all shareholders and other financial statement users or filed with the SEC. Statements of Cash Flows Cash and due from banks are considered “cash and cash equivalents” for financial reporting purposes. Loans Loans held in portfolio, which management has the intent and ability to hold for the foreseeable future or until maturity or payoff, are carried at the principal amount outstanding, net of unearned income, including net deferred loan fees and costs and unamortized premiums and discounts. We defer certain nonrefundable loan origination and commitment fees, and the direct costs of originating or acquiring loans. The net deferred amount is amortized over the estimated lives of the related loans as an adjustment to the yield. Direct financing leases are carried at the aggregate of the lease receivable plus estimated unguaranteed residual values, less unearned income and deferred initial direct fees and costs. Unearned income on direct financing leases is amortized over the lease terms using a method approximating the interest method that produces a constant rate of return. Deferred initial direct fees and costs are amortized over the lease terms as an adjustment to the yield. The residual value component of a lease represents the fair value of the leased asset at the end of the lease term. We rely on industry data, historical experience, independent appraisals and the experience of the equipment leasing asset management team to value lease residuals. Relationships with a number of equipment vendors give the asset management team insight into the life cycle of the leased equipment, pending product upgrades and competing products. Residual values are reviewed at least annually to determine if an other-than-temporary decline in value has occurred. In the event of such a decline, the residual value is adjusted to its fair value. Impairment charges and net gains or losses on sales of lease residuals are included in “other income” on the income statement. Loans Held for Sale Loans held for sale generally include certain residential and commercial mortgage loans and other commercial loans. Loans are initially classified as held for sale when they are individually identified as being available for immediate sale and a formal plan exists to sell them. Loans held for sale are recorded at either fair value, if elected, or the lower of cost or fair value. When a loan is originated as held-for-sale, we do not defer the related fees and costs. Our commercial loans (including commercial mortgage and non-mortgage loans), which we originated and intend to sell, are carried at the lower of aggregate cost or fair value. Beginning with the third quarter of 2016, we elected the fair value option for our consumer real estate - residential mortgages loans. Fair value is determined based on available market data for similar assets, expected cash flows, and appraisals of underlying collateral or the credit quality of the borrower. Subsequent declines in fair value for loans held for sale are recognized as a charge to “other income” on the income statement. Subsequent increases and decreases in fair value for loans elected to be measured at fair value are also recorded to “other income” on the income statement. Additional information regarding fair value measurements associated with our loans held for sale is provided in Note 7 (“ Fair Value Measurements ”). We may transfer certain loans to held for sale at the lower of cost or fair value. If a loan is transferred from the loan portfolio to the held-for-sale category, any write-down in the carrying amount of the loan at the date of transfer is recorded as a reduction in the ALLL. When a loan is transferred into the held for sale category, we stop amortizing the related deferred fees and costs. The remaining unamortized fees and costs are recognized as part of the cost basis of the loan at the time it is sold. We may also transfer loans from held for sale to the loan portfolio held for investment. If a loan held for sale for which fair value accounting was elected is transferred to held for investment, it will continue to be accounted for at fair value in the loan portfolio. Additional information regarding our loans held for sale is provided in Note 5 (“ Loans and Loans Held for Sale ”). Nonperforming Loans Nonperforming loans are loans for which we do not accrue interest income, and include commercial and consumer loans and leases, as well as current year TDRs and nonaccruing TDR loans from prior years. Nonperforming loans do not include loans held for sale or PCI loans. We generally classify commercial loans as nonperforming and stop accruing interest (i.e., designate the loan “nonaccrual”) when the borrower’s principal or interest payment is 90 days past due unless the loan is well-secured and in the process of collection. Commercial loans are also placed on nonaccrual status when payment is not past due but we have serious doubts about the borrower’s ability to comply with existing repayment terms. Once a loan is designated nonaccrual (and as a result assessed for impairment), the interest accrued but not collected generally is charged against the ALLL, and payments subsequently received generally are applied to principal. Commercial loans generally are charged off in full or charged down to the fair value of the underlying collateral when the borrower’s payment is 180 days past due. We generally classify consumer loans as nonperforming and stop accruing interest when the borrower’s payment is 120 days past due, unless the loan is well-secured and in the process of collection. Any second lien home equity loan with an associated first lien that is 120 days or more past due or in foreclosure, or for which the first mortgage delinquency timeframe is unknown, is reported as a nonperforming loan. Secured loans that are discharged through Chapter 7 bankruptcy and not formally re-affirmed are designated as nonperforming and TDRs. Our charge-off policy for most consumer loans takes effect when payments are 120 days past due. Home equity and residential mortgage loans generally are charged down to net realizable value when payment is 180 days past due. Credit card loans and similar unsecured products continue to accrue interest until the account is charged off at 180 days past due. Commercial and consumer loans may be returned to accrual status if we are reasonably assured that all contractually due principal and interest are collectible and the borrower has demonstrated a sustained period (generally six months) of repayment performance under the contracted terms of the loan and applicable regulation. Impaired Loans A loan is considered to be impaired when, based on current information and events, it is probable that we will be unable to collect all amounts due (both principal and interest) according to the contractual terms of the loan agreement. All commercial and consumer TDRs, regardless of size, and all non-accrual commercial loans with an outstanding balance of $2.5 million or greater are individually evaluated for impairment and assigned a specific reserve. Commercial non-accrual loans of less than $2.5 million and all non-accrual consumer loans are aggregated and collectively evaluated for impairment. The amount of the reserve is estimated based on the criteria outlined in the “Allowance for Loan and Lease Losses” section of this note. Allowance for Loan and Lease Losses The ALLL represents our estimate of incurred credit losses inherent in the loan portfolio at the balance sheet date. We establish the amount of this allowance by analyzing the quality of the loan portfolio at least quarterly, and more often if deemed necessary. We segregate our loan portfolio between commercial and consumer loans and develop and document our methodology to determine the ALLL accordingly. We believe these portfolio segments represent the most appropriate level for determining our historical loss experience, as well as the level at which we monitor credit quality and risk characteristics of the portfolios. Commercial loans, which generally have larger individual balances, constitute a significant portion of our total loan portfolio. The consumer portfolio typically includes smaller-balance homogeneous loans. We estimate the appropriate level of our ALLL by applying expected loss rates to existing loans with similar risk characteristics. Expected loss rates for commercial loans are derived from a statistical analysis of our historical default and loss severity experience. The analysis utilizes probability of default and loss given default to assign loan grades using our internal risk rating system. Our expected loss rates are reviewed quarterly and updated as necessary. As of December 31, 2017 , the probability of default ratings was based on our default data for the period from January 2008 through October 2017, which encompasses the last downturn period as well as our more recent positive credit experience. We adjust expected loss rates based on calculated estimates of the average time period from initial loss indication to the initial loss recorded for an individual loan. Expected loss rates for consumer loans are statistically derived from an analysis of our historical default and loss severity experience, and is sensitive to change in delinquency status. Consumer loans are analyzed quarterly in homogeneous product-type pools that share similar risk attributes, including the application of delinquency roll rate models and credit loss severity estimates. Incurred losses that are not yet individually identifiable are measured as the estimate of the average time period for initial loss indication to initial loss recorded for consumer loans. The ALLL may be adjusted to reflect our current assessment of many qualitative factors that may not be directly measured in the statistical analysis of expected loss, including: • changes in international, national, regional, and local economic and business conditions; • changes in the experience, ability, and depth of our lending management and staff; • changes in lending policies and procedures, including changes in underwriting standards and collection, charge-off, and recovery practices; • changes in the nature and volume of the loan portfolio, including the existence and effect of any concentrations of credit, and changes in the level of such concentrations; • changes in the volume and/or severity of past due, nonaccrual, and adversely classified or graded loans; and • external factors, such as competition, legal developments, and regulatory requirements. For all commercial and consumer loan TDRs, regardless of size, as well as non-accrual commercial loans with an outstanding balance of $2.5 million or greater, we conduct further analysis to determine the probable loss content and assign a specific allowance to the loan if deemed appropriate. We estimate the extent of the individual impairment for commercial loans and TDRs by comparing the recorded investment of the loan with the estimated present value of its future cash flows, the fair value of its underlying collateral, or the loan’s observable market price. Secured consumer loan TDRs that are discharged through Chapter 7 bankruptcy and not formally re-affirmed are adjusted to reflect the fair value of the underlying collateral, less costs to sell. Other consumer loan TDRs are assigned a specific allocation based on the estimated present value of future cash flows using the effective interest rate. A specific allowance also may be assigned — even when sources of repayment appear sufficient — if we remain uncertain about whether the loan will be repaid in full. On at least a quarterly basis, we evaluate the appropriateness of our loss estimation methods to reduce differences between estimated incurred losses and actual losses. Liability for Credit Losses on Lending-Related Commitments The liability for credit losses inherent in lending-related commitments, such as letters of credit and unfunded loan commitments, is included in “accrued expense and other liabilities” on the balance sheet. We establish the amount of this liability by considering both historical trends and current market conditions quarterly, or more often if deemed necessary. Fair Value Measurements Fair value is defined as the price to sell an asset or transfer a liability in an orderly transaction between market participants in our principal market. In other words, fair value represents an exit price at the measurement date. Market participants are buyers and sellers who are independent, knowledgeable, and willing and able to transact in the principal (or most advantageous) market for the asset or liability being measured. Current market conditions, including imbalances between supply and demand, are considered in determining fair value. We value our assets and liabilities based on the principal market where each would be sold (in the case of assets) or transferred (in the case of liabilities). The principal market is the forum with the greatest volume and level of activity. In the absence of a principal market, valuation is based on the most advantageous market (i.e., the market where the asset could be sold at a price that maximizes the amount to be received or the liability transferred at a price that minimizes the amount to be paid). In the absence of observable market transactions, we consider liquidity valuation adjustments to reflect the uncertainty in pricing the instruments. In measuring the fair value of an asset, we assume the highest and best use of the asset by a market participant — not just the intended use — to maximize the value of the asset. We also consider whether any credit valuation adjustments are necessary based on the counterparty’s credit quality. When measuring the fair value of a liability, we assume that the transfer will not affect the associated nonperformance risk. Nonperformance risk is the risk that an obligation will not be satisfied, and encompasses not only our own credit risk (i.e., the risk that we will fail to meet our obligation), but also other risks such as settlement risk (i.e., the risk that upon termination or sale, the contract will not settle). We consider the effect of our own credit risk on the fair value for any period in which fair value is measured. There are three acceptable techniques for measuring fair value: the market approach, the income approach, and the cost approach. The appropriate technique for valuing a particular asset or liability depends on the exit market, the nature of the asset or liability being valued, and how a market participant would value the same asset or liability. Ultimately, selecting the appropriate valuation method requires significant judgment, and applying the valuation technique requires sufficient knowledge and expertise. Valuation inputs refer to the assumptions market participants would use in pricing a given asset or liability. Inputs can be observable or unobservable. Observable inputs are assumptions based on market data obtained from an independent source. Unobservable inputs are assumptions based on our own information or assessment of assumptions used by other market participants in pricing the asset or liability. Our unobservable inputs are based on the best and most current information available on the measurement date. All inputs, whether observable or unobservable, are ranked in accordance with a prescribed fair value hierarchy that gives the highest ranking to quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest ranking to unobservable inputs (Level 3). Fair values for Level 2 assets or liabilities are based on one or a combination of the following factors: (i) quoted market prices for similar assets or liabilities; (ii) observable inputs, such as interest rates or yield curves; or (iii) inputs derived principally from or corroborated by observable market data. The level in the fair value hierarchy ascribed to a fair value measurement in its entirety is based on the lowest level input that is significant to the measurement. We consider an input to be significant if it drives 10% or more of the total fair value of a particular asset or liability. Assets and liabilities may transfer between levels based on the observable and unobservable inputs used at the valuation date, as the inputs may be influenced by certain market conditions. We recognize transfers between levels of the fair value hierarchy at the end of the reporting period. Typically, assets and liabilities are considered to be fair valued on a recurring basis if fair value is measured regularly. However, if the fair value measurement of an instrument does not necessarily result in a change in the amount recorded on the balance sheet, assets and liabilities are considered to be fair valued on a nonrecurring basis. This generally occurs when we apply accounting guidance that requires assets and liabilities to be recorded at the lower of cost or fair value, or assessed for impairment. At a minimum, we conduct our valuations quarterly. Additional information regarding fair value measurements and disclosures is provided in Note 7 (“ Fair Value Measurements ”). Short-Term Investments Short-term investments consist of segregated, interest-bearing deposits due from banks, the Federal Reserve, and certain non-U.S. banks as well as reverse repurchase agreements. Reverse repurchase agreements are further described under the “Repurchase agreements” heading in this section. Trading Account Assets Trading account assets are debt and equity securities, as well as commercial loans, that we purchase and hold but intend to sell in the near term. These assets are reported at fair value. Realized and unrealized gains and losses on trading account assets are reported in “other income” on the income statement. Securities Securities available for sale. Securities available for sale are securities that we intend to hold for an indefinite period of time but that may be sold in response to changes in interest rates, prepayment risk, liquidity needs, or other factors. Securities available for sale are reported at fair value. Unrealized gains and losses (net of income taxes) deemed temporary are recorded in equity as a component of AOCI on the balance sheet. Unrealized losses on equity securities deemed “other-than-temporary,” and realized gains and losses resulting from sales of securities using the specific identification method, are included in “other income” on the income statement. Unrealized losses on debt securities deemed “other-than-temporary” are included in “other income” on the income statement or in AOCI, as further described under the heading “Other-than-Temporary Impairments” in this note and in Note 8 (“ Securities ”). “Other securities” held in the available-for-sale portfolio consist of marketable equity securities that are traded on a public exchange such as the NYSE or Nasdaq and convertible preferred stock of privately held companies. Held-to-maturity securities. Held-to-maturity securities are debt securities that we have the intent and ability to hold until maturity. Debt securities are carried at cost and adjusted for amortization of premiums and accretion of discounts using the interest method. This method produces a constant rate of return on the adjusted carrying amount. “Other securities” held in the held-to-maturity portfolio consist of foreign bonds and capital securities. Other Investments Other investments include equity and mezzanine instruments, such as certain real estate-related investments that are carried at fair value, as well as other types of investments that generally are carried at cost. The carrying amounts of the investments carried at cost are adjusted for declines in value if they are considered to be other-than-temporary. These adjustments are included in “other income” on the income statement. Other-than-Temporary Impairments If the amortized cost of a debt security is greater than its fair value and we intend to sell it, or it is more-likely-than-not that we will be required to sell it, before the expected recovery of the amortized cost, then the entire impairment is recognized in earnings. If we have no intent to sell the security, or it is more-likely-than-not that we will not be required to sell it, before expected recovery, then the credit portion of the impairment is recognized in earnings, while the remaining portion attributable to factors such as liquidity and interest rate changes is recognized in equity as a component of AOCI on the balance sheet. The credit portion is equal to the difference between the cash flows expected to be collected and the amortized cost of the debt security. Generally, if the amortized cost of an equity security is greater than its fair value by more than 20% consistently for more than six months, the difference is considered to be other-than-temporary. Derivatives and Hedging All derivatives are recognized as either “derivative assets” or “derivative liabilities” on the balance sheet at fair value. The net increase or decrease in derivatives is included in “other operating activities, net” within the statement of cash flows. Accounting for changes in fair value (i.e., gains or losses) of derivatives differs depending on whether the derivative has been designated and qualifies as part of a hedge relationship, and further, on the type of hedge relationship. For derivatives that are not designated as hedging instruments, any gain or loss, as well as any premium paid or received, is recognized immediately in earnings in “corporate services income” and “other income” on the income statement. A derivative that is designated and qualifies as a hedging instrument must be designated as a fair value hedge, a cash flow hedge, or a hedge of a net investment in a foreign operation. We have only designated derivatives as hedging instruments. A fair value hedge is used to limit exposure to changes in the fair value of existing assets, liabilities, and commitments caused by changes in interest rates or other economic factors. The effective portion of a change in the fair value of an instrument designated as a fair value hedge is recorded in earnings at the same time as a change in fair value of the hedged item, resulting in no effect on net income. The ineffective portion of a change in the fair value of such a hedging instrument is recognized in “other income” on the income statement, with no corresponding offset. A cash flow hedge is used to minimize the variability of future cash flows that is caused by changes in interest rates or other economic factors. The effective portion of a gain or loss on a cash flow hedge is recorded as a component of AOCI on the balance sheet and reclassified to earnings in the same period in which the hedged transaction affects earnings (e.g., when we incur variable-rate interest on debt, earn variable-rate interest on loans, or sell commercial real estate loans). The ineffective portion of a cash flow hedge is included in “other income” on the income statement. A net investment hedge is used to hedge the exposure of changes in the carrying value of investments as a result of changes in the related foreign exchange rates. The effective portion of a gain or loss on a net investment hedge is recorded as a component of AOCI on the balance sheet when the terms of the derivative match the notional and currency risk being hedged. The effective portion is subsequently reclassified into income when the hedged transaction affects earnings (e.g., when we dispose or liquidate a foreign subsidiary). The ineffective portion of a net investment hedge is included in “other income” on the income statement. Hedge “effectiveness” is determined by the extent to which changes in the fair value of a derivative instrument offset changes in the fair value, cash flows, or carrying value attributable to the risk being hedged. If the relationship between the change in the fair value of the derivative instrument and the change in the hedged item falls within a range considered to be the industry norm, the hedge is considered “highly effective” and qualifies for hedge accounting. A hedge is “ineffective” if the relationship between the changes falls outside the acceptable range. In that case, hedge accounting is discontinued on a prospective basis. Hedge effectiveness is tested at least quarterly. Additional information regarding the accounting for derivatives is provided in Note 9 (“ Derivatives and Hedging Activities ”). Offsetting Derivative Positions We take into account the impact of bilateral collateral and master netting agreements that allow us to settle all derivative contracts held with a single counterparty on a net basis, and to offset the net derivative position with the related cash collateral when recognizing derivative assets and liabilities. As a result, we could have derivative contracts with negative fair values included in derivative assets on the balance sheet and contracts with positive fair values included in derivative liabilities. Additional information regarding derivative offsetting is provided in Note 9 (“ Derivatives and Hedging Activities ”). Servicing Assets We service commercial real estate and residential mortgages loans. Servicing assets and liabilities purchased or retained are initially measured at fair value and are recorded as a component of “accrued income and other assets” on the balance sheet. When no ready market value (such as quoted market prices, or prices based on sales or purchases of similar assets) is available to determine the fair value of servicing assets, fair value is determined by calculating the present value of future cash flows associated with servicing the loans. This calculation is based on a number of assumptions, including the market cost of servicing, the discount rate, the prepayment rate, and the default rate. We remeasure our servicing assets using the amortization method at each reporting date. The amortization of servicing assets is determined in proportion to, and over the period of, the estimated net servicing income and recorded in “mortgage servicing fees” on the income statement. Servicing assets are evaluated quarterly for possible impairment. This process involves stratifying the assets based upon one or more predominant risk characteristics and determining the fair value of each class. The characteristics may include financial asset type, size, interest rate, date of origination, term and geographic location. If the evaluation indicates that the carrying amount of the servicing assets exceeds their fair value, the carrying amount is reduced by recording a charge to income in the amount of such excess and establishing a valuation reserve allowance. Additional information pertaining to servicing assets is included in Note 10 (“ Mortgage Servicing Assets ”). Business Combinations We account for our business combinations using the acquisition method of accounting. Under this accounting method, the acquired company’s assets and liabilities are recorded at fair value at the date of acquisition, except as provided for by the applicable accounting guidance, and the results of operations of the acquired company are combined with Key’s results from that date forward. Acquisition costs are expensed when incurred. The difference between the purchase price and the fair value of the net assets acquired (including identifiable intangible assets) is recorded as goodwill. Our accounting policy for intangible assets is summarized in this note under the heading “Goodwill and Other Intangible Assets.” Additional information regarding acquisitions is provided in Note 2 (“ Business Combination ”) and Note 15 (“ Acquisitions, Divestiture, and Discontinued Operations ”). Goodwill and Other Intangible Assets Goodwill represents the amount by which the cost of net assets acquired in a business combination exceeds their f air value. Goodwill is assigned to reporting units as of the acquisition date based on the expected benefit to such reporting unit from the synergies of the business combination. Goodwill is tested at the reporting unit level for impairment, at least annually as of October 1, or as events and circumstances change that would more-likely-than-not reduce the fair value of a reporting unit below its carrying amount. We may elect to perform a qualitative analysis to determine whether or not it is more-likely-than-not that the fair value of a reporting unit is less than its carrying amount. If we elect to bypass this qualitative analysis, or conclude via qualitative analysis that it is more-likely-than-not that the fair value of a reporting unit is less than its carrying value, a two-step goodwill impairment test is performed. In the first step, the fair value of each reporting unit is compared with its carrying value. If the fair value is greater than the carrying value, then the reporting unit's goodwill is deemed not to be impaired. If the fair value is less than the carrying value, then the second step is performed, which measures the amount of impairment by comparing the carrying amount of goodwill to its implied fair value. If the implied fair value of the goodwill e

Business Combination

Business Combination	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Business Combination	2. Business Combination First Niagara On August 1, 2016 (the “Acquisition Date”), we acquired all of the outstanding common shares of First Niagara, the parent company of First Niagara Bank, for total consideration of approximately $ 4.0 billion and thereby acquired First Niagara Bank's approximately 390 branch locations across New York, Pennsylvania, Connecticut, and Massachusetts. The merger with First Niagara enabled us to expand in the New England market and into the Pennsylvania market, improve our core deposit base, and add additional scale in our banking operations. The results of First Niagara’s operations are included in our consolidated financial statements from the Acquisition Date. Under the terms of the merger agreement, each outstanding share of First Niagara common stock was converted into the right to receive 0.680 KeyCorp Common Shares and $2.30 in cash, for a total per share value of $ 10.26 , based on the $ 11.70 closing price of KeyCorp’s stock on July 29, 2016. In the aggregate, First Niagara stockholders received 240 million shares of KeyCorp common stock. Also under the terms of the merger agreement, First Niagara employee stock options and restricted stock awards converted into options to purchase and receive KeyCorp common stock. These options and restricted stock awards had a fair value of $26 million on the date of acquisition. Our methodology for valuing employee stock options is disclosed in Note 17 (“ Stock-Based Compensation ”) under the heading “Stock Options.” Our methodology for valuing restricted stock awards is disclosed in Note 17 (“ Stock-Based Compensation ”) under the heading “Long-Term Incentive Compensation Program.” In addition, at the time of the merger, each share of First Niagara preferred stock, Series B, was converted into the right to receive a share of KeyCorp preferred stock, Series C, a newly created series of KeyCorp preferred stock. Additional information on this series of preferred stock is provided in Note 24 (" Shareholders' Equity "). On October 7, 2016, First Niagara Bank merged with and into KeyBank, with KeyBank as the surviving entity. Systems and client conversion also occurred during the fourth quarter of 2016 in connection with the bank merger. The acquisition of First Niagara constituted a business combination and was accounted for under the acquisition method of accounting. Accordingly, the assets acquired, the liabilities assumed, and the consideration paid were recorded at their estimated fair value as of the acquisition date. The following table provides the final purchase price calculation as of the Acquisition Date and the identifiable assets purchased and the liabilities assumed at their estimated fair value. These fair value measurements are based on internal and third-party valuations. in millions Consideration paid: KeyCorp common stock issued $ 2,831 Cash payments to First Niagara stockholders 811 Exchange of First Niagara preferred stock for KeyCorp preferred stock 350 Total consideration paid $ 3,992 Statement of Net Assets Acquired at Fair Value: ASSETS Cash and due from banks and short-term investments $ 620 Investment securities 9,012 Other investments 297 Loans 23,590 Premises and equipment 245 Other intangible assets 385 Accrued income and other assets 1,467 Total assets $ 35,616 LIABILITIES Deposits $ 28,994 Bank notes and other short-term borrowings 2,698 Accrued expense and other liabilities 490 Long-term debt 846 Total liabilities $ 33,028 Net identifiable assets acquired 2,588 Goodwill $ 1,404 Measurement Period Adjustments We estimated the fair value of loans acquired from First Niagara by utilizing the discounted cash flow method within the income approach. This methodology aggregates the purchased loans by category and risk rating. Cash flows for each category were determined by estimating future credit losses and the rate of prepayments. Projected monthly cash flows were then discounted to present value based on a market rate for similar loans. There was no carryover of First Niagara’s ALLL associated with the loans we acquired. The valuation was final at June 30, 2017. The amounts reflected in the following table represent the change in the fair values of acquired assets as of June 30, 2017: in millions Acquired Asset or Liability Balance Sheet Line Item Provisional Estimate Final Increase (Decrease) Loans Loans $ 23,645 $ 23,590 $ (55 ) Tax adjustment on previous fair value measurement Accrued income and other assets 1,449 1,467 18 Unfunded lending-related commitments Accrued expense and other liabilities 67 65 (2 ) Deferred compensation Accrued expense and other liabilities 39 41 2 The finalization of the fair values also impacted various income statement line items on the Consolidated Statements of Income. The amounts shown in the table below represent the increase (decrease) in the respective line items for the previous reporting period had the final fair value been recorded at the Acquisition Date for the twelve months ended December 31, 2017. in millions Portion Related to Acquired Asset or Liability Income Statement Line Item Previous Reporting Period (a) Loans Interest income $ 42 Loans Provision for credit losses 1 Loans Other noninterest income (3 ) Unfunded lending-related commitments Other noninterest income (4 ) (a) Represents the change in amount that should have been reported compared to what was actually reported in the December 31, 2016, Consolidated Statements of Income. Intangible assets consisted of the core deposit intangible, the commercial purchased credit card relationships, the consumer purchased credit card relationships, and other intangible assets. The core deposit intangible asset of $356 million recognized as part of the First Niagara merger is being amortized over its estimated useful life of approximately ten years utilizing an accelerated method. The commercial purchased credit card relationships recognized as part of the First Niagara merger are being amortized over their estimated useful life of approximately six years utilizing an accelerated method. The consumer purchased credit card relationships recognized as part of the First Niagara merger are being amortized over their estimated useful life of approximately nine years utilizing an accelerated method. Goodwill of $1.4 billion was recorded as a result of the transaction and is not amortized for book purposes. $1.1 billion of goodwill was assigned to our Key Community Bank segment and $280 million of goodwill was assigned to our Key Corporate Bank segment. The goodwill recorded is not deductible for tax purposes. The following table shows the changes in the carrying amount of goodwill by reporting unit. in millions Key Community Bank Key Corporate Bank Total BALANCE AT DECEMBER 31, 2015 $ 979 $ 81 $ 1,060 Acquisition of First Niagara 1,109 277 1,386 BALANCE AT DECEMBER 31, 2016 2,088 358 2,446 Tax adjustment on previous fair value measurements (15 ) (4 ) (19 ) Loan adjustment on previous fair value measurements 30 7 37 BALANCE AT JUNE 30, 2017 $ 2,103 $ 361 $ 2,464 Certificates of deposit were valued by projecting out the expected cash flows based on the contractual terms of the certificates of deposit. These cash flows were discounted based on a market rate for a certificate of deposit with a corresponding maturity. The fair values of savings and transaction deposit accounts acquired from First Niagara were assumed to approximate the carrying value as these accounts have no stated maturity and are payable on demand. Direct acquisition costs related to the First Niagara acquisition were expensed as incurred and amounted to less than $1 million for the twelve months ended December 31, 2017 , and $44 million for the twelve months ended December 31, 2016 . Professional fees and charitable contributions comprised the majority of these direct acquisition costs, which also included franchise and business taxes and other noninterest expenses. These direct acquisition costs are part of our total merger-related charges. The following table presents unaudited pro forma information as if the acquisition of First Niagara had occurred on January 1, 2015. This pro forma information gives effect to certain adjustments, including purchase accounting fair value adjustments, amortization of core deposit and other intangibles, and related income tax effects. Merger-related charges related to the First Niagara merger that we incurred during the twelve months ended December 31, 2016 , and 2015, are not reflected in the unaudited pro forma amounts. The pro forma information does not necessarily reflect the results of operations that would have occurred had KeyCorp merged with First Niagara at the beginning of 2015. Cost savings are also not reflected in the unaudited pro forma amounts for the twelve months ended December 31, 2016 , and 2015. Pro forma Twelve months ended December 31, in millions 2016 2015 Net interest income (TE) $ 3,599 $ 3,564 Noninterest income 2,231 2,206 Net income (loss) attributable to common shareholders 1,161 1,187 For information on the Cain Brothers, HelloWallet Holdings, Inc., and KMS acquisitions, see Note 15 (“ Acquisitions, Divestiture, and Discontinued Operations ”).

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share	3. Earnings Per Common Share Basic earnings per share is the amount of earnings (adjusted for dividends declared on our preferred stock) available to each Common Share outstanding during the reporting periods. Diluted earnings per share is the amount of earnings available to each Common Share outstanding during the reporting periods adjusted to include the effects of potentially dilutive Common Shares. Potentially dilutive Common Shares include stock options and other stock-based awards. Potentially dilutive Common Shares are excluded from the computation of diluted earnings per share in the periods where the effect would be antidilutive. On March 20, 2017, all outstanding Series A Preferred Stock was converted into KeyCorp Common Shares. Prior to this conversion, for diluted earnings per share, net income available to common shareholders could have been affected by the conversion of our convertible Series A Preferred Stock. Where the effect of this conversion would have been dilutive, net income available to common shareholders was adjusted by the amount of preferred dividends associated with our Series A Preferred Stock. Our basic and diluted earnings per Common Share are calculated as follows: Year ended December 31, dollars in millions, except per share amounts 2017 2016 2015 EARNINGS Income (loss) from continuing operations $ 1,291 $ 789 $ 919 Less: Net income (loss) attributable to noncontrolling interests 2 (1 ) 4 Income (loss) from continuing operations attributable to Key 1,289 790 915 Less: Dividends on preferred stock 70 37 23 Income (loss) from continuing operations attributable to Key common shareholders 1,219 753 892 Income (loss) from discontinued operations, net of taxes 7 1 1 Net income (loss) attributable to Key common shareholders $ 1,226 $ 754 $ 893 WEIGHTED-AVERAGE COMMON SHARES Weighted-average Common Shares outstanding (000) 1,072,078 927,816 836,846 Effect of convertible preferred stock — — — Effect of common share options and other stock awards 16,515 10,720 7,643 Weighted-average common shares and potential Common Shares outstanding (000) (a) 1,088,593 938,536 844,489 EARNINGS PER COMMON SHARE Income (loss) from continuing operations attributable to Key common shareholders $ 1.13 $ .81 $ 1.06 Income (loss) from discontinued operations, net of taxes .01 — — Net income (loss) attributable to Key common shareholders (b) 1.14 .81 1.06 Income (loss) from continuing operations attributable to Key common shareholders — assuming dilution 1.12 .80 1.05 Income (loss) from discontinued operations, net of taxes .01 — — Net income (loss) attributable to Key common shareholders — assuming dilution (b) 1.13 .80 1.05 (a) Assumes conversion of Common Share options and other stock awards and/or convertible preferred stock, as applicable. (b) EPS may not foot due to rounding.

Restrictions on Cash, Dividends

Restrictions on Cash, Dividends and Lending Activities	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Restrictions on Cash, Dividends, and Lending Activities	4. Restrictions on Cash, Dividends, and Lending Activities Federal law requires a depository institution to maintain a prescribed amount of cash or deposit reserve balances with its Federal Reserve Bank. KeyBank maintained average reserve balances aggregating $349 million in 2017 to fulfill these requirements. Currently KeyBank meets the required reserve balances with vault cash, therefore any cash on deposit at the Federal Reserve is not restricted. Capital distributions from KeyBank and other subsidiaries are our principal source of cash flows for paying dividends on our common and preferred shares, servicing our debt, and financing corporate operations. Federal banking law limits the amount of capital distributions that a bank can make to its holding company without prior regulatory approval. A national bank’s dividend-paying capacity is affected by several factors, including net profits (as defined by statute) for the previous two calendar years and for the current year, up to the date the dividend is declared. During 2017 , KeyBank paid $750 million in dividends to KeyCorp. At January 1, 2018 , KeyBank had regulatory capacity to pay $925 million in dividends to KeyCorp without prior regulatory approval. At December 31, 2017 , KeyCorp held $2.3 billion in short-term investments, which can be used to pay dividends to shareholders, service debt, and finance corporate operations.

Loans and Loans Held for Sale

Loans and Loans Held for Sale	12 Months Ended
	Dec. 31, 2017
Loans Receivables [Abstract]
Loans and Loans Held for Sale	5. Loans and Loans Held for Sale Our loans by category are summarized as follows: December 31, in millions 2017 2016 Commercial and industrial (a) $ 41,859 $ 39,768 Commercial real estate: Commercial mortgage 14,088 15,111 Construction 1,960 2,345 Total commercial real estate loans 16,048 17,456 Commercial lease financing (b) 4,826 4,685 Total commercial loans 62,733 61,909 Residential — prime loans: Real estate — residential mortgage 5,483 5,547 Home equity loans 12,028 12,674 Total residential — prime loans 17,511 18,221 Consumer direct loans 1,794 1,788 Credit cards 1,106 1,111 Consumer indirect loans 3,261 3,009 Total consumer loans 23,672 24,129 Total loans (c), (d) $ 86,405 $ 86,038 (a) Loan balances include $119 million and $116 million of commercial credit card balances at December 31, 2017 , and December 31, 2016 , respectively. (b) Commercial lease financing includes receivables of $24 million and $68 million held as collateral for a secured borrowing at December 31, 2017 , and December 31, 2016 , respectively. Principal reductions are based on the cash payments received from these related receivables. Additional information pertaining to this secured borrowing is included in Note 20 (“ Long-Term Debt ”). (c) At December 31, 2017 , total loans include purchased loans of $15.4 billion , of which $738 million were purchased credit impaired. At December 31, 2016 , total loans include purchased loans of $21.0 billion , of which $865 million were purchased credit impaired. (d) Total loans exclude loans in the amount of $1.3 billion at December 31, 2017 , and $1.6 billion at December 31, 2016 , related to the discontinued operations of the education lending business. Our loans held for sale by category are summarized as follows: December 31, in millions 2017 2016 Commercial and industrial $ 139 $ 19 Real estate — commercial mortgage 897 1,022 Real estate — construction — 1 Real estate — residential mortgage (a) 71 62 Total loans held for sale $ 1,107 $ 1,104 (a) Real estate — residential mortgage loans held for sale at fair value at December 31, 2017 . The fair value option was elected for real estate — residential mortgage loans held for sale during the third quarter of 2016 with the First Niagara acquisition. The contractual amount due on these loans totaled $71 million at December 31, 2017 and $62 million at December 31, 2016 . Changes in fair value are recorded in "Consumer mortgage income" on the income statement. Additional information regarding residential mortgage loans held for sale fair value methodology is provided in Note 7 (“ Fair Value Measurements ”). Our summary of changes in loans held for sale follows: Year ended December 31, in millions 2017 2016 Balance at beginning of the period $ 1,104 $ 639 Purchases — 48 New originations 11,860 8,356 Transfers from (to) held to maturity, net (63 ) 35 Loan sales (11,780 ) (7,979 ) Loan draws (payments), net (14 ) 5 Balance at end of period (a) $ 1,107 $ 1,104 (a) Total loans held for sale include Real Estate - residential mortgage loans held for sale at fair value of $71 million at December 31, 2017 . Commercial lease financing receivables primarily are direct financing leases, but also include leveraged leases. The composition of the net investment in direct financing leases is as follows: December 31, in millions 2017 2016 Direct financing lease receivables $ 3,727 $ 3,468 Unearned income (323 ) (278 ) Unguaranteed residual value 382 316 Deferred fees and costs 19 16 Net investment in direct financing leases $ 3,805 $ 3,522 At December 31, 2017 , minimum future lease payments to be received are as follows: 2018 — $1 billion ; 2019 — $860 million ; 2020 — $614 million ; 2021 — $398 million ; 2022 — $249 million ; and all subsequent years — $467 million . The allowance related to lease financing receivables is $43 million at December 31, 2017 .

Asset Quality

Asset Quality	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Asset Quality	6. Asset Quality We assess the credit quality of the loan portfolio by monitoring net credit losses, levels of nonperforming assets and delinquencies, and credit quality ratings as defined by management. Credit Quality Indicators The prevalent risk characteristic for both commercial and consumer loans is the risk of loss arising from an obligor’s inability or failure to meet contractual payment or performance terms. Evaluation of this risk is stratified and monitored by the loan risk rating grades assigned for the commercial loan portfolios and the regulatory risk ratings assigned for the consumer loan portfolios. Most extensions of credit are subject to loan grading or scoring. Loan grades are assigned at the time of origination, verified by credit risk management, and periodically re-evaluated thereafter. This risk rating methodology blends our judgment with quantitative modeling. Commercial loans generally are assigned two internal risk ratings. The first rating reflects the probability that the borrower will default on an obligation; the second rating reflects expected recovery rates on the credit facility. Default probability is determined based on, among other factors, the financial strength of the borrower, an assessment of the borrower’s management, the borrower’s competitive position within its industry sector, and our view of industry risk in the context of the general economic outlook. Types of exposure, transaction structure, and collateral, including credit risk mitigants, affect the expected recovery assessment. Commercial Credit Exposure — Excluding PCI Credit Risk Profile by Creditworthiness Category (a), (b) December 31, in millions Commercial and industrial RE — Commercial RE — Construction Commercial Lease Total RATING 2017 2016 2017 2016 2017 2016 2017 2016 2017 2016 Pass $ 39,833 $ 37,845 $ 13,328 $ 14,308 $ 1,894 $ 2,287 $ 4,730 $ 4,632 $ 59,785 $ 59,072 Criticized (Accruing) 1,790 1,514 482 455 38 30 90 45 2,400 2,044 Criticized (Nonaccruing) 153 297 30 26 2 2 6 8 191 333 Total $ 41,776 $ 39,656 $ 13,840 $ 14,789 $ 1,934 $ 2,319 $ 4,826 $ 4,685 $ 62,376 $ 61,449 (a) Credit quality indicators are updated on an ongoing basis and reflect credit quality information as of the dates indicated. (b) The term criticized refers to those loans that are internally classified by Key as special mention or worse, which are asset quality categories defined by regulatory authorities. These assets have an elevated level of risk and may have a high probability of default or total loss. Pass rated refers to all loans not classified as criticized. Consumer Credit Exposure — Excluding PCI Non-PCI Loans by Refreshed FICO Score (a) December 31, in millions Residential — Prime Consumer direct loans Credit cards Consumer indirect loans Total FICO SCORE 2017 2016 2017 2016 2017 2016 2017 2016 2017 2016 750 and above $ 10,226 $ 9,818 $ 519 $ 498 $ 477 $ 453 $ 1,472 $ 1,266 $ 12,694 $ 12,035 660 to 749 5,181 5,266 690 661 508 525 1,184 1,195 7,563 7,647 Less than 660 1,519 1,617 225 194 121 132 529 543 2,394 2,486 No Score 208 1,122 356 428 — 1 76 5 640 1,556 Total $ 17,134 $ 17,823 $ 1,790 $ 1,781 $ 1,106 $ 1,111 $ 3,261 $ 3,009 $ 23,291 $ 23,724 (a) Borrower FICO scores provide information about the credit quality of our consumer loan portfolio as they provide an indication as to the likelihood that a debtor will repay their debts. The scores are obtained from a nationally recognized consumer rating agency and are presented in the above table at the dates indicated. Commercial Credit Exposure — PCI Credit Risk Profile by Creditworthiness Category (a), (b) December 31, in millions Commercial and industrial RE — Commercial RE — Construction Commercial Lease Total RATING 2017 2016 2017 2016 2017 2016 2017 2016 2017 2016 Pass $ 41 $ 12 $ 153 $ 139 $ 26 $ 21 — — $ 220 $ 172 Criticized 42 100 95 183 — 5 — — 137 288 Total $ 83 $ 112 $ 248 $ 322 $ 26 $ 26 — — $ 357 $ 460 (a) Credit quality indicators are updated on an ongoing basis and reflect credit quality information as of the dates indicated. (b) The term criticized refers to those loans that are internally classified by Key as special mention or worse, which are asset quality categories defined by regulatory authorities. These assets have an elevated level of risk and may have a high probability of default or total loss. Pass rated refers to all loans not classified as criticized. Consumer Credit Exposure — PCI PCI Loans by Refreshed FICO Score (a) December 31, in millions Residential — Prime Consumer direct loans Credit cards Consumer indirect loans Total FICO SCORE 2017 2016 2017 2016 2017 2016 2017 2016 2017 2016 750 and above $ 149 $ 133 — — — — — — $ 149 $ 133 660 to 749 117 127 $ 2 $ 2 — — — — 119 129 Less than 660 105 133 2 4 — — — — 107 137 No Score 6 5 — 1 — — — — 6 6 Total $ 377 $ 398 $ 4 $ 7 — — — — $ 381 $ 405 (a) Borrower FICO scores provide information about the credit quality of our consumer loan portfolio as they provide an indication as to the likelihood that a debtor will repay their debts. The scores are obtained from a nationally recognized consumer rating agency and are presented in the above table at the dates indicated. Nonperforming and Past Due Loans Our policies for determining past due loans, placing loans on nonaccrual, applying payments on nonaccrual loans, and resuming accrual of interest for our commercial and consumer loan portfolios are disclosed in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Nonperforming Loans.” The following aging analysis of current and past due loans as of December 31, 2017 , and December 31, 2016 , provides further information regarding Key’s credit exposure. Aging Analysis of Loan Portfolio (a) December 31, 2017 Current 30-59 Days Past Due (b) 60-89 Days Past Due (b) 90 and Greater Days Past Due (b) Non-performing Loans Total Past Due and Non-performing Loans Purchased Credit Impaired Total Loans (c), (d) in millions LOAN TYPE Commercial and industrial $ 41,444 $ 111 $ 34 $ 34 $ 153 $ 332 $ 83 $ 41,859 Commercial real estate: Commercial mortgage 13,750 26 13 21 30 90 248 14,088 Construction 1,919 4 9 — 2 15 26 1,960 Total commercial real estate loans 15,669 30 22 21 32 105 274 16,048 Commercial lease financing 4,791 23 4 2 6 35 — 4,826 Total commercial loans $ 61,904 $ 164 $ 60 $ 57 $ 191 $ 472 $ 357 $ 62,733 Real estate — residential mortgage $ 5,043 $ 16 $ 7 $ 4 $ 58 $ 85 $ 355 $ 5,483 Home equity loans 11,721 32 15 9 229 285 22 12,028 Consumer direct loans 1,768 9 4 5 4 22 4 1,794 Credit cards 1,081 7 5 11 2 25 — 1,106 Consumer indirect loans 3,199 33 7 3 19 62 — 3,261 Total consumer loans $ 22,812 $ 97 $ 38 $ 32 $ 312 $ 479 $ 381 $ 23,672 Total loans $ 84,716 $ 261 $ 98 $ 89 $ 503 $ 951 $ 738 $ 86,405 (a) Amounts in table represent recorded investment and exclude loans held for sale. Recorded investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. (b) Past due loan amounts exclude purchased impaired loans, even if contractually past due (or if we do not expect to collect principal or interest in full based on the original contractual terms), as we are currently accreting income over the remaining term of the loans. (c) Net of unearned income, net deferred loan fees and costs, and unamortized discounts and premiums. (d) Future accretable yield related to purchased credit impaired loans is not included in the analysis of the loan portfolio. December 31, 2016 Current 30-59 Days Past Due (b) 60-89 Days Past Due (b) 90 and Greater Days Past Due (b) Non-performing Loans Total Past Due and Non-performing Loans Purchased Credit Impaired Total Loans (c), (d) in millions LOAN TYPE Commercial and industrial $ 39,242 $ 58 $ 28 $ 31 $ 297 $ 414 $ 112 $ 39,768 Commercial real estate: Commercial mortgage 14,655 93 9 6 26 134 322 15,111 Construction 2,314 — — 2 3 5 26 2,345 Total commercial real estate loans 16,969 93 9 8 29 139 348 17,456 Commercial lease financing 4,641 28 3 5 8 44 — 4,685 Total commercial loans $ 60,852 $ 179 $ 40 $ 44 $ 334 $ 597 $ 460 $ 61,909 Real estate — residential mortgage $ 5,098 $ 17 $ 5 $ 3 $ 56 $ 81 $ 368 $ 5,547 Home equity loans 12,327 49 29 16 223 317 30 12,674 Consumer direct loans 1,705 44 15 11 6 76 7 1,788 Credit cards 1,082 9 6 12 2 29 — 1,111 Consumer indirect loans 2,993 7 4 1 4 16 — 3,009 Total consumer loans $ 23,205 $ 126 $ 59 $ 43 $ 291 $ 519 $ 405 $ 24,129 Total loans $ 84,057 $ 305 $ 99 $ 87 $ 625 $ 1,116 $ 865 $ 86,038 (a) Amounts in table represent recorded investment and exclude loans held for sale. Recorded investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. (b) Past due loan amounts exclude purchased impaired loans, even if contractually past due (or if we do not expect to collect principal or interest in full based on the original contractual terms), as we are currently accreting income over the remaining term of the loans. (c) Net of unearned income, net deferred loan fees and costs, and unamortized discounts and premiums. (d) Future accretable yield related to purchased credit impaired loans is not included in the analysis of the loan portfolio. At December 31, 2017 , the approximate carrying amount of our commercial nonperforming loans outstanding represented 71% of their original contractual amount owed, total nonperforming loans outstanding represented 80% of their original contractual amount owed, and nonperforming assets in total were carried at 80% of their original contractual amount owed. Nonperforming loans reduced expected interest income by $25 million , $26 million , and $16 million for each of the twelve months ended December 31, 2017 , December 31, 2016 , and December 31, 2015 , respectively. Impaired Loans The following tables set forth a further breakdown of individually impaired loans for the periods indicated are as follows: December 31, 2017 Recorded Investment (a) Unpaid Principal Balance (b) Specific Allowance (c) in millions With no related allowance recorded: Commercial and industrial $ 126 $ 153 — Commercial real estate: Commercial mortgage 12 18 — Construction — — — Total commercial real estate loans 12 18 — Total commercial loans 138 171 — Real estate — residential mortgage 17 17 — Home equity loans 56 56 — Consumer indirect loans 2 2 — Total consumer loans 75 75 — Total loans with no related allowance recorded 213 246 — With an allowance recorded: Commercial and industrial 10 28 $ 6 Commercial real estate: Commercial mortgage — — — Total commercial real estate loans — — — Total commercial loans 10 28 6 Real estate — residential mortgage 32 32 5 Home equity loans 61 61 9 Consumer direct loans 4 4 — Credit cards 2 2 — Consumer indirect loans 32 32 3 Total consumer loans 131 131 17 Total loans with an allowance recorded 141 159 23 Total $ 354 $ 405 $ 23 (a) The Recorded Investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. This amount is a component of total loans on our consolidated balance sheet. (b) The Unpaid Principal Balance represents the customer’s legal obligation to us. (c) See Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Impaired Loans” for a description of the specific allowance methodology. December 31, 2016 Recorded Investment (a) Unpaid Principal Balance (b) Specific Allowance (c) in millions With no related allowance recorded: Commercial and industrial $ 222 $ 301 — Commercial real estate: Commercial mortgage 2 3 — Total commercial real estate loans 2 3 — Total commercial loans 224 304 — Real estate — residential mortgage 20 20 — Home equity loans 61 61 — Consumer indirect loans 1 1 — Total consumer loans 82 82 — Total loans with no related allowance recorded 306 386 — With an allowance recorded: Commercial and industrial 62 73 $ 17 Commercial real estate: Commercial mortgage 4 4 — Total commercial real estate loans 4 4 — Total commercial loans 66 77 17 Real estate — residential mortgage 31 31 2 Home equity loans 64 64 18 Consumer direct loans 2 3 — Credit cards 3 3 — Consumer indirect loans 29 29 1 Total consumer loans 129 130 21 Total loans with an allowance recorded 195 207 38 Total $ 501 $ 593 $ 38 (a) The Recorded Investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. This amount is a component of total loans on our consolidated balance sheet. (b) The Unpaid Principal Balance represents the customer’s legal obligation to us. (c) See Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Impaired Loans” for a description of the specific allowance methodology. The following table sets forth a further breakdown of average individually impaired loans reported by Key: Average Recorded Investment (a) Twelve Months Ended December 31, in millions 2017 2016 2015 Commercial and industrial $ 210 $ 176 $ 56 Commercial real estate: Commercial mortgage 9 8 15 Construction — 3 7 Total commercial real estate loans 9 11 22 Total commercial loans 219 187 78 Real estate — residential mortgage 50 53 55 Home equity loans 121 125 122 Consumer direct loans 3 3 4 Credit cards 3 3 4 Consumer indirect loans 32 34 42 Total consumer loans 209 218 227 Total $ 428 $ 405 $ 305 (a) The Recorded Investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. This amount is a component of total loans on our consolidated balance sheet. For the twelve months ended December 31, 2017 , December 31, 2016 , and December 31, 2015 , interest income recognized on the outstanding balances of accruing impaired loans totaled $9 million , $10 million , and $6 million , respectively. TDRs We classify loan modifications as TDRs when a borrower is experiencing financial difficulties and we have granted a concession without commensurate financial, structural, or legal consideration. Acquired loans that were previously modified by First Niagara in a TDR are no longer classified as TDRs at the Acquisition Date. An acquired loan may only be classified as a TDR if a modification meeting the above TDR criteria is performed after the Acquisition Date. PCI loans cannot be classified as TDRs. All commercial and consumer loan TDRs, regardless of size, are individually evaluated for impairment to determine the probable loss content and are assigned a specific loan allowance. This designation has the effect of moving the loan from the general reserve methodology (i.e., collectively evaluated) to the specific reserve methodology (i.e., individually evaluated) and may impact the ALLL through a charge-off or increased loan loss provision. These components affect the ultimate allowance level. As TDRs are individually evaluated for impairment under the specific reserve methodology, subsequent defaults do not generally have a significant additional impact on the ALLL. Commitments outstanding to lend additional funds to borrowers whose loan terms have been modified in TDRs are $2 million and $14 million at December 31, 2017 , and December 31, 2016 , respectively. Our loan modifications are handled on a case-by-case basis and are negotiated to achieve mutually agreeable terms that maximize loan collectability and meet the borrower’s financial needs. The commercial TDR other concession category includes modification of loan terms, covenants, or conditions. The consumer TDR other concession category primarily includes those borrowers’ debts that are discharged through Chapter 7 bankruptcy and have not been formally re-affirmed. At December 31, 2017 , and December 31, 2016 , the recorded investment of consumer residential mortgage loans in the process of foreclosure was approximately $142 million and $141 million , respectively. At December 31, 2017 , and December 31, 2016 , we had $31 million and $51 million , respectively, of OREO which included the carrying value of foreclosed residential real estate of approximately $26 million and $29 million , respectively. The following table shows the period-end post-modification outstanding recorded investment by concession type for our commercial and consumer accruing and nonaccruing TDRs added during the periods indicated: Twelve Months Ended December 31, in millions 2017 2016 2015 Commercial loans: Interest rate reduction — — — Forgiveness of principal — — $ 22 Extension of maturity date $ 12 — 21 Payment or covenant modification/deferment 46 $ 19 — Bankruptcy plan modification 31 18 — Total $ 89 $ 37 $ 43 Consumer loans: Interest rate reduction $ 13 $ 10 $ 19 Forgiveness of principal — 3 4 Other 28 21 17 Total $ 41 $ 34 $ 40 Total commercial and consumer TDRs $ 130 $ 71 $ 83 The following table summarizes the change in the post-modification outstanding recorded investment of our accruing and nonaccruing TDRs during the periods indicated: Year ended December 31, in millions 2017 2016 Balance at beginning of the period $ 280 $ 280 Additions 165 107 Payments (111 ) (68 ) Charge-offs (17 ) (39 ) Balance at end of period (a) $ 317 $ 280 A further breakdown of TDRs included in nonperforming loans by loan category for the periods indicated are as follows: December 31, 2017 Number of Loans Pre-modification Outstanding Recorded Investment Post-modification Outstanding Recorded Investment dollars in millions LOAN TYPE Nonperforming: Commercial and industrial 20 $ 109 $ 86 Commercial real estate: Real estate — commercial mortgage 8 16 12 Total commercial real estate loans 8 16 12 Total commercial loans 28 125 98 Real estate — residential mortgage 308 18 18 Home equity loans 1,025 64 57 Consumer direct loans 114 2 2 Credit cards 322 2 1 Consumer indirect loans 825 16 13 Total consumer loans 2,594 102 91 Total nonperforming TDRs 2,622 227 189 Prior-year accruing: (a) Commercial and industrial 4 30 13 Total commercial loans 4 30 13 Real estate — residential mortgage 484 31 31 Home equity loans 1,276 75 59 Consumer direct loans 48 3 2 Credit cards 430 1 1 Consumer indirect loans 320 31 22 Total consumer loans 2,558 141 115 Total prior-year accruing TDRs 2,562 171 128 Total TDRs 5,184 $ 398 $ 317 (a) All TDRs that were restructured prior to January 1, 2017 , and are fully accruing. December 31, 2016 Number of Loans Pre-modification Outstanding Recorded Investment Post-modification Outstanding Recorded Investment dollars in millions LOAN TYPE Nonperforming: Commercial and industrial 18 $ 91 $ 50 Commercial real estate: Real estate — commercial mortgage 7 2 1 Total commercial real estate loans 7 2 1 Total commercial loans 25 93 51 Real estate — residential mortgage 264 16 16 Home equity loans 1,199 77 69 Consumer direct loans 32 1 — Credit cards 336 2 2 Consumer indirect loans 124 4 3 Total consumer loans 1,955 100 90 Total nonperforming TDRs 1,980 193 141 Prior-year accruing: (a) Commercial and industrial 5 30 16 Total commercial loans 5 30 16 Real estate — residential mortgage 477 35 35 Home equity loans 1,231 70 57 Consumer direct loans 35 2 2 Credit cards 410 3 1 Consumer indirect loans 377 56 28 Total consumer loans 2,530 166 123 Total prior-year accruing TDRs 2,535 196 139 Total TDRs 4,515 $ 389 $ 280 (a) All TDRs that were restructured prior to January 1, 2016 , and are fully accruing. Commercial loan TDRs are considered defaulted when principal and interest payments are 90 days past due. Consumer loan TDRs are considered defaulted when principal and interest payments are more than 60 days past due. During the year ended December 31, 2017 , there were no commercial loan TDRs and 147 consumer loan TDRs with a combined recorded investment of $4 million that experienced payment defaults after modifications resulting in TDR status during 2016 . During the year ended December 31, 2016 , there were no commercial loan TDRs and 187 consumer loan TDRs with a combined recorded investment of $9 million that experienced payment defaults after modifications resulting in TDR status during 2015 . During the year ended December 31, 2015 , there were two commercial loan TDRs with a combined recorded investment of $1 million , and 269 consumer loan TDRs with a combined recorded investment of $12 million that experienced payment defaults after modifications resulting in TDR status during 2014 . ALLL and Liability for Credit Losses on Unfunded Lending-Related Commitments We determine the appropriate level of the ALLL on at least a quarterly basis. The methodology is described in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Allowance for Loan and Lease Losses.” The ALLL on the acquired non-impaired loan portfolio is estimated using the same methodology as the originated portfolio, however, the estimated ALLL is compared to the remaining accretable yield to determine if an ALLL must be recorded. For PCI loans, Key estimates cash flows expected to be collected quarterly. Decreases in expected cash flows are recognized as impairment through a provision for loan and lease losses and an increase in the ALLL. There was $3 million of provision for loan and lease losses on these PCI loans during the year ended December 31, 2017 . There was $11 million of provision for loan and lease losses on these PCI loans during the year ended December 31, 2016 . The ALLL at December 31, 2017 , represents our best estimate of the incurred credit losses inherent in the loan portfolio at that date. A summary of the changes in the ALLL for the periods indicated is presented in the table below: December 31, in millions 2017 2016 2015 Balance at beginning of period — continuing operations $ 858 $ 796 $ 794 Charge-offs (302 ) (261 ) (203 ) Recoveries 94 56 61 Net loans and leases charged off (208 ) (205 ) (142 ) Provision for loan and lease losses from continuing operations 227 267 145 Foreign currency translation adjustment — — (1 ) Balance at end of period — continuing operations $ 877 $ 858 $ 796 The changes in the ALLL by loan category for the periods indicated are as follows: in millions December 31, 2016 Provision Charge-offs Recoveries December 31, 2017 Commercial and industrial $ 508 $ 114 $ (133 ) $ 40 $ 529 Real estate — commercial mortgage 144 (2 ) (11 ) 2 133 Real estate — construction 22 9 (2 ) 1 30 Commercial lease financing 42 9 (14 ) 6 43 Total commercial loans 716 130 (160 ) 49 735 Real estate — residential mortgage 17 (11 ) (3 ) 4 7 Home equity loans 54 4 (30 ) 15 43 Consumer direct loans 24 32 (34 ) 6 28 Credit cards 38 45 (44 ) 5 44 Consumer indirect loans 9 27 (31 ) 15 20 Total consumer loans 142 97 (142 ) 45 142 Total ALLL — continuing operations 858 227 (a) (302 ) 94 877 Discontinued operations 24 10 (26 ) 8 16 Total ALLL — including discontinued operations $ 882 $ 237 $ (328 ) $ 102 $ 893 (a) Excludes a provision for losses on lending-related commitments of $2 million . in millions December 31, 2015 Provision Charge-offs Recoveries December 31, 2016 Commercial and industrial $ 450 $ 165 $ (118 ) $ 11 $ 508 Real estate — commercial mortgage 134 6 (5 ) 9 144 Real estate — construction 25 4 (9 ) 2 22 Commercial lease financing 47 4 (12 ) 3 42 Total commercial loans 656 179 (144 ) 25 716 Real estate — residential mortgage 18 2 (4 ) 1 17 Home equity loans 57 13 (30 ) 14 54 Consumer direct loans 20 26 (27 ) 5 24 Credit cards 32 37 (35 ) 4 38 Consumer indirect loans 13 10 (21 ) 7 9 Total consumer loans 140 88 (117 ) 31 142 Total ALLL — continuing operations 796 267 (a) (261 ) 56 858 Discontinued operations 28 13 (28 ) 11 24 Total ALLL — including discontinued operations $ 824 $ 280 $ (289 ) $ 67 $ 882 (a) Excludes a credit for losses on lending-related commitments of $1 million . in millions December 31, 2014 Provision Charge-offs Recoveries December 31, 2015 Commercial and industrial $ 391 $ 120 $ (77 ) $ 16 $ 450 Real estate — commercial mortgage 148 (16 ) (4 ) 6 134 Real estate — construction 28 (3 ) (1 ) 1 25 Commercial lease financing 56 (5 ) (11 ) 7 47 Total commercial loans 623 96 (93 ) 30 656 Real estate — residential mortgage 23 (2 ) (6 ) 3 18 Home equity loans 71 7 (32 ) 11 57 Consumer direct loans 22 16 (24 ) 6 20 Credit cards 33 27 (30 ) 2 32 Consumer indirect loans 22 — (18 ) 9 13 Total consumer loans 171 48 (110 ) 31 140 Total ALLL — continuing operations 794 144 (a) (203 ) 61 796 Discontinued operations 29 21 (35 ) 13 28 Total ALLL — including discontinued operations $ 823 $ 165 $ (238 ) $ 74 $ 824 (a) Includes a $1 million foreign currency translation adjustment. Excludes a provision for losses on lending-related commitments of $21 million . A breakdown of the individual and collective ALLL and the corresponding loan balances for the periods indicated are as follows: Allowance Outstanding December 31, 2017 Individually Evaluated for Impairment Collectively Evaluated for Impairment Purchased Credit Impaired Loans Individually Evaluated for Impairment Collectively Evaluated for Impairment Purchased Credit Impaired in millions Commercial and industrial $ 6 $ 520 $ 3 $ 41,859 $ 136 $ 41,640 $ 83 Commercial real estate: Commercial mortgage — 131 2 14,088 12 13,828 248 Construction — 30 — 1,960 — 1,934 26 Total commercial real estate loans — 161 2 16,048 12 15,762 274 Commercial lease financing — 43 — 4,826 — 4,826 — Total commercial loans 6 724 5 62,733 148 62,228 357 Real estate — residential mortgage 5 2 — 5,483 49 5,079 355 Home equity loans 9 33 1 12,028 117 11,889 22 Consumer direct loans — 28 — 1,794 4 1,786 4 Credit cards — 44 — 1,106 2 1,104 — Consumer indirect loans 3 17 — 3,261 34 3,227 — Total consumer loans 17 124 1 23,672 206 23,085 381 Total ALLL — continuing operations 23 848 6 86,405 354 85,313 738 Discontinued operations 3 13 — 1,314 (a) 21 1,293 (a) — Total ALLL — including discontinued operations $ 26 $ 861 $ 6 $ 87,719 $ 375 $ 86,606 $ 738 (a) Amount includes $2 million of loans carried at fair value that are excluded from ALLL consideration. Allowance Outstanding December 31, 2016 Individually Evaluated for Impairment Collectively Evaluated for Impairment Purchased Credit Impaired Loans Individually Evaluated for Impairment Collectively Evaluated for Impairment Purchased Credit Impaired in millions Commercial and industrial $ 17 $ 486 $ 5 $ 39,768 $ 284 $ 39,372 $ 112 Commercial real estate: Commercial mortgage — 144 — 15,111 5 14,784 322 Construction — 22 — 2,345 — 2,319 26 Total commercial real estate loans — 166 — 17,456 5 17,103 348 Commercial lease financing — 42 — 4,685 — 4,685 — Total commercial loans 17 694 5 61,909 289 61,160 460 Real estate — residential mortgage 2 15 — 5,547 51 5,128 368 Home equity loans 17 37 — 12,674 125 12,519 30 Consumer direct loans — 24 — 1,788 3 1,778 7 Credit cards — 38 — 1,111 3 1,108 — Consumer indirect loans 1 8 — 3,009 30 2,979 — Total consumer loans 20 122 — 24,129 212 23,512 405 Total ALLL — continuing operations 37 816 5 86,038 501 84,672 865 Discontinued operations 2 22 — 1,565 (a) 22 1,543 (a) — Total ALLL — including discontinued operations $ 39 $ 838 $ 5 $ 87,603 $ 523 $ 86,215 $ 865 (a) Amount includes $3 million of loans carried at fair value that are excluded from ALLL consideration. The liability for credit losses inherent in lending-related unfunded commitments, such as letters of credit and unfunded loan commitments, is included in “accrued expense and other liabilities” on the balance sheet. We establish the amount of this reserve by considering both historical trends and current market conditions quarterly, or more often if deemed necessary. Changes in the liability for credit losses on unfunded lending-related commitments are summarized as follows: Year ended December 31, in millions 2017 2016 2015 Balance at beginning of period $ 55 $ 56 $ 35 Provision (credit) for losses on lending-related commitments 2 (1 ) 21 Balance at end of period $ 57 $ 55 $ 56 PCI Loans Purchased loans that have evidence of deterioration in credit quality since origination and for which it is probable, at acquisition, that all contractually required payments will not be collected are deemed PCI. Several factors were considered when evaluating whether a loan was considered a PCI loan, including the delinquency status of the loan, updated borrower credit status, geographic information, and updated LTV. In accordance with ASC 310-30, excluded from the purchased impaired loans were leases, revolving credit arrangements, and loans held for sale. Auto, boat and RV loans were also excluded from purchased impaired loans due to Key’s inability to develop a reasonable estimate of the timing and magnitude of cash flows related to these loans. We estimated the fair value of loans acquired from First Niagara by utilizing the discounted cash flow method within the income approach. See Note 2 (“ Business Combination ”) for further discussion over the fair value methodology. There was no carryover of First Niagara’s allowance for loan losses associated with the loans we acquired. The excess of a PCI loan's contractually required payments over the amount of its undiscounted cash flows expected to be collected is referred to as the nonaccretable difference. The nonaccretable difference, which is not accreted into income, reflects estimated future credit losses and uncollectible contractual interest expected to be incurred over the life of the PCI loan. The excess of cash flows expected to be collected over the carrying amount of the PCI loans is referred to as the accretable yield. This amount is accreted into interest income over the remaining life of the PCI loans or pools using the level yield method. Over the life of PCI loans, Key evaluates the remaining contractual required payments receivable and estimates cash flows expected to be collected. Contractually required payments receivable may increase or decrease for a variety of reasons, for example, when the contractual terms of the loan agreement are modified, when interest rates on variable rate loans change, or when principal and/or interest payments are received. Cash flows expected to be collected on PCI loans are estimated by incorporating several key assumptions similar to the initial estimate of fair value. These key assumptions include probability of default, loss given default, and the amount of actual prepayments after the Acquisition Date. Increases in expected cash flows of PCI loans subsequent to acquisition are recognized prospectively through adjustment of the yield on the loans or pools over its remaining life, while decreases in expected cash flows are recognized as impairment through a provision for loan and lease losses and an increase in the ALLL. The difference between the fair value of a non-impaired acquired loan and contractual amounts due at the Acquisition Date is accreted into income over the estimated life of the loan. Contractually required payments represent the total undiscounted amount of all uncollected principal and interest payments. The following table presents the PCI loans receivable balance at the First Niagara Acquisition Date: August 1, 2016 PCI in millions Contractual required payments receivable $ 1,434 Nonaccretable difference 173 Expected cash flows 1,261 Accretable yield 172 Fair Value $ 1,089 At the First Niagara Acquisition Date, the contractual required payments receivable on the purchased non-impaired loans totaled $22.5 billion , with an estimated corresponding fair value of $22.0 billion . The estimated cash flows not expected to be collected at the Acquisition Date were $500 million . These amounts do not include loans held for sale and the loans that were divested as part of the 18 branches that were sold on September 9, 2016. We have PCI loans from two separate acquisitions, one in 2012 and one during the third quarter of 2016. At the 2012 acquisition date, the estimated gross contractual amount receivable of all PCI loans totaled $41 million . The estimated cash flows not expected to be collected (the nonaccretable amount) were $11 million , and the accretable amount was approximately $5 million . The following table presents the rollforward of the accretable yield and the beginning and ending outstanding unpaid principal balance and carrying amount of PCI loans for the for the periods indicated are as follows: PCI Loans Twelve Months Ended December 31, 2017 2016 in millions Accretable Yield Carryi

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	7. Fair Value Measurements Fair Value Determination We have established and documented our process for determining the fair values of our assets and liabilities, where applicable. Fair value is based on quoted market prices, when available, for identical or similar assets or liabilities. In the absence of quoted market prices, we determine the fair value of our assets and liabilities using valuation models or third-party pricing services. Both of these approaches rely on market-based parameters, when available, such as yield curves, option volatilities, and credit spreads, or unobservable inputs. Unobservable inputs may be based on our judgment, assumptions, and estimates related to credit quality, liquidity, interest rates, and other relevant inputs. We make liquidity valuation adjustments to the fair value of certain assets to reflect the uncertainty in the pricing and trading of the instruments when we are unable to observe recent market transactions for identical or similar instruments. Liquidity valuation adjustments are based on the following factors: • the amount of time since the last relevant valuation; • whether there is an actual trade or relevant external quote available at the measurement date; and • volatility associated with the primary pricing components. We ensure that our fair value measurements are accurate and appropriate by relying upon various controls, including: • an independent review and approval of valuation models and assumptions; • recurring detailed reviews of profit and loss; and • a validation of valuation model components against benchmark data and similar products, where possible. We recognize transfers between levels of the fair value hierarchy at the end of the reporting period. Quarterly, we review any changes to our valuation methodologies to ensure they are appropriate and justified, and refine our valuation methodologies if more market-based data becomes available. The Fair Value Committee, which is governed by ALCO, oversees the valuation process. Various Working Groups that report to the Fair Value Committee analyze and approve the underlying assumptions and valuation adjustments. Changes in valuation methodologies for Level 1 and Level 2 instruments are presented to the Accounting Policy group for approval. Changes in valuation methodologies for Level 3 instruments are presented to the Fair Value Committee for approval. The Working Groups are discussed in more detail in the qualitative disclosures within this note. Formal documentation of the fair valuation methodologies is prepared by the lines of business and support areas as appropriate. The documentation details the asset or liability class and related general ledger accounts, valuation techniques, fair value hierarchy level, market participants, accounting methods, valuation methodology, group responsible for valuations, and valuation inputs. Additional information regarding our accounting policies for determining fair value is provided in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Fair Value Measurements.” Qualitative Disclosures of Valuation Techniques Loans . Most loans recorded as trading account assets are valued based on market spreads for similar assets since they are actively traded. Therefore, these loans are classified as Level 2 because the fair value recorded is based on observable market data for similar assets. Securities (trading and available for sale) . We own several types of securities, requiring a range of valuation methods: • Securities are classified as Level 1 when quoted market prices are available in an active market for the identical securities. Level 1 instruments include exchange-traded equity securities. • Securities are classified as Level 2 if quoted prices for identical securities are not available, and fair value is determined using pricing models (either by a third-party pricing service or internally) or quoted prices of similar securities. These instruments include municipal bonds; bonds backed by the U.S. government; corporate bonds; certain mortgage-backed securities; securities issued by the U.S. Treasury; money markets; and certain agency and corporate CMOs. Inputs to the pricing models include: standard inputs, such as yields, benchmark securities, bids, and offers; actual trade data (i.e., spreads, credit ratings, and interest rates) for comparable assets; spread tables; matrices; high-grade scales; and option-adjusted spreads. • Securities are classified as Level 3 when there is limited activity in the market for a particular instrument. To determine fair value in such cases, depending on the complexity of the valuations required, we use internal models based on certain assumptions or a third-party valuation service. At December 31, 2017 , our Level 3 instruments consist of debt and equity securities. Our Strategy group is responsible for reviewing the valuation model and determining the fair value of these investments on a quarterly basis. The securities are valued using a cash flow analysis of the associated private company issuers. The valuations provided by the third-party pricing service are based on observable market inputs, which include benchmark yields, reported trades, issuer spreads, benchmark securities, bids, offers, and reference data obtained from market research publications. Inputs used by the third-party pricing service in valuing CMOs and other mortgage-backed securities also include new issue data, monthly payment information, whole loan collateral performance, and “To Be Announced” prices. In valuations of securities issued by state and political subdivisions, inputs used by the third-party pricing service also include material event notices. On a monthly basis, we validate the pricing methodologies utilized by our third-party pricing service to ensure the fair value determination is consistent with the applicable accounting guidance and that our assets are properly classified in the fair value hierarchy. To perform this validation, we: • review documentation received from our third-party pricing service regarding the inputs used in their valuations and determine a level assessment for each category of securities; • substantiate actual inputs used for a sample of securities by comparing the actual inputs used by our third-party pricing service to comparable inputs for similar securities; and • substantiate the fair values determined for a sample of securities by comparing the fair values provided by our third-party pricing service to prices from other independent sources for the same and similar securities. We analyze variances and conduct additional research with our third-party pricing service and take appropriate steps based on our findings. Principal investments . Principal investments consist of investments in equity and debt instruments made by our principal investing entities. They include direct investments (investments made in a particular company) and indirect investments (investments made through funds that include other investors). Our principal investing entities are accounted for as investment companies in accordance with the applicable accounting guidance, whereby each investment is adjusted to fair value with any net realized or unrealized gain/loss recorded in the current period’s earnings. This process is a coordinated and documented effort by the Principal Investing Entities Deal Team (individuals from one of the independent investment managers who oversee these instruments), accounting staff, and the Investment Committee (individual employees and one of the independent investment managers). This process involves an in-depth review of the condition of each investment depending on the type of investment. Our direct investments include investments in debt and equity instruments of both private and public companies. In most cases, quoted market prices are not available for our direct investments, and we must perform valuations using other methods. These direct investment valuations are an in-depth analysis of the condition of each investment and are based on the unique facts and circumstances related to each individual investment. There is a certain amount of subjectivity surrounding the valuation of these investments due to the combination of quantitative and qualitative factors that are used in the valuation models. Therefore, these direct investments are classified as Level 3 assets. Our indirect investments include primary and secondary investments in private equity funds engaged mainly in venture- and growth-oriented investing. These investments do not have readily determinable fair values. Indirect investments are valued using a methodology that is consistent with accounting guidance that allows us to estimate fair value based upon net asset value per share (or its equivalent, such as member units or an ownership interest in partners’ capital to which a proportionate share of net assets is attributed). Under the requirements of the Volcker Rule, we will be required to dispose of some or all of our indirect investments. On February 14, 2017, Key’s application for an extension to comply with this rule for illiquid funds was approved. Key will retain certain indirect investments until the earlier of the date on which the investment is conformed or is expected to mature or July 21, 2022; as of December 31, 2017, we have not committed to a plan to sell these investments. Therefore, these investments continue to be valued using the net asset value per share methodology. The following table presents the fair value of our direct and indirect principal investments and related unfunded commitments at December 31, 2017 , as well as financial support provided for the years ended December 31, 2017 , and December 31, 2016 . Financial support provided Year ended December 31, December 31, 2017 2017 2016 in millions Fair Value Unfunded Commitments Funded Commitments Funded Other Funded Commitments Funded Other INVESTMENT TYPE Direct investments (a) $ 13 — — — — $ 13 Indirect investments (b) 124 $ 29 $ 1 — $ 6 — Total $ 137 $ 29 $ 1 — $ 6 $ 13 (a) Our direct investments consist of equity and debt investments directly in independent business enterprises. Operations of the business enterprises are handled by management of the portfolio company. The purpose of funding these enterprises is to provide financial support for business development and acquisition strategies. We infuse equity capital based on an initial contractual cash contribution and later from additional requests on behalf of the companies’ management. (b) Our indirect investments consist of buyout funds, venture capital funds, and fund of funds. These investments are generally not redeemable. Instead, distributions are received through the liquidation of the underlying investments of the fund. An investment in any one of these funds typically can be sold only with the approval of the fund’s general partners. We estimate that the underlying investments of the funds will be liquidated over a period of one to eight years. The purpose of funding our capital commitments to these investments is to allow the funds to make additional follow-on investments and pay fund expenses until the fund dissolves. We, and all other investors in the fund, are obligated to fund the full amount of our respective capital commitments to the fund based on our and their respective ownership percentages, as noted in the applicable Limited Partnership Agreement. Loans Held for Sale. As of August 1, 2016, we account for our residential mortgage loans held for sale at fair value on a recurring basis. The election of the fair value option aligns the accounting for the residential mortgages held for sale with the related forward mortgage loan sale commitments. Residential mortgage loans are valued based on quoted market prices, where available, prices for other traded mortgage loans with similar characteristics, and purchase commitments and bid information received from market participants. The prices are adjusted as necessary to include the embedded servicing value in the loans and to take into consideration the specific characteristics of certain loans that are priced based on the pricing of similar loans. These adjustments represent unobservable inputs to the valuation but are not considered significant given the relative insensitivity of the value to changes in these inputs to the fair value of the loans. Accordingly, the majority of residential mortgage loans held for sale are classified as Level 2. Our residential mortgage activity also includes temporarily unsalable residential mortgage loans that are includes in “Loans, net of unearned income” and loans with salability issues included in “Loans held for sale” on the balance sheet. These loans have an origination defect that makes them temporarily unable to be sold into the performing loan sales market. Because transaction details regarding sales of this type of loan are often unavailable, unobservable bid information from brokers and investors is heavily relied upon. Accordingly, based on the significance of unobservable inputs, these loans are classified as Level 3. Derivatives . Exchange-traded derivatives are valued using quoted prices and, therefore, are classified as Level 1 instruments. However, only a few types of derivatives are exchange-traded. The majority of our derivative positions are valued using internally developed models based on market convention that use observable market inputs, such as interest rate curves, yield curves, LIBOR and Overnight Index Swap (OIS) discount rates and curves, index pricing curves, foreign currency curves, and volatility surfaces (a three-dimensional graph of implied volatility against strike price and maturity), as well as current prices for mortgage securities and investor supplied prices. These derivative contracts, which are classified as Level 2 instruments, include interest rate swaps, certain options, cross currency swaps, credit default swaps, and forward mortgage loan sale commitments. We have several customized derivative instruments and risk participations that are classified as Level 3 instruments. These derivative positions are valued using internally developed models, with inputs consisting of available market data, such as bond spreads and asset values, as well as unobservable internally derived assumptions, such as loss probabilities and internal risk ratings of customers. These derivatives are priced monthly by our MRM group using a credit valuation adjustment methodology. Swap details with the customer and our related participation percentage, if applicable, are obtained from our derivatives accounting system, which is the system of record. Applicable customer rating information is obtained from the particular loan system and represents an unobservable input to this valuation process. Using these various inputs, a valuation of these Level 3 derivatives is performed using a model that was acquired from a third party. In summary, the fair value represents an estimate of the amount that the risk participation counterparty would need to pay/receive as of the measurement date based on the probability of customer default on the swap transaction and the fair value of the underlying customer swap. Therefore, a higher loss probability and a lower credit rating would negatively affect the fair value of the risk participations and a lower loss probability and higher credit rating would positively affect the fair value of the risk participations. We use interest rate lock commitments for our residential mortgage business. These instruments are accounted for as a derivative and valued using models containing unobservable significant inputs. For valuation purposes, the loan amount associated with each interest rate lock commitment is adjusted by its modeled pull through (an unobservable input) defined as the percentage of loans that will close prior to the expiration of the rate lock commitment, as adjusted for approved changes to the terms. Based on the significance of unobservable inputs, these instruments are classified as Level 3. Market convention implies a credit rating of “AA” equivalent in the pricing of derivative contracts, which assumes all counterparties have the same creditworthiness. To reflect the actual exposure on our derivative contracts related to both counterparty and our own creditworthiness, we record a fair value adjustment in the form of a credit valuation adjustment. The credit component is determined by individual counterparty based on the probability of default and considers master netting and collateral agreements. The credit valuation adjustment is classified as Level 3. Our MRM group is responsible for the valuation policies and procedures related to this credit valuation adjustment. A weekly reconciliation process is performed to ensure that all applicable derivative positions are covered in the calculation, which includes transmitting customer exposures and reserve reports to trading management, derivative traders and marketers, derivatives middle office, and corporate accounting personnel. On a quarterly basis, MRM prepares the credit valuation adjustment calculation, which includes a detailed reserve comparison with the previous quarter, an analysis for change in reserve, and a reserve forecast to ensure that the credit valuation adjustment recorded at period end is sufficient. Assets and Liabilities Measured at Fair Value on a Recurring Basis Certain assets and liabilities are measured at fair value on a recurring basis in accordance with GAAP. The following tables present these assets and liabilities at December 31, 2017 , and December 31, 2016 . December 31, 2017 Level 1 Level 2 Level 3 Total in millions ASSETS MEASURED ON A RECURRING BASIS Trading account assets: U.S. Treasury, agencies and corporations — $ 615 — $ 615 States and political subdivisions — 37 — 37 Collateralized mortgage obligations — — — — Other mortgage-backed securities — 104 — 104 Other securities — 65 — 65 Total trading account securities — 821 — 821 Commercial loans — 15 — 15 Total trading account assets — 836 — 836 Securities available for sale: U.S. Treasury, agencies and corporations — 157 — 157 States and political subdivisions — 9 — 9 Agency residential collateralized mortgage obligations — 14,660 — 14,660 Agency residential mortgage-backed securities — 1,439 — 1,439 Agency commercial mortgage-backed securities — 1,854 — 1,854 Other securities — — $ 20 20 Total securities available for sale — 18,119 20 18,139 Other investments: Principal investments: Direct — — 13 13 Indirect (measured at NAV) (a) — — — 124 Total principal investments — — 13 137 Equity investments: Direct — 4 3 7 Total equity investments — 4 3 7 Total other investments — 4 16 144 Loans, net of unearned income — — 2 2 Loans held for sale — 70 1 71 Derivative assets: Interest rate — 713 9 722 Foreign exchange $ 100 30 — 130 Commodity — 255 — 255 Credit — — 1 1 Other — 1 3 4 Derivative assets 100 999 13 1,112 Netting adjustments (b) — — — (443 ) Total derivative assets 100 999 13 669 Accrued income and other assets — — — — Total assets on a recurring basis at fair value $ 100 $ 20,028 $ 52 $ 19,861 LIABILITIES MEASURED ON A RECURRING BASIS Bank notes and other short-term borrowings: Short positions $ 72 $ 562 — $ 634 Derivative liabilities: Interest rate — 520 — 520 Foreign exchange 98 26 — 124 Commodity — 246 — 246 Credit — 4 — 4 Other — 13 — 13 Derivative liabilities 98 809 — 907 Netting adjustments (b) — — — (616 ) Total derivative liabilities 98 809 — 291 Accrued expense and other liabilities — — — — Total liabilities on a recurring basis at fair value $ 170 $ 1,371 — $ 925 (a) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheet. (b) Netting adjustments represent the amounts recorded to convert our derivative assets and liabilities from a gross basis to a net basis in accordance with applicable accounting guidance. The net basis takes into account the impact of bilateral collateral and master netting agreements that allow us to settle all derivative contracts with a single counterparty on a net basis and to offset the net derivative position with the related cash collateral. Total derivative assets and liabilities include these netting adjustments. December 31, 2016 Level 1 Level 2 Level 3 Total in millions ASSETS MEASURED ON A RECURRING BASIS Trading account assets: U.S. Treasury, agencies and corporations — $ 655 — $ 655 States and political subdivisions — 8 — 8 Collateralized mortgage obligations — — — — Other mortgage-backed securities — 113 — 113 Other securities — 73 — 73 Total trading account securities — 849 — 849 Commercial loans — 18 — 18 Total trading account assets — 867 — 867 Securities available for sale: U.S. Treasury, agencies and corporations — 184 — 184 States and political subdivisions — 11 — 11 Agency residential collateralized mortgage obligations — 16,408 — 16,408 Agency residential mortgage-backed securities — 1,846 — 1,846 Agency commercial mortgage-backed securities — 1,743 — 1,743 Other securities $ 3 — $ 17 20 Total securities available for sale 3 20,192 17 20,212 Other investments: Principal investments: Direct — — 27 27 Indirect (measured at NAV) (a) — — — 158 Total principal investments — — 27 185 Equity and mezzanine investments: Indirect (measured at NAV) (a) — — — 6 Total equity and mezzanine investments — — — 6 Total other investments — — 27 191 Loans, net of unearned income — — — — Loans held for sale — 62 — 62 Derivative assets: Interest rate — 923 7 930 Foreign exchange 114 9 — 123 Commodity — 176 — 176 Credit — — 1 1 Other — 2 2 4 Derivative assets 114 1,110 10 1,234 Netting adjustments (b) — — — (431 ) Total derivative assets 114 1,110 10 803 Accrued income and other assets — 8 — 8 Total assets on a recurring basis at fair value $ 117 $ 22,239 $ 54 $ 22,143 LIABILITIES MEASURED ON A RECURRING BASIS Bank notes and other short-term borrowings: Short positions $ 192 $ 616 — $ 808 Derivative liabilities: Interest rate — 737 — 737 Foreign exchange 102 11 — 113 Commodity — 165 — 165 Credit — 4 — 4 Other — 1 — 1 Derivative liabilities 102 918 — 1,020 Netting adjustments (b) — — — (384 ) Total derivative liabilities 102 918 — 636 Accrued expense and other liabilities — 14 — 14 Total liabilities on a recurring basis at fair value $ 294 $ 1,548 — $ 1,458 (a) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheet. (b) Netting adjustments represent the amounts recorded to convert our derivative assets and liabilities from a gross basis to a net basis in accordance with applicable accounting guidance. The net basis takes into account the impact of bilateral collateral and master netting agreements that allow us to settle all derivative contracts with a single counterparty on a net basis and to offset the net derivative position with the related cash collateral. Total derivative assets and liabilities include these netting adjustments. Changes in Level 3 Fair Value Measurements The following table shows the change in the fair values of our Level 3 financial instruments for the years ended December 31, 2017 , and December 31, 2016 . We mitigate the credit risk, interest rate risk, and risk of loss related to many of these Level 3 instruments by using securities and derivative positions classified as Level 1 or Level 2. Level 1 and Level 2 instruments are not included in the following table. Therefore, the gains or losses shown do not include the impact of our risk management activities. in millions Beginning of Period Balance Gains (Losses) included in comprehensive income Gains (Losses) Included in Earnings Purchases Sales Settlements Transfers Other Transfers into Level 3 (e) Transfers out of Level 3 (e) End of Period Balance Unrealized Gains (Losses) Included in Earnings Year ended December 31, 2017 Securities available for sale Other securities $ 17 $ 3 — — — — — — — $ 20 — Other investments Principal investments Direct 27 — $ (6 ) (c) — $ (8 ) — — — — 13 $ (1 ) (c) Equity investments Direct — — — — — — — $ 3 — 3 — Loans held for sale — — — — (3 ) — $ 4 — — 1 — Loans held for investment — — — — — — 2 — — 2 — Derivative instruments (b) Interest rate 7 — (2 ) (d) — — — — 13 (f) $ (9 ) (f) 9 — Credit 1 — (16 ) (d) — — $ 16 — — — 1 — Other (a) 2 — — — — — 1 — — 3 — in millions Beginning of Period Balance Gains (Losses) Included in Earnings Purchases Sales Settlements Transfers Other Transfers into Level 3 (e) Transfers out of Level 3 (e) End of Period Balance Unrealized Gains (Losses) Included in Earnings Year ended December 31, 2016 Securities available for sale Other securities $ 17 — — — — — — — $ 17 — Other investments Principal investments Direct 50 $ 16 (c) — $ (39 ) — — — — 27 $ 2 (c) Other indirect — — — (20 ) — — $ 20 — — (1 ) (c) Derivative instruments (b) Interest rate 16 4 (d) $ 1 — — — 9 (f) $ (23 ) (f) 7 — Credit 1 (13 ) (d) 1 — $ 12 — — — 1 — Other (a) — — 5 — — $ (3 ) — — 2 — (a) Amounts represent Level 3 interest rate lock commitments. (b) Amounts represent Level 3 derivative assets less Level 3 derivative liabilities. (c) Realized and unrealized gains and losses on principal investments are reported in “net gains (losses) from principal investing” on the income statement. Realized and unrealized losses on private equity and mezzanine investments are reported in “other income” on the income statement. (d) Realized and unrealized gains and losses on derivative instruments are reported in “corporate services income” and “other income” on the income statement. (e) Our policy is to recognize transfers into and transfers out of Level 3 as of the end of the reporting period. (f) Certain derivatives previously classified as Level 2 were transferred to Level 3 because Level 3 unobservable inputs became significant. Certain derivatives previously classified as Level 3 were transferred to Level 2 because Level 3 unobservable inputs became less significant. Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis Certain assets and liabilities are measured at fair value on a nonrecurring basis in accordance with GAAP. The adjustments to fair value generally result from the application of accounting guidance that requires assets and liabilities to be recorded at the lower of cost or fair value, or assessed for impairment. There were no liabilities measured at fair value on a nonrecurring basis at December 31, 2017 , and December 31, 2016 . The following table presents our assets measured at fair value on a nonrecurring basis at December 31, 2017 , and December 31, 2016 : December 31, 2017 December 31, 2016 in millions Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total ASSETS MEASURED ON A NONRECURRING BASIS Impaired loans — — $ 9 $ 9 — — $ 11 $ 11 Loans held for sale (a) — — — — — — — — Accrued income and other assets (b) — $ 5 133 138 — — 11 11 Total assets on a nonrecurring basis at fair value — $ 5 $ 142 $ 147 — — $ 22 $ 22 (a) During 2017 , we transferred $63 million , net, of commercial and residential loans and leases at their current fair value from held-for-sale status to the held-to-maturity portfolio, compared to $35 million , net, during 2016 that was transferred from held-to-maturity to held-for-sale status. (b) At December 31, 2017, we recorded $31 million of impairment related to $119 million of LIHTC and Historic Tax Credit investments impacted by the enactment of the TCJ Act. Refer to the “Other Assets” section below for a description of the valuation technique and inputs applied for this fair value measurement. Impaired loans . Loans are evaluated for impairment on a quarterly basis. Loans included in the previous quarter’s review are re-evaluated, and if their values have changed materially, the underlying information (loan balance and in most cases, collateral value) is compared. Material differences are evaluated for reasonableness, and the relationship managers and their senior managers consider these differences and determine if any adjustment is necessary. The inputs are developed and substantiated on a quarterly basis based on current borrower developments, market conditions, and collateral values. The following two internal methods are used to value impaired loans: • Cash flow analysis considers internally developed inputs, such as discount rates, default rates, costs of foreclosure, and changes in collateral values. • The fair value of the collateral, which may take the form of real estate or personal property, is based on internal estimates, field observations, and assessments provided by third-party appraisers. We perform or reaffirm appraisals of collateral-dependent impaired loans at least annually. Appraisals may occur more frequently if the most recent appraisal does not accurately reflect the current market, the debtor is seriously delinquent or chronically past due, or there has been a material deterioration in the performance of the project or condition of the property. Adjustments to outdated appraisals that result in an appraisal value less than the carrying amount of a collateral-dependent impaired loan are reflected in the ALLL. We adjust the carrying amount of our impaired loans when there is evidence of probable loss and the expected fair value of the loan is less than its contractual amount. The amount of the impairment may be determined based on the estimated present value of future cash flows, the fair value of the underlying collateral, or the loan’s observable market price. Impaired loans with a specifically allocated allowance based on a cash flow analysis or the value of the underlying collateral are classified as Level 3 assets. Impaired loans with a specifically allocated allowance based on an observable market price that reflects recent sale transactions for similar loans and collateral are classified as Level 2 assets. Impairment valuations are back-tested each quarter, based on a look-back of actual incurred losses on closed deals previously evaluated for impairment. The overall percent variance of actual net loan charge-offs on closed deals compared to the specific allocations on such deals is considered in determining each quarter’s specific allocations. The evaluations for impairment are prepared by the responsible relationship managers in our Asset Recovery Group and are reviewed and approved by the Asset Recovery Group Executive. The Asset Recovery Group is part of the Risk Management Group and reports to our Chief Credit Officer. These evaluations are performed in conjunction with the quarterly ALLL process. Commercial loans held for sale . Through a quarterly analysis of our loan portfolios held for sale, which include both performing and nonperforming commercial loans, we determine any adjustments necessary to record the portfolios at the lower of cost or fair value in accordance with GAAP. Our analysis concluded that there were no loans held for sale adjusted to fair value at December 31, 2017 , or December 31, 2016 . Direct financing leases and operating lease assets held for sale . Our KEF Accounting and Capital Markets groups are responsible for the valuation policies and procedures related to these assets. The Managing Director of the KEF Capital Markets group reports to the President of the KEF line of business. A weekly report is distributed to both groups that lists all equipment finance deals booked in the warehouse portfolio. On a quarterly basis, the KEF Accounting group prepares a detailed held-for-sale roll-forward schedule that is reconciled to the general ledger and the above mentioned weekly report. KEF management uses the held-for-sale roll-forward schedule to determine if an impairment adjustment is necessary in accordance with lower of cost or fair value guidelines. Valuations of direct financing leases and operating lease assets held for sale are performed using an internal model that relies on market data, such as swap rates and bond ratings, as well as our own assumptions about the exit market for the leases and details about the individual leases in the portfolio. The inputs based on our assumption

Securities

Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Securities	8. Securities The amortized cost, unrealized gains and losses, and approximate fair value of our securities available for sale and held-to-maturity securities are presented in the following tables. Gross unrealized gains and losses represent the difference between the amortized cost and the fair value of securities on the balance sheet as of the dates indicated. Accordingly, the amount of these gains and losses may change in the future as market conditions change. 2017 2016 December 31, in millions Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value SECURITIES AVAILABLE FOR SALE U.S. Treasury, Agencies, and Corporations $ 159 — $ 2 $ 157 $ 188 — $ 4 $ 184 States and political subdivisions 9 — — 9 11 — — 11 Agency residential collateralized mortgage obligations 14,985 $ 10 335 14,660 16,652 $ 31 275 16,408 Agency residential mortgage-backed securities 1,456 3 20 1,439 1,857 6 17 1,846 Agency commercial mortgage-backed securities 1,920 — 66 1,854 1,778 — 35 1,743 Other securities 17 3 — 20 21 — 1 20 Total securities available for sale $ 18,546 $ 16 $ 423 $ 18,139 $ 20,507 $ 37 $ 332 $ 20,212 HELD-TO-MATURITY SECURITIES Agency residential collateralized mortgage obligations $ 8,055 — $ 224 $ 7,831 $ 8,404 $ 1 $ 173 $ 8,232 Agency residential mortgage-backed securities 574 $ 1 4 571 629 — 5 624 Agency commercial mortgage-backed securities 3,186 6 44 3,148 1,184 1 49 1,136 Other securities 15 — — 15 15 — — 15 Total held-to-maturity securities $ 11,830 $ 7 $ 272 $ 11,565 $ 10,232 $ 2 $ 227 $ 10,007 The following table summarizes our securities that were in an unrealized loss position as of December 31, 2017 , and December 31, 2016 : Duration of Unrealized Loss Position Less than 12 Months 12 Months or Longer Total in millions Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses December 31, 2017 Securities available for sale: U.S. Treasury, Agencies, and Corporations $ 41 — $ 116 $ 2 $ 157 $ 2 States and political subdivisions — — — — — — Agency residential collateralized mortgage obligations 6,153 $ 74 7,270 261 13,423 335 Agency residential mortgage-backed securities 666 7 702 13 1,368 20 Agency commercial mortgage-backed securities 205 4 1,649 62 1,854 66 Other securities — — — — — — Held-to-maturity securities: U.S. Treasury, Agencies, and Corporations — — — — — — States and political subdivisions — — — — — — Agency residential collateralized mortgage obligations 2,201 27 5,599 197 7,800 224 Agency residential mortgage-backed securities 252 1 206 3 458 4 Agency commercial mortgage-backed securities 1,470 12 495 32 1,965 44 Other securities (b) 3 — 4 — 7 — Total temporarily impaired securities $ 10,991 $ 125 $ 16,041 $ 570 $ 27,032 $ 695 December 31, 2016 Securities available for sale: U.S. Treasury, Agencies, and Corporations $ 182 $ 4 — — $ 182 $ 4 Agency residential collateralized mortgage obligations 12,345 231 $ 1,410 $ 44 13,755 275 Agency residential mortgage-backed securities 1,452 17 — — 1,452 17 Agency commercial mortgage-backed securities 1,482 35 — — 1,482 35 Other securities (a) 2 — 3 1 5 1 Held-to-maturity securities: Agency residential collateralized mortgage obligations 7,028 156 518 17 7,546 173 Agency residential mortgage-backed securities 547 5 — — 547 5 Agency commercial mortgage-backed securities 996 49 — — 996 49 Other securities (b) 4 — — — 4 — Total temporarily impaired securities $ 24,038 $ 497 $ 1,931 $ 62 $ 25,969 $ 559 (a) Gross unrealized losses totaled less than $1 million for other securities available for sale at December 31, 2016 . (b) Gross unrealized losses totaled less than $1 million for other securities held to maturity at December 31, 2017 , and December 31, 2016 . At December 31, 2017 , we had $335 million of gross unrealized losses related to 428 fixed-rate agency residential CMOs that we invested in as part of our overall A/LM strategy. These securities had a weighted-average maturity of 4.15 years at December 31, 2017 . At December 31, 2017 , we also had $20 million of gross unrealized losses related to 248 agency residential mortgage-backed securities positions and $66 million of gross unrealized losses related to 14 agency commercial mortgage-backed securities positions with weighted-average maturities of 3.84 years and 4.07 years, respectively, at December 31, 2017 . Because these securities have a fixed interest rate, their fair value is sensitive to movements in market interest rates. These unrealized losses are considered temporary since we expect to collect all contractually due amounts from these securities. Accordingly, these investments were reduced to their fair value through OCI, not earnings. We regularly assess our securities portfolio for OTTI. The assessments are based on the nature of the securities, the underlying collateral, the financial condition of the issuer, the extent and duration of the loss, our intent related to the individual securities, and the likelihood that we will have to sell securities prior to expected recovery. As shown in the following table, we did not have any impairment losses recognized in earnings for the year ended December 31, 2017 . in millions Balance at December 31, 2016 $ 4 Impairment recognized in earnings — Balance at December 31, 2017 $ 4 Realized gains and losses related to securities available for sale were as follows: Year ended December 31, in millions 2017 (a) 2016 (b) 2015 Realized gains $ 1 — $ 1 Realized losses — — 1 Net securities gains (losses) $ 1 — — (a) Realized losses totaled less than $1 million for the year ended December 31, 2017 . (b) Realized gains and losses totaled less than $1 million for the year ended December 31, 2016 . At December 31, 2017 , securities available-for-sale and held-to-maturity securities totaling $7.0 billion were pledged to secure securities sold under repurchase agreements, to secure public and trust deposits, to facilitate access to secured funding, and for other purposes required or permitted by law. The following table shows securities by remaining maturity. CMOs and other mortgage-backed securities in the available-for-sale and held-to-maturity portfolios are presented based on their expected average lives. The remaining securities, in both the available-for-sale and held-to-maturity portfolios, are presented based on their remaining contractual maturity. Actual maturities may differ from expected or contractual maturities since borrowers have the right to prepay obligations with or without prepayment penalties. Securities Available for Sale Held-to-Maturity Securities December 31, 2017 Amortized Cost Fair Value Amortized Cost Fair Value in millions Due in one year or less $ 190 $ 190 $ 56 $ 56 Due after one through five years 14,990 14,635 7,977 7,776 Due after five through ten years 3,358 3,305 3,190 3,142 Due after ten years 8 9 607 591 Total $ 18,546 $ 18,139 $ 11,830 $ 11,565

Derivatives and Hedging Activit

Derivatives and Hedging Activities	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging Activities	9. Derivatives and Hedging Activities We are a party to various derivative instruments, mainly through our subsidiary, KeyBank. Derivative instruments are contracts between two or more parties that have a notional amount and an underlying variable, require a small or no net investment, and allow for the net settlement of positions. A derivative’s notional amount serves as the basis for the payment provision of the contract and takes the form of units, such as shares or dollars. A derivative’s underlying variable is a specified interest rate, security price, commodity price, foreign exchange rate, index, or other variable. The interaction between the notional amount and the underlying variable determines the number of units to be exchanged between the parties and influences the fair value of the derivative contract. The primary derivatives that we use are interest rate swaps, caps, floors, and futures; foreign exchange contracts; commodity derivatives; and credit derivatives. Generally, these instruments help us manage exposure to interest rate risk, mitigate the credit risk inherent in our loan portfolio, hedge against changes in foreign currency exchange rates, and meet client financing and hedging needs. As further discussed in this note: • interest rate risk is the risk that the EVE or net interest income will be adversely affected by fluctuations in interest rates; • credit risk is the risk of loss arising from an obligor’s inability or failure to meet contractual payment or performance terms; and • foreign exchange risk is the risk that an exchange rate will adversely affect the fair value of a financial instrument. At December 31, 2017 , after taking into account the effects of bilateral collateral and master netting agreements, we had a negative $12 million of derivative assets and $2 million of derivative liabilities that relate to contracts entered into for hedging purposes. As of the same date, after taking into account the effects of bilateral collateral and master netting agreements and a reserve for potential future losses, we had derivative assets of $681 million and derivative liabilities of $289 million that were not designated as hedging instruments. These positions are primarily comprised of derivative contracts entered into for client accommodation purposes. Additional information regarding our accounting policies for derivatives is provided in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Derivatives.” Derivatives Designated in Hedge Relationships Net interest income and the EVE change in response to changes in the mix of assets, liabilities, and off-balance sheet instruments; associated interest rates tied to each instrument; and differences in the repricing and maturity characteristics of interest-earning assets and interest-bearing liabilities. We utilize derivatives that have been designated as part of a hedge relationship in accordance with the applicable accounting guidance to manage net interest income and EVE to within our stated risk tolerances. The primary derivative instruments used to manage interest rate risk are interest rate swaps, which convert the contractual interest rate index of agreed-upon amounts of assets and liabilities (i.e., notional amounts) to another interest rate index. We designate certain “receive fixed/pay variable” interest rate swaps as fair value hedges. These contracts convert certain fixed-rate long-term debt into variable-rate obligations, thereby modifying our exposure to changes in interest rates. As a result, we receive fixed-rate interest payments in exchange for making variable-rate payments over the lives of the contracts without exchanging the notional amounts. Similarly, we designate certain “receive fixed/pay variable” interest rate swaps as cash flow hedges. These contracts effectively convert certain floating-rate loans into fixed-rate loans to reduce the potential adverse effect of interest rate decreases on future interest income. Again, we receive fixed-rate interest payments in exchange for making variable-rate payments over the lives of the contracts without exchanging the notional amounts. We also designate certain “pay fixed/receive variable” interest rate swaps as cash flow hedges. These swaps convert certain floating-rate debt into fixed-rate debt. We also use these swaps to manage the interest rate risk associated with anticipated sales of certain commercial real estate loans. The swaps protect against the possible short-term decline in the value of the loans that could result from changes in interest rates between the time they are originated and the time they are sold. We use foreign currency forward transactions to hedge the foreign currency exposure of our net investment in various foreign equipment finance entities. These entities are denominated in a non-U.S. currency. These swaps are designated as net investment hedges to mitigate the exposure of measuring the net investment at the spot foreign exchange rate. Derivatives Not Designated in Hedge Relationships On occasion, we enter into interest rate swap contracts to manage economic risks but do not designate the instruments in hedge relationships. Excluding contracts addressing customer exposures, the amount of derivatives hedging risks on an economic basis at December 31, 2017 , was not significant. Like other financial services institutions, we originate loans and extend credit, both of which expose us to credit risk. We actively manage our overall loan portfolio and the associated credit risk in a manner consistent with asset quality objectives and concentration risk tolerances to mitigate portfolio credit risk. Purchasing credit default swaps enables us to transfer to a third party a portion of the credit risk associated with a particular extension of credit, including situations where there is a forecasted sale of loans. We purchase credit default swaps to reduce the credit risk associated with the debt securities held in our trading portfolio. Although we use credit default swaps for risk management purposes, they are not accounted for as hedging instruments. We also enter into derivative contracts for other purposes, including: • interest rate swap, cap, and floor contracts entered into generally to accommodate the needs of commercial loan clients; • energy and base metal swap and option contracts entered into to accommodate the needs of clients; • foreign exchange forward and option contracts entered into primarily to accommodate the needs of clients; and • futures contracts and positions with third parties that are intended to offset or mitigate the interest rate or market risk related to client positions discussed above. These contracts are not designated as part of hedge relationships. Fair Values, Volume of Activity, and Gain/Loss Information Related to Derivative Instruments The following table summarizes the fair values of our derivative instruments on a gross and net basis as of December 31, 2017 , and December 31, 2016 . The change in the notional amounts of these derivatives by type from December 31, 2016 , to December 31, 2017 , indicates the volume of our derivative transaction activity during 2017 . The notional amounts are not affected by bilateral collateral and master netting agreements. The derivative asset and liability balances are presented on a gross basis, prior to the application of bilateral collateral and master netting agreements. Total derivative assets and liabilities are adjusted to take into account the impact of legally enforceable master netting agreements that allow us to settle all derivative contracts with a single counterparty on a net basis and to offset the net derivative position with the related cash collateral. Where master netting agreements are not in effect or are not enforceable under bankruptcy laws, we do not adjust those derivative assets and liabilities with counterparties. Securities collateral related to legally enforceable master netting agreements is not offset on the balance sheet. Our derivative instruments are included in “derivative assets” or “derivative liabilities” on the balance sheet, as indicated in the following table: December 31, 2017 December 31, 2016 Fair Value Fair Value in millions Notional Amount Derivative Assets Derivative Liabilities Notional Amount Derivative Assets Derivative Liabilities Derivatives designated as hedging instruments: Interest rate $ 26,176 $ 81 $ 46 $ 24,237 $ 189 $ 94 Foreign exchange 302 1 4 282 6 4 Total 26,478 82 50 24,519 195 98 Derivatives not designated as hedging instruments: Interest rate 61,390 641 474 55,315 741 643 Foreign exchange 8,317 129 120 6,230 117 109 Commodity 1,687 255 246 1,474 176 165 Credit 315 1 4 360 1 4 Other (a) 2,006 4 13 390 4 1 Total 73,715 1,030 857 63,769 1,039 922 Netting adjustments (b) — (443 ) (616 ) — (431 ) (384 ) Net derivatives in the balance sheet 100,193 669 291 88,288 803 636 Other collateral (c) — (5 ) (84 ) — (21 ) (97 ) Net derivative amounts $ 100,193 $ 664 $ 207 $ 88,288 $ 782 $ 539 (a) Other derivatives include interest rate lock commitments and forward sale commitments related to our residential mortgage banking activities, forward purchase and sales contracts consisting of contractual commitments associated with “to be announced” securities and when issued securities, and when-issued security transactions in connection with an “at-the-market” equity offering program. (b) Netting adjustments represent the amounts recorded to convert our derivative assets and liabilities from a gross basis to a net basis in accordance with the applicable accounting guidance. (c) Other collateral represents the amount that cannot be used to offset our derivative assets and liabilities from a gross basis to a net basis in accordance with the applicable accounting guidance. The other collateral consists of securities and is exchanged under bilateral collateral and master netting agreements that allow us to offset the net derivative position with the related collateral. The application of the other collateral cannot reduce the net derivative position below zero. Therefore, excess other collateral, if any, is not reflected above. Fair value hedges. During the year ended December 31, 2017 , we did not exclude any portion of these hedging instruments from the assessment of hedge effectiveness. While there is some immaterial ineffectiveness in our hedging relationships, all of our fair value hedges remained “highly effective” as of December 31, 2017 . The following table summarizes the pre-tax net gains (losses) on our fair value hedges for the years ended December 31, 2017 , and December 31, 2016 , and where they are recorded on the income statement. Year Ended December 31, 2017 in millions Income Statement Location of Net Gains (Losses) on Derivative Net Gains (Losses) on Derivative Hedged Item Income Statement Location of Net Gains (Losses) on Hedged Item Net Gains (Losses) on Hedged Item Interest rate Other income $ (103 ) Long-term debt Other income $ 107 (a) Interest rate Interest expense – Long-term debt 49 Total $ (54 ) $ 107 Year Ended December 31, 2016 in millions Income Statement Location of Net Gains (Losses) on Derivative Net Gains (Losses) on Derivative Hedged Item Income Statement Location of Net Gains (Losses) on Hedged Item Net Gains (Losses) on Hedged Item Interest rate Other income $ (95 ) Long-term debt Other income $ 97 (a) Interest rate Interest expense – Long-term debt 96 Total $ 1 $ 97 (a) Net gains (losses) on hedged items represent the change in fair value caused by fluctuations in interest rates. Cash flow hedges. During the year ended December 31, 2017 , we did not exclude any portion of these hedging instruments from the assessment of hedge effectiveness. While there is some immaterial ineffectiveness in our hedging relationships, all of our cash flow hedges remained “highly effective” as of December 31, 2017 . Considering the interest rates, yield curves, and notional amounts as of December 31, 2017 , we would expect to reclassify an estimated $39 million of after-tax net losses on derivative instruments from AOCI to income during the next 12 months for our cash flow hedges. In addition, we expect to reclassify approximately $3 million of net losses related to terminated cash flow hedges from AOCI to income during the next 12 months . As of December 31, 2017 , the maximum length of time over which we hedge forecasted transactions is 11 years . Net investment hedges. We enter into foreign currency forward contracts to hedge our exposure to changes in the carrying value of our investments as a result of changes in the related foreign exchange rates. At December 31, 2017 , AOCI reflected unrecognized after-tax gains totaling $37 million related to cumulative changes in the fair value of our net investment hedges, which offset the unrecognized after-tax foreign currency losses on net investment balances. The ineffective portion of net investment hedging transactions is included in “other income” on the income statement, but there was no net investment hedge ineffectiveness as of December 31, 2017 . We did not exclude any portion of our hedging instruments from the assessment of hedge effectiveness during the year ended December 31, 2017 . The following table summarizes the pre-tax net gains (losses) on our cash flow and net investment hedges for the years ended December 31, 2017 , and December 31, 2016 , and where they are recorded on the income statement. The table includes the effective portion of net gains (losses) recognized in OCI during the period, the effective portion of net gains (losses) reclassified from OCI into income during the current period, and the portion of net gains (losses) recognized directly in income, representing the amount of hedge ineffectiveness. Year Ended December 31, 2017 in millions Net Gains (Losses) Recognized in OCI (Effective Portion) Income Statement Location of Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion) Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion) Income Statement Location of Net Gains (Losses) Recognized in Income (Ineffective Portion) Net Gains (Losses) Recognized in Income (Ineffective Portion) Cash Flow Hedges Interest rate $ (59 ) Interest income –Loans $ 19 Other income — Interest rate — Interest expense –Long-term debt (4 ) Other income — Interest rate (1 ) Investment banking and debt placement fees — Other income — Net Investment Hedges Foreign exchange contracts (17 ) Other Income — Other income — Total $ (77 ) $ 15 — Year Ended December 31, 2016 in millions Net Gains (Losses) Recognized in OCI (Effective Portion) Income Statement Location of Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion) Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion) Income Statement Location of Net Gains (Losses) Recognized in Income (Ineffective Portion) Net Gains (Losses) Recognized in Income (Ineffective Portion) Cash Flow Hedges Interest rate $ 29 Interest income – Loans $ 85 Other income — Interest rate — Interest expense – Long-term debt (4 ) Other income — Interest rate 1 Investment banking and debt placement fees — Other income — Net Investment Hedges Foreign exchange contracts (2 ) Other Income — Other income — Total $ 28 $ 81 — The after-tax change in AOCI resulting from cash flow and net investment hedges is as follows: December 31, 2017 Hedging Activity Reclassification of Gains to Net Income Reclassification to retained earnings resulting from new federal income tax rate December 31, in millions AOCI resulting from cash flow and net investment hedges $ (14 ) (48 ) (10 ) (14 ) $ (86 ) Nonhedging instruments. The following table summarizes the pre-tax net gains (losses) on our derivatives that are not designated as hedging instruments for the years ended December 31, 2017 , December 31, 2016 , and December 31, 2015 , and where they are recorded on the income statement. 2017 2016 2015 Year ended December 31, in millions Corporate Services Income Consumer Mortgage Income (a) Other Income Total Corporate Services Income Consumer Mortgage Income (a) Other Income Total Corporate Services Income Other Income Total NET GAINS (LOSSES) Interest rate $ 29 — $ (1 ) $ 28 $ 30 — $ 1 $ 31 $ 28 — $ 28 Foreign exchange 41 — — 41 40 — — 40 36 — 36 Commodity 6 — — 6 4 — — 4 5 — 5 Credit 2 — (21 ) (19 ) 1 — (16 ) (15 ) (1 ) $ (15 ) (16 ) Other — $ (1 ) (6 ) (7 ) — $ 1 — 1 — — — Total net gains (losses) $ 78 $ (1 ) $ (28 ) $ 49 $ 75 $ 1 $ (15 ) $ 61 $ 68 $ (15 ) $ 53 (a) As a result of the First Niagara acquisition, we began recognizing net gains (losses) on other derivatives related to our residential mortgage banking activities in “consumer mortgage income” in 2016. Counterparty Credit Risk Like other financial instruments, derivatives contain an element of credit risk. This risk is measured as the expected positive replacement value of the contracts. We use several means to mitigate and manage exposure to credit risk on derivative contracts. We generally enter into bilateral collateral and master netting agreements that provide for the net settlement of all contracts with a single counterparty in the event of default. Additionally, we monitor counterparty credit risk exposure on each contract to determine appropriate limits on our total credit exposure across all product types. We review our collateral positions on a daily basis and exchange collateral with our counterparties in accordance with standard ISDA documentation, central clearing rules, and other related agreements. We generally hold collateral in the form of cash and highly rated securities issued by the U.S. Treasury, government-sponsored enterprises, or GNMA. The cash collateral netted against derivative assets on the balance sheet totaled $23 million at December 31, 2017 , and $155 million at December 31, 2016 . The cash collateral netted against derivative liabilities totaled $150 million at December 31, 2017 , and $108 million at December 31, 2016 . During the first quarter of 2017, the relevant agreements that allow us to access the central clearing organizations to clear derivative transactions became qualified master netting agreements resulting in a change in how cash collateral is reflected on our balance sheet and in related disclosures. As a result, all cash collateral exchanged with central clearing organizations is now netted against the related derivative contracts on our balance sheet and related disclosures. Cash collateral exchanged with central clearing organizations was included in “short-term investments” and “NOW and money market deposit accounts” on the balance sheet in all periods prior to March 31, 2017. At December 31, 2017 and December 31, 2016 , respectively, we posted $383 million and $448 million of cash collateral with clearing organizations and held $99 million and $59 million of cash collateral from clearing organizations. Additionally, the CME amended its rulebook effective January 3, 2017, to characterize variation margin payments made to and received from the CME as settlement of derivatives, not collateral against derivative exposure. As a result, variation margin payments with the CME are presented on the balance sheet and in related disclosures as part of the gross fair value of CME-cleared derivative assets and liabilities. At December 31, 2017 , we had paid $239 million and received $64 million in variation margin to settle CME-cleared derivatives. In addition, under the CME’s settlement rulebook, CME-cleared derivative assets and liabilities are offset against one another to determine the gross asset or liability exposure of CME-cleared derivatives. Netting cash collateral exchanged with all central clearing organizations and applying variation margin payments as settlement to CME-cleared derivative transactions resulted in an increase of net derivative assets on our balance sheet of $2 million and a reduction of net derivative liabilities on our balance sheet of $283 million as of December 31, 2017 , as compared to December 31, 2016 . The following table summarizes the fair value of our derivative assets by type at the dates indicated. These assets represent our gross exposure to potential loss after taking into account the effects of bilateral collateral and master netting agreements and other means used to mitigate risk. December 31, in millions 2017 2016 Interest rate $ 401 $ 782 Foreign exchange 77 62 Commodity 163 110 Credit 1 — Other 4 4 Derivative assets before collateral 646 958 Less: Related collateral (23 ) 155 Total derivative assets $ 669 $ 803 We enter into derivative transactions with two primary groups: broker-dealers and banks, and clients. Since these groups have different economic characteristics, we have different methods for managing counterparty credit exposure and credit risk. We enter into transactions with broker-dealers and banks for various risk management purposes. These types of transactions generally are high dollar volume. We generally enter into bilateral collateral and master netting agreements with these counterparties. We clear certain types of derivative transactions with these counterparties, whereby central clearing organizations become the counterparties to our derivative contracts. In addition, we enter into derivative contracts through swap execution facilities. Swap clearing and swap execution facilities reduce our exposure to counterparty credit risk. At December 31, 2017 , we had gross exposure of $450 million to broker-dealers and banks. We had net exposure of $210 million after the application of master netting agreements and cash collateral, where such qualifying agreements exist. We had net exposure of $197 million after considering $13 million of additional collateral held in the form of securities. We enter into transactions with clients to accommodate their business needs. These types of transactions generally are low dollar volume. We generally enter into master netting agreements with these counterparties. In addition, we mitigate our overall portfolio exposure and market risk by buying and selling U.S. Treasuries and Eurodollar futures and entering into offsetting positions and other derivative contracts, sometimes with entities other than broker-dealers and banks. Due to the smaller size and magnitude of the individual contracts with clients, we generally do not exchange collateral in connection with these derivative transactions. To address the risk of default associated with the uncollateralized contracts, we have established a credit valuation adjustment (included in “derivative assets”) in the amount of $4 million at December 31, 2017 , which we estimate to be the potential future losses on amounts due from client counterparties in the event of default. At December 31, 2017 , we had gross exposure of $503 million to client counterparties and other entities that are not broker-dealers or banks for derivatives that have associated master netting agreements. We had net exposure of $459 million on our derivatives with these counterparties after the application of master netting agreements, collateral, and the related reserve. Credit Derivatives We are a buyer and, under limited circumstances, may be a seller of credit protection through the credit derivative market. We purchase credit derivatives to manage the credit risk associated with specific commercial lending and swap obligations as well as exposures to debt securities. The following table summarizes the fair value of our credit derivatives purchased and sold by type as of December 31, 2017 , and December 31, 2016 . The fair value of credit derivatives presented below does not take into account the effects of bilateral collateral or master netting agreements. December 31, in millions 2017 2016 Purchased Sold Net Purchased Sold Net Single-name credit default swaps $ (1 ) — $ (1 ) $ (2 ) — $ (2 ) Traded credit default swap indices (2 ) — (2 ) (1 ) — (1 ) Other (a) — — — — — — Total credit derivatives $ (3 ) — $ (3 ) $ (3 ) — $ (3 ) (a) As of December 31, 2017 and December 31, 2016 , the fair value of other credit derivatives purchased and sold totaled less than $1 million . Single-name credit default swaps are bilateral contracts whereby the seller agrees, for a premium, to provide protection against the credit risk of a specific entity (the “reference entity”) in connection with a specific debt obligation. The protected credit risk is related to adverse credit events, such as bankruptcy, failure to make payments, and acceleration or restructuring of obligations, identified in the credit derivative contract. A traded credit default swap index represents a position on a basket or portfolio of reference entities. The majority of transactions represented by the “other” category shown in the above table are risk participation agreements. In these transactions, the lead participant has a swap agreement with a customer. The lead participant (purchaser of protection) then enters into a risk participation agreement with a counterparty (seller of protection), under which the counterparty receives a fee to accept a portion of the lead participant’s credit risk. If the customer defaults on the swap contract, the counterparty to the risk participation agreement must reimburse the lead participant for the counterparty’s percentage of the positive fair value of the customer swap as of the default date. If the customer swap has a negative fair value, the counterparty has no reimbursement requirements. If the customer defaults on the swap contract and the seller fulfills its payment obligations under the risk participation agreement, the seller is entitled to a pro rata share of the lead participant’s claims against the customer under the terms of the swap agreement. The following table provides information on the types of credit derivatives sold by us and held on the balance sheet at December 31, 2017 , and December 31, 2016 . The notional amount represents the maximum amount that the seller could be required to pay. The payment/performance risk assessment is based on the default probabilities for the underlying reference entities’ debt obligations using a Moody’s credit ratings matrix known as Moody’s “Idealized” Cumulative Default Rates. The payment/performance risk shown in the table represents a weighted-average of the default probabilities for all reference entities in the respective portfolios. These default probabilities are directly correlated to the probability that we will have to make a payment under the credit derivative contracts. 2017 2016 December 31, dollars in millions Notional Amount Average Term (Years) Payment / Performance Risk Notional Amount Average Term (Years) Payment / Performance Risk Other $ 15 3.08 6.64 % $ 4 6.49 17.93 % Total credit derivatives sold $ 15 — — $ 4 — — Credit Risk Contingent Features We have entered into certain derivative contracts that require us to post collateral to the counterparties when these contracts are in a net liability position. The amount of collateral to be posted is based on the amount of the net liability and thresholds generally related to our long-term senior unsecured credit ratings with Moody’s and S&P. Collateral requirements also are based on minimum transfer amounts, which are specific to each Credit Support Annex (a component of the ISDA Master Agreement) that we have signed with the counterparties. In a limited number of instances, counterparties have the right to terminate their ISDA Master Agreements with us if our ratings fall below a certain level, usually investment-grade level (i.e., “Baa3” for Moody’s and “BBB-” for S&P). At December 31, 2017 , KeyBank’s rating was “ A3 ” with Moody’s and “ A- ” with S&P, and KeyCorp’s rating was “ Baa1 ” with Moody’s and “ BBB+ ” with S&P. As of December 31, 2017 , the aggregate fair value of all derivative contracts with credit risk contingent features (i.e., those containing collateral posting or termination provisions based on our ratings) held by KeyBank that were in a net liability position totaled $215 million , which includes $188 million in derivative assets and $403 million in derivative liabilities. We had $202 million in cash and securities collateral posted to cover those positions as of December 31, 2017 . There were no derivative contracts with credit risk contingent features held by KeyCorp at December 31, 2017 . The following table summarizes the additional cash and securities collateral that KeyBank would have been required to deliver under the ISDA Master Agreements had the credit risk contingent features been triggered for the derivative contracts in a net liability position as of December 31, 2017 , and December 31, 2016 . The additional collateral amounts were calculated based on scenarios under which KeyBank’s ratings are downgraded one, two, or three ratings as of December 31, 2017 , and December 31, 2016 , and take into account all collateral already posted. A similar calculation was performed for KeyCorp, and no additional collateral would have been required at December 31, 2017 , or December 31, 2016 . December 31, in millions 2017 2016 Moody’s S&P Moody’s S&P KeyBank’s long-term senior unsecured credit ratings A3 A- A3 A- One rating downgrade $ 2 $ 2 $ 2 $ 2 Two rating downgrades 2 2 2 2 Three rating downgrades 2 2 2 2 KeyBank’s long-term senior unsecured credit rating was four ratings above noninvestment grade at Moody’s and S&P as of December 31, 2017 , and December 31, 2016 . If KeyBank’s ratings had been downgraded below investment grade as of December 31, 2017 , and December 31, 2016 , payments of up to $12 million and $4 million , respectively, would have been required to either terminate the contracts or post additional collateral for those contracts in a net liability position, taking into account all collateral already posted. If KeyCorp’s ratings had been downgraded below investment grade as of December 31, 2017 , and December 31, 2016 , payments of $0 and less than $1 million would have been required to either terminate the contracts or post additional collateral for those contracts in a net liability position, taking into account all collateral already posted.

Mortgage Servicing Assets

Mortgage Servicing Assets	12 Months Ended
	Dec. 31, 2017
Servicing Asset [Abstract]
Mortgage Servicing Assets	10. Mortgage Servicing Assets We originate and periodically sell commercial and residential mortgage loans but continue to service those loans for the buyers. We also may purchase the right to service commercial mortgage loans for other lenders. We record a servicing asset if we purchase or retain the right to service loans in exchange for servicing fees that exceed the going market servicing rate and are considered more than adequate compensation for servicing. Additional information pertaining to the accounting for mortgage and other servicing assets is included in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Servicing Assets.” Commercial Changes in the carrying amount of commercial mortgage servicing assets are summarized as follows: Year ended December 31, in millions 2017 2016 Balance at beginning of period $ 356 $ 322 Servicing retained from loan sales 110 80 Purchases 36 41 Amortization (90 ) (87 ) Balance at end of period $ 412 $ 356 Fair value at end of period $ 537 $ 459 The fair value of commercial mortgage servicing assets is determined by calculating the present value of future cash flows associated with servicing the commercial mortgage loans. This calculation uses a number of assumptions that are based on current market conditions. The range and weighted-average of the significant unobservable inputs used to fair value our commercial mortgage servicing assets at December 31, 2017 , and December 31, 2016 , along with the valuation techniques, are shown in the following table: Valuation Technique Significant Unobservable Input Range (Weighted-Average) December 31, 2017 Commercial mortgage servicing assets Discounted cash flow Expected defaults 1.00 - 3.00% (1.20%) Residual cash flows discount rate 7.00 - 15.00% (9.10%) Escrow earn rate 0.90 - 3.10% (2.50%) Servicing cost $150 - $38,500 ($1,468) Loan assumption rate 0.00 - 3.00% (1.22%) Percentage late 0.00 - 1.30% (.25%) Valuation Technique Significant Unobservable Input Range (Weighted-Average) December 31, 2016 Commercial mortgage servicing assets Discounted cash flow Expected defaults 1.00 - 3.00% (1.40%) Residual cash flows discount rate 7.00 - 12.00% (8.00%) Escrow earn rate 1.10 - 3.00% (2.40%) Servicing cost $150 - $2,700 ($1,124) Loan assumption rate 0.00 - 3.00% (1.13%) Percentage late 0.00 - 2.00% (.34%) If these economic assumptions change or prove incorrect, the fair value of commercial mortgage servicing assets may also change. Expected credit losses, escrow earn rates, and discount rates are critical to the valuation of commercial mortgage servicing assets. Estimates of these assumptions are based on how a market participant would view the respective rates and reflect historical data associated with the commercial mortgage loans, industry trends, and other considerations. Actual rates may differ from those estimated due to changes in a variety of economic factors. A decrease in the value assigned to the escrow earn rates would cause a decrease in the fair value of our commercial mortgage servicing assets. An increase in the assumed default rates of commercial mortgage loans or an increase in the assigned discount rates would cause a decrease in the fair value of our commercial mortgage servicing assets. Prepayment activity on commercial serviced loans does not significantly impact the valuation of our commercial mortgage servicing assets. Unlike residential mortgages, commercial mortgages experience significantly lower prepayments due to certain contractual restrictions impacting the borrower’s ability to prepay the mortgage. The amortization of commercial mortgage servicing assets for each period, as shown in the table at the beginning of this note, is recorded as a reduction to contractual fee income. The contractual fee income from servicing commercial mortgage loans totaled $150 million for the year ended December 31, 2017 , $139 million for the year ended December 31, 2016 , and $142 million for the year ended December 31, 2015 . This fee income was partially offset by $90 million of amortization for the year ended December 31, 2017 , $87 million for the year ended December 31, 2016 , and $94 million for the year ended December 31, 2015 . Both the contractual fee income and the amortization are recorded, net, in “mortgage servicing fees” on the income statement. Residential With the First Niagara acquisition, we acquired residential mortgage servicing assets with a fair value of $28 million as of the Acquisition Date. Changes in the carrying amount of residential mortgage servicing assets are summarized as follows: in millions 2017 2016 Balance at beginning of period $ 28 — Servicing retained from loan sales 7 $ 2 Purchases — 28 Amortization (4 ) (2 ) Balance at end of period $ 31 $ 28 Fair value at end of period $ 37 $ 33 The fair value of residential mortgage servicing assets is determined by calculating the present value of future cash flows associated with servicing the residential mortgage loans. This calculation uses a number of assumptions that are based on current market conditions. The range and weighted-average of the significant unobservable inputs used to fair value our residential mortgage servicing assets at December 31, 2017 , along with the valuation techniques, are shown in the following table: Valuation Technique Significant Unobservable Input Range (Weighted-Average) December 31, 2017 Residential mortgage servicing assets Discounted cash flow Prepayment speed 9.16 - 51.52% (10.46%) Discount rate 8.50 - 11.00% (8.54%) Servicing cost $76 - $4,385 ($83.11) Valuation Technique Significant Unobservable Input Range (Weighted-Average) December 31, 2016 Residential mortgage servicing assets Discounted cash flow Prepayment speed 7.79 - 18.61% (9.42%) Discount rate 8.50 - 11.00% (8.55%) Servicing cost $76 - $3,335 ($83.04) If these economic assumptions change or prove incorrect, the fair value of residential mortgage servicing assets may also change. Prepayment speed, discount rates, and servicing cost are critical to the valuation of residential mortgage servicing assets. Estimates of these assumptions are based on how a market participant would view the respective rates and reflect historical data associated with the residential mortgage loans, industry trends, and other considerations. Actual rates may differ from those estimated due to changes in a variety of economic factors. An increase in the prepayment speed would cause a negative impact on the fair value of our residential mortgage servicing assets. An increase in the assigned discount rates and servicing cost assumptions would cause a decrease in the fair value of our residential mortgage servicing assets. The amortization of residential mortgage servicing assets for December 31, 2017 , as shown in the table above, is recorded as a reduction to contractual fee income. The contractual fee income from servicing residential mortgage loans totaled $12 million for the year ended December 31, 2017 . This fee income was offset by $4 million of amortization for the year ended December 31, 2017 . Both the contractual fee income and the amortization are recorded, net, in “mortgage servicing fees” on the income statement.

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises and Equipment	11. Premises and Equipment Premises and equipment at December 31, 2017 , and December 31, 2016 , consisted of the following: December 31, dollars in millions Useful life (in years) 2017 2016 Land Indefinite $ 138 $ 139 Buildings and improvements 15-40 741 727 Leasehold improvements 1-15 633 663 Furniture and equipment 2-15 931 943 Capitalized building leases 1-15 (a) 27 27 Construction in process N/A 38 42 Total premises and equipment 2,508 2,541 Less: Accumulated depreciation and amortization (1,578 ) (1,563 ) Premises and equipment, net $ 930 $ 978 (a) Capitalized building and equipment leases are amortized over the lesser of the useful life of asset or lease term. Depreciation and amortization expense related to premises and equipment for the years ended December 31, 2017 , December 31, 2016 , and December 31, 2015 was $138 million , $123 million , and $120 million , respectively. This includes amortization of assets under capital leases.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	12. Goodwill and Other Intangible Assets Our annual goodwill impairment testing is performed as of October 1 each year, or more frequently as events occur or circumstances change that would more-likely-than-not reduce the fair value of a reporting unit below its carrying amount. Additional information pertaining to our accounting policy for goodwill and other intangible assets is summarized in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Goodwill and Other Intangible Assets.” We conducted a quantitative Step 1 analysis as of October 1, 2017 . We determined that the estimated fair value of the Key Community Bank unit was 48% greater than its carrying amount and the estimated fair value of the Key Corporate Bank unit was 39% greater than its carrying amount. As such, goodwill was not impaired. The carrying amounts of the Key Community Bank and Key Corporate Bank units represent the average equity based on risk-weighted regulatory capital for goodwill impairment testing and management reporting purposes. In 2016 , we conducted a qualitative assessment and concluded that it was not more likely than not that the fair values of our reporting units were less than their respective carrying values; therefore, goodwill was not impaired. Based on our quarterly review of impairment indicators during 2017 and 2016 , it was not necessary to perform further reviews of goodwill recorded in our Key Community Bank or Key Corporate Bank units. We will continue to monitor the Key Community Bank and Key Corporate Bank units as appropriate since it is particularly dependent upon economic conditions that impact credit risk and behavior. Changes in the carrying amount of goodwill by reporting unit are presented in the following table: in millions Key Community Bank Key Corporate Bank Total BALANCE AT DECEMBER 31, 2015 $ 979 $ 81 $ 1,060 Acquisition of First Niagara 1,109 277 1,386 BALANCE AT DECEMBER 31, 2016 2,088 358 2,446 Fair value measurement adjustments - First Niagara acquisition 15 3 18 Additional ownership interest in Key Merchant Services 4 — 4 Acquisition of HelloWallet 17 — 17 Acquisition of Cain Brothers — 53 53 BALANCE AT DECEMBER 31, 2017 $ 2,124 $ 414 $ 2,538 Additional information regarding the above acquisitions is provided in Note 2 (“ Business Combination ”) and Note 15 (“ Acquisitions, Divestiture, and Discontinued Operations ”). As of December 31, 2017 , we expected goodwill in the amount of $627 million to be deductible for tax purposes in future periods. There were no accumulated impairment losses related to the Key Community Bank unit or the Key Corporate Bank unit at December 31, 2017 , December 31, 2016 , and December 31, 2015 . The following table shows the gross carrying amount and the accumulated amortization of intangible assets subject to amortization: 2017 2016 December 31, in millions Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Intangible assets subject to amortization: Core deposit intangibles $ 461 $ 192 $ 461 $ 125 PCCR intangibles 152 126 152 110 Other intangible assets (a) 128 7 74 68 Total $ 741 $ 325 $ 687 $ 303 (a) Carrying amount and accumulated amortization excludes $18 million at December 31, 2016 , related to the discontinued operations of Austin and the sale of Victory. As a result of the acquisition of First Niagara on August 1, 2016, intangible assets were recognized at the acquisition date fair value of $385 million . The core deposit intangible asset recognized as part of the First Niagara merger of $356 million is being amortized over its estimated useful life of approximately ten years utilizing an accelerated method. The commercial purchased credit card relationships recognized as part of the First Niagara merger are being amortized over their estimated useful life of approximately six years utilizing an accelerated method. The consumer purchased credit card relationships recognized as part of the First Niagara merger are being amortized over their estimated useful life of approximately nine years utilizing an accelerated method. Intangible assets acquired during the year ended December 31, 2017 were as follows: in millions KMS HelloWallet Cain Brothers Total Intangible assets subject to amortization: Customer relationships $ 85 — $ 29 $ 114 Trade name — — 1 1 Proprietary software — $ 12 — 12 Total $ 85 $ 12 $ 30 $ 127 Acquired customer relationships of KMS are being amortized over an estimated useful life of ten years utilizing an accelerated method. Proprietary software intangible assets of HelloWallet are being amortized on a straight line basis over their average useful life of three years. Acquired customer relationships of Cain Brothers are being amortized on an accelerated basis over an average useful life of eight years. The Cain Brothers trade name intangible asset is being amortized on a straight line basis over the estimated useful life of three years. The following table presents estimated intangible asset amortization expense for the next five years. Estimated 2018 2019 2020 2021 2022 Intangible asset amortization expense $ 96 $ 79 $ 64 $ 52 $ 42

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Variable Interest Entities	13. Variable Interest Entities A VIE is a partnership, limited liability company, trust, or other legal entity that meets any one of the following criteria: • The entity does not have sufficient equity to conduct its activities without additional subordinated financial support from another party. • The entity’s investors lack the power to direct the activities that most significantly impact the entity’s economic performance. • The entity’s equity at risk holders do not have the obligation to absorb losses or the right to receive residual returns. • The voting rights of some investors are not proportional to their economic interests in the entity, and substantially all of the entity’s activities involve, or are conducted on behalf of, investors with disproportionately few voting rights. Our significant VIEs are summarized below. We define a “significant interest” in a VIE as a subordinated interest that exposes us to a significant portion, but not the majority, of the VIE’s expected losses or residual returns, even though we do not have the power to direct the activities that most significantly impact the entity’s economic performance. LIHTC investments. Through KCDC, we have made investments directly and indirectly in LIHTC operating partnerships formed by third parties. As a limited partner in these operating partnerships, we are allocated tax credits and deductions associated with the underlying properties. We have determined that we are not the primary beneficiary of these investments because the general partners have the power to direct the activities that most significantly influence the economic performance of their respective partnerships and have the obligation to absorb expected losses and the right to receive residual returns. As we are not the primary beneficiary of these investments, we do not consolidate them. Our maximum exposure to loss in connection with these partnerships consists of our unamortized investment balance plus any unfunded equity commitments and tax credits claimed but subject to recapture. We had $1.3 billion and $1.2 billion of investments in LIHTC operating partnerships at December 31, 2017 , and December 31, 2016 , respectively. These investments are recorded in “accrued income and other assets” on our balance sheet. We do not have any loss reserves recorded related to these investments because we believe the likelihood of any loss is remote. For all legally binding unfunded equity commitments, we increase our recognized investment and recognize a liability. As of December 31, 2017 , and December 31, 2016 , we had liabilities of $476 million and $462 million , respectively, related to investments in qualified affordable housing projects, which are recorded in “accrued expense and other liabilities” on our balance sheet. We continue to invest in these LIHTC operating partnerships. The assets and liabilities presented in the table below convey the size of KCDC’s direct and indirect investments at December 31, 2017 , and December 31, 2016 . As these investments represent unconsolidated VIEs, the assets and liabilities of the investments themselves are not recorded on our balance sheet. Unconsolidated VIEs in millions Total Assets Total Liabilities Maximum Exposure to Loss December 31, 2017 LIHTC investments $ 6,003 $ 2,943 $ 1,561 December 31, 2016 LIHTC investments $ 4,814 $ 2,003 $ 1,465 We amortize our LIHTC investments over the period that we expect to receive the tax benefits. In 2017 , we recognized $172 million of amortization and $171 million of tax credits associated with these investments within “income taxes” on our income statement. Also, in the fourth quarter of 2017, we recognized $12 million in LIHTC impairment expense related to tax reform and $3 million unrelated to tax reform within “other noninterest expense.” In 2016 , we recognized $ 131 million of amortization and $ 144 million of tax credits associated with these investments within “income taxes” on our income statement. Principal investments. Through our principal investing entity, KCC, we have made investments in private equity funds engaged in venture- and growth-oriented investing. As a limited partner to these funds, KCC records these investments at fair value and receives distributions from the funds in accordance with the funds’ partnership agreements. We are not the primary beneficiary of these investments as we do not hold the power to direct the activities that most significantly affect the funds’ economic performance. Such power rests with the funds’ general partners. In addition, we neither have the obligation to absorb the funds’ expected losses nor the right to receive their residual returns. Our voting rights are also disproportionate to our economic interests, and substantially all of the funds’ activities are conducted on behalf of investors with disproportionately few voting rights. Because we are not the primary beneficiary of these investments, we do not consolidate them. Our maximum exposure to loss associated with indirect principal investments consists of the investments’ fair value plus any unfunded equity commitments. The fair value of our indirect principal investments totaled $124 million and $158 million at December 31, 2017 , and December 31, 2016 , respectively. These investments are recorded in “other investments” on our balance sheet. Additional information on indirect principal investments is provided in Note 7 (“ Fair Value Measurements ”). The table below reflects the size of the private equity funds in which KCC was invested as well as our maximum exposure to loss in connection with these investments at December 31, 2017 . Unconsolidated VIEs in millions Total Assets Total Liabilities Maximum Exposure to Loss December 31, 2017 KCC indirect investments $ 26,817 $ 292 $ 153 December 31, 2016 KCC indirect investments $ 32,755 $ 201 $ 195 Other unconsolidated VIEs. We are involved with other various entities in the normal course of business which we have determined to be VIEs. We have determined that we are not the primary beneficiary of these VIEs because we do not have the power to direct the activities that most significantly impact their economic performance. Our assets associated with these unconsolidated VIEs totaled $230 million at December 31, 2017 , and $178 million at December 31, 2016 . These assets are recorded in “accrued income and other assets,” “other investments,” “securities available for sale,” and “loans, net of unearned income” on our balance sheet. We had liabilities totaling $4 million associated with these unconsolidated VIEs at December 31, 2017 , and $4 million at December 31, 2016 . These liabilities are recorded in “accrued expenses and other liabilities” on our balance sheet. We have excluded certain transactions with unconsolidated VIEs from the balances above where we determine our continuing involvement is not significant. In addition, where we only have a lending arrangement in the normal course of business with unconsolidated VIEs we present the balances related to the lending arrangements in Note 6 (“ Asset Quality ”). Consolidated VIEs. Through our principal investing entity, KPP, we have formed and funded operating entities that provide management and other related services to our investment company funds, which directly invest in portfolio companies. In return for providing services to our direct investment funds, these entities’ receive a minority equity interest in the funds. This minority equity ownership is recorded at fair value on the entities’ financial statements. Additional information on our direct principal investments is provided in Note 7 (“ Fair Value Measurements ”). While other equity investors manage the daily operations of these entities, we retain the power, through voting rights, to direct the activities of the entities that most significantly impact their economic performance. In addition, we have the obligation to absorb losses and the right to receive residual returns that could potentially be significant to these entities. As a result, we have determined that we are the primary beneficiary of these funds and have consolidated them since formation. The assets of these KPP entities that can only be used to settle the entities’ obligations totaled $4 million at December 31, 2017 , and $1 million at December 31, 2016 . These assets are recorded in “cash and due from banks” and “accrued income and other assets” on our balance sheet. The entities had no liabilities at both December 31, 2017 , and December 31, 2016 , and other equity investors have no recourse to our general credit.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes Income taxes included in the income statement are summarized below. We file a consolidated federal income tax return. Year ended December 31, in millions 2017 2016 2015 Currently payable: Federal $ 334 $ 149 $ 337 State — 19 42 Total currently payable 334 168 379 Deferred: Federal 274 13 (69 ) State 29 (2 ) (7 ) Total deferred 303 11 (76 ) Total income tax (benefit) expense (a) $ 637 $ 179 $ 303 (a) There was no income tax (benefit) expense on securities transactions in 2017 , 2016 , and 2015 . Income tax expense excludes equity- and gross receipts-based taxes, which are assessed in lieu of an income tax in certain states in which we operate. These taxes, which are recorded in “noninterest expense” on the income statement, totaled $22 million in 2017 , $18 million in 2016 , and $16 million in 2015 . Significant components of our deferred tax assets and liabilities included in “accrued income and other assets” and “accrued expense and other liabilities,” respectively, on the balance sheet, are as follows: December 31, in millions 2017 2016 Allowance for loan and lease losses $ 233 $ 373 Employee benefits 147 276 Net unrealized securities losses 138 146 Federal net operating losses and credits 205 130 Fair value adjustments 63 136 Non-tax accruals 89 150 State net operating losses and credits 7 15 Other 223 236 Gross deferred tax assets 1,105 1,462 Less: Valuation Allowance 15 26 Total deferred tax assets 1,090 1,436 Leasing transactions 588 728 Other 182 101 Total deferred tax liabilities 770 829 Net deferred tax assets (liabilities) (a) $ 320 $ 607 (a) From continuing operations. On December 22, 2017, the TCJ Act was signed into law. This comprehensive tax legislation provides for significant changes to the U.S. Internal Revenue Code of 1986, as amended, that impact corporate taxation requirements, such as the reduction in the federal corporate income tax rate from 35% to 21% effective January 1, 2018. The TCJ Act retains the low-income housing and research and development credits and repeals the corporate alternative minimum tax. Other relevant corporate changes include earlier recognition of certain revenue; accelerating expensing of investments in tangible property, including leasing assets; and limiting several deductions such as FDIC premiums, certain executive compensation, and meals and entertainment expenses. Key is required to re-value certain tax-related assets under the provisions of the TCJ Act at December 31, 2017. Under current U.S. GAAP, deferred tax assets and liabilities are to be adjusted for the effect of a change in tax laws or rates with the effect included in income from continuing operations in the reporting period that includes the enactment date. The tax-related assets consist primarily of deferred tax assets and liabilities and investments in low-income housing transactions. Due to the close proximity of our year end to the date the TCJ Act was signed into law, we estimated the impact of the income tax effects as of December 31, 2017 based upon currently available information which resulted in a reduction to our net income of $161 million . The significant components of this reduction included a $14 million reduction in our investments in certain low-income housing that is reflected in other expenses and a $147 million , or 7.6% , increase in our income tax provision due to the reduction to our net deferred tax asset and related actions. T his reduction is primarily the result of the lower federal corporate income tax rate, is based on information available at this time, and is subject to change due to a variety of factors, including among others: (i) completion of Key’s 2017 federal and state income tax returns, and (ii) management’s further assessment of the TCJ Act and related regulatory guidance. Adjustments may be made in future periods to these estimates as we continue to obtain, prepare and analyze information about facts and circumstances that existed as of the enactment date that, if known, would have affected the income tax effects reported as provisional amounts. Key expects to finalize this impact in the quarter ending September 30, 2018. The accounting for the changes in tax law resulted in stranded tax effects within accumulated other comprehensive income for items that were originally recognized in other comprehensive income rather than in net income. The FASB recently issued an accounting standard update allowing companies to reclassify stranded tax effects resulting from the TCJ Act from accumulated other comprehensive income to retained earnings. We early adopted this guidance during the quarter ended December 31, 2017 and utilizing the portfolio method reclassified $141 million from accumulated other comprehensive income to retained earnings to eliminate the stranded tax effects. We conduct quarterly assessments of all available evidence to determine the amount of deferred tax assets that are more-likely-than-not to be realized, and therefore recorded. The available evidence used in connection with these assessments includes taxable income in prior periods, projected future taxable income, potential tax-planning strategies, and projected future reversals of deferred tax items. These assessments involve a degree of subjectivity and may undergo significant change. Based on these criteria, we have recorded $15 million of valuation allowances at December 31, 2017 ; primarily against federal and state capital loss carryforwards acquired in the First Niagara acquisition. At December 31, 2017 , we have federal net operating loss carryforwards of $79 million , federal credit carryforwards of $189 million , and capital loss carryforwards of $15 million . The federal net operating loss carryforwards are from prior acquisitions by First Niagara and are subject to annual limitations under the tax code and, if not utilized, will expire in the years beginning 2027. We currently expect to fully utilize these losses. The federal credit carryforwards which consist primarily of AMT credit carryforwards, have no expiration under the Internal Revenue Code and general business credits which expire in 2037. The capital loss carryforwards if not utilized, will expire in 2018 and 2019. Realization of these tax benefits is dependent upon Key’s ability to generate sufficient capital gain in an appropriate tax year to offset the capital loss carryforwards. At this time, generation of sufficient capital gain income is uncertain. We had state net operating loss carryforwards of $72 million , and state credit carryforwards of $5 million , resulting in a net state deferred tax asset of $7 million . Additionally, we had state capital loss carryforwards of $2 million . These carryforwards, if not utilized, will gradually expire through 2031. The following table shows how our total income tax expense (benefit) and the resulting effective tax rate were derived: Year ended December 31, dollars in millions 2017 2016 2015 Amount Rate Amount Rate Amount Rate Income (loss) before income taxes times 35% statutory federal tax rate $ 675 35.0 % $ 339 35.0 % $ 428 35.0 % Amortization of tax-advantaged investments 104 5.4 88 9.0 81 6.7 Foreign tax adjustments 1 .1 1 .1 (1 ) (.1 ) Tax-exempt interest income (37 ) (1.9 ) (25 ) (2.6 ) (18 ) (1.5 ) Corporate-owned life insurance income (46 ) (2.4 ) (44 ) (4.5 ) (45 ) (3.6 ) State income tax, net of federal tax benefit 19 1.0 11 1.1 22 1.8 Tax credits (218 ) (11.3 ) (208 ) (21.3 ) (155 ) (12.7 ) Tax Cuts and Jobs Act 147 7.6 — — — — Other (8 ) (.5 ) 17 1.7 (9 ) (.8 ) Total income tax expense (benefit) $ 637 33.0 % $ 179 18.5 % $ 303 24.8 % Liability for Unrecognized Tax Benefits The change in our liability for unrecognized tax benefits is as follows: Year ended December 31, in millions 2017 2016 Balance at beginning of year $ 53 $ 12 Increase for other tax positions of prior years 3 10 Increase from Acquisitions 3 33 Decrease for payments and settlements (4 ) — Decrease related to tax positions taken in prior years (16 ) (2 ) Balance at end of year $ 39 $ 53 Each quarter, we review the amount of unrecognized tax benefits recorded in accordance with the applicable accounting guidance. Any adjustment to unrecognized tax benefits is recorded in income tax expense. The amount of unrecognized tax benefits that, if recognized, would affect our effective tax rate was $39 million at December 31, 2017 , and $53 million at December 31, 2016 . We do not currently anticipate that the amount of unrecognized tax benefits will significantly change over the next 12 months . As permitted under the applicable accounting guidance, it is our policy to record interest and penalties related to unrecognized tax benefits in income tax expense. We recorded net interest benefit of $1.3 million and $.4 million in 2017 and 2016 , respectively and net interest expense of $.6 million in 2015 . We recovered state tax penalties of $1 million in 2017 and $.3 million in 2015 . We did not recover any state tax penalties in 2016 . At December 31, 2017 , we had an accrued interest payable of $4 million , compared to $3 million at December 31, 2016 . Our liability for accrued state tax penalties was $0 million at December 31, 2017 , and $1 million at December 31, 2016 . The amount of unrecognized tax benefits to be presented in the financial statements as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward if certain criteria are met at December 31, 2017 , and December 31, 2016 , are $17.2 million and $10.1 million , respectively. We file federal income tax returns, as well as returns in various state and foreign jurisdictions. We are subject to income tax examination by the IRS for the tax years 2013 and forward. Currently, we are not under audit for the tax years 2013 and forward. We are not subject to income tax examinations by other tax authorities for years prior to 2007. Pre-1988 Bank Reserves acquired in a business combination Retained earnings of KeyBank included approximately $92 million of allocated bad debt deductions for which no income taxes have been recorded. Under current federal law, these reserves are subject to recapture into taxable income if KeyBank, or any successor, fails to maintain its bank status under the Internal Revenue Code or makes non-dividend distributions or distributions greater than its accumulated earnings and profits. No deferred tax liability has been established as these events are not expected to occur in the foreseeable future.

Acquisition, Divestiture, and D

Acquisition, Divestiture, and Discontinued Operations	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisition, Divestiture, and Discontinued Operations	15. Acquisitions, Divestiture, and Discontinued Operations Acquisitions Cain Brothers & Company, LLC. On October 2, 2017, KBCM acquired all outstanding interests in Cain Brothers, a healthcare-focused investment banking and public finance firm. This acquisition expands KBCM’s investment banking group in the healthcare vertical by adding distinctive capabilities and broadening KBCM’s existing healthcare investment banking network. The acquisition is accounted for as a business combination. During the fourth quarter of 2017, Key recognized provisional identifiable intangible assets of $30 million and goodwill of $53 million as a result of this acquisition, which are deductible for tax purposes. These fair value estimates represent our best estimate of fair value and are expected to be finalized over a period of up to one year from the acquisition date. Additional information regarding acquired identifiable intangible assets and goodwill is provided in Note 12 (“ Goodwill and Other Intangible Assets ”). HelloWallet Holdings, Inc. On July 1, 2017, KeyBank acquired all of the outstanding capital stock of HelloWallet Holdings, Inc., the sole owner of HelloWallet, LLC, a digital financial wellness company. Key’s retail banking franchise is leveraging HelloWallet’s technology to provide data-driven insights to clients, allowing clients to better understand and improve their personal finances. The acquisition is accounted for as a business combination. During the third quarter of 2017, Key recognized provisional identifiable intangible assets with an estimated fair value of $12 million , comprised primarily of propriety software. Key also recognized provisional goodwill of $17 million in connection with this acquisition. These fair value estimates represent our best estimate of fair value and are expected to be finalized over a period of up to one year from the acquisition date. Key Merchant Services, LLC. On June 30, 2017, KeyBank (consolidated) acquired an additional 51% interest in KMS, increasing our ownership interest from 49% to 100% . This acquisition enables us to grow our merchant services business and enhance our merchant product offerings. This transaction is accounted for as a business combination achieved in stages. Prior to the acquisition, KMS was operated as a merchant services joint venture and accounted for as an equity method investment in our consolidated financial statements. As of June 30, 2017, the provisional estimated fair value of our equity interest in KMS immediately before the acquisition was $74 million . The fair value of our previously held equity interest was measured using discounted cash flow modeling that incorporates an appropriate risk premium and forecast earnings information. On June 30, 2017, we recognized a provisional non-cash holding gain of $64 million for the difference between the fair value and the book value of our previously held equity interest. In the third quarter of 2017, we recognized a measurement-period adjustment of $5 million to reduce the provisional estimated fair value of our equity interest immediately before the acquisition to $69 million , which reduced the total non-cash holding gain to $59 million . The initial gain and subsequent adjustment were included in “other income” on the income statement for the twelve months ended December 31, 2017 . Upon acquisition, we recorded estimated identifiable intangible assets of $95 million and goodwill of less than $1 million . In the third quarter of 2017, we recognized a measurement-period adjustment of $10 million to reduce the fair value of acquired identifiable intangible assets to $85 million . In the fourth quarter of 2017, we recognized a measurement period adjustment increasing deferred tax assets and decreasing goodwill by $2 million . In aggregate, the measurement-period adjustments recognized as of December 31, 2017 increased goodwill recorded in connection with the KMS acquisition to $4 million . The fair value estimates related to this acquisition represent our best estimate of fair value and are expected to be finalized over a period of up to one year from the acquisition date. First Niagara Financial Group, Inc. As previously disclosed, on October 30, 2015, KeyCorp entered into a definitive agreement and plan of merger (“Agreement”) to acquire all of the outstanding capital stock of First Niagara, headquartered in Buffalo, New York. On August 1, 2016, First Niagara merged with and into KeyCorp, with KeyCorp as the surviving entity. The total consideration for the transaction was approximately $4.0 billion . Under the terms of the Agreement, at the effective time of the merger, each share of First Niagara common stock was converted into the right to receive (i) 0.680 of a share of KeyCorp common stock and (ii) $2.30 in cash. The exchange ratio of KeyCorp stock for First Niagara stock was fixed per the Agreement and did not adjust based on changes in KeyCorp’s share trading price. First Niagara equity awards outstanding immediately prior to the effective time of the merger were converted into equity awards for KeyCorp common stock as provided in the Agreement. Each share of First Niagara’s Fixed-to-Floating Rate Perpetual Non-Cumulative Preferred Stock, Series B, was converted into a share of a newly created series of preferred stock of KeyCorp having substantially the same terms as First Niagara’s preferred stock. For more information on the acquisition, see Note 2 (“ Business Combination ”). On October 7, 2016, First Niagara Bank merged with and into KeyBank, with KeyBank as the surviving entity. Systems and client conversion also occurred during the fourth quarter of 2016 in connection with the bank merger. Divestiture On September 9, 2016, KeyCorp sold to Northwest Bank, a wholly-owned subsidiary of Northwest Bancshares, Inc., 18 branches in the Buffalo, New York market. The branches were divested in connection with the merger between First Niagara and KeyCorp and pursuant to an agreement with the United States Department of Justice and commitments to the Board of Governors of the Federal Reserve System following a customary antitrust review in connection with the merger. The divestiture included $439 million of loans and $1.6 billion of deposits associated with the 18 branches. Discontinued operations Discontinued operations primarily includes our government-guaranteed education lending business. At December 31, 2017, and December 31, 2016, approximately $1.3 billion and $1.6 billion , respectively, of education loans are included in discontinued assets on the consolidated balance sheets. Net interest income after provision for credit losses for this business is not material and is included in income (loss) from discontinued operations, net of taxes on the consolidated statements of income.

Securities Financing Activities

Securities Financing Activities	12 Months Ended
	Dec. 31, 2017
Brokers and Dealers [Abstract]
Securities Financing Activities	16. Securities Financing Activities The following table summarizes our securities financing agreements at December 31, 2017 , and December 31, 2016 : December 31, 2017 in millions Gross Amount Presented in Balance Sheet Netting Adjustments (a) Collateral (b) Net Amounts Offsetting of financial assets: Reverse repurchase agreements $ 3 $ (3 ) — — Total $ 3 $ (3 ) — — Offsetting of financial liabilities: Repurchase agreements (c) $ 374 $ (4 ) $ (370 ) — Total $ 374 $ (4 ) $ (370 ) — December 31, 2016 in millions Gross Amount Presented in Balance Sheet Netting Adjustments (a) Collateral (b) Net Amounts Offsetting of financial assets: Reverse repurchase agreements $ 3 $ (3 ) — — Total $ 3 $ (3 ) — — Offsetting of financial liabilities: Repurchase agreements (c) $ 497 $ (3 ) $ (494 ) — Total $ 497 $ (3 ) $ (494 ) — (a) Netting adjustments take into account the impact of master netting agreements that allow us to settle with a single counterparty on a net basis. (b) These adjustments take into account the impact of bilateral collateral agreements that allow us to offset the net positions with the related collateral. The application of collateral cannot reduce the net position below zero. Therefore, excess collateral, if any, is not reflected above. (c) Repurchase agreements are collateralized by mortgaged-backed agency securities and are contracted on an overnight or continuous basis. As of December 31, 2017 , the carrying amount of assets pledged as collateral against repurchase agreements totaled $463 million . Assets pledged as collateral are reported in “available for sale” and “held-to-maturity” securities on our balance sheet. At December 31, 2017 , the liabilities associated with collateral pledged were solely comprised of customer sweep financing activity and had a carrying value of $370 million . The collateral pledged under customer sweep repurchase agreements is posted to a third-party custodian and cannot be sold or repledged by the secured party. The risk related to a decline in the market value of collateral pledged is minimal given the collateral's high credit quality and the overnight duration of the repurchase agreements. Like other financing transactions, securities financing agreements contain an element of credit risk. To mitigate and manage credit risk exposure, we generally enter into master netting agreements and other collateral arrangements that give us the right, in the event of default, to liquidate collateral held and to offset receivables and payables with the same counterparty. Additionally, we establish and monitor limits on our counterparty credit risk exposure by product type. For the reverse repurchase agreements, we monitor the value of the underlying securities we received from counterparties and either request additional collateral or return a portion of the collateral based on the value of those securities. We generally hold collateral in the form of highly rated securities issued by the U.S. Treasury and fixed income securities. In addition, we may need to provide collateral to counterparties under our repurchase agreements. With the exception of collateral pledged against customer sweep repurchase agreements, the collateral we pledge and receive can generally be sold or repledged by the secured parties.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	17. Stock-Based Compensation We maintain several stock-based compensation plans, which are described below. Total compensation expense for these plans was $104 million for 2017 , $102 million for 2016 , and $59 million for 2015 . The total income tax benefit recognized in the income statement for these plans was $39 million for 2017 , $38 million for 2016 , and $22 million for 2015 . Our compensation plans allow us to grant stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance units, other awards which may be denominated or payable in or valued by reference to our Common Shares or other factors, discounted stock purchases, and deferred compensation to eligible employees and directors. At December 31, 2017 , we had 40,088,115 Common Shares available for future grant under our compensation plans. In accordance with a resolution adopted by the Compensation and Organization Committee of KeyCorp’s Board of Directors, we may not grant options to purchase Common Shares, restricted stock or other shares under any long-term compensation plan in an aggregate amount that exceeds 6% of our outstanding Common Shares in any rolling three -year period. Stock Options Stock options granted to employees generally become exercisable at the rate of 25% per year. No option granted by KeyCorp will be exercisable less than one year after, or expire later than ten years from, the grant date. The exercise price is the closing price of our Common Shares on the grant date. We determine the fair value of options granted using the Black-Scholes option-pricing model. This model was originally developed to determine the fair value of exchange-traded equity options, which (unlike employee stock options) have no vesting period or transferability restrictions. Because of these differences, the Black-Scholes model does not precisely value an employee stock option, but it is commonly used for this purpose. The model assumes that the estimated fair value of an option is amortized as compensation expense over the option’s vesting period. The Black-Scholes model requires several assumptions, which we developed and update based on historical trends and current market observations. Our determination of the fair value of options is only as accurate as the underlying assumptions. The assumptions pertaining to options issued during 2017 , 2016 , and 2015 are shown in the following table. Year ended December 31, 2017 2016 2015 Average option life 6.0 years 6.0 years 6.0 years Future dividend yield 1.79 % 2.86 % 1.84 % Historical share price volatility .287 .297 .382 Weighted-average risk-free interest rate 2.1 % 1.3 % 1.7 % Under KeyCorp’s 2013 Equity Compensation Plan, the Compensation and Organization Committee has authority to approve all stock option grants but may delegate some of its authority to grant awards from time to time. The committee has delegated to our Chief Executive Officer the authority to grant equity awards, including stock options, to any employee who is not designated an “officer” for purposes of Section 16 of the Exchange Act. No more than 3,000,000 Common Shares may be issued under this authority. The following table summarizes activity, pricing and other information for our stock options for the year ended December 31, 2017 : Number of Options Weighted-Average Exercise Price Per Option Weighted-Average Remaining Life Aggregate Intrinsic Value (a) Outstanding at December 31, 2016 13,885,566 $ 13.00 4.5 years $ 101 Granted 1,370,069 18.96 Exercised (3,755,177 ) 10.16 Lapsed or canceled (1,617,841 ) 35.15 Outstanding at December 31, 2017 9,882,617 $ 11.28 5.5 88 Expected to vest 3,422,790 13.97 8.3 21 Exercisable at December 31, 2017 6,183,136 $ 9.63 3.8 $ 65 (a) The intrinsic value of a stock option is the amount by which the fair value of the underlying stock exceeds the exercise price of the option. The weighted-average grant-date fair value of options was $4.60 for options granted during 2017 , $2.14 for options granted during 2016 , and $4.33 for options granted during 2015 . Stock option exercises numbered 3,755,177 in 2017 , 2,849,010 in 2016 , and 2,496,965 in 2015 . The aggregate intrinsic value of exercised options was $31 million for 2017 , $12 million for 2016 , and $14 million for 2015 . As of December 31, 2017 , unrecognized compensation cost related to nonvested options under the plans totaled $5 million . We expect to recognize this cost over a weighted-average period of 2.6 years . Cash received from options exercised was $25 million , $32 million , and $22 million in 2017 , 2016 , and 2015 , respectively. The actual tax benefit realized for the tax deductions from options exercised totaled $4 million for 2017 , $2 million for 2016 , and $2 million for 2015 . Long-Term Incentive Compensation Program Our Long-Term Incentive Compensation Program (the “Program”) rewards senior executives critical to our long-term financial success. Awards are granted annually in a variety of forms: • deferred cash payments that generally vest and are payable at the rate of 25% per year; • time-lapsed (service condition) restricted stock units payable in stock, which generally vest at the rate of 25% per year; • performance units payable in stock, which vest at the end of the three -year performance cycle and will not vest unless Key attains defined performance levels; and • performance units payable in cash, which vest at the end of the three -year performance cycle and will not vest unless Key attains defined performance levels. During 2017 , the total of performance units vested numbered 887,489 and were payable in cash. The total fair value of the performance units that vested during 2017 was $14 million . Performance units vested in 2016 and payable in cash numbered 1,915,239 and had a fair value of $21 million . The following table summarizes activity and pricing information for the nonvested shares in the Program for the year ended December 31, 2017 . Vesting Contingent on Service Conditions Vesting Contingent on Performance and Service Conditions Number of Nonvested Shares Weighted- Average Grant-Date Fair Value Number of Nonvested Shares Weighted- Average Grant-Date Fair Value Outstanding at December 31, 2016 13,918,806 $ 11.78 2,765,622 $ 14.45 Granted 3,899,826 18.96 2,321,041 19.82 Vested (5,324,226 ) 11.64 (887,489 ) 16.27 Forfeited (661,450 ) 13.19 (51,154 ) 20.33 Outstanding at December 31, 2017 11,832,956 $ 14.05 4,148,020 $ 17.51 The compensation cost of time-lapsed and performance-based restricted stock or unit awards granted under the Program is calculated using the closing trading price of our Common Shares on the grant date. Unlike time-lapsed and performance-based restricted stock or units, we do not pay dividends during the vesting period for performance shares or units that may become payable in excess of targeted performance. The weighted-average grant-date fair value of awards granted under the Program was $19.82 during 2017 , $10.49 during 2016 , and $13.99 during 2015 . As of December 31, 2017 , unrecognized compensation cost related to nonvested shares under the Program totaled $82 million . We expect to recognize this cost over a weighted-average period of 2.2 years . The total fair value of shares vested was $76 million in 2017 , $57 million in 2016 , and $39 million in 2015 . Deferred Compensation and Other Restricted Stock Awards Our deferred compensation arrangements include voluntary and mandatory deferral programs for Common Shares awarded to certain employees and directors. Mandatory deferred incentive awards vest at the rate of 25% per year beginning one year after the deferral date for awards granted in 2012 and after. Deferrals under the voluntary programs are immediately vested. We also may grant, upon approval by the Compensation and Organization Committee (or our Chief Executive Officer with respect to her delegated authority), other time-lapsed restricted stock or unit awards under various programs to recognize outstanding performance. The following table summarizes activity and pricing information for the nonvested shares granted under our deferred compensation plans and these other restricted stock or unit award programs for the year ended December 31, 2017 . Number of Nonvested Shares Weighted-Average Grant-Date Fair Value Outstanding at December 31, 2016 3,858,152 $ 12.22 Granted 2,347,005 18.55 Dividend equivalents 14 12.54 Vested (1,684,824 ) 12.50 Forfeited (296,573 ) 12.14 Outstanding at December 31, 2017 4,223,774 $ 15.61 The weighted-average grant-date fair value of awards granted was $18.55 during 2017 , $11.46 during 2016 , and $14.22 during 2015 . As of December 31, 2017 , unrecognized compensation cost related to nonvested shares granted under our deferred compensation plans and the other restricted stock or unit award programs totaled $37 million . We expect to recognize this cost over a weighted-average period of 3.7 years . The total fair value of shares vested was $21 million in 2017 , $16 million in 2016 , and $15 million in 2015 . Dividend equivalents presented in the preceding table represent the value of dividends accumulated during the vesting period. Discounted Stock Purchase Plan Our Discounted Stock Purchase Plan provides employees the opportunity to purchase our Common Shares at a 10% discount through payroll deductions or cash payments. Purchases are limited to $10,000 in any month and $50,000 in any calendar year, and are immediately vested. To accommodate employee purchases, we issue treasury shares on or around the fifteenth day of the month following the month employee payments are received. We issued 257,738 Common Shares at a weighted-average cost to the employee of $16.61 during 2017 , 310,604 Common Shares at a weighted-average cost to the employee of $11.04 during 2016 , and 250,913 Common Shares at a weighted-average cost to the employee of $12.55 during 2015 . Information pertaining to our method of accounting for stock-based compensation is included in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Stock-Based Compensation.”

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Employee Benefits	18. Employee Benefits Pension Plans Effective December 31, 2009, we amended our cash balance pension plan and other defined benefit plans to freeze all benefit accruals and close the plans to new employees. We will continue to credit participants’ existing account balances for interest until they receive their plan benefits. We changed certain pension plan assumptions after freezing the plans. As part of the acquisition of First Niagara, Key also obtained two frozen defined benefit plans sponsored by First Niagara, both of which provide benefits based upon length of service and compensation levels. Effective September 30, 2016, the two First Niagara plans merged into another defined benefit plan maintained by Key to form the KeyCorp Consolidated Cash Balance Plan. Effective December 31, 2016, our original cash balance pension plan merged into the KeyCorp Consolidated Cash Balance Plan. Pre-tax AOCI not yet recognized as net pension cost was $525 million at December 31, 2017 , and $550 million at December 31, 2016 , consisting entirely of net unrecognized losses. During 2018 , we expect to recognize $17 million of net unrecognized losses in pre-tax AOCI as net pension cost. During 2016 and 2015 , lump sum payments made under certain pension plans triggered settlement accounting. In accordance with the applicable accounting guidance for defined benefit plans, we performed a remeasurement of the affected plans in conjunction with the settlement and recognized the settlement loss as reflected in the following table. The components of net pension cost and the amount recognized in OCI for all funded and unfunded plans are as follows: Year ended December 31, in millions 2017 2016 2015 Interest cost on PBO $ 48 $ 44 $ 41 Expected return on plan assets (68 ) (58 ) (56 ) Amortization of losses 15 17 18 Settlement loss — 18 23 Net pension cost $ (5 ) $ 21 $ 26 Other changes in plan assets and benefit obligations recognized in OCI: Net (gain) loss $ (10 ) $ (9 ) $ 47 Amortization of gains (15 ) (35 ) (41 ) Total recognized in comprehensive income $ (25 ) $ (44 ) $ 6 Total recognized in net pension cost and comprehensive income $ (30 ) $ (23 ) $ 32 The information related to our pension plans presented in the following tables is based on current actuarial reports using measurement dates of December 31, 2017 , and December 31, 2016 . The following table summarizes changes in the PBO related to our pension plans. Year ended December 31, in millions 2017 2016 PBO at beginning of year $ 1,338 $ 1,136 Interest cost 48 44 Actuarial losses (gains) 37 (25 ) Benefit payments (100 ) (85 ) Plan acquisitions — 268 PBO at end of year $ 1,323 $ 1,338 The following table summarizes changes in the FVA. Year ended December 31, in millions 2017 2016 FVA at beginning of year $ 1,133 $ 869 Actual return on plan assets 115 42 Employer contributions 15 14 Benefit payments (100 ) (85 ) Plan acquisitions — 293 FVA at end of year $ 1,163 $ 1,133 The following table summarizes the funded status of the pension plans, which equals the amounts recognized in the balance sheets at December 31, 2017 , and December 31, 2016 . December 31, in millions 2017 2016 Funded status (a) $ (160 ) $ (205 ) Net prepaid pension cost recognized consists of: Noncurrent assets $ 29 — Current liabilities (15 ) $ (16 ) Noncurrent liabilities (174 ) (189 ) Net prepaid pension cost recognized (b) $ (160 ) $ (205 ) (a) The shortage of the FVA under the PBO. (b) Represents the accrued benefit liability of the pension plans. At December 31, 2017 , our primary qualified cash balance pension plan was sufficiently funded under the requirements of ERISA. Consequently, we are not required to make a minimum contribution to that plan in 2018 . We also do not expect to make any significant discretionary contributions during 2018 . At December 31, 2017 , we expect to pay the benefits from all funded and unfunded pension plans as follows: 2018 — $115 million ; 2019 — $114 million ; 2020 — $115 million ; 2021 — $101 million ; 2022 — $99 million and $412 million in the aggregate from 2023 through 2027. The ABO for all of our pension plans was $1.3 billion at December 31, 2017 , and $1.3 billion at December 31, 2016 . As indicated in the table below, collectively our plans had an ABO in excess of plan assets as follows: December 31, in millions 2017 2016 PBO $ 1,323 $ 1,338 ABO 1,323 1,338 Fair value of plan assets 1,163 1,133 To determine the actuarial present value of benefit obligations, we assumed the following weighted-average rates. December 31, 2017 2016 Discount rate 3.25 % 3.75 % Compensation increase rate N/A N/A To determine net pension cost, we assumed the following weighted-average rates. Year ended December 31, 2017 2016 2015 Discount rate 3.75 % 3.75 % 3.50 % Compensation increase rate N/A N/A N/A Expected return on plan assets 6.00 6.00 6.25 We estimate that we will recognize $5 million in net pension cost for 2018, compared to net pension benefit of $5 million in 2017, and net pension cost of $21 million for 2016. A net pension cost is expected in 2018 as compared to net pension benefit in 2017 primarily due to a reduction in the expected return on plan assets as a result of a change to the investment allocation policy of the pension fund. A benefit was recorded in 2017 as compared to cost in 2016 due to the lack of settlement loss. Costs decreased from 2015 to 2016 due to a smaller settlement loss and increased discount rate. We estimate that a 25 basis point increase or decrease in the expected return on plan assets would either decrease or increase, respectively, our net pension cost for 2018 by approximately $3 million . Pension cost also is affected by an assumed discount rate. We estimate that a 25 basis point change in the assumed discount rate would change net pension cost for 2018 by approximately $2 million . The expected return on plan assets is determined by considering a number of factors, the most significant of which are: • Our expectations for returns on plan assets over the long term, weighted for the investment mix of the assets. These expectations consider, among other factors, historical capital market returns of equity, fixed income, convertible, and other securities, and forecasted returns that are modeled under various economic scenarios. • Historical returns on our plan assets. Based on an annual reassessment of current and expected future capital market returns, our expected return on plan assets was 6% for 2017 , 6% for 2016 and 6.25% for 2015 . As a result of a change in our investment allocation policy, we deemed a rate of 4.75% to be appropriate in estimating 2018 pension cost. The investment objectives of the pension fund are developed to reflect the characteristics of the plan, such as pension formulas, cash lump sum distribution features, and the liability profiles of the plan’s participants. An executive oversight committee reviews the plan’s investment performance at least quarterly, and compares performance against appropriate market indices. The pension fund’s investment objectives are to balance total return objectives with a continued management of plan liabilities, and to minimize the mismatch between assets and liabilities. These objectives are being implemented through liability driven investing and the adoption of a de-risking glide path. The following table shows the asset target allocations prescribed by the pension fund’s investment policies based on the plan’s funded status at December 31, 2017 . Target Allocation Asset Class 2017 Equity securities: U.S. 5 % International 4 Fixed income securities 81 Real assets 6 Other assets 4 Total 100 % Equity securities include common stocks of domestic and foreign companies, as well as foreign company stocks traded as American Depositary Shares on U.S. stock exchanges. Debt securities include investments in domestic- and foreign-issued corporate bonds, U.S. government and agency bonds, international government bonds, and mutual funds. Convertible securities include investments in convertible bonds. Real assets include an investment in a diversified real asset strategy separate account designed to provide exposure to the three core real assets: Treasury Inflation-Protected Securities, commodities, and real estate. Other assets include investments in a multi-strategy investment fund and a limited partnership. Although the pension funds’ investment policies conditionally permit the use of derivative contracts, we have not entered into any such contracts, and we do not expect to employ such contracts in the future. The valuation methodologies used to measure the fair value of pension plan assets vary depending on the type of asset, as described below. For an explanation of the fair value hierarchy, see Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Fair Value Measurements.” Equity securities. Equity securities traded on securities exchanges are valued at the closing price on the exchange or system where the security is principally traded. These securities are classified as Level 1 since quoted prices for identical securities in active markets are available. Debt securities. Substantially all debt securities are investment grade and include domestic- and foreign-issued corporate bonds and U.S. government and agency bonds. These securities are valued using evaluated prices based on observable inputs, such as dealer quotes, available trade information, spreads, bids and offers, prepayment speeds, U.S. Treasury curves, and interest rate movements. Debt securities are classified as Level 2. Mutual funds. Exchange-traded mutual funds listed or traded on securities exchanges are valued at the closing price on the exchange or system where the security is principally traded. These securities are classified as Level 1 because quoted prices for identical securities in active markets are available. All other investments in mutual funds are valued at their closing net asset values. Because net asset values are based primarily on observable inputs, most notably quoted prices for the underlying assets, these nonexchange-traded investments are classified as Level 2. Collective investment funds. Investments in collective investment funds are valued at their closing net asset values. Because net asset values are based primarily on observable inputs, most notably quoted prices for the underlying assets, these investments are classified as Level 2. Insurance investment contracts and pooled separate accounts. Deposits under insurance investment contracts and pooled separate accounts with insurance companies do not have readily determinable fair values and are valued using a methodology that is consistent with accounting guidance that allows the plan to estimate fair value based upon net asset value per share (or its equivalent, such as member units or an ownership in partners’ capital to which a proportionate share of net assets is attributed); thus, these investments are not classified within the fair value hierarchy. Other assets. Other assets include an investment in a multi-strategy investment fund and an investment in a limited partnership. These investments do not have readily determinable fair values and are valued using a methodology consistent with accounting guidance that allows the plan to estimate fair value based upon net asset value per share (or its equivalent, such as member units or an ownership in partners’ capital to which a proportionate share of net assets is attributed); thus, these investments are not classified within the fair value hierarchy. The following tables show the fair values of our pension plan assets by asset class at December 31, 2017 , and December 31, 2016 . December 31, 2017 in millions Level 1 Level 2 Level 3 Total ASSET CLASS Cash and cash equivalents — — — — Equity securities: Common — U.S. $ 11 — — $ 11 Common — International 1 — — 1 Preferred — U.S. 3 — — 3 Debt securities: Corporate bonds — U.S. — $ 152 — 152 Corporate bonds — International — 61 — 61 Government and agency bonds — U.S. — 203 — 203 Government bonds — International — 2 — 2 State and municipal bonds — 31 — 31 Mutual funds: Equity — U.S. — — — — Equity — International 7 — — 7 Fixed income — U.S. — — — — Fixed income — International — — — — Real assets — — — — Collective investment funds: Equity — U.S. — 45 — 45 Equity — International — 41 — 41 Convertible securities — — — — Fixed income securities — 456 — 456 Short-term investments — 16 — 16 Real assets — 70 — 70 Insurance investment contracts and pooled separate accounts (measured at NAV) (a) — — — 14 Other assets (measured at NAV) (a) — — — 50 Total net assets at fair value $ 22 $ 1,077 — $ 1,163 (a) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the fair value of plan assets presented elsewhere within this footnote. December 31, 2016 in millions Level 1 Level 2 Level 3 Total ASSET CLASS Cash and cash equivalents $ 14 — — $ 14 Equity securities: Common — U.S. 133 — — 133 Common — International 15 — — 15 Preferred — U.S. 2 — — 2 Debt securities: Corporate bonds — U.S. — $ 90 — 90 Corporate bonds — International — 26 — 26 Government and agency bonds — U.S. — 101 — 101 Government bonds — International — 1 — 1 State and municipal bonds — 5 — 5 Mutual funds: Equity — U.S. 118 — — 118 Equity — International 35 — — 35 Fixed income — U.S. 152 — — 152 Fixed income — International 19 — — 19 Real assets 9 — — 9 Collective investment funds: Equity — U.S. — 15 — 15 Equity — International — 97 — 97 Convertible securities — 43 — 43 Fixed income securities — 79 — 79 Short-term investments — 18 — 18 Real assets — 95 — 95 Insurance investment contracts and pooled separate accounts (measured at NAV) — — — 14 Other assets (measured at NAV) — — — 52 Total net assets at fair value $ 497 $ 570 — $ 1,133 (a) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the fair value of plan assets presented elsewhere within this footnote. Other Postretirement Benefit Plans We sponsor a retiree healthcare plan in which all employees age 55 with five years of service (or employees age 50 with 15 years of service who are terminated under conditions that entitle them to a severance benefit) are eligible to participate. Participant contributions are adjusted annually. Key may provide a subsidy toward the cost of coverage for certain employees hired before 2001 with a minimum of 15 years of service at the time of termination. We use a separate VEBA trust to fund the retiree healthcare plan. Effective November 29, 2016, an unfunded retiree welfare plan previously sponsored by First Niagara merged into our current retiree healthcare plan. The components of pre-tax AOCI not yet recognized as net postretirement benefit cost are shown below. December 31, in millions 2017 2016 Net unrecognized losses (gains) $ (12 ) $ (9 ) Net unrecognized prior service credit (1 ) (2 ) Total unrecognized AOCI $ (13 ) $ (11 ) During 2018 , we expect to recognize $1 million of pre-tax AOCI resulting from prior service credit as a reduction of net postretirement benefit cost. The components of net postretirement benefit cost and the amount recognized in OCI for all funded and unfunded plans are as follows: December 31, in millions 2017 2016 2015 Service cost of benefits earned $ 1 $ 1 $ 1 Interest cost on APBO 3 2 3 Expected return on plan assets (2 ) (2 ) (3 ) Amortization of prior service credit (1 ) (1 ) (1 ) Amortization of gains — — — Net postretirement benefit $ 1 — — Other changes in plan assets and benefit obligations recognized in OCI: Net (gain) loss $ (4 ) $ (4 ) $ (6 ) Amortization of prior service credit 1 1 1 Amortization of losses — — — Total recognized in comprehensive income $ (3 ) $ (3 ) $ (5 ) Total recognized in net postretirement benefit cost and comprehensive income $ (2 ) $ (3 ) $ (5 ) The information related to our postretirement benefit plans presented in the following tables is based on current actuarial reports using measurement dates of December 31, 2017 , and December 31, 2016 . The following table summarizes changes in the APBO. Year ended December 31, in millions 2017 2016 APBO at beginning of year $ 69 $ 67 Service cost 1 1 Interest cost 3 2 Plan participants’ contributions 1 2 Actuarial losses (gains) 3 (1 ) Benefit payments (8 ) (6 ) Plan acquisition — 4 APBO at end of year $ 69 $ 69 The following table summarizes changes in FVA. Year ended December 31, in millions 2017 2016 FVA at beginning of year $ 50 $ 49 Employer contributions — — Plan participants’ contributions 1 2 Benefit payments (8 ) (6 ) Actual return on plan assets 9 5 FVA at end of year $ 52 $ 50 The following table summarizes the funded status of the postretirement plans, which corresponds to the amounts recognized in the balance sheets at December 31, 2017 , and December 31, 2016 . December 31, in millions 2017 2016 Funded status (a) $ (16 ) $ (19 ) Accrued postretirement benefit cost recognized (b) (16 ) (19 ) (a) The shortage of the FVA under the APBO. (b) Consists entirely of noncurrent liabilities. There are no regulations that require contributions to the VEBA trust that funds our retiree healthcare plan, so there is no minimum funding requirement. We are permitted to make discretionary contributions to the VEBA trust, subject to certain IRS restrictions and limitations. We anticipate that our discretionary contributions in 2018 , if any, will be minimal. At December 31, 2017 , we expect to pay the benefits from other postretirement plans as follows: 2018 — $5 million ; 2019 — $5 million ; 2020 — $5 million ; 2021 — $5 million ; 2022 — $5 million ; and $22 million in the aggregate from 2023 through 2027. To determine the APBO, we assumed discount rates of 3.50% at December 31, 2017 , and 3.75% at December 31, 2016 . To determine net postretirement benefit cost, we assumed the following weighted-average rates. Year ended December 31, 2017 2016 2015 Discount rate 3.75 % 4.00 % 3.75 % Expected return on plan assets 4.50 4.50 4.50 The realized net investment income for the postretirement healthcare plan VEBA trust is subject to federal income taxes, which are reflected in the weighted-average expected return on plan assets shown above. Assumed healthcare cost trend rates do not have a material impact on net postretirement benefit cost or obligations since the postretirement plan has cost-sharing provisions and benefit limitations. We estimate that we will recognize a credit of $1 million in net postretirement benefit cost for 2018 , compared to a credit of less than $1 million for 2017 and a break-even position of no credit or expense for 2016 . We estimate the expected returns on plan assets for the VEBA trust much the same way we estimate returns on our pension funds. The primary investment objectives of the VEBA trust are to obtain a market rate of return, take into consideration the safety and/or risk of the investment, and to diversify the portfolio in order to satisfy the trust’s anticipated liquidity requirements. The following table shows the asset target allocations prescribed by the trust’s investment policy. Target Allocation Asset Class 2017 Equity securities 80 % Fixed income securities 10 Convertible securities 5 Cash equivalents 5 Total 100 % Investments consist of mutual funds and common investment funds that invest in underlying assets in accordance with the target asset allocations shown above. Exchange-traded mutual funds are valued using quoted prices and, therefore, are classified as Level 1. Investments in common investment funds are valued at their closing net asset value. Because net asset values are based primarily on observable inputs, most notably quoted prices for the underlying assets, these nonexchange-traded investments are classified as Level 2. The following tables show the fair values of our postretirement plan assets by asset class at December 31, 2017 , and December 31, 2016 . December 31, 2017 in millions Level 1 Level 2 Level 3 Total ASSET CLASS Mutual funds: Equity — U.S. $ 25 — — $ 25 Equity — International 10 — — 10 Fixed income — U.S. 4 — — 4 Fixed income — lnternational 3 — — 3 Common investment funds: Equity — U.S. — $ 10 — 10 Total net assets at fair value $ 42 $ 10 — $ 52 December 31, 2016 in millions Level 1 Level 2 Level 3 Total ASSET CLASS Mutual funds: Equity — U.S. $ 23 — — $ 23 Equity — International 5 — — 5 Fixed income — U.S. 5 — — 5 Common investment funds: Equity — U.S. — $ 10 — 10 Short-term investments — 7 — 7 Total net assets at fair value $ 33 $ 17 — $ 50 The Medicare Prescription Drug, Improvement and Modernization Act of 2003 introduced a prescription drug benefit under Medicare and prescribes a federal subsidy to sponsors of retiree healthcare benefit plans that offer prescription drug coverage that is “actuarially equivalent” to the benefits under Medicare Part D. Based on our application of the relevant regulatory formula, we determined that the prescription drug coverage related to our retiree healthcare benefit plan is not actuarially equivalent to the Medicare benefit for the vast majority of retirees. For the years ended December 31, 2017 , and December 31, 2016 , we did not receive federal subsidies. Employee 401(k) Savings Plan A substantial number of our employees are covered under a savings plan that is qualified under Section 401(k) of the Internal Revenue Code. The plan permits employees to contribute from 1% to 100% of eligible compensation, with up to 6% being eligible for matching contributions. Commencing January 1, 2010, an automatic enrollment feature was added to the plan for all new employees. The initial default contribution percentage for employees is 2% and will increase by 1% at the beginning of each plan year until the default contribution is 10% for plan years on and after January 1, 2012. The plan also permits us to provide a discretionary annual profit sharing contribution to eligible employees who have at least one year of service. First Niagara employees who joined Key retained their years of services, and those employees that met eligibility requirements under Key’s savings plan have been included. We accrued a 2% contribution for 2017 and made contributions of 2.5% and 2% for 2016 and 2015 , respectively, on eligible compensation for employees eligible on the last business day of the respective plan years. In addition to the discretionary annual profit sharing contribution, in 2017 we accrued a one-time $1,000 contribution per eligible full-time employee and $500 per eligible part-time employee within the 401(k) savings plan. Employees eligible for the additional contribution must have been employed as of December 31, 2017 and have a salary of $100,000 or less. We also maintain a deferred savings plan that provides certain employees with benefits they otherwise would not have been eligible to receive under the qualified plan once their compensation for the plan year reached the IRS contribution limits. Total expense associated with the above plans was $129 million in 2017 , $94 million in 2016 , and $79 million in 2015 .

Short-Term Borrowings

Short-Term Borrowings	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Short-Term Borrowings	19. Short-Term Borrowings Selected financial information pertaining to the components of our short-term borrowings is as follows: December 31, dollars in millions 2017 2016 2015 FEDERAL FUNDS PURCHASED Balance at year end $ 3 $ 1,005 $ 20 Average during the year 128 44 195 Maximum month-end balance 2,331 1,005 678 Weighted-average rate during the year (a) .72 % .68 % .14 % Weighted-average rate at December 31 (a) — .55 .05 SECURITIES SOLD UNDER REPURCHASE AGREEMENTS Balance at year end $ 374 $ 497 $ 352 Average during the year 389 443 437 Maximum month-end balance 472 684 589 Weighted-average rate during the year (a) .08 % .04 % .00 % Weighted-average rate at December 31 (a) .08 .07 .00 OTHER SHORT-TERM BORROWINGS Balance at year end $ 634 $ 808 $ 533 Average during the year 1,140 852 572 Maximum month-end balance 1,242 872 1,122 Weighted-average rate during the year (a) 1.34 % 1.18 % 1.52 % Weighted-average rate at December 31 (a) 2.01 1.11 1.78 (a) Rates exclude the effects of interest rate swaps and caps, which modify the repricing characteristics of certain short-term borrowings. For more information about such financial instruments, see Note 9 (“ Derivatives and Hedging Activities ”). As described below and in Note 20 (“ Long-Term Debt ”), KeyCorp and KeyBank have a number of programs and facilities that support our short-term financing needs. Certain subsidiaries maintain credit facilities with third parties, which provide alternative sources of funding. KeyCorp is the guarantor of some of the third-party facilities. Short-term credit facilities. We maintain cash on deposit in our Federal Reserve account, which has reduced our need to obtain funds through various short-term unsecured money market products. This account, which was maintained at $3.7 billion at December 31, 2017 , and the unpledged securities in our investment portfolio provide a buffer to address unexpected short-term liquidity needs. We also have secured borrowing facilities at the FHLB and the Federal Reserve Bank of Cleveland to satisfy short-term liquidity requirements. As of December 31, 2017 , our unused secured borrowing capacity was $23.8 billion at the Federal Reserve Bank of Cleveland and $6.6 billion at the FHLB.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	20. Long-Term Debt The following table presents the components of our long-term debt, net of unamortized discounts and adjustments related to hedging with derivative financial instruments. We use interest rate swaps and caps, which modify the repricing characteristics of certain long-term debt, to manage interest rate risk. For more information about such financial instruments, see Note 9 (“ Derivatives and Hedging Activities ”). December 31, dollars in millions 2017 2016 Senior medium-term notes due through 2021 (a) $ 2,766 $ 2,799 2.075% Subordinated notes due 2028 (b) 161 162 6.875% Subordinated notes due 2029 (b) 109 111 7.750% Subordinated notes due 2029 (b) 141 141 7.25% Subordinated notes due 2021 (c) 348 358 6.75% Senior notes due 2020 (d) 327 338 Other subordinated notes (b), (e) 69 78 Total parent company 3,921 3,987 Senior medium-term notes due through 2039 (f) 8,011 6,715 3.18% Senior remarketable notes due 2027 (g) 202 193 5.70% Subordinated notes due 2017 (h) — 207 4.625% Subordinated notes due 2018 (h) 100 102 3.40% Subordinated notes due 2026 (h) 565 567 6.95% Subordinated notes due 2028 (h) 299 299 Secured borrowing due through 2021 (i) 24 68 Federal Home Loan Bank advances due through 2036 (j) 1,106 126 Investment Fund Financing due through 2052 (k) 88 100 Obligations under Capital Leases due through 2032 (l) 17 20 Total subsidiaries 10,412 8,397 Total long-term debt $ 14,333 $ 12,384 (a) Senior medium-term notes had a weighted-average interest rate of 3.56% at December 31, 2017 , and 3.57% at December 31, 2016 . These notes had fixed interest rates at December 31, 2017 , and December 31, 2016 . These notes may not be redeemed prior to their maturity dates. (b) See Note 21 (“ Trust Preferred Securities Issued by Unconsolidated Subsidiaries ”) for a description of these notes. (c) The First Niagara subordinated debt had a weighted-average interest rate of 7.25% at December 31, 2017 , and December 31, 2016 . These notes may not be redeemed prior to their maturity dates. (d) The First Niagara senior notes had a weighted-average interest rate of 6.75% at December 31, 2017 , and December 31, 2016 . These notes may not be redeemed prior to their maturity dates. (e) The First Niagara variable rate trust preferred securities had a weighted-average interest rates of 3.022% at December 31, 2017 , and 4.612% at December 31, 2016 . These notes may be redeemed prior to their maturity dates. (f) Senior medium-term notes had weighted-average interest rates of 2.24% at December 31, 2017 , and 1.93% at December 31, 2016 . These notes are a combination of fixed and floating rates. These notes may not be redeemed prior to their maturity dates. (g) Remarketable senior medium-term notes had a fixed interest rate at December 31, 2017. These notes may not be redeemed prior to their maturity dates. (h) These notes are all obligations of KeyBank and may not be redeemed prior to their maturity dates. (i) The secured borrowing had weighted-average interest rates of 4.46% at December 31, 2017 , and 4.45% at December 31, 2016 . This borrowing is collateralized by commercial lease financing receivables, and principal reductions are based on the cash payments received from the related receivables. Additional information pertaining to these commercial lease financing receivables is included in Note 5 (“ Loans and Loans Held for Sale ”). (j) Long-term advances from the Federal Home Loan Bank had a weighted-average interest rate of 2.318% at December 31, 2017 , and 3.64% at December 31, 2016 . These advances, which had fixed interest rates, were secured by real estate loans and securities totaling $1.1 billion at December 31, 2017 , and $126 million at December 31, 2016 . (k) Investment Fund Financing had a weighted-average interest rate of 1.94% at December 31, 2017 , and December 31, 2016 . (l) These are capital leases acquired in the First Niagara merger with a maturity range from June 2019 through October 2032. At December 31, 2017 , scheduled principal payments on long-term debt were as follows: in millions Parent Subsidiaries Total 2018 $ 746 $ 2,325 $ 3,071 2019 — 2,048 2,048 2020 1,310 1,396 2,706 2021 1,381 1,243 2,624 2022 — 1,426 1,426 All subsequent years 483 1,975 2,458 As described below, KeyBank and KeyCorp have a number of programs that support our long-term financing needs. Global bank note program. On September 29, 2015, KeyBank updated its Global Bank Note Program, authorizing the issuance of up to $20 billion of notes domestically and abroad. Under the program, KeyBank is authorized to issue notes with original maturities of seven days or more for senior notes or five years or more for subordinated notes. Notes may be denominated in U.S. dollars or in foreign currencies. Amounts outstanding under the program and any prior bank note programs are classified as “long-term debt” on the balance sheet. In 2016, KeyBank issued the following notes under the 2015 Global Bank Note Program: on March 8, 2016, $1 billion of 2.35% Senior Bank Notes due March 8, 2019; on May 20, 2016, $600 million of 3.40% Subordinated Bank Notes due May 20, 2026; on August 22, 2016, $500 million of 1.60% Senior Bank Notes due August 22, 2019; and on November 22, 2016, $250 million of Floating Rate Senior Notes and $500 million of 2.50% Senior Notes each due November 22, 2021. In 2017, KeyBank issued the following notes under the 2015 Global Bank Note Program: on June 9, 2017, $600 million of 2.40% Senior Bank Notes due June 9, 2022; and on September 14, 2017, $750 million of 2.30% Senior Bank Notes due September 14, 2022. At December 31, 2017 , $15.8 billion remained available for future issuance under the Global Bank Note Program. KeyCorp shelf registration, including Medium-Term Note Program . KeyCorp has a shelf registration statement on file with the SEC under rules that allow companies to register various types of debt and equity securities without limitations on the aggregate amounts available for issuance. KeyCorp also maintains a Medium-Term Note Program that permits KeyCorp to issue notes with original maturities of nine months or more. On September 15, 2015, KeyCorp issued $1 billion of 2.90% Medium-Term Notes due September 15, 2020. At December 31, 2017 , KeyCorp had authorized and available for issuance up to $4 billion of additional debt securities under the Medium-Term Note Program. Issuances of capital securities or preferred stock by KeyCorp must be approved by the Board and cannot be objected to by the Federal Reserve.

Trust Preferred Securities Issu

Trust Preferred Securities Issued by Unconsolidated Subsidiaries	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Trust Preferred Securities Issued by Unconsolidated Subsidiaries	21. Trust Preferred Securities Issued by Unconsolidated Subsidiaries We own the outstanding common stock of business trusts formed by us that issued corporation-obligated mandatorily redeemable trust preferred securities. The trusts used the proceeds from the issuance of their trust preferred securities and common stock to buy debentures issued by KeyCorp. These debentures are the trusts’ only assets; the interest payments from the debentures finance the distributions paid on the mandatorily redeemable trust preferred securities. The outstanding common stock of these business trusts is recorded in “other investments” on our balance sheet. We unconditionally guarantee the following payments or distributions on behalf of the trusts: • required distributions on the trust preferred securities; • the redemption price when a capital security is redeemed; and • the amounts due if a trust is liquidated or terminated. The Regulatory Capital Rules implement a phase-out of trust preferred securities as Tier 1 capital, consistent with the requirements of the Dodd-Frank Act. For standardized approach banking organizations such as Key, the phase-out period began on January 1, 2015, and starting in 2016 requires us to treat our mandatorily redeemable trust preferred securities as Tier 2 capital. During 2017, we redeemed $9 million of trust preferred that were acquired in First Niagara acquisition. The trust preferred securities, common stock, and related debentures are summarized as follows: dollars in millions Trust Preferred Securities, Net of Discount (a) Common Stock Principal Amount of Debentures, Net of Discount (b) Interest Rate of Trust Preferred Securities and (c) Maturity of Trust Preferred Securities and Debentures December 31, 2017 KeyCorp Capital I $ 155 $ 6 $ 161 2.750 % 2028 KeyCorp Capital II 105 4 109 6.875 2029 KeyCorp Capital III 137 4 141 7.750 2029 HNC Statutory Trust III 18 1 19 2.854 2035 Willow Grove Statutory Trust I 18 1 19 2.898 2036 HNC Statutory Trust IV 16 1 17 2.658 2037 Westbank Capital Trust II 7 — 7 3.815 2034 Westbank Capital Trust III 7 — 7 3.815 2034 Total $ 463 $ 17 $ 480 4.977 % — December 31, 2016 $ 475 $ 17 $ 492 4.845 % — (a) The trust preferred securities must be redeemed when the related debentures mature, or earlier if provided in the governing indenture. Each issue of trust preferred securities carries an interest rate identical to that of the related debenture. Certain trust preferred securities include basis adjustments related to fair value hedges totaling $55 million at December 31, 2017 , and $59 million at December 31, 2016 . See Note 9 (“Derivatives and Hedging Activities”) for an explanation of fair value hedges. (b) We have the right to redeem these debentures. If the debentures purchased by KeyCorp Capital I, HNC Statutory Trust III, Willow Grove Statutory Trust I, HNC Statutory Trust IV, Westbank Capital Trust II, or Westbank Capital Trust III are redeemed before they mature, the redemption price will be the principal amount, plus any accrued but unpaid interest. If the debentures purchased by KeyCorp Capital II or KeyCorp Capital III are redeemed before they mature, the redemption price will be the greater of: (i) the principal amount, plus any accrued but unpaid interest, or (ii) the sum of the present values of principal and interest payments discounted at the Treasury Rate (as defined in the applicable indenture), plus 20 basis points for KeyCorp Capital II or 25 basis points for KeyCorp Capital III or 50 basis points in the case of redemption upon either a tax or a capital treatment event for either KeyCorp Capital II or KeyCorp Capital III, plus any accrued but unpaid interest. The principal amount of certain debentures includes basis adjustments related to fair value hedges totaling $55 million at December 31, 2017 , and $59 million at December 31, 2016 . See Note 9 for an explanation of fair value hedges. The principal amount of debentures, net of discounts, is included in “long-term debt” on the balance sheet. (c) The interest rates for the trust preferred securities issued by KeyCorp Capital II and KeyCorp Capital III are fixed. The trust preferred securities issued by KeyCorp Capital I have a floating interest rate, equal to three-month LIBOR plus 74 basis points, that reprices quarterly. The trust preferred securities issued by HNC Statutory Trust III have a floating interest rate, equal to three-month LIBOR plus 140 basis points, that reprices quarterly. The trust preferred securities issued by Willow Grove Statutory Trust I have a floating interest rate, equal to three-month LIBOR plus 131 basis points, that reprices quarterly. The trust preferred securities issued by HNC Statutory Trust IV have a floating interest rate, equal to three-month LIBOR plus 128 basis points, that reprices quarterly. The trust preferred securities issued by Westbank Capital Trust II and Westbank Capital Trust III each have a floating interest rate, equal to three-month LIBOR plus 219 basis points, that reprices quarterly. The total interest rates are weighted-average rates.

Commitments, Contingent Liabili

Commitments, Contingent Liabilities and Guarantees	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingent Liabilities and Guarantees	22. Commitments, Contingent Liabilities, and Guarantees Obligations under Noncancelable Leases We are obligated under various noncancelable operating leases for land, buildings and other property, consisting principally of data processing equipment. Rental expense under all operating leases totaled $153 million in 2017 , $118 million in 2016 , and $122 million in 2015 . Minimum future rental payments under noncancelable operating leases at December 31, 2017 , are as follows: 2018 — $142 million ; 2019 — $132 million ; 2020 — $117 million ; 2021 — $101 million ; 2022 — $89 million ; all subsequent years — $381 million . Commitments to Extend Credit or Funding Loan commitments provide for financing on predetermined terms as long as the client continues to meet specified criteria. These agreements generally carry variable rates of interest and have fixed expiration dates or termination clauses. We typically charge a fee for our loan commitments. Since a commitment may expire without resulting in a loan, our aggregate outstanding commitments may significantly exceed our eventual cash outlay. Loan commitments involve credit risk not reflected on our balance sheet. We mitigate exposure to credit risk with internal controls that guide how we review and approve applications for credit, establish credit limits and, when necessary, demand collateral. In particular, we evaluate the creditworthiness of each prospective borrower on a case-by-case basis and, when appropriate, adjust the allowance for credit losses on lending-related commitments. Additional information pertaining to this allowance is included in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Liability for Credit Losses on Lending-Related Commitments,” and in Note 6 (“ Asset Quality ”). We also provide financial support to private equity investments, including existing direct portfolio companies and indirect private equity funds, to satisfy unfunded commitments. These unfunded commitments are not recorded on our balance sheet. Additional information on principal investing commitments is provided in Note 7 (“ Fair Value Measurements ”). Other unfunded equity investment commitments at December 31, 2017 , and December 31, 2016 , related to tax credit investments and were primarily attributable to LIHTC investments. Unfunded tax credit investment commitments are recorded on our balance sheet in “other liabilities.” Additional information on LIHTC commitments is provided in Note 13 (“ Variable Interest Entities ”). The following table shows the remaining contractual amount of each class of commitment related to extending credit or funding principal investments as of December 31, 2017 , and December 31, 2016 . For loan commitments and commercial letters of credit, this amount represents our maximum possible accounting loss on the unused commitment if the borrower were to draw upon the full amount of the commitment and subsequently default on payment for the total amount of the then outstanding loan. December 31, in millions 2017 2016 Loan commitments: Commercial and other $ 40,315 $ 34,372 Commercial real estate and construction 2,774 3,034 Home equity 9,673 9,666 Credit cards 5,890 5,653 Total loan commitments 58,652 52,725 When-issued and to be announced securities commitments (a) — 34 Commercial letters of credit 231 143 Purchase card commitments 425 293 Principal investing commitments 29 37 Tax credit investment commitments 481 466 Liabilities of certain limited partnerships and other commitments — 2 Securities underwriting 9 — Total loan and other commitments $ 59,827 $ 53,700 (a) Beginning in first quarter of 2017, we now disclose amounts previously reported as “When-issued and to be announced securities commitments” in the Notional category of the “Other” line in the “Fair Values, Volume of Activity, and Gain/Loss Information Related to Derivative Instruments” table found in Note 9 (“ Derivatives and Hedging Activities “). Legal Proceedings Checking Account Overdraft Litigation. In February 2010, KeyBank was named a defendant in a putative class action seeking to represent a national class of KeyBank customers allegedly harmed by KeyBank’s overdraft practices. The case was transferred and consolidated for purposes of pretrial discovery and motion proceedings to a multidistrict proceeding styled In Re: Checking Account Overdraft Litigation pending in the United States District Court for the Southern District of Florida (the “District Court”). KeyBank filed a notice of appeal in regard to the denial by the District Court of a motion to compel arbitration. In August 2012, the United States Court of Appeals for the Eleventh Circuit (the “Eleventh Circuit”) vacated the District Court’s order denying KeyBank’s motion to compel arbitration and remanded the case for further consideration. In June 2013, KeyBank filed with the District Court its renewed motion to compel arbitration and stay or dismiss litigation. The District Court granted KeyBank’s renewed motion to compel arbitration and dismissed the case. The plaintiff appealed. On June 18, 2014, the Eleventh Circuit vacated the District Court’s order granting KeyBank’s renewed motion to compel arbitration and remanded the case to the District Court to address the issue of the enforceability of KeyBank’s arbitration provision. On February 3, 2015, the District Court denied KeyBank’s Second Renewed Motion to Compel Arbitration and Dismiss the Complaint. KeyBank filed an appeal. On September 26, 2017, the Eleventh Circuit reversed the District Court’s order denying KeyBank’s motion to compel arbitration and remanded the case with instructions to compel arbitration. As previously reported, on October 27, 2017, the District Court ordered KeyBank’s arbitration provision to be enforced and dismissed the case. Other litigation. From time to time, in the ordinary course of business, we and our subsidiaries are subject to various litigation, investigations, and administrative proceedings. Private, civil litigations may range from individual actions involving a single plaintiff to putative class action lawsuits with potentially thousands of class members. Investigations may involve both formal and informal proceedings, by both government agencies and self-regulatory bodies. These matters may involve claims for substantial monetary relief. At times, these matters may present novel claims or legal theories. Due to the complex nature of these various other matters, it may be years before some matters are resolved. While it is impossible to ascertain the ultimate resolution or range of financial liability, based on information presently known to us, we do not believe there is any matter to which we are a party, or involving any of our properties that, individually or in the aggregate, would reasonably be expected to have a material adverse effect on our financial condition. We continually monitor and reassess the potential materiality of these litigation matters. We note, however, that in light of the inherent uncertainty in legal proceedings there can be no assurance that the ultimate resolution will not exceed established reserves. As a result, the outcome of a particular matter, or a combination of matters, may be material to our results of operations for a particular period, depending upon the size of the loss or our income for that particular period. Guarantees We are a guarantor in various agreements with third parties. The following table shows the types of guarantees that we had outstanding at December 31, 2017 . Information pertaining to the basis for determining the liabilities recorded in connection with these guarantees is included in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Guarantees.” December 31, 2017 Maximum Potential Undiscounted Future Payments Liability Recorded in millions Financial guarantees: Standby letters of credit $ 3,142 $ 67 Recourse agreement with FNMA 3,261 6 Residential mortgage reserve 1,362 5 Return guarantee agreement with LIHTC investors 3 3 Written put options (a) 2,080 50 Total $ 9,848 $ 131 (a) The maximum potential undiscounted future payments represent notional amounts of derivatives qualifying as guarantees. We determine the payment/performance risk associated with each type of guarantee described below based on the probability that we could be required to make the maximum potential undiscounted future payments shown in the preceding table. We use a scale of low ( 0% to 30% probability of payment), moderate (greater than 30% to 70% probability of payment), or high (greater than 70% probability of payment) to assess the payment/performance risk, and have determined that the payment/performance risk associated with each type of guarantee outstanding at December 31, 2017 , is low. Standby letters of credit. KeyBank issues standby letters of credit to address clients’ financing needs. These instruments obligate us to pay a specified third party when a client fails to repay an outstanding loan or debt instrument or fails to perform some contractual nonfinancial obligation. Any amounts drawn under standby letters of credit are treated as loans to the client; they bear interest (generally at variable rates) and pose the same credit risk to us as a loan. At December 31, 2017 , our standby letters of credit had a remaining weighted-average life of 2 years , with remaining actual lives ranging from less than 1 year to as many as 17 years . Recourse agreement with FNMA. We participate as a lender in the FNMA Delegated Underwriting and Servicing program. FNMA delegates responsibility for originating, underwriting, and servicing mortgages, and we assume a limited portion of the risk of loss during the remaining term on each commercial mortgage loan that we sell to FNMA. We maintain a reserve for such potential losses in an amount that we believe approximates the fair value of our liability. At December 31, 2017 , the outstanding commercial mortgage loans in this program had a weighted-average remaining term of 7.9 years , and the unpaid principal balance outstanding of loans sold by us as a participant was $11.6 billion . The maximum potential amount of undiscounted future payments that we could be required to make under this program, as shown in the preceding table, is equal to approximately 28% of the principal balance of loans outstanding at December 31, 2017 . If we are required to make a payment, we would have an interest in the collateral underlying the related commercial mortgage loan; any loss we incur could be offset by the amount of any recovery from the collateral. Residential Mortgage Banking. We often originate and sell residential mortgage loans and retain the servicing rights. Our loan sales activity is generally conducted through loan sales in a secondary market sponsored by FNMA and FHLMC. Subsequent to the sale of mortgage loans, we do not typically retain any interest in the underlying loans except through our relationship as the servicer of the loans. As is customary in the mortgage banking industry, we, or banks we have acquired, have made certain representations and warranties related to the sale of residential mortgage loans (including loans sold with servicing rights released) and to the performance of our obligations as servicer. The breach of any such representations or warranties could result in losses for us. Our maximum exposure to loss is equal to the outstanding principal balance of the sold loans; however, any loss would be reduced by any payments received on the loans or through the sale of collateral. At December 31, 2017 , the outstanding residential mortgage loans in this program had an original weighted-average loan to value ratio of 72% , and the unpaid principal balance outstanding of loans sold by us was $4.5 billion . The risk assessment is low for the residential mortgage product. The maximum potential amount of undiscounted future payments that we could be required to make under this program, as shown in the preceding table, is equal to approximately 30% of the principal balance of loans outstanding at December 31, 2017 . Our liability for estimated repurchase obligations on loans sold, which is included in other liabilities on our balance sheet, was $5 million at December 31, 2017 . Return guarantee agreement with LIHTC investors. KAHC, a subsidiary of KeyBank, offered limited partnership interests to qualified investors. Partnerships formed by KAHC invested in low-income residential rental properties that qualify for federal low-income housing tax credits under Section 42 of the Internal Revenue Code. In certain partnerships, investors paid a fee to KAHC for a guaranteed return that is based on the financial performance of the property and the property’s confirmed LIHTC status throughout a 15 -year compliance period. Typically, KAHC fulfills these guaranteed returns by distributing tax credits and deductions associated with the specific properties. If KAHC defaults on its obligation to provide the guaranteed return, KeyBank is obligated to make any necessary payments to investors. No recourse or collateral is available to offset our guarantee obligation other than the underlying income streams from the properties and the residual value of the operating partnership interests. As shown in the previous table, KAHC maintained a reserve in the amount of $3 million at December 31, 2017 , which is sufficient to cover estimated future obligations under the guarantees. The maximum exposure to loss reflected in the table represents undiscounted future payments due to investors for the return on and of their investments. These guarantees have expiration dates that extend through 2018, but KAHC has not formed any new partnerships under this program since October 2003. Additional information regarding these partnerships is included in Note 13 (“ Variable Interest Entities ”). Written put options. In the ordinary course of business, we “write” put options for clients that wish to mitigate their exposure to changes in interest rates and commodity prices. At December 31, 2017 , our written put options had an average life of 3 years . These instruments are considered to be guarantees, as we are required to make payments to the counterparty (the client) based on changes in an underlying variable that is related to an asset, a liability, or an equity security that the client holds. We are obligated to pay the client if the applicable benchmark interest rate or commodity price is above or below a specified level (known as the “strike rate”). These written put options are accounted for as derivatives at fair value, as further discussed in Note 9 (“ Derivatives and Hedging Activities ”). We mitigate our potential future payment obligations by entering into offsetting positions with third parties. Written put options where the counterparty is a broker-dealer or bank are accounted for as derivatives at fair value but are not considered guarantees since these counterparties typically do not hold the underlying instruments. In addition, we are a purchaser and seller of credit derivatives, which are further discussed in Note 9 . Default guarantees. Some lines of business participate in guarantees that obligate us to perform if the debtor (typically a client) fails to satisfy all of its payment obligations to third parties. We generally undertake these guarantees for one of two possible reasons: (i) either the risk profile of the debtor should provide an investment return, or (ii) we are supporting our underlying investment in the debtor. We do not hold collateral for the default guarantees. If we were required to make a payment under a guarantee, we would receive a pro rata share should the third party collect some or all of the amounts due from the debtor. At December 31, 2017 , we had less than $1 million default guarantees. Other Off-Balance Sheet Risk Other off-balance sheet risk stems from financial instruments that do not meet the definition of a guarantee as specified in the applicable accounting guidance, and from other relationships. Indemnifications provided in the ordinary course of business. We provide certain indemnifications, primarily through representations and warranties in contracts that we execute in the ordinary course of business in connection with loan and lease sales and other ongoing activities, as well as in connection with purchases and sales of businesses. We maintain reserves, when appropriate, with respect to liability that reasonably could arise as a result of these indemnities. Intercompany guarantees. KeyCorp, KeyBank, and certain of our affiliates are parties to various guarantees that facilitate the ongoing business activities of other affiliates. These business activities encompass issuing debt, assuming certain lease and insurance obligations, purchasing or issuing investments and securities, and engaging in certain leasing transactions involving clients.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Accumulated Other Comprehensive Income	23. Accumulated Other Comprehensive Income Our changes in AOCI for the years ended December 31, 2017 , and December 31, 2016 , are as follows: in millions Unrealized gains (losses) on securities available for sale Unrealized gains (losses) on derivative financial instruments Foreign currency translation adjustment Net pension and postretirement benefit costs Total Balance at December 31, 2015 $ (58 ) $ 20 $ (2 ) $ (365 ) $ (405 ) Other comprehensive income before reclassification, net of income taxes (127 ) 17 (1 ) 5 (106 ) Amounts reclassified from accumulated other comprehensive income, net of income taxes (a) — (51 ) — 21 (30 ) Net current-period other comprehensive income, net of income taxes (127 ) (34 ) (1 ) 26 (136 ) Balance at December 31, 2016 $ (185 ) $ (14 ) $ (3 ) $ (339 ) $ (541 ) Other comprehensive income before reclassification, net of income taxes (69 ) (48 ) 12 9 (96 ) Amounts reclassified from accumulated other comprehensive income, net of income taxes (a) (1 ) (10 ) 1 9 (1 ) Amounts reclassified from accumulated other comprehensive income resulting from new federal corporate income tax rate (b) (56 ) (14 ) (1 ) (70 ) (141 ) Net current-period other comprehensive income, net of income taxes (126 ) (72 ) 12 (52 ) (238 ) Balance at December 31, 2017 $ (311 ) $ (86 ) $ 9 $ (391 ) $ (779 ) (a) See table below for details about these reclassifications. (b) See Note 14, Income Taxes, for details about the accounting impacts resulting from the TCJ Act. Our reclassifications out of AOCI for the years ended December 31, 2017 , and December 31, 2016 , are as follows: Year ended December 31, 2017 Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Statement Where Net Income is Presented in millions Unrealized gains (losses) on available for sale securities Realized gains $ 1 Other income Realized losses — Other income 1 Income (loss) from continuing operations before income taxes — Income taxes $ 1 Income (loss) from continuing operations Unrealized gains (losses) on derivative financial instruments Interest rate $ 19 Interest income — Loans Interest rate (4 ) Interest expense — Long-term debt 15 Income (loss) from continuing operations before income taxes 5 Income taxes $ 10 Income (loss) from continuing operations Foreign currency translation adjustment $ (1 ) Corporate services income (1 ) Income (loss) from continuing operations before income taxes — Income taxes $ (1 ) Income (loss) from continuing operations Net pension and postretirement benefit costs Amortization of losses $ (15 ) Personnel expense Amortization of prior service credit 1 Personnel expense (14 ) Income (loss) from continuing operations before income taxes (5 ) Income taxes $ (9 ) Income (loss) from continuing operations Year ended December 31, 2016 Amount Reclassified from Affected Line Item in the Statement Where Net Income is Presented in millions Unrealized gains (losses) on derivative financial instruments Interest rate $ 85 Interest income — Loans Interest rate (4 ) Interest expense — Long-term debt 81 Income (loss) from continuing operations before income taxes 30 Income taxes $ 51 Income (loss) from continuing operations Net pension and postretirement benefit costs Amortization of losses $ (17 ) Personnel expense Settlement loss (18 ) Personnel expense Amortization of prior service credit 1 Personnel expense (34 ) Income (loss) from continuing operations before income taxes (13 ) Income taxes $ (21 ) Income (loss) from continuing operations

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Shareholders' Equity	24. Shareholders' Equity Comprehensive Capital Plan As previously reported and as authorized by the Board and pursuant to our 2017 capital plan (which is effective through the second quarter of 2018 ) submitted to and not objected to by the Federal Reserve, we have authority to repurchase up to $800 million of our Common Shares, which includes repurchases to offset issuances of Common Shares under our employee compensation plans. During 2017 , we repurchased $254 million of Common Shares under our 2016 capital plan authorization and $476 million under our 2017 capital plan authorization. Consistent with our 2016 capital plan, the Board declared a quarterly dividend of $.085 per Common Share for the first quarter of 2017 , and $.095 per Common Share for the second quarter of 2017 . The Board declared a quarterly dividend of $.095 per Common Share for the third quarter of 2017 , and a quarterly dividend of $.105 per Common Share for the fourth quarter of 2017 , consistent with our 2017 capital plan. These quarterly dividend payments brought our annual dividend to $.38 per Common Share for 2017 . Our 2017 capital plan proposed an increase in our quarterly Common Share dividend, up to $.12 per Common Share, which will be considered by the Board for the second quarter of 2018 . Preferred Stock On March 9, 2017, we announced that all of our 7.75% Noncumulative Perpetual Convertible Series A Preferred Stock would convert into KeyCorp Common Shares. On March 20, 2017, the conversion date, holders of the Series A Preferred Stock received 7.0922 Common Shares for each share of Series A Preferred Stock. Cash was paid in lieu of fractional shares. Prior to the conversion of the Series A Preferred Stock, we made a dividend payment of $1.9375 per share, or $6 million , on our Series A Preferred Stock during the first quarter of 2017 . Prior to the conversion, we had $290 million of 7.75% Noncumulative Perpetual Convertible Series A Preferred Stock outstanding at December 31, 2016. Our Series A Preferred Stock had a $1 par value and a $100 liquidation preference. There were 7,475,000 shares authorized and 2,900,234 shares outstanding at December 31, 2016 . On January 12, 2017, we provided notice of our intention to redeem all outstanding shares of the Series C Preferred Stock on February 15, 2017. On February 15, 2017, the Series C Preferred Stock was redeemed for cash at a redemption price of $25 per share. The redemption date was also a dividend payment date, and declared dividends of $.539063 per share, or $7 million , were also paid separately on February 15, 2017. The Series C Preferred Stock was initially issued in connection with the First Niagara acquisition to replace First Niagara’s outstanding preferred stock. Prior to the redemption, we had $350 million of Fixed-to-Floating Rate Perpetual Noncumulative Series C Preferred Stock. Our Series C Preferred Stock had a $1 par value with a $25 liquidation preference. There were 14,000,000 shares authorized and outstanding at December 31, 2016 . We have $525 million of depositary shares, each representing a 1/25 th ownership interest in a share of our Fixed-to-Floating Rate Perpetual Noncumulative Series D Preferred Stock outstanding at December 31, 2017 , and December 31, 2016 . Our Series D Preferred Stock has a $1 par value with a $25,000 liquidation preference. There are 21,000 shares authorized and 21,000 shares outstanding at December 31, 2017 , and December 31, 2016 . We made total payments of $50.00 per depositary share on the depositary shares related to our Series D Preferred Stock during 2017 for a total of $26 million . We have $500 million of depositary shares, each representing a 1/40 th ownership interest in a share of our Fixed-to-Floating Rate Perpetual Noncumulative Series E Preferred Stock outstanding at December 31, 2017 , and December 31, 2016 . Our Series E Preferred Stock has a $1 par value with a $1,000 liquidation preference. There are 500,000 shares authorized and 500,000 shares outstanding at December 31, 2017 , and December 31, 2016 . We made total payments of $1.544012 per depositary share on the depositary shares related to our Series E Preferred Stock during 2017 for a total of $31 million . Capital Adequacy KeyCorp and KeyBank (consolidated) must meet specific capital requirements imposed by federal banking regulators. Sanctions for failure to meet applicable capital requirements may include regulatory enforcement actions that restrict dividend payments, require the adoption of remedial measures to increase capital, terminate FDIC deposit insurance, and mandate the appointment of a conservator or receiver in severe cases. In addition, failure to maintain a “well capitalized” status affects how regulators evaluate applications for certain endeavors, including acquisitions, continuation and expansion of existing activities, and commencement of new activities, and could make clients and potential investors less confident. As of December 31, 2017 , KeyCorp and KeyBank (consolidated) met all regulatory capital requirements. KeyBank (consolidated) qualified for the “well capitalized” prompt corrective action capital category at December 31, 2017 , because its capital and leverage ratios exceeded the prescribed threshold ratios for that capital category and it was not subject to any written agreement, order, or directive to meet and maintain a specific capital level for any capital measure. Since that date, we believe there has been no change in condition or event that has occurred that would cause the capital category for KeyBank (consolidated) to change. BHCs are not assigned to any of the five prompt corrective action capital categories applicable to insured depository institutions. If, however, those categories applied to BHCs, we believe that KeyCorp would satisfy the criteria for a “well capitalized” institution at December 31, 2017 , and since that date, we believe there has been no change in condition or event that has occurred that would cause such capital category to change. Because the regulatory capital categories under the prompt corrective action regulations serve a limited supervisory function, investors should not use them as a representation of the overall financial condition or prospects of KeyBank or KeyCorp. At December 31, 2017 , Key and KeyBank (consolidated) had regulatory capital in excess of all current minimum risk-based capital (including all adjustments for market risk) and leverage ratio requirements as shown in the following table. Actual To Meet Minimum Capital Adequacy Requirements To Qualify as Well Capitalized Under Federal Deposit Insurance Act dollars in millions Amount Ratio Amount Ratio Amount Ratio December 31, 2017 TOTAL CAPITAL TO NET RISK-WEIGHTED ASSETS Key $ 15,345 12.92 % $ 9,505 8.00 % N/A N/A KeyBank (consolidated) 14,957 12.86 9,306 8.00 $ 11,633 10.00 % TIER 1 CAPITAL TO NET RISK-WEIGHTED ASSETS Key $ 13,083 11.01 % $ 7,129 6.00 % N/A N/A KeyBank (consolidated) 13,110 11.27 6,980 6.00 $ 6,980 6.00 % TIER 1 CAPITAL TO AVERAGE QUARTERLY TANGIBLE ASSETS Key $ 13,083 9.73 % $ 5,379 4.00 % N/A N/A KeyBank (consolidated) 13,110 9.91 5,293 4.00 $ 6,617 5.00 % December 31, 2016 TOTAL CAPITAL TO NET RISK-WEIGHTED ASSETS Key $ 15,638 12.85 % $ 9,734 8.00 % N/A N/A KeyBank (consolidated) 14,291 12.36 9,251 8.00 $ 11,564 10.00 % TIER 1 CAPITAL TO NET RISK-WEIGHTED ASSETS Key $ 13,249 10.89 % $ 7,300 6.00 % N/A N/A KeyBank (consolidated) 12,439 10.76 6,939 6.00 $ 6,939 6.00 % TIER 1 CAPITAL TO AVERAGE QUARTERLY TANGIBLE ASSETS Key $ 13,249 9.90 % $ 5,442 4.00 % N/A N/A KeyBank (consolidated) 12,439 9.46 5,353 4.00 $ 6,691 5.00 %

Line of Business Results

Line of Business Results	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Line of Business Results	25. Line of Business Results The specific lines of business that constitute each of the major business segments (operating segments) are described below. Key Community Bank Key Community Bank serves individuals and small to mid-sized businesses through its 15 -state branch network. Individuals are provided branch-based deposit and investment products, personal finance services, and loans, including residential mortgages, home equity, credit card, and various types of installment loans. Key Community Bank offers personal property and casualty insurance, such as home, auto, renters, watercraft, and umbrella. Key Community Bank also purchases retail auto sales contracts via a network of auto dealerships. The auto dealerships finance the sale of automobiles as the initial lender and then assign the contracts to us pursuant to dealer agreements. In addition, financial, estate and retirement planning, asset management services, and Delaware Trust capabilities are offered to assist high-net-worth clients with their banking, trust, portfolio management, life insurance, charitable giving, and related needs. Small businesses are provided deposit, investment and credit products, and business advisory services. Mid-sized businesses are provided products and services, some of which are delivered by Key Corporate Bank, that include commercial lending, cash management, equipment leasing, investment, insurance including Commercial Property and Casualty as well as Captive Insurance and employee benefit programs, succession planning, access to capital markets, derivatives, and foreign exchange. Key Corporate Bank Key Corporate Bank is a full-service corporate and investment bank focused principally on serving the needs of middle market clients in seven industry sectors: consumer, energy, healthcare, industrial, public sector, real estate, and technology. Key Corporate Bank delivers a broad suite of banking and capital markets products to its clients, including syndicated finance, debt and equity capital markets, commercial payments, equipment finance, commercial mortgage banking, derivatives, foreign exchange, financial advisory, and public finance. Key Corporate Bank is also a significant servicer of commercial mortgage loans and a significant special servicer of CMBS. Key Corporate Bank delivers many of its product capabilities to clients of Key Community Bank. Other Segments Other Segments consists of Corporate Treasury, Principal Investing, and various exit portfolios. Reconciling Items Total assets included under “Reconciling Items” primarily represent the unallocated portion of nonearning assets of corporate support functions. Reconciling Items also includes intercompany eliminations and certain items that are not allocated to the business segments because they do not reflect their normal operations including merger-related charges and certain estimated impacts of tax reform. The table on the following pages shows selected financial data for our major business segments for the years ended December 31, 2017 , 2016 , and 2015 . The information was derived from the internal financial reporting system that we use to monitor and manage our financial performance. GAAP guides financial accounting, but there is no authoritative guidance for “management accounting” — the way we use our judgment and experience to make reporting decisions. Consequently, the line of business results we report may not be comparable to line of business results presented by other companies. The selected financial data is based on internal accounting policies designed to compile results on a consistent basis and in a manner that reflects the underlying economics of the businesses. In accordance with our policies: • Net interest income is determined by assigning a standard cost for funds used or a standard credit for funds provided based on their assumed maturity, prepayment, and/or repricing characteristics. • Indirect expenses, such as computer servicing costs and corporate overhead, are allocated based on assumptions regarding the extent that each line of business actually uses the services. • The consolidated provision for credit losses is allocated among the lines of business primarily based on their actual net loan charge-offs, adjusted periodically for loan growth and changes in risk profile. The amount of the consolidated provision is based on the methodology that we use to estimate our consolidated ALLL. This methodology is described in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Allowance for Loan and Lease Losses. • Income taxes are allocated based on the 2017 statutory federal income tax rate of 35% and a blended state income tax rate (net of the federal income tax benefit) of 2.2% . • Capital is assigned to each line of business based on economic equity. Developing and applying the methodologies that we use to allocate items among our lines of business is a dynamic process. Accordingly, financial results may be revised periodically to reflect enhanced alignment of expense base allocation drivers, changes in the risk profile of a particular business, or changes in our organizational structure. Year ended December 31, Key Community Bank Key Corporate Bank dollars in millions 2017 2016 2015 2017 2016 2015 SUMMARY OF OPERATIONS Net interest income (TE) $ 2,643 $ 1,953 $ 1,487 $ 1,190 $ 1,049 $ 886 Noninterest income 1,200 925 788 1,147 1,013 926 Total revenue (TE) (a) 3,843 2,878 2,275 2,337 2,062 1,812 Provision for credit losses 209 143 90 20 127 83 Depreciation and amortization expense 116 76 56 96 60 43 Other noninterest expense 2,486 2,077 1,723 1,161 1,071 945 Income (loss) from continuing operations before income taxes (TE) 1,032 582 406 1,060 804 741 Allocated income taxes (benefit) and TE adjustments 383 217 151 246 178 196 Income (loss) from continuing operations 649 365 255 814 626 545 Income (loss) from discontinued operations, net of taxes — — — — — — Net income (loss) 649 365 255 814 626 545 Less: Net income (loss) attributable to noncontrolling interests — — — — (2 ) 1 Net income (loss) attributable to Key $ 649 $ 365 $ 255 $ 814 $ 628 $ 544 AVERAGE BALANCES (b) Loans and leases $ 47,383 $ 37,620 $ 30,834 $ 37,732 $ 31,929 $ 25,865 Total assets (a) 51,433 40,300 32,948 44,521 37,801 31,541 Deposits 79,669 63,873 51,163 21,318 20,783 19,043 OTHER FINANCIAL DATA Expenditures for additions to long-lived assets (a), (b) $ 2,438 $ 1,478 $ 75 $ 559 $ 340 $ 16 Net loan charge-offs (b) 166 114 92 40 83 40 Return on average allocated equity (b) 13.59 % 10.62 % 9.42 % 28.69 % 26.80 % 28.91 % Return on average allocated equity 13.59 10.62 9.42 28.69 26.80 28.91 Average full-time equivalent employees (c) 10,924 8,936 7,520 2,407 2,244 2,100 (a) Substantially all revenue generated by our major business segments is derived from clients that reside in the United States. Substantially all long-lived assets, including premises and equipment, capitalized software, and goodwill held by our major business segments, are located in the United States. (b) From continuing operations. (c) The number of average full-time equivalent employees was not adjusted for discontinued operations. Other Segments Total Segments Reconciling Items Key 2017 2016 2015 2017 2016 2015 2017 2016 2015 2017 2016 2015 $ (23 ) $ (45 ) $ (8 ) $ 3,810 $ 2,957 $ 2,365 $ 20 $ (4 ) $ 11 $ 3,830 $ 2,953 $ 2,376 151 151 183 2,498 2,089 1,897 (20 ) (18 ) (17 ) 2,478 2,071 1,880 128 106 175 6,308 5,046 4,262 — (22 ) (6 ) 6,308 5,024 4,256 — (4 ) (8 ) 229 266 165 — — 1 229 266 166 3 4 8 215 140 107 169 163 148 384 303 255 39 35 46 3,686 3,183 2,714 28 270 (129 ) 3,714 3,453 2,585 86 71 129 2,178 1,457 1,276 (197 ) (455 ) (26 ) 1,981 1,002 1,250 (42 ) (20 ) 1 587 375 348 103 (162 ) (17 ) 690 213 331 128 91 128 1,591 1,082 928 (300 ) (293 ) (9 ) 1,291 789 919 — — — — — — 7 1 1 7 1 1 128 91 128 1,591 1,082 928 (293 ) (292 ) (8 ) 1,298 790 920 3 2 3 3 — 4 (1 ) (1 ) — 2 (1 ) 4 $ 125 $ 89 $ 125 $ 1,588 $ 1,082 $ 924 $ (292 ) $ (291 ) $ (8 ) $ 1,296 $ 791 $ 916 $ 1,225 $ 1,486 $ 1,852 $ 86,340 $ 71,035 $ 58,551 $ 25 $ 113 $ 43 $ 86,365 $ 71,148 $ 58,594 37,079 31,934 26,935 133,033 110,035 91,424 686 2,502 602 133,719 112,537 92,026 1,988 1,213 467 102,975 85,869 70,673 (29 ) 483 (43 ) 102,946 86,352 70,630 $ 19 — — $ 3,016 $ 1,818 $ 91 $ 81 $ 116 $ 49 $ 3,097 $ 1,934 $ 139 1 $ 7 $ 9 207 204 141 1 1 1 208 205 142 86.81 % 52.66 % 58.96 % 20.47 % 18.19 % 19.25 % (4.00 )% (4.36 )% (.15 )% 8.47 % 6.25 % 8.61 % 86.81 52.66 58.96 20.47 18.19 19.25 (3.91 ) (4.34 ) (.14 ) 8.51 6.25 8.62 2 5 14 13,333 11,185 9,634 5,082 4,515 3,849 18,415 15,700 13,483

Condensed Financial Information

Condensed Financial Information of the Parent Company	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Information of the Parent Company	26. Condensed Financial Information of the Parent Company CONDENSED BALANCE SHEETS December 31, in millions 2017 2016 ASSETS Cash and due from banks $ 2,257 $ 3,286 Short-term investments 22 70 Securities available for sale 10 10 Other investments 29 25 Loans to: Banks 250 250 Nonbank subsidiaries 31 31 Total loans 281 281 Investment in subsidiaries: Banks 15,169 14,564 Nonbank subsidiaries 885 668 Total investment in subsidiaries 16,054 15,232 Goodwill 167 167 Corporate-owned life insurance 208 207 Derivative assets 29 53 Accrued income and other assets 353 451 Total assets $ 19,410 $ 19,782 LIABILITIES Accrued expense and other liabilities $ 466 $ 553 Derivative liabilities — 2 Long-term debt due to: Subsidiaries 480 492 Unaffiliated companies 3,441 3,495 Total long-term debt 3,921 3,987 Total liabilities 4,387 4,542 SHAREHOLDERS’ EQUITY (a) 15,023 15,240 Total liabilities and shareholders’ equity $ 19,410 $ 19,782 (a) See Key’s Consolidated Statements of Changes in Equity. CONDENSED STATEMENTS OF INCOME Year ended December 31, in millions 2017 2016 2015 INCOME Dividends from subsidiaries: Bank subsidiaries $ 750 $ 625 $ 1,000 Nonbank subsidiaries — 50 1 Interest income from subsidiaries 10 10 10 Other income 9 11 20 Total income 769 696 1,031 EXPENSE Interest on long-term debt with subsidiary trusts 17 14 10 Interest on other borrowed funds 95 69 52 Personnel and other expense 46 101 73 Total expense 158 184 135 Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries 611 512 896 Income tax (expense) benefit 29 54 39 Income (loss) before equity in net income (loss) less dividends from subsidiaries 640 566 935 Equity in net income (loss) less dividends from subsidiaries 658 224 (15 ) NET INCOME (LOSS) 1,298 790 920 Less: Net income attributable to noncontrolling interests 2 (1 ) 4 NET INCOME (LOSS) ATTRIBUTABLE TO KEY $ 1,296 $ 791 $ 916 . CONDENSED STATEMENTS OF CASH FLOWS Year ended December 31, in millions 2017 2016 2015 OPERATING ACTIVITIES Net income (loss) attributable to Key $ 1,296 $ 791 $ 916 Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Deferred income taxes (benefit) 38 (24 ) 10 Stock-based compensation expense 11 12 9 Equity in net (income) loss less dividends from subsidiaries (658 ) (224 ) 15 Other intangible asset amortization — — 2 Net (increase) decrease in goodwill and other intangibles — — 86 Net (increase) decrease in other assets 82 (93 ) 29 Net increase (decrease) in other liabilities (82 ) 9 (7 ) Other operating activities, net (114 ) — (52 ) NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES 573 471 1,008 INVESTING ACTIVITIES Net (increase) decrease in securities available for sale and in short-term and other investments 47 (17 ) (38 ) Cash infusion from purchase of Cain Brothers (90 ) — — Cash used in acquisitions — (481 ) — Proceeds from sales, prepayments and maturities of securities available for sale 1 — 20 Net (increase) decrease in loans to subsidiaries — 160 (146 ) NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES (42 ) (338 ) (164 ) FINANCING ACTIVITIES Net proceeds from issuance of long-term debt — — 1,000 Payments on long-term debt — (21 ) (750 ) Repurchase of Treasury Shares (730 ) (140 ) (448 ) Net proceeds from the issuance of Common Shares and preferred stock (350 ) 1,041 22 Cash dividends paid (480 ) (335 ) (267 ) NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES (1,560 ) 545 (443 ) NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS (1,029 ) 678 401 CASH AND DUE FROM BANKS AT BEGINNING OF YEAR 3,286 2,608 2,207 CASH AND DUE FROM BANKS AT END OF YEAR $ 2,257 $ 3,286 $ 2,608 KeyCorp paid interest on borrowed funds totaling $120 million in 2017 , $114 million in 2016 , and $112 million in 2015 .

Summary of Significant Accoun37

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates Our accounting policies conform to GAAP and prevailing practices within the financial services industry. We must make certain estimates and judgments when determining the amounts presented in our consolidated financial statements and the related notes. If these estimates prove to be inaccurate, actual results could differ from those reported.
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of KeyCorp and its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. Some previously reported amounts have been reclassified to conform to current reporting practices. The consolidated financial statements include any voting rights entities in which we have a controlling financial interest. In accordance with the applicable accounting guidance for consolidations, we consolidate a VIE if we have: (i) a variable interest in the entity; (ii) the power to direct activities of the VIE that most significantly impact the entity’s economic performance; and (iii) the obligation to absorb losses of the entity or the right to receive benefits from the entity that could potentially be significant to the VIE (i.e., we are considered to be the primary beneficiary). Variable interests can include equity interests, subordinated debt, derivative contracts, leases, service agreements, guarantees, standby letters of credit, loan commitments, and other contracts, agreements and financial instruments. See Note 13 (“ Variable Interest Entities ”) for information on our involvement with VIEs. We use the equity method to account for unconsolidated investments in voting rights entities or VIEs if we have significant influence over the entity’s operating and financing decisions (usually defined as a voting or economic interest of 20% to 50% , but not controlling). Unconsolidated investments in voting rights entities or VIEs in which we have a voting or economic interest of less than 20% generally are carried at cost or fair value. Investments held by our registered broker-dealer and investment company subsidiaries (primarily principal investments) are carried at fair value. In preparing these financial statements, subsequent events were evaluated through the time the financial statements were issued. Financial statements are considered issued when they are widely distributed to all shareholders and other financial statement users or filed with the SEC.
Statements of Cash Flows	Statements of Cash Flows Cash and due from banks are considered “cash and cash equivalents” for financial reporting purposes.
Loans	Loans Loans held in portfolio, which management has the intent and ability to hold for the foreseeable future or until maturity or payoff, are carried at the principal amount outstanding, net of unearned income, including net deferred loan fees and costs and unamortized premiums and discounts. We defer certain nonrefundable loan origination and commitment fees, and the direct costs of originating or acquiring loans. The net deferred amount is amortized over the estimated lives of the related loans as an adjustment to the yield. Direct financing leases are carried at the aggregate of the lease receivable plus estimated unguaranteed residual values, less unearned income and deferred initial direct fees and costs. Unearned income on direct financing leases is amortized over the lease terms using a method approximating the interest method that produces a constant rate of return. Deferred initial direct fees and costs are amortized over the lease terms as an adjustment to the yield. The residual value component of a lease represents the fair value of the leased asset at the end of the lease term. We rely on industry data, historical experience, independent appraisals and the experience of the equipment leasing asset management team to value lease residuals. Relationships with a number of equipment vendors give the asset management team insight into the life cycle of the leased equipment, pending product upgrades and competing products. Residual values are reviewed at least annually to determine if an other-than-temporary decline in value has occurred. In the event of such a decline, the residual value is adjusted to its fair value. Impairment charges and net gains or losses on sales of lease residuals are included in “other income” on the income statement.
Loans Held for Sale	Loans Held for Sale Loans held for sale generally include certain residential and commercial mortgage loans and other commercial loans. Loans are initially classified as held for sale when they are individually identified as being available for immediate sale and a formal plan exists to sell them. Loans held for sale are recorded at either fair value, if elected, or the lower of cost or fair value. When a loan is originated as held-for-sale, we do not defer the related fees and costs. Our commercial loans (including commercial mortgage and non-mortgage loans), which we originated and intend to sell, are carried at the lower of aggregate cost or fair value. Beginning with the third quarter of 2016, we elected the fair value option for our consumer real estate - residential mortgages loans. Fair value is determined based on available market data for similar assets, expected cash flows, and appraisals of underlying collateral or the credit quality of the borrower. Subsequent declines in fair value for loans held for sale are recognized as a charge to “other income” on the income statement. Subsequent increases and decreases in fair value for loans elected to be measured at fair value are also recorded to “other income” on the income statement. Additional information regarding fair value measurements associated with our loans held for sale is provided in Note 7 (“ Fair Value Measurements ”). We may transfer certain loans to held for sale at the lower of cost or fair value. If a loan is transferred from the loan portfolio to the held-for-sale category, any write-down in the carrying amount of the loan at the date of transfer is recorded as a reduction in the ALLL. When a loan is transferred into the held for sale category, we stop amortizing the related deferred fees and costs. The remaining unamortized fees and costs are recognized as part of the cost basis of the loan at the time it is sold. We may also transfer loans from held for sale to the loan portfolio held for investment. If a loan held for sale for which fair value accounting was elected is transferred to held for investment, it will continue to be accounted for at fair value in the loan portfolio.
Nonperforming Loans	Nonperforming Loans Nonperforming loans are loans for which we do not accrue interest income, and include commercial and consumer loans and leases, as well as current year TDRs and nonaccruing TDR loans from prior years. Nonperforming loans do not include loans held for sale or PCI loans. We generally classify commercial loans as nonperforming and stop accruing interest (i.e., designate the loan “nonaccrual”) when the borrower’s principal or interest payment is 90 days past due unless the loan is well-secured and in the process of collection. Commercial loans are also placed on nonaccrual status when payment is not past due but we have serious doubts about the borrower’s ability to comply with existing repayment terms. Once a loan is designated nonaccrual (and as a result assessed for impairment), the interest accrued but not collected generally is charged against the ALLL, and payments subsequently received generally are applied to principal. Commercial loans generally are charged off in full or charged down to the fair value of the underlying collateral when the borrower’s payment is 180 days past due. We generally classify consumer loans as nonperforming and stop accruing interest when the borrower’s payment is 120 days past due, unless the loan is well-secured and in the process of collection. Any second lien home equity loan with an associated first lien that is 120 days or more past due or in foreclosure, or for which the first mortgage delinquency timeframe is unknown, is reported as a nonperforming loan. Secured loans that are discharged through Chapter 7 bankruptcy and not formally re-affirmed are designated as nonperforming and TDRs. Our charge-off policy for most consumer loans takes effect when payments are 120 days past due. Home equity and residential mortgage loans generally are charged down to net realizable value when payment is 180 days past due. Credit card loans and similar unsecured products continue to accrue interest until the account is charged off at 180 days past due. Commercial and consumer loans may be returned to accrual status if we are reasonably assured that all contractually due principal and interest are collectible and the borrower has demonstrated a sustained period (generally six months) of repayment performance under the contracted terms of the loan and applicable regulation.
Impaired Loans	Impaired Loans A loan is considered to be impaired when, based on current information and events, it is probable that we will be unable to collect all amounts due (both principal and interest) according to the contractual terms of the loan agreement. All commercial and consumer TDRs, regardless of size, and all non-accrual commercial loans with an outstanding balance of $2.5 million or greater are individually evaluated for impairment and assigned a specific reserve. Commercial non-accrual loans of less than $2.5 million and all non-accrual consumer loans are aggregated and collectively evaluated for impairment. The amount of the reserve is estimated based on the criteria outlined in the “Allowance for Loan and Lease Losses” section of this note.
Allowance for Loan and Lease Losses	Allowance for Loan and Lease Losses The ALLL represents our estimate of incurred credit losses inherent in the loan portfolio at the balance sheet date. We establish the amount of this allowance by analyzing the quality of the loan portfolio at least quarterly, and more often if deemed necessary. We segregate our loan portfolio between commercial and consumer loans and develop and document our methodology to determine the ALLL accordingly. We believe these portfolio segments represent the most appropriate level for determining our historical loss experience, as well as the level at which we monitor credit quality and risk characteristics of the portfolios. Commercial loans, which generally have larger individual balances, constitute a significant portion of our total loan portfolio. The consumer portfolio typically includes smaller-balance homogeneous loans. We estimate the appropriate level of our ALLL by applying expected loss rates to existing loans with similar risk characteristics. Expected loss rates for commercial loans are derived from a statistical analysis of our historical default and loss severity experience. The analysis utilizes probability of default and loss given default to assign loan grades using our internal risk rating system. Our expected loss rates are reviewed quarterly and updated as necessary. As of December 31, 2017 , the probability of default ratings was based on our default data for the period from January 2008 through October 2017, which encompasses the last downturn period as well as our more recent positive credit experience. We adjust expected loss rates based on calculated estimates of the average time period from initial loss indication to the initial loss recorded for an individual loan. Expected loss rates for consumer loans are statistically derived from an analysis of our historical default and loss severity experience, and is sensitive to change in delinquency status. Consumer loans are analyzed quarterly in homogeneous product-type pools that share similar risk attributes, including the application of delinquency roll rate models and credit loss severity estimates. Incurred losses that are not yet individually identifiable are measured as the estimate of the average time period for initial loss indication to initial loss recorded for consumer loans. The ALLL may be adjusted to reflect our current assessment of many qualitative factors that may not be directly measured in the statistical analysis of expected loss, including: • changes in international, national, regional, and local economic and business conditions; • changes in the experience, ability, and depth of our lending management and staff; • changes in lending policies and procedures, including changes in underwriting standards and collection, charge-off, and recovery practices; • changes in the nature and volume of the loan portfolio, including the existence and effect of any concentrations of credit, and changes in the level of such concentrations; • changes in the volume and/or severity of past due, nonaccrual, and adversely classified or graded loans; and • external factors, such as competition, legal developments, and regulatory requirements. For all commercial and consumer loan TDRs, regardless of size, as well as non-accrual commercial loans with an outstanding balance of $2.5 million or greater, we conduct further analysis to determine the probable loss content and assign a specific allowance to the loan if deemed appropriate. We estimate the extent of the individual impairment for commercial loans and TDRs by comparing the recorded investment of the loan with the estimated present value of its future cash flows, the fair value of its underlying collateral, or the loan’s observable market price. Secured consumer loan TDRs that are discharged through Chapter 7 bankruptcy and not formally re-affirmed are adjusted to reflect the fair value of the underlying collateral, less costs to sell. Other consumer loan TDRs are assigned a specific allocation based on the estimated present value of future cash flows using the effective interest rate. A specific allowance also may be assigned — even when sources of repayment appear sufficient — if we remain uncertain about whether the loan will be repaid in full. On at least a quarterly basis, we evaluate the appropriateness of our loss estimation methods to reduce differences between estimated incurred losses and actual losses.
Liability for Credit Losses on Lending-Related Commitments	Liability for Credit Losses on Lending-Related Commitments The liability for credit losses inherent in lending-related commitments, such as letters of credit and unfunded loan commitments, is included in “accrued expense and other liabilities” on the balance sheet. We establish the amount of this liability by considering both historical trends and current market conditions quarterly, or more often if deemed necessary.
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price to sell an asset or transfer a liability in an orderly transaction between market participants in our principal market. In other words, fair value represents an exit price at the measurement date. Market participants are buyers and sellers who are independent, knowledgeable, and willing and able to transact in the principal (or most advantageous) market for the asset or liability being measured. Current market conditions, including imbalances between supply and demand, are considered in determining fair value. We value our assets and liabilities based on the principal market where each would be sold (in the case of assets) or transferred (in the case of liabilities). The principal market is the forum with the greatest volume and level of activity. In the absence of a principal market, valuation is based on the most advantageous market (i.e., the market where the asset could be sold at a price that maximizes the amount to be received or the liability transferred at a price that minimizes the amount to be paid). In the absence of observable market transactions, we consider liquidity valuation adjustments to reflect the uncertainty in pricing the instruments. In measuring the fair value of an asset, we assume the highest and best use of the asset by a market participant — not just the intended use — to maximize the value of the asset. We also consider whether any credit valuation adjustments are necessary based on the counterparty’s credit quality. When measuring the fair value of a liability, we assume that the transfer will not affect the associated nonperformance risk. Nonperformance risk is the risk that an obligation will not be satisfied, and encompasses not only our own credit risk (i.e., the risk that we will fail to meet our obligation), but also other risks such as settlement risk (i.e., the risk that upon termination or sale, the contract will not settle). We consider the effect of our own credit risk on the fair value for any period in which fair value is measured. There are three acceptable techniques for measuring fair value: the market approach, the income approach, and the cost approach. The appropriate technique for valuing a particular asset or liability depends on the exit market, the nature of the asset or liability being valued, and how a market participant would value the same asset or liability. Ultimately, selecting the appropriate valuation method requires significant judgment, and applying the valuation technique requires sufficient knowledge and expertise. Valuation inputs refer to the assumptions market participants would use in pricing a given asset or liability. Inputs can be observable or unobservable. Observable inputs are assumptions based on market data obtained from an independent source. Unobservable inputs are assumptions based on our own information or assessment of assumptions used by other market participants in pricing the asset or liability. Our unobservable inputs are based on the best and most current information available on the measurement date. All inputs, whether observable or unobservable, are ranked in accordance with a prescribed fair value hierarchy that gives the highest ranking to quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest ranking to unobservable inputs (Level 3). Fair values for Level 2 assets or liabilities are based on one or a combination of the following factors: (i) quoted market prices for similar assets or liabilities; (ii) observable inputs, such as interest rates or yield curves; or (iii) inputs derived principally from or corroborated by observable market data. The level in the fair value hierarchy ascribed to a fair value measurement in its entirety is based on the lowest level input that is significant to the measurement. We consider an input to be significant if it drives 10% or more of the total fair value of a particular asset or liability. Assets and liabilities may transfer between levels based on the observable and unobservable inputs used at the valuation date, as the inputs may be influenced by certain market conditions. We recognize transfers between levels of the fair value hierarchy at the end of the reporting period. Typically, assets and liabilities are considered to be fair valued on a recurring basis if fair value is measured regularly. However, if the fair value measurement of an instrument does not necessarily result in a change in the amount recorded on the balance sheet, assets and liabilities are considered to be fair valued on a nonrecurring basis. This generally occurs when we apply accounting guidance that requires assets and liabilities to be recorded at the lower of cost or fair value, or assessed for impairment. At a minimum, we conduct our valuations quarterly.
Short-Term Investments	Short-Term Investments Short-term investments consist of segregated, interest-bearing deposits due from banks, the Federal Reserve, and certain non-U.S. banks as well as reverse repurchase agreements. Reverse repurchase agreements are further described under the “Repurchase agreements” heading in this section.
Trading Account Assets	Trading Account Assets Trading account assets are debt and equity securities, as well as commercial loans, that we purchase and hold but intend to sell in the near term. These assets are reported at fair value. Realized and unrealized gains and losses on trading account assets are reported in “other income” on the income statement.
Securities	Securities Securities available for sale. Securities available for sale are securities that we intend to hold for an indefinite period of time but that may be sold in response to changes in interest rates, prepayment risk, liquidity needs, or other factors. Securities available for sale are reported at fair value. Unrealized gains and losses (net of income taxes) deemed temporary are recorded in equity as a component of AOCI on the balance sheet. Unrealized losses on equity securities deemed “other-than-temporary,” and realized gains and losses resulting from sales of securities using the specific identification method, are included in “other income” on the income statement. Unrealized losses on debt securities deemed “other-than-temporary” are included in “other income” on the income statement or in AOCI, as further described under the heading “Other-than-Temporary Impairments” in this note and in Note 8 (“ Securities ”). “Other securities” held in the available-for-sale portfolio consist of marketable equity securities that are traded on a public exchange such as the NYSE or Nasdaq and convertible preferred stock of privately held companies. Held-to-maturity securities. Held-to-maturity securities are debt securities that we have the intent and ability to hold until maturity. Debt securities are carried at cost and adjusted for amortization of premiums and accretion of discounts using the interest method. This method produces a constant rate of return on the adjusted carrying amount. “Other securities” held in the held-to-maturity portfolio consist of foreign bonds and capital securities. Other Investments Other investments include equity and mezzanine instruments, such as certain real estate-related investments that are carried at fair value, as well as other types of investments that generally are carried at cost. The carrying amounts of the investments carried at cost are adjusted for declines in value if they are considered to be other-than-temporary. These adjustments are included in “other income” on the income statement.
Other-than-Temporary Impairments	Other-than-Temporary Impairments If the amortized cost of a debt security is greater than its fair value and we intend to sell it, or it is more-likely-than-not that we will be required to sell it, before the expected recovery of the amortized cost, then the entire impairment is recognized in earnings. If we have no intent to sell the security, or it is more-likely-than-not that we will not be required to sell it, before expected recovery, then the credit portion of the impairment is recognized in earnings, while the remaining portion attributable to factors such as liquidity and interest rate changes is recognized in equity as a component of AOCI on the balance sheet. The credit portion is equal to the difference between the cash flows expected to be collected and the amortized cost of the debt security. Generally, if the amortized cost of an equity security is greater than its fair value by more than 20% consistently for more than six months, the difference is considered to be other-than-temporary.
Derivatives and Hedging	Derivatives and Hedging All derivatives are recognized as either “derivative assets” or “derivative liabilities” on the balance sheet at fair value. The net increase or decrease in derivatives is included in “other operating activities, net” within the statement of cash flows. Accounting for changes in fair value (i.e., gains or losses) of derivatives differs depending on whether the derivative has been designated and qualifies as part of a hedge relationship, and further, on the type of hedge relationship. For derivatives that are not designated as hedging instruments, any gain or loss, as well as any premium paid or received, is recognized immediately in earnings in “corporate services income” and “other income” on the income statement. A derivative that is designated and qualifies as a hedging instrument must be designated as a fair value hedge, a cash flow hedge, or a hedge of a net investment in a foreign operation. We have only designated derivatives as hedging instruments. A fair value hedge is used to limit exposure to changes in the fair value of existing assets, liabilities, and commitments caused by changes in interest rates or other economic factors. The effective portion of a change in the fair value of an instrument designated as a fair value hedge is recorded in earnings at the same time as a change in fair value of the hedged item, resulting in no effect on net income. The ineffective portion of a change in the fair value of such a hedging instrument is recognized in “other income” on the income statement, with no corresponding offset. A cash flow hedge is used to minimize the variability of future cash flows that is caused by changes in interest rates or other economic factors. The effective portion of a gain or loss on a cash flow hedge is recorded as a component of AOCI on the balance sheet and reclassified to earnings in the same period in which the hedged transaction affects earnings (e.g., when we incur variable-rate interest on debt, earn variable-rate interest on loans, or sell commercial real estate loans). The ineffective portion of a cash flow hedge is included in “other income” on the income statement. A net investment hedge is used to hedge the exposure of changes in the carrying value of investments as a result of changes in the related foreign exchange rates. The effective portion of a gain or loss on a net investment hedge is recorded as a component of AOCI on the balance sheet when the terms of the derivative match the notional and currency risk being hedged. The effective portion is subsequently reclassified into income when the hedged transaction affects earnings (e.g., when we dispose or liquidate a foreign subsidiary). The ineffective portion of a net investment hedge is included in “other income” on the income statement. Hedge “effectiveness” is determined by the extent to which changes in the fair value of a derivative instrument offset changes in the fair value, cash flows, or carrying value attributable to the risk being hedged. If the relationship between the change in the fair value of the derivative instrument and the change in the hedged item falls within a range considered to be the industry norm, the hedge is considered “highly effective” and qualifies for hedge accounting. A hedge is “ineffective” if the relationship between the changes falls outside the acceptable range. In that case, hedge accounting is discontinued on a prospective basis. Hedge effectiveness is tested at least quarterly.
Offsetting Derivative Positions	Offsetting Derivative Positions We take into account the impact of bilateral collateral and master netting agreements that allow us to settle all derivative contracts held with a single counterparty on a net basis, and to offset the net derivative position with the related cash collateral when recognizing derivative assets and liabilities. As a result, we could have derivative contracts with negative fair values included in derivative assets on the balance sheet and contracts with positive fair values included in derivative liabilities.
Servicing Assets	Servicing Assets We service commercial real estate and residential mortgages loans. Servicing assets and liabilities purchased or retained are initially measured at fair value and are recorded as a component of “accrued income and other assets” on the balance sheet. When no ready market value (such as quoted market prices, or prices based on sales or purchases of similar assets) is available to determine the fair value of servicing assets, fair value is determined by calculating the present value of future cash flows associated with servicing the loans. This calculation is based on a number of assumptions, including the market cost of servicing, the discount rate, the prepayment rate, and the default rate. We remeasure our servicing assets using the amortization method at each reporting date. The amortization of servicing assets is determined in proportion to, and over the period of, the estimated net servicing income and recorded in “mortgage servicing fees” on the income statement. Servicing assets are evaluated quarterly for possible impairment. This process involves stratifying the assets based upon one or more predominant risk characteristics and determining the fair value of each class. The characteristics may include financial asset type, size, interest rate, date of origination, term and geographic location. If the evaluation indicates that the carrying amount of the servicing assets exceeds their fair value, the carrying amount is reduced by recording a charge to income in the amount of such excess and establishing a valuation reserve allowance.
Business Combinations	Business Combinations We account for our business combinations using the acquisition method of accounting. Under this accounting method, the acquired company’s assets and liabilities are recorded at fair value at the date of acquisition, except as provided for by the applicable accounting guidance, and the results of operations of the acquired company are combined with Key’s results from that date forward. Acquisition costs are expensed when incurred. The difference between the purchase price and the fair value of the net assets acquired (including identifiable intangible assets) is recorded as goodwill. Our accounting policy for intangible assets is summarized in this note under the heading “Goodwill and Other Intangible Assets.”
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill represents the amount by which the cost of net assets acquired in a business combination exceeds their f air value. Goodwill is assigned to reporting units as of the acquisition date based on the expected benefit to such reporting unit from the synergies of the business combination. Goodwill is tested at the reporting unit level for impairment, at least annually as of October 1, or as events and circumstances change that would more-likely-than-not reduce the fair value of a reporting unit below its carrying amount. We may elect to perform a qualitative analysis to determine whether or not it is more-likely-than-not that the fair value of a reporting unit is less than its carrying amount. If we elect to bypass this qualitative analysis, or conclude via qualitative analysis that it is more-likely-than-not that the fair value of a reporting unit is less than its carrying value, a two-step goodwill impairment test is performed. In the first step, the fair value of each reporting unit is compared with its carrying value. If the fair value is greater than the carrying value, then the reporting unit's goodwill is deemed not to be impaired. If the fair value is less than the carrying value, then the second step is performed, which measures the amount of impairment by comparing the carrying amount of goodwill to its implied fair value. If the implied fair value of the goodwill exceeds the carrying amount, there is no impairment. If the carrying amount exceeds the implied fair value of the goodwill, an impairment charge is recorded for the excess. Other intangible assets with finite lives are amortized on either an accelerated or straight-line basis and are evaluated for impairment whenever events or circumstances indicate that the carrying value of the asset may not be recoverable .
Purchased Loans	Purchased Loans Purchased performing loans that do not have evidence of deterioration in credit quality at acquisition are recorded at fair value at the acquisition date. Any premium or discount associated with purchased performing loans is recognized as an expense or income based on the effective yield method of amortization for term loans or the straight-line method of amortization for revolving loans. Subsequent to the purchase date, the methods utilized to estimate the required ALLL for these loans is similar to originated loans; however, we record a provision for loan and lease losses only when the required ALLL exceeds any remaining purchase discount at the product level. Purchased loans that have evidence of deterioration in credit quality since origination and for which it is probable, at acquisition, that all contractually required payments will not be collected, are deemed PCI. Revolving loans, including lines of credit and credit card loans, leases, and loans where cash flows cannot be reasonably estimated are excluded from PCI accounting. Purchased loans are initially recorded at fair value without recording an allowance for loan losses. Fair value of these loans is determined using market participant assumptions in estimating the amount and timing of both principal and interest cash flows expected to be collected, as adjusted for an estimate of future credit losses and prepayments, and then a market-based discount rate is applied to those cash flows. PCI loans that have similar risk characteristics, primarily credit risk, collateral type and interest rate risk, and are homogeneous in size, are pooled and accounted for as a single asset with a single composite interest rate and an aggregate expectation of cash flows. PCI loans that cannot be aggregated into a pool are accounted for individually. The excess of cash flows expected to be collected, measured as of the acquisition date, over the estimated fair value is referred to as the “accretable yield” and is recognized in interest income over the remaining life of the loan or pool using the effective yield method. Accordingly, PCI loans are not subject to classification as nonaccrual (and nonperforming) in the same manner as originated loans. Rather, acquired PCI loans are considered to be accruing loans because their interest income relates to the accretable yield recognized on the individual loan or pool and not to the contractual interest payments of the loan. The difference between the contractually required principal and interest payments as of the acquisition date and the cash flows expected to be collected is referred to as the “nonaccretable difference.” The nonaccretable difference, which is not accreted into income, reflects estimated future credit losses and uncollectible contractual payments over the life of the PCI loan. After we acquire loans determined to be PCI loans, actual cash collections are monitored to determine if they conform to management’s expectations. Revised cash flow expectations are prepared each quarter. A decrease in expected cash flows in subsequent periods may indicate impairment and would require us to establish an ALLL by recording a charge to the provision for loan and lease losses. An increase in expected cash flows in subsequent periods initially reduces any previously established ALLL by the increase in the present value of cash flows expected to be collected, and requires us to recalculate the amount of accretable yield for the PCI loan or pool. The adjustment of accretable yield due to an increase in expected cash flows is accounted for as a change in estimate. The additional cash flows expected to be collected are reclassified from the nonaccretable difference to the accretable yield, and the amount of periodic accretion is adjusted accordingly over the remaining life of the PCI loan or pool. A PCI loan may be derecognized either through receipt of payment (in full or in part) from the borrower, the sale of the loan to a third party, foreclosure of the collateral, or charge-off. If one of these events occurs, the loan is removed from the loan pool, or derecognized if it is accounted for as an individual loan. PCI loans subject to modification are not removed from a PCI pool even if those loans would otherwise be deemed TDRs since the pool, and not the individual loan, represents the unit of account. Individually accounted for PCI loans that are modified in a TDR are no longer classified as PCI loans and are subject to TDR recognition.
Premises and Equipment	Premises and Equipment Premises and equipment, including leasehold improvements, are stated at cost less accumulated depreciation and amortization. We determine depreciation of premises and equipment using the straight-line method over the estimated useful lives of the particular assets. Leasehold improvements are amortized using the straight-line method over the shorter of their economic lives or terms of the leases. Premises and equipment are evaluated for impairment whenever events or circumstances indicate that the carrying value of the asset may not be recoverable.
Securities Financing Activities	Securities Financing Activities We enter into repurchase agreements to finance overnight customer sweep deposits. We also enter into repurchase and reverse repurchase agreements to settle other securities obligations. We account for these securities financing agreements as collateralized financing transactions. Repurchase and reverse repurchase agreements are recorded on the balance sheet at the amounts that the securities will be subsequently sold or repurchased. Securities borrowed transactions are recorded on the balance sheet at the amounts of cash collateral advanced. While our securities financing agreements incorporate a right of set off, the assets and liabilities are reported on a gross basis. Reverse repurchase agreements and securities borrowed transactions are included in “short-term investments” on the balance sheet; repurchase agreements are included in “federal funds purchased and securities sold under repurchase agreements.” Fees received in connection with these transactions are recorded in interest income; fees paid are recorded in interest expense.
Guarantees	Guarantees We recognize liabilities, which are included in “accrued expense and other liabilities” on the balance sheet, for the fair value of our obligations under certain guarantees issued. If we receive a fee for a guarantee requiring liability recognition, the amount of the fee represents the initial fair value of the “stand ready” obligation. If there is no fee, the fair value of the stand ready obligation is determined using expected present value measurement techniques, unless observable transactions for comparable guarantees are available. The subsequent accounting for these stand ready obligations depends on the nature of the underlying guarantees. We account for our release from risk under a particular guarantee when the guarantee expires or is settled, or by a systematic and rational amortization method, depending on the risk profile of the guarantee.
Revenue Recognition	Revenue Recognition We recognize revenues as they are earned based on contractual terms, as transactions occur, or as services are provided and collectability is reasonably assured. Our principal source of revenue is interest income from loans and investments. We also earn noninterest income from various banking and financial services offered through both the Corporate and Community banks. Interest Income. The largest source of revenue for us is interest income. Interest income is primarily recognized on an accrual basis according to nondiscretionary formulas in written contracts, such as loan agreements or securities contracts. Noninterest Income. We earn noninterest income through a variety of financial and transaction services provided to corporate and consumer clients. Revenue is recorded for noninterest income based on the contractual terms for the service or transaction performed. In certain circumstances, noninterest income is reported net of associated expenses. Trust and Investment Services Income. Trust and investment services revenues include brokerage commissions, trust and asset management commissions, and insurance income. Revenue from trade execution and brokerage services is earned through commissions from trade execution on behalf of clients. Revenue from these transactions is recognized at the trade date. Any ongoing service fees are recognized on a monthly basis as services are performed. Trust and asset management services include asset custody and investment management services provided to individual and institutional customers. Revenue is recognized monthly based on a minimum annual fee, and the market value of assets in custody. Additional fees are recognized for transactional activity. Insurance revenue is earned through commissions on insurance sales and third party administrative services. Based on the nature of the commission agreement with each insurance provider, we may recognize revenue from insurance commissions over-time or at a point in time. Revenue from third party administrative services is recognized over the life of the contract. Investment Banking and Debt Placement Fees. Investment banking and debt placement fees primarily represent revenues earned by KeyBank Capital Markets for various corporate services including advisory, debt placement and underwriting. Revenues for these services are recorded at a point in time, upon completion of a contractually identified transaction, or when an advisory opinion is provided. Certain underwriting costs are presented net against underwriting revenues. Service Charges on Deposit Accounts. Revenue from service charges on deposit accounts is earned through cash management, wire transfer, and other deposit-related services; as well as overdraft, non-sufficient funds, account management and other deposit-related fees. Revenue is recognized for these services either over time, corresponding with deposit accounts’ monthly cycle, or at a point in time for transactional related services and fees. Cards and Payments. Cards and payments income includes interchange fees from consumer credit and debit cards processed through card association networks, merchant services, and other card related services. Interchange rates are generally set by the credit card associations and based on purchase volumes and other factors. Interchange fees are recognized as transactions occur. Merchant services income represents account management fees and transaction fees charged to merchants for the processing of card association network transactions. Merchant services revenue is recognized as transactions occur, or as services are performed. Corporate Services Income. Corporate services income includes various ancillary service revenue including letter of credit fees, loan fees, and certain capital markets’ revenue. Revenue from these fees is recorded in a manner that reflects the timing of when transactions occur, and as services are provided. Corporate-Owned Life Insurance Income. Income from corporate-owned life insurance primarily represents changes in the cash surrender value of life insurance policies held on certain key employees. Revenue is recognized in each period based on the change in the cash surrender value during the period.
Pension Costs	Pension Costs The Company utilizes its fiscal year-end as the measurement date for its pension and other postretirement employee benefit plans. At the measurement date, plan assets are determined based on fair value, generally representing observable market prices or the net asset value provided by the funds’ trustee or administrator. The actuarial cost method used to compute the pension liabilities and related expense is the projected unit credit method. The projected benefit obligation is principally determined based on the present value of projected benefit distributions at an assumed discount rate. We determine the assumed discount rate based on the rate of return on a hypothetical portfolio of high quality corporate bonds with interest rates and maturities that provide the necessary cash flows to pay benefits when due. Periodic pension expense (or income) includes service costs, interest costs based on the assumed discount rate, the expected return on plan assets based on an actuarially derived market-related value and amortization of actuarial gains and losses. Pension accounting reflects the long-term nature of benefit obligations and the investment horizon of plan assets, and can have the effect of reducing earnings volatility related to short-term changes in interest rates and market valuations. Actuarial gains and losses include the impact of plan amendments and various unrecognized gains and losses which are deferred and amortized over the future service periods of active employees. We determine the expected return on plan assets using a calculated market-related value of plan assets that smooths what might otherwise be significant year-to-year volatility in net pension cost. Changes in the value of plan assets are not recognized in the year they occur. Rather, they are combined with any other cumulative unrecognized asset- and obligation-related gains and losses and reflected evenly in the market-related value during the five years after they occur as long as the market-related value does not vary more than 10% from the plan’s FVA. The overfunded or underfunded status of the plans is recorded as an asset or liability on the Consolidated Balance Sheet, with changes in that status recognized through other comprehensive income (loss).
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation is measured using the fair value method of accounting on the grant date. The measured cost is recognized over the period during which the recipient is required to provide service in exchange for the award. We estimate expected forfeitures when stock-based awards are granted and record compensation expense only for awards that are expected to vest. Compensation expense related to awards granted to employees is recorded in “personnel expense” on the income statement while compensation expense related to awards granted to directors is recorded in “other expense.” We recognize compensation cost for stock-based, mandatory deferred incentive compensation awards using the accelerated method of amortization over a period of approximately 5 years (the current year performance period and a four -year vesting period, which generally starts in the first quarter following the performance period) for awards granted in 2012 and after. Employee stock options typically become exercisable at the rate of 25% per year, beginning one year after the grant date. Options expire no later than 10 years after their grant date. We recognize stock-based compensation expense for stock options with graded vesting using an accelerated method of amortization. We use shares repurchased under our annual capital plan submitted to our regulators (treasury shares) for share issuances under all stock-based compensation programs. We estimate the fair value of options granted using the Black-Scholes option-pricing model
Income Taxes	Income Taxes Deferred tax assets and liabilities are determined based on temporary differences between financial statement asset and liability amounts and their respective tax bases, and are measured using enacted tax laws and rates that are expected to apply in the periods in which the deferred tax assets or liabilities are expected to be realized. Deferred tax assets are also recorded for any tax attributes, such as tax credit and net operating loss carryforwards. The net balance of deferred tax assets and liabilities is reported in other assets or other liabilities in the consolidated balance sheets, as appropriate. Subsequent changes in the tax laws require adjustment to these assets and liabilities with the cumulative effect included in the provision for income taxes for the period in which the change is enacted. A valuation allowance is recognized for a DTA if, based on the weight of available evidence, it is more-likely-than-not that some portion or all of the DTA will not be realized.
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 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 incurred losses. 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 service- and performance-based restricted stock and stock units granted under the our stock plans using the treasury stock method, if dilutive. It also considers the conversion of convertible preferred shares. 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.
Accounting Guidance Adopted and Pending Adoption	Accounting Guidance Adopted in 2017 Standard Date of Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2016-09, Improvements to Employee Share-Based Payment Accounting January 1, 2017 The ASU requires entities to recognize the income tax effects of share-based awards in the income statement when the awards vest or are settled (i.e. the additional paid-in capital pools will be eliminated). The guidance on employers’ accounting for an employee’s use of shares to satisfy the employer’s statutory income tax withholding obligation and for forfeitures is changing. The standard also provides an entity the option to make an entity-wide accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur. During the year ended December 31, 2017, the application of this guidance resulted in recognition of $28 million in excess tax benefits within “income taxes” on our income statement. Adoption did not materially affect our Consolidated Statements of Cash Flows, nor did it affect retained earnings as of the beginning of the period of adoption. We elected to retain our existing accounting policy of estimating award forfeitures upon the award’s grant date. ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220) October 1, 2017 On December 22, 2017, the TCJ Act was signed into law. Under current U.S. GAAP, deferred tax assets and liabilities are to be adjusted for the effect of a change in tax laws or rates with the effect included in income from continuing operations in the reporting period that includes the enactment date. This accounting treatment resulted in the tax effect of items within accumulated other comprehensive income not reflecting the appropriate tax rate. This ASU allows stranded tax effects resulting from the TCJ Act to be reclassified from accumulated other comprehensive income to retained earnings. We early adopted this guidance during the quarter ended December 31, 2017, resulting in a reclassification of $141 million from accumulated other comprehensive income to retained earnings to adjust the tax effect of items within accumulated other comprehensive income to reflect the newly enacted federal corporate income tax rate. Refer to Note 14, Income Taxes, for additional information. Accounting Guidance Pending Adoption at December 31, 2017 Standard Required Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2014-09, Revenue from Contracts with Customers (Topic 606) ASU 2015-14, Deferral of Effective Date ASU 2016-08, Principal versus Agent Considerations ASU 2016-10, Identifying Performance Obligations and Licensing ASU 2016-11, Rescission of SEC Guidance because of Accounting Standard Updates 2014-09 and 2014-16 pursuant to Staff Announcements at the March 3, 2016 EITF Meeting ASU 2016-12, Narrow-scope Improvements and Practical Expedients ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers January 1, 2018 Early adoption is permitted for interim and annual reporting periods beginning after December 15, 2016 These ASUs supersede the revenue recognition guidance in ASC 605, Revenue Recognition, and most industry-specific guidance. The core principle of these ASUs is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. These ASUs can be implemented using a retrospective method, or a cumulative-effect approach to new contracts and existing contracts with performance obligations as of the effective date. We have identified the revenue line items within the scope of the new guidance and have finalized our contract testing related to trust and investment services income, investment banking and debt placement fees, service charges on deposit accounts, and cards and payments income. The new guidance will change our presentation of certain underwriting and credit and debit card related costs. Underwriting costs will change from a net presentation to a gross expense. Certain credit and debit card related costs will change from a gross presentation to a reduction in revenue. Additionally, we will expand our qualitative and quantitative disclosures pursuant to the new requirements Key will adopt using a cumulative-effect approach. The adoption of this accounting guidance will not have a material effect on our financial condition or results of operations. Standard Required Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities January 1, 2018 Early adoption is not permitted, except under certain circumstances The ASU amends ASC Topic 825, Financial Instruments-Overall, and re quires equity investments, except those accounted for under the equity method of accounting or consolidated, to be measured at fair value with changes recognized in net income. If there is no readily determinable fair value, the guidance allows entities the ability to measure investments at cost less impairment, whereby impairment is based on a qualitative assessment. The guidance eliminates the requirement to disclose the methods and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost and changes the presentation of financial assets and financial liabilities on the balance sheet or in the footnotes. If an entity has elected the fair value option to measure liabilities, the new accounting guidance requires the portion of the change in the fair value of a liability resulting from credit risk to be presented in OCI. With the exception of disclosure requirements that will be adopted prospectively, the ASU must be adopted on a modified retrospective basis. The adoption of this guidance will not have a material effect on our financial condition or results of operations. ASU 2016-02, Leases (Topic 842) January 1, 2019 Early adoption is permitted The ASU creates ASC Topic 842, Leases , and supersedes Topic 840, Leases. The ASU requires that a lessee recognize assets and liabilities for leases with lease terms of more than 12 months. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities. Leveraged leases that commenced before the effective date of the new guidance are grandfathered. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance or operating lease. However, the ASU will require both types of leases to be recognized on the balance sheet. It also requires disclosures to better understand the amount, timing, and uncertainty of cash flows arising from leases. These disclosures include qualitative and quantitative requirements, providing additional information about the amounts recorded in the financial statements. Upon transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. Key has formed a cross-functional team to oversee the implementation of this ASU. Implementation efforts are ongoing, including the review of our lease portfolios and related lease accounting policies, the review of our service contracts for embedded leases, and the deployment of a new lease software solution. Key’s adoption of this ASU will result in an increase in right-of-use assets and associated lease liabilities, arising from operating leases in which Key is the lessee, on our Consolidated Balance Sheet. The amount of the right-of-use assets and associated lease liabilities recorded upon adoption will be based primarily on the present value of unpaid future minimum lease payments, the amount of which will depend on the population of leases in effect at the date of adoption. Key’s minimum future rental payments under noncancelable operating leases would be measured and recognized when the new guidance is adopted (refer to Note 22 (“Commitments, Contingent Liabilities, and Guarantees”). While these leases represent a large majority of the leases that are within scope of the new leasing standard, we will continue to review service contracts up through the effective date and may identify additional leases embedded in those arrangements that will be within the scope of the new standard. In addition to final determination of the lease portfolio at the effective date, the initial measurement of the right-of-use asset and the corresponding liability will be affected by certain key assumptions such as expectations of renewals or extensions and the interest rate to be used to discount the future lease obligations. We do not expect the adoption of this guidance to have a material impact on our Consolidated Statements of Income. ASU 2016-13 Measurement of Credit Losses on Financial Instruments January 1, 2020 Early adoption is permitted as of January 1, 2019 The ASU amends ASC Topic 326, Financial Instruments-Credit Losses, and significantly changes how entities will measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The standard replaces today’s “incurred loss” approach with an “expected loss” model for instruments such as loans and HTM securities that are measured at amortized cost. The standard requires credit losses relating to AFS debt securities to be recorded through an allowance rather than a reduction of the carrying amount. It also changes the accounting for purchased credit-impaired debt securities and loans. The ASU retains many of the current disclosure requirements in current GAAP and expands certain disclosure requirements. This new guidance will affect the accounting for our loans, debt securities held to maturity and available for sale, and liabilities for credit losses on unfunded lending-related commitments as well as purchased financial assets with a more-than-insignificant amount of credit deterioration since origination. Key has formed a cross-functional implementation working group comprised of teams throughout Key, including finance and credit. The implementation team has developed a high-level project plan, is identifying and researching key interpretive issues, and is in the process of developing models that meet the requirements of the new guidance. The implementation team is also in the process of assessing forecast accuracy and potential macroeconomic factors that will be used to determine the reasonable and supportable forecast period. Key expects that the new guidance will generally result in an increase in its allowance for credit losses, as it will cover credit losses over the full remaining expected life of loans and commitments and will consider future changes in macroeconomic conditions. Since the magnitude of the anticipated increase in the allowance for credit losses will be impacted by economic conditions and trends in the Company’s portfolio at the time of adoption, the quantitative impact cannot yet be reasonably estimated. Standard Required Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments. January 1, 2018 Early adoption is permitted The ASU amends ASC Topic 230, Statement of Cash Flows , and clarifies how cash receipts and cash payments in certain transactions should be presented and classified in the statement of cash flows. These specific transactions include, but are not limited to, debt prepayment or extinguishment costs, contingent considerations made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, and distributions from equity method investees. This guidance also clarifies that in instances of cash flows with multiple aspects that cannot be separately identified, classification should be based on the activity that is likely to be the predominant source of or use of cash flow. The guidance should be implemented using a retrospective approach. The adoption of this accounting guidance will not have a material effect on the presentation of our Consolidated Statements of Cash Flows, as Key’s current policies are either already in-line with the clarifications in the updated guidance, or the related cash flows are not material. ASU 2017-04, Simplifying the Test for Goodwill Impairment January 1, 2020 Early adoption is permitted The ASU amends ASC Topic 350, Intangibles - Goodwill and Other and eliminates the second step of the test for goodwill impairment. Under the new guidance, entities will compare the fair value of a reporting unit with its carrying amount. If the carrying amount exceeds the reporting unit’s fair value, the entity is required to recognize an impairment charge for this amount. The new method applies to all reporting units and the performance of a qualitative assessment is still allowable. The guidance should be implemented using a prospective approach. The adoption of this accounting guidance is not expected to have a material effect on our financial condition or results of operations. ASU 2017-05, Other Income- Gains and Losses from the Derecognition of Nonfinancial Assets January 1, 2018 Early adoption is permitted The ASU amends ASC Topic 610-20, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets to clarify the scope of the Topic by clarifying the definition of the term "in substance nonfinancial asset" and also adding guidance for partial sales of nonfinancial assets. Under the new guidance, an entity will derecognize a nonfinancial asset when it does not have or ceases to have a controlling interest in the legal entity that holds the asset and when control of the asset has transferred in accordance with ASC 606. The ASU can be adopted on a retrospective or modified retrospective approach. The adoption of this guidance will not have a material effect on our financial condition or results of operations. ASU 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost January 1, 2018 Early adoption is permitted within the first interim period if the entity issues interim financial statements. The ASU amends ASC Topic 715, Compensation - Retirement Benefits , and requires service costs to be included in the same line item as certain other compensation costs related to services rendered by employees. We record compensation costs under personnel expense on the income statement. Other elements of net benefit cost should be presented separately. The guidance should be implemented on a retrospective basis. The adoption of this guidance will result in a reclassification of certain net benefit cost components from personnel expense to other expense on the income statement. There will be no material effect on our financial condition or results of operations. ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities January 1, 2019 Early adoption is permitted. The ASU amends ASC Topic 310-20, Receivables — Nonrefundable Fees and Other Costs , and shortens the amortization period to the earliest call date for certain callable debt securities held at a premium. Securities held at a discount will continue to be amortized to maturity. The guidance should be implemented on a modified retrospective basis using a cumulative-effect adjustment. The adoption of this guidance is not expected to have a material effect on our financial condition or results of operations. ASU 2017-09, Scope of Modification Accounting January 1, 2018 Early adoption is permitted, including interim periods. The ASU amends ASC Topic 718, Compensation - Stock Compensation , and clarifies when changes to terms and conditions for share-based payment awards should be accounted for as modifications. Under the new guidance, entities should apply the modification guidance unless the fair value of the modified award is the same as the fair value of the original award immediately before modification, the vesting conditions of the modified award are the same as the vesting conditions of the original award immediately before modification, and the classification of the modified award (as equity or liability instrument) is the same as the classification of the original award immediately before modification. The guidance should be applied on a prospective basis. The adoption of this guidance will not have a material effect on our financial condition or results of operations. Standard Required Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2017-01, Clarifying the Definition of a Business January 1, 2018 Early application is allowed for certain transactions. The ASU amends Topic 805, Business Combinations, and clarifies the definition of a business and removes the requirement for a market participant to consider whether it could replace missing elements in an integrated set of assets and activities. The guidance states that if substantially all of the fair value of the assets acquired or disposed of is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. The guidance should be implemented using a prospective approach. The adoption of this guidance will not have a material effect on our financial condition or results of operations. ASU 2017-12, Targeted Improvements to Accounting for Hedging Activities January 1, 2019 Early adoption is permitted, including interim periods. Key anticipates early adopting this standard as of January 1, 2018. The ASU amends ASC Topic 815, Derivatives and Hedging , to simplify the requirements for hedge accounting and facilitate financial reporting that more closely aligns with an entity’s risk management activities. Key amendments include: eliminating the requirement to separately measure and report hedge ineffectiveness, requiring changes in the value of the hedging instrument to be presented in the same income statement line as the earnings effect of the hedged item, and the ability to measure the hedged item based on the benchmark interest rate component of the total contractual coupon for fair value hedges. Additional disclosures are also required for reporting periods subsequent to the date of adoption. The guidance should be implemented on a modified retrospective basis to existing hedge relationships as of the adoption date. We will adopt this ASU in the first quarter of 2018. Our financial statements for the quarter ended March 31, 2018, will include a cumulative-effect adjustment to opening retained earnings to reflect the application of the new guidance as of January 1, 2018. The primary impact to Key at adoption is the election to measure the change in fair value of the hedged item in fair value hedges on the basis of the benchmark interest rate component of contractual coupon cash flows. The cumulative-effect entry at adoption will reflect a cumulative basis adjustment for existing fair value hedges to be under the benchmark component approach. We expect adoption of this ASU to reduce hedge ineffectiveness going forward; however, we do not anticipate this guidance to have a material effect on our financial condition and results of operations.

Summary of Significant Accoun38

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	Accounting Guidance Adopted in 2017 Standard Date of Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2016-09, Improvements to Employee Share-Based Payment Accounting January 1, 2017 The ASU requires entities to recognize the income tax effects of share-based awards in the income statement when the awards vest or are settled (i.e. the additional paid-in capital pools will be eliminated). The guidance on employers’ accounting for an employee’s use of shares to satisfy the employer’s statutory income tax withholding obligation and for forfeitures is changing. The standard also provides an entity the option to make an entity-wide accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur. During the year ended December 31, 2017, the application of this guidance resulted in recognition of $28 million in excess tax benefits within “income taxes” on our income statement. Adoption did not materially affect our Consolidated Statements of Cash Flows, nor did it affect retained earnings as of the beginning of the period of adoption. We elected to retain our existing accounting policy of estimating award forfeitures upon the award’s grant date. ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220) October 1, 2017 On December 22, 2017, the TCJ Act was signed into law. Under current U.S. GAAP, deferred tax assets and liabilities are to be adjusted for the effect of a change in tax laws or rates with the effect included in income from continuing operations in the reporting period that includes the enactment date. This accounting treatment resulted in the tax effect of items within accumulated other comprehensive income not reflecting the appropriate tax rate. This ASU allows stranded tax effects resulting from the TCJ Act to be reclassified from accumulated other comprehensive income to retained earnings. We early adopted this guidance during the quarter ended December 31, 2017, resulting in a reclassification of $141 million from accumulated other comprehensive income to retained earnings to adjust the tax effect of items within accumulated other comprehensive income to reflect the newly enacted federal corporate income tax rate. Refer to Note 14, Income Taxes, for additional information. Accounting Guidance Pending Adoption at December 31, 2017 Standard Required Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2014-09, Revenue from Contracts with Customers (Topic 606) ASU 2015-14, Deferral of Effective Date ASU 2016-08, Principal versus Agent Considerations ASU 2016-10, Identifying Performance Obligations and Licensing ASU 2016-11, Rescission of SEC Guidance because of Accounting Standard Updates 2014-09 and 2014-16 pursuant to Staff Announcements at the March 3, 2016 EITF Meeting ASU 2016-12, Narrow-scope Improvements and Practical Expedients ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers January 1, 2018 Early adoption is permitted for interim and annual reporting periods beginning after December 15, 2016 These ASUs supersede the revenue recognition guidance in ASC 605, Revenue Recognition, and most industry-specific guidance. The core principle of these ASUs is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. These ASUs can be implemented using a retrospective method, or a cumulative-effect approach to new contracts and existing contracts with performance obligations as of the effective date. We have identified the revenue line items within the scope of the new guidance and have finalized our contract testing related to trust and investment services income, investment banking and debt placement fees, service charges on deposit accounts, and cards and payments income. The new guidance will change our presentation of certain underwriting and credit and debit card related costs. Underwriting costs will change from a net presentation to a gross expense. Certain credit and debit card related costs will change from a gross presentation to a reduction in revenue. Additionally, we will expand our qualitative and quantitative disclosures pursuant to the new requirements Key will adopt using a cumulative-effect approach. The adoption of this accounting guidance will not have a material effect on our financial condition or results of operations. Standard Required Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities January 1, 2018 Early adoption is not permitted, except under certain circumstances The ASU amends ASC Topic 825, Financial Instruments-Overall, and re quires equity investments, except those accounted for under the equity method of accounting or consolidated, to be measured at fair value with changes recognized in net income. If there is no readily determinable fair value, the guidance allows entities the ability to measure investments at cost less impairment, whereby impairment is based on a qualitative assessment. The guidance eliminates the requirement to disclose the methods and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost and changes the presentation of financial assets and financial liabilities on the balance sheet or in the footnotes. If an entity has elected the fair value option to measure liabilities, the new accounting guidance requires the portion of the change in the fair value of a liability resulting from credit risk to be presented in OCI. With the exception of disclosure requirements that will be adopted prospectively, the ASU must be adopted on a modified retrospective basis. The adoption of this guidance will not have a material effect on our financial condition or results of operations. ASU 2016-02, Leases (Topic 842) January 1, 2019 Early adoption is permitted The ASU creates ASC Topic 842, Leases , and supersedes Topic 840, Leases. The ASU requires that a lessee recognize assets and liabilities for leases with lease terms of more than 12 months. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities. Leveraged leases that commenced before the effective date of the new guidance are grandfathered. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance or operating lease. However, the ASU will require both types of leases to be recognized on the balance sheet. It also requires disclosures to better understand the amount, timing, and uncertainty of cash flows arising from leases. These disclosures include qualitative and quantitative requirements, providing additional information about the amounts recorded in the financial statements. Upon transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. Key has formed a cross-functional team to oversee the implementation of this ASU. Implementation efforts are ongoing, including the review of our lease portfolios and related lease accounting policies, the review of our service contracts for embedded leases, and the deployment of a new lease software solution. Key’s adoption of this ASU will result in an increase in right-of-use assets and associated lease liabilities, arising from operating leases in which Key is the lessee, on our Consolidated Balance Sheet. The amount of the right-of-use assets and associated lease liabilities recorded upon adoption will be based primarily on the present value of unpaid future minimum lease payments, the amount of which will depend on the population of leases in effect at the date of adoption. Key’s minimum future rental payments under noncancelable operating leases would be measured and recognized when the new guidance is adopted (refer to Note 22 (“Commitments, Contingent Liabilities, and Guarantees”). While these leases represent a large majority of the leases that are within scope of the new leasing standard, we will continue to review service contracts up through the effective date and may identify additional leases embedded in those arrangements that will be within the scope of the new standard. In addition to final determination of the lease portfolio at the effective date, the initial measurement of the right-of-use asset and the corresponding liability will be affected by certain key assumptions such as expectations of renewals or extensions and the interest rate to be used to discount the future lease obligations. We do not expect the adoption of this guidance to have a material impact on our Consolidated Statements of Income. ASU 2016-13 Measurement of Credit Losses on Financial Instruments January 1, 2020 Early adoption is permitted as of January 1, 2019 The ASU amends ASC Topic 326, Financial Instruments-Credit Losses, and significantly changes how entities will measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The standard replaces today’s “incurred loss” approach with an “expected loss” model for instruments such as loans and HTM securities that are measured at amortized cost. The standard requires credit losses relating to AFS debt securities to be recorded through an allowance rather than a reduction of the carrying amount. It also changes the accounting for purchased credit-impaired debt securities and loans. The ASU retains many of the current disclosure requirements in current GAAP and expands certain disclosure requirements. This new guidance will affect the accounting for our loans, debt securities held to maturity and available for sale, and liabilities for credit losses on unfunded lending-related commitments as well as purchased financial assets with a more-than-insignificant amount of credit deterioration since origination. Key has formed a cross-functional implementation working group comprised of teams throughout Key, including finance and credit. The implementation team has developed a high-level project plan, is identifying and researching key interpretive issues, and is in the process of developing models that meet the requirements of the new guidance. The implementation team is also in the process of assessing forecast accuracy and potential macroeconomic factors that will be used to determine the reasonable and supportable forecast period. Key expects that the new guidance will generally result in an increase in its allowance for credit losses, as it will cover credit losses over the full remaining expected life of loans and commitments and will consider future changes in macroeconomic conditions. Since the magnitude of the anticipated increase in the allowance for credit losses will be impacted by economic conditions and trends in the Company’s portfolio at the time of adoption, the quantitative impact cannot yet be reasonably estimated. Standard Required Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments. January 1, 2018 Early adoption is permitted The ASU amends ASC Topic 230, Statement of Cash Flows , and clarifies how cash receipts and cash payments in certain transactions should be presented and classified in the statement of cash flows. These specific transactions include, but are not limited to, debt prepayment or extinguishment costs, contingent considerations made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, and distributions from equity method investees. This guidance also clarifies that in instances of cash flows with multiple aspects that cannot be separately identified, classification should be based on the activity that is likely to be the predominant source of or use of cash flow. The guidance should be implemented using a retrospective approach. The adoption of this accounting guidance will not have a material effect on the presentation of our Consolidated Statements of Cash Flows, as Key’s current policies are either already in-line with the clarifications in the updated guidance, or the related cash flows are not material. ASU 2017-04, Simplifying the Test for Goodwill Impairment January 1, 2020 Early adoption is permitted The ASU amends ASC Topic 350, Intangibles - Goodwill and Other and eliminates the second step of the test for goodwill impairment. Under the new guidance, entities will compare the fair value of a reporting unit with its carrying amount. If the carrying amount exceeds the reporting unit’s fair value, the entity is required to recognize an impairment charge for this amount. The new method applies to all reporting units and the performance of a qualitative assessment is still allowable. The guidance should be implemented using a prospective approach. The adoption of this accounting guidance is not expected to have a material effect on our financial condition or results of operations. ASU 2017-05, Other Income- Gains and Losses from the Derecognition of Nonfinancial Assets January 1, 2018 Early adoption is permitted The ASU amends ASC Topic 610-20, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets to clarify the scope of the Topic by clarifying the definition of the term "in substance nonfinancial asset" and also adding guidance for partial sales of nonfinancial assets. Under the new guidance, an entity will derecognize a nonfinancial asset when it does not have or ceases to have a controlling interest in the legal entity that holds the asset and when control of the asset has transferred in accordance with ASC 606. The ASU can be adopted on a retrospective or modified retrospective approach. The adoption of this guidance will not have a material effect on our financial condition or results of operations. ASU 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost January 1, 2018 Early adoption is permitted within the first interim period if the entity issues interim financial statements. The ASU amends ASC Topic 715, Compensation - Retirement Benefits , and requires service costs to be included in the same line item as certain other compensation costs related to services rendered by employees. We record compensation costs under personnel expense on the income statement. Other elements of net benefit cost should be presented separately. The guidance should be implemented on a retrospective basis. The adoption of this guidance will result in a reclassification of certain net benefit cost components from personnel expense to other expense on the income statement. There will be no material effect on our financial condition or results of operations. ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities January 1, 2019 Early adoption is permitted. The ASU amends ASC Topic 310-20, Receivables — Nonrefundable Fees and Other Costs , and shortens the amortization period to the earliest call date for certain callable debt securities held at a premium. Securities held at a discount will continue to be amortized to maturity. The guidance should be implemented on a modified retrospective basis using a cumulative-effect adjustment. The adoption of this guidance is not expected to have a material effect on our financial condition or results of operations. ASU 2017-09, Scope of Modification Accounting January 1, 2018 Early adoption is permitted, including interim periods. The ASU amends ASC Topic 718, Compensation - Stock Compensation , and clarifies when changes to terms and conditions for share-based payment awards should be accounted for as modifications. Under the new guidance, entities should apply the modification guidance unless the fair value of the modified award is the same as the fair value of the original award immediately before modification, the vesting conditions of the modified award are the same as the vesting conditions of the original award immediately before modification, and the classification of the modified award (as equity or liability instrument) is the same as the classification of the original award immediately before modification. The guidance should be applied on a prospective basis. The adoption of this guidance will not have a material effect on our financial condition or results of operations. Standard Required Adoption Description Effect on Financial Statements or Other Significant Matters ASU 2017-01, Clarifying the Definition of a Business January 1, 2018 Early application is allowed for certain transactions. The ASU amends Topic 805, Business Combinations, and clarifies the definition of a business and removes the requirement for a market participant to consider whether it could replace missing elements in an integrated set of assets and activities. The guidance states that if substantially all of the fair value of the assets acquired or disposed of is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. The guidance should be implemented using a prospective approach. The adoption of this guidance will not have a material effect on our financial condition or results of operations. ASU 2017-12, Targeted Improvements to Accounting for Hedging Activities January 1, 2019 Early adoption is permitted, including interim periods. Key anticipates early adopting this standard as of January 1, 2018. The ASU amends ASC Topic 815, Derivatives and Hedging , to simplify the requirements for hedge accounting and facilitate financial reporting that more closely aligns with an entity’s risk management activities. Key amendments include: eliminating the requirement to separately measure and report hedge ineffectiveness, requiring changes in the value of the hedging instrument to be presented in the same income statement line as the earnings effect of the hedged item, and the ability to measure the hedged item based on the benchmark interest rate component of the total contractual coupon for fair value hedges. Additional disclosures are also required for reporting periods subsequent to the date of adoption. The guidance should be implemented on a modified retrospective basis to existing hedge relationships as of the adoption date. We will adopt this ASU in the first quarter of 2018. Our financial statements for the quarter ended March 31, 2018, will include a cumulative-effect adjustment to opening retained earnings to reflect the application of the new guidance as of January 1, 2018. The primary impact to Key at adoption is the election to measure the change in fair value of the hedged item in fair value hedges on the basis of the benchmark interest rate component of contractual coupon cash flows. The cumulative-effect entry at adoption will reflect a cumulative basis adjustment for existing fair value hedges to be under the benchmark component approach. We expect adoption of this ASU to reduce hedge ineffectiveness going forward; however, we do not anticipate this guidance to have a material effect on our financial condition and results of operations.

Business Combination (Tables)

Business Combination (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Schedule of Purchase Price Calculation and Identifiable Assets Purchased and Liabilities Assumed	The following table provides the final purchase price calculation as of the Acquisition Date and the identifiable assets purchased and the liabilities assumed at their estimated fair value. These fair value measurements are based on internal and third-party valuations. in millions Consideration paid: KeyCorp common stock issued $ 2,831 Cash payments to First Niagara stockholders 811 Exchange of First Niagara preferred stock for KeyCorp preferred stock 350 Total consideration paid $ 3,992 Statement of Net Assets Acquired at Fair Value: ASSETS Cash and due from banks and short-term investments $ 620 Investment securities 9,012 Other investments 297 Loans 23,590 Premises and equipment 245 Other intangible assets 385 Accrued income and other assets 1,467 Total assets $ 35,616 LIABILITIES Deposits $ 28,994 Bank notes and other short-term borrowings 2,698 Accrued expense and other liabilities 490 Long-term debt 846 Total liabilities $ 33,028 Net identifiable assets acquired 2,588 Goodwill $ 1,404 The amounts reflected in the following table represent the change in the fair values of acquired assets as of June 30, 2017: in millions Acquired Asset or Liability Balance Sheet Line Item Provisional Estimate Final Increase (Decrease) Loans Loans $ 23,645 $ 23,590 $ (55 ) Tax adjustment on previous fair value measurement Accrued income and other assets 1,449 1,467 18 Unfunded lending-related commitments Accrued expense and other liabilities 67 65 (2 ) Deferred compensation Accrued expense and other liabilities 39 41 2 The amounts shown in the table below represent the increase (decrease) in the respective line items for the previous reporting period had the final fair value been recorded at the Acquisition Date for the twelve months ended December 31, 2017. in millions Portion Related to Acquired Asset or Liability Income Statement Line Item Previous Reporting Period (a) Loans Interest income $ 42 Loans Provision for credit losses 1 Loans Other noninterest income (3 ) Unfunded lending-related commitments Other noninterest income (4 ) (a) Represents the change in amount that should have been reported compared to what was actually reported in the December 31, 2016, Consolidated Statements of Income.
Schedule of Changes in Goodwill by Reporting Unit	The following table shows the changes in the carrying amount of goodwill by reporting unit. in millions Key Community Bank Key Corporate Bank Total BALANCE AT DECEMBER 31, 2015 $ 979 $ 81 $ 1,060 Acquisition of First Niagara 1,109 277 1,386 BALANCE AT DECEMBER 31, 2016 2,088 358 2,446 Tax adjustment on previous fair value measurements (15 ) (4 ) (19 ) Loan adjustment on previous fair value measurements 30 7 37 BALANCE AT JUNE 30, 2017 $ 2,103 $ 361 $ 2,464 Changes in the carrying amount of goodwill by reporting unit are presented in the following table: in millions Key Community Bank Key Corporate Bank Total BALANCE AT DECEMBER 31, 2015 $ 979 $ 81 $ 1,060 Acquisition of First Niagara 1,109 277 1,386 BALANCE AT DECEMBER 31, 2016 2,088 358 2,446 Fair value measurement adjustments - First Niagara acquisition 15 3 18 Additional ownership interest in Key Merchant Services 4 — 4 Acquisition of HelloWallet 17 — 17 Acquisition of Cain Brothers — 53 53 BALANCE AT DECEMBER 31, 2017 $ 2,124 $ 414 $ 2,538
Schedule of Operations Included in Consolidated Statement of Income and Unaudited Pro Forma Information	The following table presents unaudited pro forma information as if the acquisition of First Niagara had occurred on January 1, 2015. This pro forma information gives effect to certain adjustments, including purchase accounting fair value adjustments, amortization of core deposit and other intangibles, and related income tax effects. Merger-related charges related to the First Niagara merger that we incurred during the twelve months ended December 31, 2016 , and 2015, are not reflected in the unaudited pro forma amounts. The pro forma information does not necessarily reflect the results of operations that would have occurred had KeyCorp merged with First Niagara at the beginning of 2015. Cost savings are also not reflected in the unaudited pro forma amounts for the twelve months ended December 31, 2016 , and 2015. Pro forma Twelve months ended December 31, in millions 2016 2015 Net interest income (TE) $ 3,599 $ 3,564 Noninterest income 2,231 2,206 Net income (loss) attributable to common shareholders 1,161 1,187

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Basic and Diluted Earnings Per Common Share	Our basic and diluted earnings per Common Share are calculated as follows: Year ended December 31, dollars in millions, except per share amounts 2017 2016 2015 EARNINGS Income (loss) from continuing operations $ 1,291 $ 789 $ 919 Less: Net income (loss) attributable to noncontrolling interests 2 (1 ) 4 Income (loss) from continuing operations attributable to Key 1,289 790 915 Less: Dividends on preferred stock 70 37 23 Income (loss) from continuing operations attributable to Key common shareholders 1,219 753 892 Income (loss) from discontinued operations, net of taxes 7 1 1 Net income (loss) attributable to Key common shareholders $ 1,226 $ 754 $ 893 WEIGHTED-AVERAGE COMMON SHARES Weighted-average Common Shares outstanding (000) 1,072,078 927,816 836,846 Effect of convertible preferred stock — — — Effect of common share options and other stock awards 16,515 10,720 7,643 Weighted-average common shares and potential Common Shares outstanding (000) (a) 1,088,593 938,536 844,489 EARNINGS PER COMMON SHARE Income (loss) from continuing operations attributable to Key common shareholders $ 1.13 $ .81 $ 1.06 Income (loss) from discontinued operations, net of taxes .01 — — Net income (loss) attributable to Key common shareholders (b) 1.14 .81 1.06 Income (loss) from continuing operations attributable to Key common shareholders — assuming dilution 1.12 .80 1.05 Income (loss) from discontinued operations, net of taxes .01 — — Net income (loss) attributable to Key common shareholders — assuming dilution (b) 1.13 .80 1.05 (a) Assumes conversion of Common Share options and other stock awards and/or convertible preferred stock, as applicable. (b) EPS may not foot due to rounding.

Loans and Loans Held for Sale (

Loans and Loans Held for Sale (Tables)	12 Months Ended
	Dec. 31, 2017
Loans Receivables [Abstract]
Loans by Category	Our loans by category are summarized as follows: December 31, in millions 2017 2016 Commercial and industrial (a) $ 41,859 $ 39,768 Commercial real estate: Commercial mortgage 14,088 15,111 Construction 1,960 2,345 Total commercial real estate loans 16,048 17,456 Commercial lease financing (b) 4,826 4,685 Total commercial loans 62,733 61,909 Residential — prime loans: Real estate — residential mortgage 5,483 5,547 Home equity loans 12,028 12,674 Total residential — prime loans 17,511 18,221 Consumer direct loans 1,794 1,788 Credit cards 1,106 1,111 Consumer indirect loans 3,261 3,009 Total consumer loans 23,672 24,129 Total loans (c), (d) $ 86,405 $ 86,038 (a) Loan balances include $119 million and $116 million of commercial credit card balances at December 31, 2017 , and December 31, 2016 , respectively. (b) Commercial lease financing includes receivables of $24 million and $68 million held as collateral for a secured borrowing at December 31, 2017 , and December 31, 2016 , respectively. Principal reductions are based on the cash payments received from these related receivables. Additional information pertaining to this secured borrowing is included in Note 20 (“ Long-Term Debt ”). (c) At December 31, 2017 , total loans include purchased loans of $15.4 billion , of which $738 million were purchased credit impaired. At December 31, 2016 , total loans include purchased loans of $21.0 billion , of which $865 million were purchased credit impaired. (d) Total loans exclude loans in the amount of $1.3 billion at December 31, 2017 , and $1.6 billion at December 31, 2016 , related to the discontinued operations of the education lending business.
Loans Held for Sale	Our loans held for sale by category are summarized as follows: December 31, in millions 2017 2016 Commercial and industrial $ 139 $ 19 Real estate — commercial mortgage 897 1,022 Real estate — construction — 1 Real estate — residential mortgage (a) 71 62 Total loans held for sale $ 1,107 $ 1,104 (a) Real estate — residential mortgage loans held for sale at fair value at December 31, 2017 . The fair value option was elected for real estate — residential mortgage loans held for sale during the third quarter of 2016 with the First Niagara acquisition. The contractual amount due on these loans totaled $71 million at December 31, 2017 and $62 million at December 31, 2016 . Changes in fair value are recorded in "Consumer mortgage income" on the income statement. Additional information regarding residential mortgage loans held for sale fair value methodology is provided in Note 7 (“ Fair Value Measurements ”).
Summary of Changes in Loans Held for Sale	Our summary of changes in loans held for sale follows: Year ended December 31, in millions 2017 2016 Balance at beginning of the period $ 1,104 $ 639 Purchases — 48 New originations 11,860 8,356 Transfers from (to) held to maturity, net (63 ) 35 Loan sales (11,780 ) (7,979 ) Loan draws (payments), net (14 ) 5 Balance at end of period (a) $ 1,107 $ 1,104 (a) Total loans held for sale include Real Estate - residential mortgage loans held for sale at fair value of $71 million at December 31, 2017 .
Composition of Net Investment in Direct Financing Leases	The composition of the net investment in direct financing leases is as follows: December 31, in millions 2017 2016 Direct financing lease receivables $ 3,727 $ 3,468 Unearned income (323 ) (278 ) Unguaranteed residual value 382 316 Deferred fees and costs 19 16 Net investment in direct financing leases $ 3,805 $ 3,522

Asset Quality (Tables)

Asset Quality (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Financing Receivable Credit Quality Indicators	Commercial Credit Exposure — Excluding PCI Credit Risk Profile by Creditworthiness Category (a), (b) December 31, in millions Commercial and industrial RE — Commercial RE — Construction Commercial Lease Total RATING 2017 2016 2017 2016 2017 2016 2017 2016 2017 2016 Pass $ 39,833 $ 37,845 $ 13,328 $ 14,308 $ 1,894 $ 2,287 $ 4,730 $ 4,632 $ 59,785 $ 59,072 Criticized (Accruing) 1,790 1,514 482 455 38 30 90 45 2,400 2,044 Criticized (Nonaccruing) 153 297 30 26 2 2 6 8 191 333 Total $ 41,776 $ 39,656 $ 13,840 $ 14,789 $ 1,934 $ 2,319 $ 4,826 $ 4,685 $ 62,376 $ 61,449 (a) Credit quality indicators are updated on an ongoing basis and reflect credit quality information as of the dates indicated. (b) The term criticized refers to those loans that are internally classified by Key as special mention or worse, which are asset quality categories defined by regulatory authorities. These assets have an elevated level of risk and may have a high probability of default or total loss. Pass rated refers to all loans not classified as criticized. Consumer Credit Exposure — Excluding PCI Non-PCI Loans by Refreshed FICO Score (a) December 31, in millions Residential — Prime Consumer direct loans Credit cards Consumer indirect loans Total FICO SCORE 2017 2016 2017 2016 2017 2016 2017 2016 2017 2016 750 and above $ 10,226 $ 9,818 $ 519 $ 498 $ 477 $ 453 $ 1,472 $ 1,266 $ 12,694 $ 12,035 660 to 749 5,181 5,266 690 661 508 525 1,184 1,195 7,563 7,647 Less than 660 1,519 1,617 225 194 121 132 529 543 2,394 2,486 No Score 208 1,122 356 428 — 1 76 5 640 1,556 Total $ 17,134 $ 17,823 $ 1,790 $ 1,781 $ 1,106 $ 1,111 $ 3,261 $ 3,009 $ 23,291 $ 23,724 (a) Borrower FICO scores provide information about the credit quality of our consumer loan portfolio as they provide an indication as to the likelihood that a debtor will repay their debts. The scores are obtained from a nationally recognized consumer rating agency and are presented in the above table at the dates indicated. Commercial Credit Exposure — PCI Credit Risk Profile by Creditworthiness Category (a), (b) December 31, in millions Commercial and industrial RE — Commercial RE — Construction Commercial Lease Total RATING 2017 2016 2017 2016 2017 2016 2017 2016 2017 2016 Pass $ 41 $ 12 $ 153 $ 139 $ 26 $ 21 — — $ 220 $ 172 Criticized 42 100 95 183 — 5 — — 137 288 Total $ 83 $ 112 $ 248 $ 322 $ 26 $ 26 — — $ 357 $ 460 (a) Credit quality indicators are updated on an ongoing basis and reflect credit quality information as of the dates indicated. (b) The term criticized refers to those loans that are internally classified by Key as special mention or worse, which are asset quality categories defined by regulatory authorities. These assets have an elevated level of risk and may have a high probability of default or total loss. Pass rated refers to all loans not classified as criticized. Consumer Credit Exposure — PCI PCI Loans by Refreshed FICO Score (a) December 31, in millions Residential — Prime Consumer direct loans Credit cards Consumer indirect loans Total FICO SCORE 2017 2016 2017 2016 2017 2016 2017 2016 2017 2016 750 and above $ 149 $ 133 — — — — — — $ 149 $ 133 660 to 749 117 127 $ 2 $ 2 — — — — 119 129 Less than 660 105 133 2 4 — — — — 107 137 No Score 6 5 — 1 — — — — 6 6 Total $ 377 $ 398 $ 4 $ 7 — — — — $ 381 $ 405 (a) Borrower FICO scores provide information about the credit quality of our consumer loan portfolio as they provide an indication as to the likelihood that a debtor will repay their debts. The scores are obtained from a nationally recognized consumer rating agency and are presented in the above table at the dates indicated.
Past Due Loans Including Current Loans	The following aging analysis of current and past due loans as of December 31, 2017 , and December 31, 2016 , provides further information regarding Key’s credit exposure. Aging Analysis of Loan Portfolio (a) December 31, 2017 Current 30-59 Days Past Due (b) 60-89 Days Past Due (b) 90 and Greater Days Past Due (b) Non-performing Loans Total Past Due and Non-performing Loans Purchased Credit Impaired Total Loans (c), (d) in millions LOAN TYPE Commercial and industrial $ 41,444 $ 111 $ 34 $ 34 $ 153 $ 332 $ 83 $ 41,859 Commercial real estate: Commercial mortgage 13,750 26 13 21 30 90 248 14,088 Construction 1,919 4 9 — 2 15 26 1,960 Total commercial real estate loans 15,669 30 22 21 32 105 274 16,048 Commercial lease financing 4,791 23 4 2 6 35 — 4,826 Total commercial loans $ 61,904 $ 164 $ 60 $ 57 $ 191 $ 472 $ 357 $ 62,733 Real estate — residential mortgage $ 5,043 $ 16 $ 7 $ 4 $ 58 $ 85 $ 355 $ 5,483 Home equity loans 11,721 32 15 9 229 285 22 12,028 Consumer direct loans 1,768 9 4 5 4 22 4 1,794 Credit cards 1,081 7 5 11 2 25 — 1,106 Consumer indirect loans 3,199 33 7 3 19 62 — 3,261 Total consumer loans $ 22,812 $ 97 $ 38 $ 32 $ 312 $ 479 $ 381 $ 23,672 Total loans $ 84,716 $ 261 $ 98 $ 89 $ 503 $ 951 $ 738 $ 86,405 (a) Amounts in table represent recorded investment and exclude loans held for sale. Recorded investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. (b) Past due loan amounts exclude purchased impaired loans, even if contractually past due (or if we do not expect to collect principal or interest in full based on the original contractual terms), as we are currently accreting income over the remaining term of the loans. (c) Net of unearned income, net deferred loan fees and costs, and unamortized discounts and premiums. (d) Future accretable yield related to purchased credit impaired loans is not included in the analysis of the loan portfolio. December 31, 2016 Current 30-59 Days Past Due (b) 60-89 Days Past Due (b) 90 and Greater Days Past Due (b) Non-performing Loans Total Past Due and Non-performing Loans Purchased Credit Impaired Total Loans (c), (d) in millions LOAN TYPE Commercial and industrial $ 39,242 $ 58 $ 28 $ 31 $ 297 $ 414 $ 112 $ 39,768 Commercial real estate: Commercial mortgage 14,655 93 9 6 26 134 322 15,111 Construction 2,314 — — 2 3 5 26 2,345 Total commercial real estate loans 16,969 93 9 8 29 139 348 17,456 Commercial lease financing 4,641 28 3 5 8 44 — 4,685 Total commercial loans $ 60,852 $ 179 $ 40 $ 44 $ 334 $ 597 $ 460 $ 61,909 Real estate — residential mortgage $ 5,098 $ 17 $ 5 $ 3 $ 56 $ 81 $ 368 $ 5,547 Home equity loans 12,327 49 29 16 223 317 30 12,674 Consumer direct loans 1,705 44 15 11 6 76 7 1,788 Credit cards 1,082 9 6 12 2 29 — 1,111 Consumer indirect loans 2,993 7 4 1 4 16 — 3,009 Total consumer loans $ 23,205 $ 126 $ 59 $ 43 $ 291 $ 519 $ 405 $ 24,129 Total loans $ 84,057 $ 305 $ 99 $ 87 $ 625 $ 1,116 $ 865 $ 86,038 (a) Amounts in table represent recorded investment and exclude loans held for sale. Recorded investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. (b) Past due loan amounts exclude purchased impaired loans, even if contractually past due (or if we do not expect to collect principal or interest in full based on the original contractual terms), as we are currently accreting income over the remaining term of the loans. (c) Net of unearned income, net deferred loan fees and costs, and unamortized discounts and premiums. (d) Future accretable yield related to purchased credit impaired loans is not included in the analysis of the loan portfolio.
Breakdown of Individually Impaired Loans	The following tables set forth a further breakdown of individually impaired loans for the periods indicated are as follows: December 31, 2017 Recorded Investment (a) Unpaid Principal Balance (b) Specific Allowance (c) in millions With no related allowance recorded: Commercial and industrial $ 126 $ 153 — Commercial real estate: Commercial mortgage 12 18 — Construction — — — Total commercial real estate loans 12 18 — Total commercial loans 138 171 — Real estate — residential mortgage 17 17 — Home equity loans 56 56 — Consumer indirect loans 2 2 — Total consumer loans 75 75 — Total loans with no related allowance recorded 213 246 — With an allowance recorded: Commercial and industrial 10 28 $ 6 Commercial real estate: Commercial mortgage — — — Total commercial real estate loans — — — Total commercial loans 10 28 6 Real estate — residential mortgage 32 32 5 Home equity loans 61 61 9 Consumer direct loans 4 4 — Credit cards 2 2 — Consumer indirect loans 32 32 3 Total consumer loans 131 131 17 Total loans with an allowance recorded 141 159 23 Total $ 354 $ 405 $ 23 (a) The Recorded Investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. This amount is a component of total loans on our consolidated balance sheet. (b) The Unpaid Principal Balance represents the customer’s legal obligation to us. (c) See Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Impaired Loans” for a description of the specific allowance methodology. December 31, 2016 Recorded Investment (a) Unpaid Principal Balance (b) Specific Allowance (c) in millions With no related allowance recorded: Commercial and industrial $ 222 $ 301 — Commercial real estate: Commercial mortgage 2 3 — Total commercial real estate loans 2 3 — Total commercial loans 224 304 — Real estate — residential mortgage 20 20 — Home equity loans 61 61 — Consumer indirect loans 1 1 — Total consumer loans 82 82 — Total loans with no related allowance recorded 306 386 — With an allowance recorded: Commercial and industrial 62 73 $ 17 Commercial real estate: Commercial mortgage 4 4 — Total commercial real estate loans 4 4 — Total commercial loans 66 77 17 Real estate — residential mortgage 31 31 2 Home equity loans 64 64 18 Consumer direct loans 2 3 — Credit cards 3 3 — Consumer indirect loans 29 29 1 Total consumer loans 129 130 21 Total loans with an allowance recorded 195 207 38 Total $ 501 $ 593 $ 38 (a) The Recorded Investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. This amount is a component of total loans on our consolidated balance sheet. (b) The Unpaid Principal Balance represents the customer’s legal obligation to us. (c) See Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Impaired Loans” for a description of the specific allowance methodology. The following table sets forth a further breakdown of average individually impaired loans reported by Key: Average Recorded Investment (a) Twelve Months Ended December 31, in millions 2017 2016 2015 Commercial and industrial $ 210 $ 176 $ 56 Commercial real estate: Commercial mortgage 9 8 15 Construction — 3 7 Total commercial real estate loans 9 11 22 Total commercial loans 219 187 78 Real estate — residential mortgage 50 53 55 Home equity loans 121 125 122 Consumer direct loans 3 3 4 Credit cards 3 3 4 Consumer indirect loans 32 34 42 Total consumer loans 209 218 227 Total $ 428 $ 405 $ 305 (a) The Recorded Investment represents the face amount of the loan increased or decreased by applicable accrued interest, net deferred loan fees and costs, and unamortized premium or discount, and reflects direct charge-offs. This amount is a component of total loans on our consolidated balance sheet.
Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs	The following table shows the period-end post-modification outstanding recorded investment by concession type for our commercial and consumer accruing and nonaccruing TDRs added during the periods indicated: Twelve Months Ended December 31, in millions 2017 2016 2015 Commercial loans: Interest rate reduction — — — Forgiveness of principal — — $ 22 Extension of maturity date $ 12 — 21 Payment or covenant modification/deferment 46 $ 19 — Bankruptcy plan modification 31 18 — Total $ 89 $ 37 $ 43 Consumer loans: Interest rate reduction $ 13 $ 10 $ 19 Forgiveness of principal — 3 4 Other 28 21 17 Total $ 41 $ 34 $ 40 Total commercial and consumer TDRs $ 130 $ 71 $ 83
Summary Of Post-Modification Outstanding Recorded Investment, Accruing And Nonaccruing TDRs	The following table summarizes the change in the post-modification outstanding recorded investment of our accruing and nonaccruing TDRs during the periods indicated: Year ended December 31, in millions 2017 2016 Balance at beginning of the period $ 280 $ 280 Additions 165 107 Payments (111 ) (68 ) Charge-offs (17 ) (39 ) Balance at end of period (a) $ 317 $ 280
Breakdown of Nonperforming TDRs by Loans Category	A further breakdown of TDRs included in nonperforming loans by loan category for the periods indicated are as follows: December 31, 2017 Number of Loans Pre-modification Outstanding Recorded Investment Post-modification Outstanding Recorded Investment dollars in millions LOAN TYPE Nonperforming: Commercial and industrial 20 $ 109 $ 86 Commercial real estate: Real estate — commercial mortgage 8 16 12 Total commercial real estate loans 8 16 12 Total commercial loans 28 125 98 Real estate — residential mortgage 308 18 18 Home equity loans 1,025 64 57 Consumer direct loans 114 2 2 Credit cards 322 2 1 Consumer indirect loans 825 16 13 Total consumer loans 2,594 102 91 Total nonperforming TDRs 2,622 227 189 Prior-year accruing: (a) Commercial and industrial 4 30 13 Total commercial loans 4 30 13 Real estate — residential mortgage 484 31 31 Home equity loans 1,276 75 59 Consumer direct loans 48 3 2 Credit cards 430 1 1 Consumer indirect loans 320 31 22 Total consumer loans 2,558 141 115 Total prior-year accruing TDRs 2,562 171 128 Total TDRs 5,184 $ 398 $ 317 (a) All TDRs that were restructured prior to January 1, 2017 , and are fully accruing. December 31, 2016 Number of Loans Pre-modification Outstanding Recorded Investment Post-modification Outstanding Recorded Investment dollars in millions LOAN TYPE Nonperforming: Commercial and industrial 18 $ 91 $ 50 Commercial real estate: Real estate — commercial mortgage 7 2 1 Total commercial real estate loans 7 2 1 Total commercial loans 25 93 51 Real estate — residential mortgage 264 16 16 Home equity loans 1,199 77 69 Consumer direct loans 32 1 — Credit cards 336 2 2 Consumer indirect loans 124 4 3 Total consumer loans 1,955 100 90 Total nonperforming TDRs 1,980 193 141 Prior-year accruing: (a) Commercial and industrial 5 30 16 Total commercial loans 5 30 16 Real estate — residential mortgage 477 35 35 Home equity loans 1,231 70 57 Consumer direct loans 35 2 2 Credit cards 410 3 1 Consumer indirect loans 377 56 28 Total consumer loans 2,530 166 123 Total prior-year accruing TDRs 2,535 196 139 Total TDRs 4,515 $ 389 $ 280 (a) All TDRs that were restructured prior to January 1, 2016 , and are fully accruing.
Summary of Allowance for Loan and Lease Losses	A summary of the changes in the ALLL for the periods indicated is presented in the table below: December 31, in millions 2017 2016 2015 Balance at beginning of period — continuing operations $ 858 $ 796 $ 794 Charge-offs (302 ) (261 ) (203 ) Recoveries 94 56 61 Net loans and leases charged off (208 ) (205 ) (142 ) Provision for loan and lease losses from continuing operations 227 267 145 Foreign currency translation adjustment — — (1 ) Balance at end of period — continuing operations $ 877 $ 858 $ 796
Changes in Allowance for Loan and Lease Losses by Loan Category	The changes in the ALLL by loan category for the periods indicated are as follows: in millions December 31, 2016 Provision Charge-offs Recoveries December 31, 2017 Commercial and industrial $ 508 $ 114 $ (133 ) $ 40 $ 529 Real estate — commercial mortgage 144 (2 ) (11 ) 2 133 Real estate — construction 22 9 (2 ) 1 30 Commercial lease financing 42 9 (14 ) 6 43 Total commercial loans 716 130 (160 ) 49 735 Real estate — residential mortgage 17 (11 ) (3 ) 4 7 Home equity loans 54 4 (30 ) 15 43 Consumer direct loans 24 32 (34 ) 6 28 Credit cards 38 45 (44 ) 5 44 Consumer indirect loans 9 27 (31 ) 15 20 Total consumer loans 142 97 (142 ) 45 142 Total ALLL — continuing operations 858 227 (a) (302 ) 94 877 Discontinued operations 24 10 (26 ) 8 16 Total ALLL — including discontinued operations $ 882 $ 237 $ (328 ) $ 102 $ 893 (a) Excludes a provision for losses on lending-related commitments of $2 million . in millions December 31, 2015 Provision Charge-offs Recoveries December 31, 2016 Commercial and industrial $ 450 $ 165 $ (118 ) $ 11 $ 508 Real estate — commercial mortgage 134 6 (5 ) 9 144 Real estate — construction 25 4 (9 ) 2 22 Commercial lease financing 47 4 (12 ) 3 42 Total commercial loans 656 179 (144 ) 25 716 Real estate — residential mortgage 18 2 (4 ) 1 17 Home equity loans 57 13 (30 ) 14 54 Consumer direct loans 20 26 (27 ) 5 24 Credit cards 32 37 (35 ) 4 38 Consumer indirect loans 13 10 (21 ) 7 9 Total consumer loans 140 88 (117 ) 31 142 Total ALLL — continuing operations 796 267 (a) (261 ) 56 858 Discontinued operations 28 13 (28 ) 11 24 Total ALLL — including discontinued operations $ 824 $ 280 $ (289 ) $ 67 $ 882 (a) Excludes a credit for losses on lending-related commitments of $1 million . in millions December 31, 2014 Provision Charge-offs Recoveries December 31, 2015 Commercial and industrial $ 391 $ 120 $ (77 ) $ 16 $ 450 Real estate — commercial mortgage 148 (16 ) (4 ) 6 134 Real estate — construction 28 (3 ) (1 ) 1 25 Commercial lease financing 56 (5 ) (11 ) 7 47 Total commercial loans 623 96 (93 ) 30 656 Real estate — residential mortgage 23 (2 ) (6 ) 3 18 Home equity loans 71 7 (32 ) 11 57 Consumer direct loans 22 16 (24 ) 6 20 Credit cards 33 27 (30 ) 2 32 Consumer indirect loans 22 — (18 ) 9 13 Total consumer loans 171 48 (110 ) 31 140 Total ALLL — continuing operations 794 144 (a) (203 ) 61 796 Discontinued operations 29 21 (35 ) 13 28 Total ALLL — including discontinued operations $ 823 $ 165 $ (238 ) $ 74 $ 824 (a) Includes a $1 million foreign currency translation adjustment. Excludes a provision for losses on lending-related commitments of $21 million .
Allowance for Loan and Lease Losses and Corresponding Loan Balances	A breakdown of the individual and collective ALLL and the corresponding loan balances for the periods indicated are as follows: Allowance Outstanding December 31, 2017 Individually Evaluated for Impairment Collectively Evaluated for Impairment Purchased Credit Impaired Loans Individually Evaluated for Impairment Collectively Evaluated for Impairment Purchased Credit Impaired in millions Commercial and industrial $ 6 $ 520 $ 3 $ 41,859 $ 136 $ 41,640 $ 83 Commercial real estate: Commercial mortgage — 131 2 14,088 12 13,828 248 Construction — 30 — 1,960 — 1,934 26 Total commercial real estate loans — 161 2 16,048 12 15,762 274 Commercial lease financing — 43 — 4,826 — 4,826 — Total commercial loans 6 724 5 62,733 148 62,228 357 Real estate — residential mortgage 5 2 — 5,483 49 5,079 355 Home equity loans 9 33 1 12,028 117 11,889 22 Consumer direct loans — 28 — 1,794 4 1,786 4 Credit cards — 44 — 1,106 2 1,104 — Consumer indirect loans 3 17 — 3,261 34 3,227 — Total consumer loans 17 124 1 23,672 206 23,085 381 Total ALLL — continuing operations 23 848 6 86,405 354 85,313 738 Discontinued operations 3 13 — 1,314 (a) 21 1,293 (a) — Total ALLL — including discontinued operations $ 26 $ 861 $ 6 $ 87,719 $ 375 $ 86,606 $ 738 (a) Amount includes $2 million of loans carried at fair value that are excluded from ALLL consideration. Allowance Outstanding December 31, 2016 Individually Evaluated for Impairment Collectively Evaluated for Impairment Purchased Credit Impaired Loans Individually Evaluated for Impairment Collectively Evaluated for Impairment Purchased Credit Impaired in millions Commercial and industrial $ 17 $ 486 $ 5 $ 39,768 $ 284 $ 39,372 $ 112 Commercial real estate: Commercial mortgage — 144 — 15,111 5 14,784 322 Construction — 22 — 2,345 — 2,319 26 Total commercial real estate loans — 166 — 17,456 5 17,103 348 Commercial lease financing — 42 — 4,685 — 4,685 — Total commercial loans 17 694 5 61,909 289 61,160 460 Real estate — residential mortgage 2 15 — 5,547 51 5,128 368 Home equity loans 17 37 — 12,674 125 12,519 30 Consumer direct loans — 24 — 1,788 3 1,778 7 Credit cards — 38 — 1,111 3 1,108 — Consumer indirect loans 1 8 — 3,009 30 2,979 — Total consumer loans 20 122 — 24,129 212 23,512 405 Total ALLL — continuing operations 37 816 5 86,038 501 84,672 865 Discontinued operations 2 22 — 1,565 (a) 22 1,543 (a) — Total ALLL — including discontinued operations $ 39 $ 838 $ 5 $ 87,603 $ 523 $ 86,215 $ 865 (a) Amount includes $3 million of loans carried at fair value that are excluded from ALLL consideration.
Changes in Liability for Credit Losses on Lending Related Commitments	Changes in the liability for credit losses on unfunded lending-related commitments are summarized as follows: Year ended December 31, in millions 2017 2016 2015 Balance at beginning of period $ 55 $ 56 $ 35 Provision (credit) for losses on lending-related commitments 2 (1 ) 21 Balance at end of period $ 57 $ 55 $ 56
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period	The following table presents the PCI loans receivable balance at the First Niagara Acquisition Date: August 1, 2016 PCI in millions Contractual required payments receivable $ 1,434 Nonaccretable difference 173 Expected cash flows 1,261 Accretable yield 172 Fair Value $ 1,089
Schedule of Changes in Outstanding Unpaid Principal Balance, Carrying Amount, and Accretable Yield	PCI Loans Twelve Months Ended December 31, 2017 2016 in millions Accretable Yield Carrying Amount Outstanding Unpaid Principal Balance Accretable Yield Carrying Amount Outstanding Unpaid Principal Balance Balance at beginning of period $ 197 $ 865 $ 1,002 $ 5 $ 11 $ 17 Additions (32 ) 205 Accretion (44 ) (29 ) Net reclassifications from non-accretable to accretable 15 35 Payments received, net (4 ) (19 ) Disposals (1 ) — Balance at end of period $ 131 $ 738 $ 803 $ 197 $ 865 $ 1,002

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Values Of Funds And Unfunded Commitments	The following table presents the fair value of our direct and indirect principal investments and related unfunded commitments at December 31, 2017 , as well as financial support provided for the years ended December 31, 2017 , and December 31, 2016 . Financial support provided Year ended December 31, December 31, 2017 2017 2016 in millions Fair Value Unfunded Commitments Funded Commitments Funded Other Funded Commitments Funded Other INVESTMENT TYPE Direct investments (a) $ 13 — — — — $ 13 Indirect investments (b) 124 $ 29 $ 1 — $ 6 — Total $ 137 $ 29 $ 1 — $ 6 $ 13 (a) Our direct investments consist of equity and debt investments directly in independent business enterprises. Operations of the business enterprises are handled by management of the portfolio company. The purpose of funding these enterprises is to provide financial support for business development and acquisition strategies. We infuse equity capital based on an initial contractual cash contribution and later from additional requests on behalf of the companies’ management. (b) Our indirect investments consist of buyout funds, venture capital funds, and fund of funds. These investments are generally not redeemable. Instead, distributions are received through the liquidation of the underlying investments of the fund. An investment in any one of these funds typically can be sold only with the approval of the fund’s general partners. We estimate that the underlying investments of the funds will be liquidated over a period of one to eight years. The purpose of funding our capital commitments to these investments is to allow the funds to make additional follow-on investments and pay fund expenses until the fund dissolves. We, and all other investors in the fund, are obligated to fund the full amount of our respective capital commitments to the fund based on our and their respective ownership percentages, as noted in the applicable Limited Partnership Agreement.
Fair Value of Assets and Liabilities Measured on Recurring Basis	The following tables present these assets and liabilities at December 31, 2017 , and December 31, 2016 . December 31, 2017 Level 1 Level 2 Level 3 Total in millions ASSETS MEASURED ON A RECURRING BASIS Trading account assets: U.S. Treasury, agencies and corporations — $ 615 — $ 615 States and political subdivisions — 37 — 37 Collateralized mortgage obligations — — — — Other mortgage-backed securities — 104 — 104 Other securities — 65 — 65 Total trading account securities — 821 — 821 Commercial loans — 15 — 15 Total trading account assets — 836 — 836 Securities available for sale: U.S. Treasury, agencies and corporations — 157 — 157 States and political subdivisions — 9 — 9 Agency residential collateralized mortgage obligations — 14,660 — 14,660 Agency residential mortgage-backed securities — 1,439 — 1,439 Agency commercial mortgage-backed securities — 1,854 — 1,854 Other securities — — $ 20 20 Total securities available for sale — 18,119 20 18,139 Other investments: Principal investments: Direct — — 13 13 Indirect (measured at NAV) (a) — — — 124 Total principal investments — — 13 137 Equity investments: Direct — 4 3 7 Total equity investments — 4 3 7 Total other investments — 4 16 144 Loans, net of unearned income — — 2 2 Loans held for sale — 70 1 71 Derivative assets: Interest rate — 713 9 722 Foreign exchange $ 100 30 — 130 Commodity — 255 — 255 Credit — — 1 1 Other — 1 3 4 Derivative assets 100 999 13 1,112 Netting adjustments (b) — — — (443 ) Total derivative assets 100 999 13 669 Accrued income and other assets — — — — Total assets on a recurring basis at fair value $ 100 $ 20,028 $ 52 $ 19,861 LIABILITIES MEASURED ON A RECURRING BASIS Bank notes and other short-term borrowings: Short positions $ 72 $ 562 — $ 634 Derivative liabilities: Interest rate — 520 — 520 Foreign exchange 98 26 — 124 Commodity — 246 — 246 Credit — 4 — 4 Other — 13 — 13 Derivative liabilities 98 809 — 907 Netting adjustments (b) — — — (616 ) Total derivative liabilities 98 809 — 291 Accrued expense and other liabilities — — — — Total liabilities on a recurring basis at fair value $ 170 $ 1,371 — $ 925 (a) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheet. (b) Netting adjustments represent the amounts recorded to convert our derivative assets and liabilities from a gross basis to a net basis in accordance with applicable accounting guidance. The net basis takes into account the impact of bilateral collateral and master netting agreements that allow us to settle all derivative contracts with a single counterparty on a net basis and to offset the net derivative position with the related cash collateral. Total derivative assets and liabilities include these netting adjustments. December 31, 2016 Level 1 Level 2 Level 3 Total in millions ASSETS MEASURED ON A RECURRING BASIS Trading account assets: U.S. Treasury, agencies and corporations — $ 655 — $ 655 States and political subdivisions — 8 — 8 Collateralized mortgage obligations — — — — Other mortgage-backed securities — 113 — 113 Other securities — 73 — 73 Total trading account securities — 849 — 849 Commercial loans — 18 — 18 Total trading account assets — 867 — 867 Securities available for sale: U.S. Treasury, agencies and corporations — 184 — 184 States and political subdivisions — 11 — 11 Agency residential collateralized mortgage obligations — 16,408 — 16,408 Agency residential mortgage-backed securities — 1,846 — 1,846 Agency commercial mortgage-backed securities — 1,743 — 1,743 Other securities $ 3 — $ 17 20 Total securities available for sale 3 20,192 17 20,212 Other investments: Principal investments: Direct — — 27 27 Indirect (measured at NAV) (a) — — — 158 Total principal investments — — 27 185 Equity and mezzanine investments: Indirect (measured at NAV) (a) — — — 6 Total equity and mezzanine investments — — — 6 Total other investments — — 27 191 Loans, net of unearned income — — — — Loans held for sale — 62 — 62 Derivative assets: Interest rate — 923 7 930 Foreign exchange 114 9 — 123 Commodity — 176 — 176 Credit — — 1 1 Other — 2 2 4 Derivative assets 114 1,110 10 1,234 Netting adjustments (b) — — — (431 ) Total derivative assets 114 1,110 10 803 Accrued income and other assets — 8 — 8 Total assets on a recurring basis at fair value $ 117 $ 22,239 $ 54 $ 22,143 LIABILITIES MEASURED ON A RECURRING BASIS Bank notes and other short-term borrowings: Short positions $ 192 $ 616 — $ 808 Derivative liabilities: Interest rate — 737 — 737 Foreign exchange 102 11 — 113 Commodity — 165 — 165 Credit — 4 — 4 Other — 1 — 1 Derivative liabilities 102 918 — 1,020 Netting adjustments (b) — — — (384 ) Total derivative liabilities 102 918 — 636 Accrued expense and other liabilities — 14 — 14 Total liabilities on a recurring basis at fair value $ 294 $ 1,548 — $ 1,458 (a) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheet. (b) Netting adjustments represent the amounts recorded to convert our derivative assets and liabilities from a gross basis to a net basis in accordance with applicable accounting guidance. The net basis takes into account the impact of bilateral collateral and master netting agreements that allow us to settle all derivative contracts with a single counterparty on a net basis and to offset the net derivative position with the related cash collateral. Total derivative assets and liabilities include these netting adjustments.
Change in Fair Values of Level 3 Financial Instruments	The following table shows the change in the fair values of our Level 3 financial instruments for the years ended December 31, 2017 , and December 31, 2016 . We mitigate the credit risk, interest rate risk, and risk of loss related to many of these Level 3 instruments by using securities and derivative positions classified as Level 1 or Level 2. Level 1 and Level 2 instruments are not included in the following table. Therefore, the gains or losses shown do not include the impact of our risk management activities. in millions Beginning of Period Balance Gains (Losses) included in comprehensive income Gains (Losses) Included in Earnings Purchases Sales Settlements Transfers Other Transfers into Level 3 (e) Transfers out of Level 3 (e) End of Period Balance Unrealized Gains (Losses) Included in Earnings Year ended December 31, 2017 Securities available for sale Other securities $ 17 $ 3 — — — — — — — $ 20 — Other investments Principal investments Direct 27 — $ (6 ) (c) — $ (8 ) — — — — 13 $ (1 ) (c) Equity investments Direct — — — — — — — $ 3 — 3 — Loans held for sale — — — — (3 ) — $ 4 — — 1 — Loans held for investment — — — — — — 2 — — 2 — Derivative instruments (b) Interest rate 7 — (2 ) (d) — — — — 13 (f) $ (9 ) (f) 9 — Credit 1 — (16 ) (d) — — $ 16 — — — 1 — Other (a) 2 — — — — — 1 — — 3 — in millions Beginning of Period Balance Gains (Losses) Included in Earnings Purchases Sales Settlements Transfers Other Transfers into Level 3 (e) Transfers out of Level 3 (e) End of Period Balance Unrealized Gains (Losses) Included in Earnings Year ended December 31, 2016 Securities available for sale Other securities $ 17 — — — — — — — $ 17 — Other investments Principal investments Direct 50 $ 16 (c) — $ (39 ) — — — — 27 $ 2 (c) Other indirect — — — (20 ) — — $ 20 — — (1 ) (c) Derivative instruments (b) Interest rate 16 4 (d) $ 1 — — — 9 (f) $ (23 ) (f) 7 — Credit 1 (13 ) (d) 1 — $ 12 — — — 1 — Other (a) — — 5 — — $ (3 ) — — 2 — (a) Amounts represent Level 3 interest rate lock commitments. (b) Amounts represent Level 3 derivative assets less Level 3 derivative liabilities. (c) Realized and unrealized gains and losses on principal investments are reported in “net gains (losses) from principal investing” on the income statement. Realized and unrealized losses on private equity and mezzanine investments are reported in “other income” on the income statement. (d) Realized and unrealized gains and losses on derivative instruments are reported in “corporate services income” and “other income” on the income statement. (e) Our policy is to recognize transfers into and transfers out of Level 3 as of the end of the reporting period. (f) Certain derivatives previously classified as Level 2 were transferred to Level 3 because Level 3 unobservable inputs became significant. Certain derivatives previously classified as Level 3 were transferred to Level 2 because Level 3 unobservable inputs became less significant.
Assets and Liabilities Measured at Fair Value on Nonrecurring Basis	The following table presents our assets measured at fair value on a nonrecurring basis at December 31, 2017 , and December 31, 2016 : December 31, 2017 December 31, 2016 in millions Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total ASSETS MEASURED ON A NONRECURRING BASIS Impaired loans — — $ 9 $ 9 — — $ 11 $ 11 Loans held for sale (a) — — — — — — — — Accrued income and other assets (b) — $ 5 133 138 — — 11 11 Total assets on a nonrecurring basis at fair value — $ 5 $ 142 $ 147 — — $ 22 $ 22 (a) During 2017 , we transferred $63 million , net, of commercial and residential loans and leases at their current fair value from held-for-sale status to the held-to-maturity portfolio, compared to $35 million , net, during 2016 that was transferred from held-to-maturity to held-for-sale status. (b) At December 31, 2017, we recorded $31 million of impairment related to $119 million of LIHTC and Historic Tax Credit investments impacted by the enactment of the TCJ Act. Refer to the “Other Assets” section below for a description of the valuation technique and inputs applied for this fair value measurement.
Quantitative Information about Level 3 Fair Value Measurements	The range and weighted-average of the significant unobservable inputs used to fair value our material Level 3 recurring and nonrecurring assets at December 31, 2017 , and December 31, 2016 , along with the valuation techniques used, are shown in the following table: December 31, 2017 Fair Value of Level 3 Assets Valuation Technique Significant Unobservable Input Range (Weighted-Average) Dollars in millions Recurring Other investments — principal investments — direct: $ 13 Individual analysis of the condition of each investment Debt instruments EBITDA multiple N/A (6.00) Equity instruments of private companies EBITDA multiple (where applicable) N/A (6.00) Nonrecurring Impaired loans $ 9 Fair value of underlying collateral Discount 00.00 - 50.00% (23.00%) December 31, 2016 Fair Value of Level 3 Assets Valuation Technique Significant Unobservable Input Range (Weighted-Average) dollars in millions Recurring Other investments — principal investments — direct: $ 27 Individual analysis of the condition of each investment Debt instruments EBITDA multiple 6.30 - 7.00 (6.50) Equity instruments of private companies EBITDA multiple (where applicable) N/A (6.3) Nonrecurring Impaired loans (a) $ 11 Fair value of underlying collateral Discount 00.00 - 70.00% (46.00%)
Fair Value Disclosures of Financial Instruments	The levels in the fair value hierarchy ascribed to our financial instruments and the related carrying amounts at December 31, 2017 , and December 31, 2016 , are shown in the following table. December 31, 2017 Fair Value in millions Carrying Amount Level 1 Level 2 Level 3 Measured at NAV Netting Adjustment Total ASSETS Cash and short-term investments (a) $ 5,118 $ 5,118 — — — — $ 5,118 Trading account assets (b) 836 — $ 836 — — — 836 Securities available for sale (b) 18,139 — 18,119 $ 20 — — 18,139 Held-to-maturity securities (c) 11,830 — 11,565 — — — 11,565 Other investments (b) 726 — 4 598 $ 124 — 726 Loans, net of allowance (d) 85,528 — — 84,005 — — 84,005 Loans held for sale (b) 1,107 — 70 1,037 — — 1,107 Derivative assets (b) 669 100 999 13 — $ (443 ) (f) 669 LIABILITIES Deposits with no stated maturity (a) $ 93,588 — $ 93,588 — — — $ 93,588 Time deposits (e) 11,647 — 11,750 — — — 11,750 Short-term borrowings (a) 1,011 $ 72 939 — — — 1,011 Long-term debt (e) 14,333 13,407 1,219 — — — 14,626 Derivative liabilities (b) 291 98 809 — — $ (616 ) (f) 291 December 31, 2016 Fair Value in millions Carrying Amount Level 1 Level 2 Level 3 Measured at NAV Netting Adjustment Total ASSETS Cash and short-term investments (a) $ 3,452 $ 3,452 — — — — $ 3,452 Trading account assets (b) 867 — $ 867 — — — 867 Securities available for sale (b) 20,212 3 20,192 $ 17 — — 20,212 Held-to-maturity securities (c) 10,232 — 10,007 — — — 10,007 Other investments (b) 738 — — 569 $ 164 — 733 Loans, net of allowance (d) 85,180 — — 83,285 — — 83,285 Loans held for sale (b) 1,104 — 62 1,042 — — 1,104 Derivative assets (b) 803 114 1,110 10 — $ (431 ) (f) 803 LIABILITIES Deposits with no stated maturity (a) $ 93,906 — $ 93,906 — — — $ 93,906 Time deposits (e) 10,181 — 10,267 — — — 10,267 Short-term borrowings (a) 2,310 $ 192 2,118 — — — 2,310 Long-term debt (e) 12,384 12,386 304 — — — 12,690 Derivative liabilities (b) 636 102 918 — — $ (384 ) (f) 636 Valuation Methods and Assumptions (a) Fair value equals or approximates carrying amount. The fair value of deposits with no stated maturity does not take into consideration the value ascribed to core deposit intangibles. (b) Information pertaining to our methodology for measuring the fair values of these assets and liabilities is included in the sections entitled “Qualitative Disclosures of Valuation Techniques” and “Assets Measured at Fair Value on a Nonrecurring Basis” in this Note. (c) Fair values of held-to-maturity securities are determined by using models that are based on security-specific details, as well as relevant industry and economic factors. The most significant of these inputs are quoted market prices, interest rate spreads on relevant benchmark securities, and certain prepayment assumptions. We review the valuations derived from the models to ensure they are reasonable and consistent with the values placed on similar securities traded in the secondary markets. (d) The fair value of loans is based on the present value of the expected cash flows. The projected cash flows are based on the contractual terms of the loans, adjusted for prepayments and use of a discount rate based on the relative risk of the cash flows, taking into account the loan type, maturity of the loan, liquidity risk, servicing costs, and a required return on debt and capital. In addition, an incremental liquidity discount is applied to certain loans, using historical sales of loans during periods of similar economic conditions as a benchmark. The fair value of loans includes lease financing receivables at their aggregate carrying amount, which is equivalent to their fair value. (e) Fair values of time deposits and long-term debt are based on discounted cash flows utilizing relevant market inputs. (f) Netting adjustments represent the amounts recorded to convert our derivative assets and liabilities from a gross basis to a net basis in accordance with applicable accounting guidance. The net basis takes into account the impact of bilateral collateral and master netting agreements that allow us to settle all derivative contracts with a single counterparty on a net basis and to offset the net derivative position with the related cash collateral. Total derivative assets and liabilities include these netting adjustments.

Securities (Tables)

Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Details of Securities	2017 2016 December 31, in millions Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value SECURITIES AVAILABLE FOR SALE U.S. Treasury, Agencies, and Corporations $ 159 — $ 2 $ 157 $ 188 — $ 4 $ 184 States and political subdivisions 9 — — 9 11 — — 11 Agency residential collateralized mortgage obligations 14,985 $ 10 335 14,660 16,652 $ 31 275 16,408 Agency residential mortgage-backed securities 1,456 3 20 1,439 1,857 6 17 1,846 Agency commercial mortgage-backed securities 1,920 — 66 1,854 1,778 — 35 1,743 Other securities 17 3 — 20 21 — 1 20 Total securities available for sale $ 18,546 $ 16 $ 423 $ 18,139 $ 20,507 $ 37 $ 332 $ 20,212 HELD-TO-MATURITY SECURITIES Agency residential collateralized mortgage obligations $ 8,055 — $ 224 $ 7,831 $ 8,404 $ 1 $ 173 $ 8,232 Agency residential mortgage-backed securities 574 $ 1 4 571 629 — 5 624 Agency commercial mortgage-backed securities 3,186 6 44 3,148 1,184 1 49 1,136 Other securities 15 — — 15 15 — — 15 Total held-to-maturity securities $ 11,830 $ 7 $ 272 $ 11,565 $ 10,232 $ 2 $ 227 $ 10,007
Available for Sale Securities (Unrealized Loss Position)	The following table summarizes our securities that were in an unrealized loss position as of December 31, 2017 , and December 31, 2016 : Duration of Unrealized Loss Position Less than 12 Months 12 Months or Longer Total in millions Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses December 31, 2017 Securities available for sale: U.S. Treasury, Agencies, and Corporations $ 41 — $ 116 $ 2 $ 157 $ 2 States and political subdivisions — — — — — — Agency residential collateralized mortgage obligations 6,153 $ 74 7,270 261 13,423 335 Agency residential mortgage-backed securities 666 7 702 13 1,368 20 Agency commercial mortgage-backed securities 205 4 1,649 62 1,854 66 Other securities — — — — — — Held-to-maturity securities: U.S. Treasury, Agencies, and Corporations — — — — — — States and political subdivisions — — — — — — Agency residential collateralized mortgage obligations 2,201 27 5,599 197 7,800 224 Agency residential mortgage-backed securities 252 1 206 3 458 4 Agency commercial mortgage-backed securities 1,470 12 495 32 1,965 44 Other securities (b) 3 — 4 — 7 — Total temporarily impaired securities $ 10,991 $ 125 $ 16,041 $ 570 $ 27,032 $ 695 December 31, 2016 Securities available for sale: U.S. Treasury, Agencies, and Corporations $ 182 $ 4 — — $ 182 $ 4 Agency residential collateralized mortgage obligations 12,345 231 $ 1,410 $ 44 13,755 275 Agency residential mortgage-backed securities 1,452 17 — — 1,452 17 Agency commercial mortgage-backed securities 1,482 35 — — 1,482 35 Other securities (a) 2 — 3 1 5 1 Held-to-maturity securities: Agency residential collateralized mortgage obligations 7,028 156 518 17 7,546 173 Agency residential mortgage-backed securities 547 5 — — 547 5 Agency commercial mortgage-backed securities 996 49 — — 996 49 Other securities (b) 4 — — — 4 — Total temporarily impaired securities $ 24,038 $ 497 $ 1,931 $ 62 $ 25,969 $ 559 (a) Gross unrealized losses totaled less than $1 million for other securities available for sale at December 31, 2016 . (b) Gross unrealized losses totaled less than $1 million for other securities held to maturity at December 31, 2017 , and December 31, 2016 .
Cumulative Credit Portion of Impairments on Debt Securities	As shown in the following table, we did not have any impairment losses recognized in earnings for the year ended December 31, 2017 . in millions Balance at December 31, 2016 $ 4 Impairment recognized in earnings — Balance at December 31, 2017 $ 4
Available for Sale Securities Realized Gains and Losses	Realized gains and losses related to securities available for sale were as follows: Year ended December 31, in millions 2017 (a) 2016 (b) 2015 Realized gains $ 1 — $ 1 Realized losses — — 1 Net securities gains (losses) $ 1 — — (a) Realized losses totaled less than $1 million for the year ended December 31, 2017 . (b) Realized gains and losses totaled less than $1 million for the year ended December 31, 2016 .
Securities by Maturity	The following table shows securities by remaining maturity. CMOs and other mortgage-backed securities in the available-for-sale and held-to-maturity portfolios are presented based on their expected average lives. The remaining securities, in both the available-for-sale and held-to-maturity portfolios, are presented based on their remaining contractual maturity. Actual maturities may differ from expected or contractual maturities since borrowers have the right to prepay obligations with or without prepayment penalties. Securities Available for Sale Held-to-Maturity Securities December 31, 2017 Amortized Cost Fair Value Amortized Cost Fair Value in millions Due in one year or less $ 190 $ 190 $ 56 $ 56 Due after one through five years 14,990 14,635 7,977 7,776 Due after five through ten years 3,358 3,305 3,190 3,142 Due after ten years 8 9 607 591 Total $ 18,546 $ 18,139 $ 11,830 $ 11,565

Derivatives and Hedging Activ45

Derivatives and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Values, Volume of Activity and Gain (Loss) Information Related to Derivative Instruments	The following table summarizes the fair values of our derivative instruments on a gross and net basis as of December 31, 2017 , and December 31, 2016 . The change in the notional amounts of these derivatives by type from December 31, 2016 , to December 31, 2017 , indicates the volume of our derivative transaction activity during 2017 . The notional amounts are not affected by bilateral collateral and master netting agreements. The derivative asset and liability balances are presented on a gross basis, prior to the application of bilateral collateral and master netting agreements. Total derivative assets and liabilities are adjusted to take into account the impact of legally enforceable master netting agreements that allow us to settle all derivative contracts with a single counterparty on a net basis and to offset the net derivative position with the related cash collateral. Where master netting agreements are not in effect or are not enforceable under bankruptcy laws, we do not adjust those derivative assets and liabilities with counterparties. Securities collateral related to legally enforceable master netting agreements is not offset on the balance sheet. Our derivative instruments are included in “derivative assets” or “derivative liabilities” on the balance sheet, as indicated in the following table: December 31, 2017 December 31, 2016 Fair Value Fair Value in millions Notional Amount Derivative Assets Derivative Liabilities Notional Amount Derivative Assets Derivative Liabilities Derivatives designated as hedging instruments: Interest rate $ 26,176 $ 81 $ 46 $ 24,237 $ 189 $ 94 Foreign exchange 302 1 4 282 6 4 Total 26,478 82 50 24,519 195 98 Derivatives not designated as hedging instruments: Interest rate 61,390 641 474 55,315 741 643 Foreign exchange 8,317 129 120 6,230 117 109 Commodity 1,687 255 246 1,474 176 165 Credit 315 1 4 360 1 4 Other (a) 2,006 4 13 390 4 1 Total 73,715 1,030 857 63,769 1,039 922 Netting adjustments (b) — (443 ) (616 ) — (431 ) (384 ) Net derivatives in the balance sheet 100,193 669 291 88,288 803 636 Other collateral (c) — (5 ) (84 ) — (21 ) (97 ) Net derivative amounts $ 100,193 $ 664 $ 207 $ 88,288 $ 782 $ 539 (a) Other derivatives include interest rate lock commitments and forward sale commitments related to our residential mortgage banking activities, forward purchase and sales contracts consisting of contractual commitments associated with “to be announced” securities and when issued securities, and when-issued security transactions in connection with an “at-the-market” equity offering program. (b) Netting adjustments represent the amounts recorded to convert our derivative assets and liabilities from a gross basis to a net basis in accordance with the applicable accounting guidance. (c) Other collateral represents the amount that cannot be used to offset our derivative assets and liabilities from a gross basis to a net basis in accordance with the applicable accounting guidance. The other collateral consists of securities and is exchanged under bilateral collateral and master netting agreements that allow us to offset the net derivative position with the related collateral. The application of the other collateral cannot reduce the net derivative position below zero. Therefore, excess other collateral, if any, is not reflected above.
Pre-Tax Net Gains (Losses) on Fair Value Hedges	The following table summarizes the pre-tax net gains (losses) on our fair value hedges for the years ended December 31, 2017 , and December 31, 2016 , and where they are recorded on the income statement. Year Ended December 31, 2017 in millions Income Statement Location of Net Gains (Losses) on Derivative Net Gains (Losses) on Derivative Hedged Item Income Statement Location of Net Gains (Losses) on Hedged Item Net Gains (Losses) on Hedged Item Interest rate Other income $ (103 ) Long-term debt Other income $ 107 (a) Interest rate Interest expense – Long-term debt 49 Total $ (54 ) $ 107 Year Ended December 31, 2016 in millions Income Statement Location of Net Gains (Losses) on Derivative Net Gains (Losses) on Derivative Hedged Item Income Statement Location of Net Gains (Losses) on Hedged Item Net Gains (Losses) on Hedged Item Interest rate Other income $ (95 ) Long-term debt Other income $ 97 (a) Interest rate Interest expense – Long-term debt 96 Total $ 1 $ 97 (a) Net gains (losses) on hedged items represent the change in fair value caused by fluctuations in interest rates.
Derivative Instrument Cash Flow Hedge Earning Recognized by Income Statement Location	The following table summarizes the pre-tax net gains (losses) on our cash flow and net investment hedges for the years ended December 31, 2017 , and December 31, 2016 , and where they are recorded on the income statement. The table includes the effective portion of net gains (losses) recognized in OCI during the period, the effective portion of net gains (losses) reclassified from OCI into income during the current period, and the portion of net gains (losses) recognized directly in income, representing the amount of hedge ineffectiveness. Year Ended December 31, 2017 in millions Net Gains (Losses) Recognized in OCI (Effective Portion) Income Statement Location of Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion) Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion) Income Statement Location of Net Gains (Losses) Recognized in Income (Ineffective Portion) Net Gains (Losses) Recognized in Income (Ineffective Portion) Cash Flow Hedges Interest rate $ (59 ) Interest income –Loans $ 19 Other income — Interest rate — Interest expense –Long-term debt (4 ) Other income — Interest rate (1 ) Investment banking and debt placement fees — Other income — Net Investment Hedges Foreign exchange contracts (17 ) Other Income — Other income — Total $ (77 ) $ 15 — Year Ended December 31, 2016 in millions Net Gains (Losses) Recognized in OCI (Effective Portion) Income Statement Location of Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion) Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion) Income Statement Location of Net Gains (Losses) Recognized in Income (Ineffective Portion) Net Gains (Losses) Recognized in Income (Ineffective Portion) Cash Flow Hedges Interest rate $ 29 Interest income – Loans $ 85 Other income — Interest rate — Interest expense – Long-term debt (4 ) Other income — Interest rate 1 Investment banking and debt placement fees — Other income — Net Investment Hedges Foreign exchange contracts (2 ) Other Income — Other income — Total $ 28 $ 81 —
After-Tax Change in AOCI Resulting from Cash Flow Hedges	The after-tax change in AOCI resulting from cash flow and net investment hedges is as follows: December 31, 2017 Hedging Activity Reclassification of Gains to Net Income Reclassification to retained earnings resulting from new federal income tax rate December 31, in millions AOCI resulting from cash flow and net investment hedges $ (14 ) (48 ) (10 ) (14 ) $ (86 )
Pre-Tax Net Gains (Losses) on Derivatives Not Designated as Hedging Instruments	The following table summarizes the pre-tax net gains (losses) on our derivatives that are not designated as hedging instruments for the years ended December 31, 2017 , December 31, 2016 , and December 31, 2015 , and where they are recorded on the income statement. 2017 2016 2015 Year ended December 31, in millions Corporate Services Income Consumer Mortgage Income (a) Other Income Total Corporate Services Income Consumer Mortgage Income (a) Other Income Total Corporate Services Income Other Income Total NET GAINS (LOSSES) Interest rate $ 29 — $ (1 ) $ 28 $ 30 — $ 1 $ 31 $ 28 — $ 28 Foreign exchange 41 — — 41 40 — — 40 36 — 36 Commodity 6 — — 6 4 — — 4 5 — 5 Credit 2 — (21 ) (19 ) 1 — (16 ) (15 ) (1 ) $ (15 ) (16 ) Other — $ (1 ) (6 ) (7 ) — $ 1 — 1 — — — Total net gains (losses) $ 78 $ (1 ) $ (28 ) $ 49 $ 75 $ 1 $ (15 ) $ 61 $ 68 $ (15 ) $ 53 (a) As a result of the First Niagara acquisition, we began recognizing net gains (losses) on other derivatives related to our residential mortgage banking activities in “consumer mortgage income” in 2016.
Fair Value of Derivative Assets by Type	December 31, in millions 2017 2016 Interest rate $ 401 $ 782 Foreign exchange 77 62 Commodity 163 110 Credit 1 — Other 4 4 Derivative assets before collateral 646 958 Less: Related collateral (23 ) 155 Total derivative assets $ 669 $ 803
Fair Value of Credit Derivatives Purchased and Sold	The following table summarizes the fair value of our credit derivatives purchased and sold by type as of December 31, 2017 , and December 31, 2016 . The fair value of credit derivatives presented below does not take into account the effects of bilateral collateral or master netting agreements. December 31, in millions 2017 2016 Purchased Sold Net Purchased Sold Net Single-name credit default swaps $ (1 ) — $ (1 ) $ (2 ) — $ (2 ) Traded credit default swap indices (2 ) — (2 ) (1 ) — (1 ) Other (a) — — — — — — Total credit derivatives $ (3 ) — $ (3 ) $ (3 ) — $ (3 ) (a) As of December 31, 2017 and December 31, 2016 , the fair value of other credit derivatives purchased and sold totaled less than $1 million .
Credit Derivatives Sold and Held	The following table provides information on the types of credit derivatives sold by us and held on the balance sheet at December 31, 2017 , and December 31, 2016 . The notional amount represents the maximum amount that the seller could be required to pay. The payment/performance risk assessment is based on the default probabilities for the underlying reference entities’ debt obligations using a Moody’s credit ratings matrix known as Moody’s “Idealized” Cumulative Default Rates. The payment/performance risk shown in the table represents a weighted-average of the default probabilities for all reference entities in the respective portfolios. These default probabilities are directly correlated to the probability that we will have to make a payment under the credit derivative contracts. 2017 2016 December 31, dollars in millions Notional Amount Average Term (Years) Payment / Performance Risk Notional Amount Average Term (Years) Payment / Performance Risk Other $ 15 3.08 6.64 % $ 4 6.49 17.93 % Total credit derivatives sold $ 15 — — $ 4 — —
Credit Risk Contingent Feature	The following table summarizes the additional cash and securities collateral that KeyBank would have been required to deliver under the ISDA Master Agreements had the credit risk contingent features been triggered for the derivative contracts in a net liability position as of December 31, 2017 , and December 31, 2016 . The additional collateral amounts were calculated based on scenarios under which KeyBank’s ratings are downgraded one, two, or three ratings as of December 31, 2017 , and December 31, 2016 , and take into account all collateral already posted. A similar calculation was performed for KeyCorp, and no additional collateral would have been required at December 31, 2017 , or December 31, 2016 . December 31, in millions 2017 2016 Moody’s S&P Moody’s S&P KeyBank’s long-term senior unsecured credit ratings A3 A- A3 A- One rating downgrade $ 2 $ 2 $ 2 $ 2 Two rating downgrades 2 2 2 2 Three rating downgrades 2 2 2 2

Mortgage Servicing Assets (Tabl

Mortgage Servicing Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Servicing Asset [Abstract]
Changes in Carrying Amount of Mortgage Servicing Assets	Changes in the carrying amount of commercial mortgage servicing assets are summarized as follows: Year ended December 31, in millions 2017 2016 Balance at beginning of period $ 356 $ 322 Servicing retained from loan sales 110 80 Purchases 36 41 Amortization (90 ) (87 ) Balance at end of period $ 412 $ 356 Fair value at end of period $ 537 $ 459 Changes in the carrying amount of residential mortgage servicing assets are summarized as follows: in millions 2017 2016 Balance at beginning of period $ 28 — Servicing retained from loan sales 7 $ 2 Purchases — 28 Amortization (4 ) (2 ) Balance at end of period $ 31 $ 28 Fair value at end of period $ 37 $ 33
Schedule of Range and Weighted-Average of Significant Unobservable Inputs	The range and weighted-average of the significant unobservable inputs used to fair value our residential mortgage servicing assets at December 31, 2017 , along with the valuation techniques, are shown in the following table: Valuation Technique Significant Unobservable Input Range (Weighted-Average) December 31, 2017 Residential mortgage servicing assets Discounted cash flow Prepayment speed 9.16 - 51.52% (10.46%) Discount rate 8.50 - 11.00% (8.54%) Servicing cost $76 - $4,385 ($83.11) Valuation Technique Significant Unobservable Input Range (Weighted-Average) December 31, 2016 Residential mortgage servicing assets Discounted cash flow Prepayment speed 7.79 - 18.61% (9.42%) Discount rate 8.50 - 11.00% (8.55%) Servicing cost $76 - $3,335 ($83.04) The range and weighted-average of the significant unobservable inputs used to fair value our commercial mortgage servicing assets at December 31, 2017 , and December 31, 2016 , along with the valuation techniques, are shown in the following table: Valuation Technique Significant Unobservable Input Range (Weighted-Average) December 31, 2017 Commercial mortgage servicing assets Discounted cash flow Expected defaults 1.00 - 3.00% (1.20%) Residual cash flows discount rate 7.00 - 15.00% (9.10%) Escrow earn rate 0.90 - 3.10% (2.50%) Servicing cost $150 - $38,500 ($1,468) Loan assumption rate 0.00 - 3.00% (1.22%) Percentage late 0.00 - 1.30% (.25%) Valuation Technique Significant Unobservable Input Range (Weighted-Average) December 31, 2016 Commercial mortgage servicing assets Discounted cash flow Expected defaults 1.00 - 3.00% (1.40%) Residual cash flows discount rate 7.00 - 12.00% (8.00%) Escrow earn rate 1.10 - 3.00% (2.40%) Servicing cost $150 - $2,700 ($1,124) Loan assumption rate 0.00 - 3.00% (1.13%) Percentage late 0.00 - 2.00% (.34%)

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Premises and equipment at December 31, 2017 , and December 31, 2016 , consisted of the following: December 31, dollars in millions Useful life (in years) 2017 2016 Land Indefinite $ 138 $ 139 Buildings and improvements 15-40 741 727 Leasehold improvements 1-15 633 663 Furniture and equipment 2-15 931 943 Capitalized building leases 1-15 (a) 27 27 Construction in process N/A 38 42 Total premises and equipment 2,508 2,541 Less: Accumulated depreciation and amortization (1,578 ) (1,563 ) Premises and equipment, net $ 930 $ 978 (a) Capitalized building and equipment leases are amortized over the lesser of the useful life of asset or lease term.

Goodwill and Other Intangible48

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in Carrying Amount of Goodwill	The following table shows the changes in the carrying amount of goodwill by reporting unit. in millions Key Community Bank Key Corporate Bank Total BALANCE AT DECEMBER 31, 2015 $ 979 $ 81 $ 1,060 Acquisition of First Niagara 1,109 277 1,386 BALANCE AT DECEMBER 31, 2016 2,088 358 2,446 Tax adjustment on previous fair value measurements (15 ) (4 ) (19 ) Loan adjustment on previous fair value measurements 30 7 37 BALANCE AT JUNE 30, 2017 $ 2,103 $ 361 $ 2,464 Changes in the carrying amount of goodwill by reporting unit are presented in the following table: in millions Key Community Bank Key Corporate Bank Total BALANCE AT DECEMBER 31, 2015 $ 979 $ 81 $ 1,060 Acquisition of First Niagara 1,109 277 1,386 BALANCE AT DECEMBER 31, 2016 2,088 358 2,446 Fair value measurement adjustments - First Niagara acquisition 15 3 18 Additional ownership interest in Key Merchant Services 4 — 4 Acquisition of HelloWallet 17 — 17 Acquisition of Cain Brothers — 53 53 BALANCE AT DECEMBER 31, 2017 $ 2,124 $ 414 $ 2,538
Gross Carrying Amount and Accumulated Amortization of Intangible Assets	The following table shows the gross carrying amount and the accumulated amortization of intangible assets subject to amortization: 2017 2016 December 31, in millions Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Intangible assets subject to amortization: Core deposit intangibles $ 461 $ 192 $ 461 $ 125 PCCR intangibles 152 126 152 110 Other intangible assets (a) 128 7 74 68 Total $ 741 $ 325 $ 687 $ 303 (a) Carrying amount and accumulated amortization excludes $18 million at December 31, 2016 , related to the discontinued operations of Austin and the sale of Victory.
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	Intangible assets acquired during the year ended December 31, 2017 were as follows: in millions KMS HelloWallet Cain Brothers Total Intangible assets subject to amortization: Customer relationships $ 85 — $ 29 $ 114 Trade name — — 1 1 Proprietary software — $ 12 — 12 Total $ 85 $ 12 $ 30 $ 127
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The following table presents estimated intangible asset amortization expense for the next five years. Estimated 2018 2019 2020 2021 2022 Intangible asset amortization expense $ 96 $ 79 $ 64 $ 52 $ 42

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Variable Interest Entities Information	The assets and liabilities presented in the table below convey the size of KCDC’s direct and indirect investments at December 31, 2017 , and December 31, 2016 . As these investments represent unconsolidated VIEs, the assets and liabilities of the investments themselves are not recorded on our balance sheet. Unconsolidated VIEs in millions Total Assets Total Liabilities Maximum Exposure to Loss December 31, 2017 LIHTC investments $ 6,003 $ 2,943 $ 1,561 December 31, 2016 LIHTC investments $ 4,814 $ 2,003 $ 1,465 The table below reflects the size of the private equity funds in which KCC was invested as well as our maximum exposure to loss in connection with these investments at December 31, 2017 . Unconsolidated VIEs in millions Total Assets Total Liabilities Maximum Exposure to Loss December 31, 2017 KCC indirect investments $ 26,817 $ 292 $ 153 December 31, 2016 KCC indirect investments $ 32,755 $ 201 $ 195

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes Included in Income Statement	Income taxes included in the income statement are summarized below. We file a consolidated federal income tax return. Year ended December 31, in millions 2017 2016 2015 Currently payable: Federal $ 334 $ 149 $ 337 State — 19 42 Total currently payable 334 168 379 Deferred: Federal 274 13 (69 ) State 29 (2 ) (7 ) Total deferred 303 11 (76 ) Total income tax (benefit) expense (a) $ 637 $ 179 $ 303 (a) There was no income tax (benefit) expense on securities transactions in 2017 , 2016 , and 2015 . Income tax expense excludes equity- and gross receipts-based taxes, which are assessed in lieu of an income tax in certain states in which we operate. These taxes, which are recorded in “noninterest expense” on the income statement, totaled $22 million in 2017 , $18 million in 2016 , and $16 million in 2015 .
Significant Components of Deferred Tax Assets and Liabilities Included in "Accrued Income and Other Assets" and "Accrued Expense and Other Liabilities"	Significant components of our deferred tax assets and liabilities included in “accrued income and other assets” and “accrued expense and other liabilities,” respectively, on the balance sheet, are as follows: December 31, in millions 2017 2016 Allowance for loan and lease losses $ 233 $ 373 Employee benefits 147 276 Net unrealized securities losses 138 146 Federal net operating losses and credits 205 130 Fair value adjustments 63 136 Non-tax accruals 89 150 State net operating losses and credits 7 15 Other 223 236 Gross deferred tax assets 1,105 1,462 Less: Valuation Allowance 15 26 Total deferred tax assets 1,090 1,436 Leasing transactions 588 728 Other 182 101 Total deferred tax liabilities 770 829 Net deferred tax assets (liabilities) (a) $ 320 $ 607 (a) From continuing operations.
Total Income Tax Expense (Benefit) and Resulting Effective Tax Rate	The following table shows how our total income tax expense (benefit) and the resulting effective tax rate were derived: Year ended December 31, dollars in millions 2017 2016 2015 Amount Rate Amount Rate Amount Rate Income (loss) before income taxes times 35% statutory federal tax rate $ 675 35.0 % $ 339 35.0 % $ 428 35.0 % Amortization of tax-advantaged investments 104 5.4 88 9.0 81 6.7 Foreign tax adjustments 1 .1 1 .1 (1 ) (.1 ) Tax-exempt interest income (37 ) (1.9 ) (25 ) (2.6 ) (18 ) (1.5 ) Corporate-owned life insurance income (46 ) (2.4 ) (44 ) (4.5 ) (45 ) (3.6 ) State income tax, net of federal tax benefit 19 1.0 11 1.1 22 1.8 Tax credits (218 ) (11.3 ) (208 ) (21.3 ) (155 ) (12.7 ) Tax Cuts and Jobs Act 147 7.6 — — — — Other (8 ) (.5 ) 17 1.7 (9 ) (.8 ) Total income tax expense (benefit) $ 637 33.0 % $ 179 18.5 % $ 303 24.8 %
Change in Liability for Unrecognized Tax Benefits	The change in our liability for unrecognized tax benefits is as follows: Year ended December 31, in millions 2017 2016 Balance at beginning of year $ 53 $ 12 Increase for other tax positions of prior years 3 10 Increase from Acquisitions 3 33 Decrease for payments and settlements (4 ) — Decrease related to tax positions taken in prior years (16 ) (2 ) Balance at end of year $ 39 $ 53

Securities Financing Activiti51

Securities Financing Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Brokers and Dealers [Abstract]
Summarized Securities Financing Agreements	The following table summarizes our securities financing agreements at December 31, 2017 , and December 31, 2016 : December 31, 2017 in millions Gross Amount Presented in Balance Sheet Netting Adjustments (a) Collateral (b) Net Amounts Offsetting of financial assets: Reverse repurchase agreements $ 3 $ (3 ) — — Total $ 3 $ (3 ) — — Offsetting of financial liabilities: Repurchase agreements (c) $ 374 $ (4 ) $ (370 ) — Total $ 374 $ (4 ) $ (370 ) — December 31, 2016 in millions Gross Amount Presented in Balance Sheet Netting Adjustments (a) Collateral (b) Net Amounts Offsetting of financial assets: Reverse repurchase agreements $ 3 $ (3 ) — — Total $ 3 $ (3 ) — — Offsetting of financial liabilities: Repurchase agreements (c) $ 497 $ (3 ) $ (494 ) — Total $ 497 $ (3 ) $ (494 ) — (a) Netting adjustments take into account the impact of master netting agreements that allow us to settle with a single counterparty on a net basis. (b) These adjustments take into account the impact of bilateral collateral agreements that allow us to offset the net positions with the related collateral. The application of collateral cannot reduce the net position below zero. Therefore, excess collateral, if any, is not reflected above. (c) Repurchase agreements are collateralized by mortgaged-backed agency securities and are contracted on an overnight or continuous basis.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Assumptions Used in Options Pricing Model	The assumptions pertaining to options issued during 2017 , 2016 , and 2015 are shown in the following table. Year ended December 31, 2017 2016 2015 Average option life 6.0 years 6.0 years 6.0 years Future dividend yield 1.79 % 2.86 % 1.84 % Historical share price volatility .287 .297 .382 Weighted-average risk-free interest rate 2.1 % 1.3 % 1.7 %
Activity, Pricing and Other Information for Stock Options	The following table summarizes activity, pricing and other information for our stock options for the year ended December 31, 2017 : Number of Options Weighted-Average Exercise Price Per Option Weighted-Average Remaining Life Aggregate Intrinsic Value (a) Outstanding at December 31, 2016 13,885,566 $ 13.00 4.5 years $ 101 Granted 1,370,069 18.96 Exercised (3,755,177 ) 10.16 Lapsed or canceled (1,617,841 ) 35.15 Outstanding at December 31, 2017 9,882,617 $ 11.28 5.5 88 Expected to vest 3,422,790 13.97 8.3 21 Exercisable at December 31, 2017 6,183,136 $ 9.63 3.8 $ 65 (a) The intrinsic value of a stock option is the amount by which the fair value of the underlying stock exceeds the exercise price of the option.
Activity and Pricing Information for Nonvested Shares in Long-Term Incentive Compensation Program	The following table summarizes activity and pricing information for the nonvested shares in the Program for the year ended December 31, 2017 . Vesting Contingent on Service Conditions Vesting Contingent on Performance and Service Conditions Number of Nonvested Shares Weighted- Average Grant-Date Fair Value Number of Nonvested Shares Weighted- Average Grant-Date Fair Value Outstanding at December 31, 2016 13,918,806 $ 11.78 2,765,622 $ 14.45 Granted 3,899,826 18.96 2,321,041 19.82 Vested (5,324,226 ) 11.64 (887,489 ) 16.27 Forfeited (661,450 ) 13.19 (51,154 ) 20.33 Outstanding at December 31, 2017 11,832,956 $ 14.05 4,148,020 $ 17.51
Activity and Pricing Information for Nonvested Shares Granted Under Deferred Compensation Plans and Other Restricted Stock Awards	The following table summarizes activity and pricing information for the nonvested shares granted under our deferred compensation plans and these other restricted stock or unit award programs for the year ended December 31, 2017 . Number of Nonvested Shares Weighted-Average Grant-Date Fair Value Outstanding at December 31, 2016 3,858,152 $ 12.22 Granted 2,347,005 18.55 Dividend equivalents 14 12.54 Vested (1,684,824 ) 12.50 Forfeited (296,573 ) 12.14 Outstanding at December 31, 2017 4,223,774 $ 15.61

Employee Benefits (Tables)

Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Net Pension Cost and Amount Recognized in OCI for All Funded and Unfunded Plans	The components of net pension cost and the amount recognized in OCI for all funded and unfunded plans are as follows: Year ended December 31, in millions 2017 2016 2015 Interest cost on PBO $ 48 $ 44 $ 41 Expected return on plan assets (68 ) (58 ) (56 ) Amortization of losses 15 17 18 Settlement loss — 18 23 Net pension cost $ (5 ) $ 21 $ 26 Other changes in plan assets and benefit obligations recognized in OCI: Net (gain) loss $ (10 ) $ (9 ) $ 47 Amortization of gains (15 ) (35 ) (41 ) Total recognized in comprehensive income $ (25 ) $ (44 ) $ 6 Total recognized in net pension cost and comprehensive income $ (30 ) $ (23 ) $ 32
Changes in PBO Related to Pension Plans	The following table summarizes changes in the PBO related to our pension plans. Year ended December 31, in millions 2017 2016 PBO at beginning of year $ 1,338 $ 1,136 Interest cost 48 44 Actuarial losses (gains) 37 (25 ) Benefit payments (100 ) (85 ) Plan acquisitions — 268 PBO at end of year $ 1,323 $ 1,338
Changes in FVA	The following table summarizes changes in the FVA. Year ended December 31, in millions 2017 2016 FVA at beginning of year $ 1,133 $ 869 Actual return on plan assets 115 42 Employer contributions 15 14 Benefit payments (100 ) (85 ) Plan acquisitions — 293 FVA at end of year $ 1,163 $ 1,133
Funded Status of Pension Plans Recognized in Balance Sheets	The following table summarizes the funded status of the pension plans, which equals the amounts recognized in the balance sheets at December 31, 2017 , and December 31, 2016 . December 31, in millions 2017 2016 Funded status (a) $ (160 ) $ (205 ) Net prepaid pension cost recognized consists of: Noncurrent assets $ 29 — Current liabilities (15 ) $ (16 ) Noncurrent liabilities (174 ) (189 ) Net prepaid pension cost recognized (b) $ (160 ) $ (205 ) (a) The shortage of the FVA under the PBO. (b) Represents the accrued benefit liability of the pension plans.
Plans ABO in Excess of Plan Assets	As indicated in the table below, collectively our plans had an ABO in excess of plan assets as follows: December 31, in millions 2017 2016 PBO $ 1,323 $ 1,338 ABO 1,323 1,338 Fair value of plan assets 1,163 1,133
Weighted-Average Rates to Determine Actuarial Present Value of Benefit Obligations	To determine the actuarial present value of benefit obligations, we assumed the following weighted-average rates. December 31, 2017 2016 Discount rate 3.25 % 3.75 % Compensation increase rate N/A N/A
Weighted-Average Rates to Determine Net Pension Cost	To determine net pension cost, we assumed the following weighted-average rates. Year ended December 31, 2017 2016 2015 Discount rate 3.75 % 3.75 % 3.50 % Compensation increase rate N/A N/A N/A Expected return on plan assets 6.00 6.00 6.25
Asset Target Allocations Prescribed by Pension Funds' Investment Policies	The following table shows the asset target allocations prescribed by the pension fund’s investment policies based on the plan’s funded status at December 31, 2017 . Target Allocation Asset Class 2017 Equity securities: U.S. 5 % International 4 Fixed income securities 81 Real assets 6 Other assets 4 Total 100 %
Fair Values of Pension Plan Assets by Asset Category	The following tables show the fair values of our pension plan assets by asset class at December 31, 2017 , and December 31, 2016 . December 31, 2017 in millions Level 1 Level 2 Level 3 Total ASSET CLASS Cash and cash equivalents — — — — Equity securities: Common — U.S. $ 11 — — $ 11 Common — International 1 — — 1 Preferred — U.S. 3 — — 3 Debt securities: Corporate bonds — U.S. — $ 152 — 152 Corporate bonds — International — 61 — 61 Government and agency bonds — U.S. — 203 — 203 Government bonds — International — 2 — 2 State and municipal bonds — 31 — 31 Mutual funds: Equity — U.S. — — — — Equity — International 7 — — 7 Fixed income — U.S. — — — — Fixed income — International — — — — Real assets — — — — Collective investment funds: Equity — U.S. — 45 — 45 Equity — International — 41 — 41 Convertible securities — — — — Fixed income securities — 456 — 456 Short-term investments — 16 — 16 Real assets — 70 — 70 Insurance investment contracts and pooled separate accounts (measured at NAV) (a) — — — 14 Other assets (measured at NAV) (a) — — — 50 Total net assets at fair value $ 22 $ 1,077 — $ 1,163 (a) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the fair value of plan assets presented elsewhere within this footnote. December 31, 2016 in millions Level 1 Level 2 Level 3 Total ASSET CLASS Cash and cash equivalents $ 14 — — $ 14 Equity securities: Common — U.S. 133 — — 133 Common — International 15 — — 15 Preferred — U.S. 2 — — 2 Debt securities: Corporate bonds — U.S. — $ 90 — 90 Corporate bonds — International — 26 — 26 Government and agency bonds — U.S. — 101 — 101 Government bonds — International — 1 — 1 State and municipal bonds — 5 — 5 Mutual funds: Equity — U.S. 118 — — 118 Equity — International 35 — — 35 Fixed income — U.S. 152 — — 152 Fixed income — International 19 — — 19 Real assets 9 — — 9 Collective investment funds: Equity — U.S. — 15 — 15 Equity — International — 97 — 97 Convertible securities — 43 — 43 Fixed income securities — 79 — 79 Short-term investments — 18 — 18 Real assets — 95 — 95 Insurance investment contracts and pooled separate accounts (measured at NAV) — — — 14 Other assets (measured at NAV) — — — 52 Total net assets at fair value $ 497 $ 570 — $ 1,133 (a) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the fair value of plan assets presented elsewhere within this footnote.
Pre-tax AOCI Not Yet Recognized as Net Postretirement Benefit Cost	The components of pre-tax AOCI not yet recognized as net postretirement benefit cost are shown below. December 31, in millions 2017 2016 Net unrecognized losses (gains) $ (12 ) $ (9 ) Net unrecognized prior service credit (1 ) (2 ) Total unrecognized AOCI $ (13 ) $ (11 )
Net Postretirement Benefit Cost and Amount Recognized in OCI for All Funded and Unfunded Plans	The components of net postretirement benefit cost and the amount recognized in OCI for all funded and unfunded plans are as follows: December 31, in millions 2017 2016 2015 Service cost of benefits earned $ 1 $ 1 $ 1 Interest cost on APBO 3 2 3 Expected return on plan assets (2 ) (2 ) (3 ) Amortization of prior service credit (1 ) (1 ) (1 ) Amortization of gains — — — Net postretirement benefit $ 1 — — Other changes in plan assets and benefit obligations recognized in OCI: Net (gain) loss $ (4 ) $ (4 ) $ (6 ) Amortization of prior service credit 1 1 1 Amortization of losses — — — Total recognized in comprehensive income $ (3 ) $ (3 ) $ (5 ) Total recognized in net postretirement benefit cost and comprehensive income $ (2 ) $ (3 ) $ (5 )
Changes in APBO	The following table summarizes changes in the APBO. Year ended December 31, in millions 2017 2016 APBO at beginning of year $ 69 $ 67 Service cost 1 1 Interest cost 3 2 Plan participants’ contributions 1 2 Actuarial losses (gains) 3 (1 ) Benefit payments (8 ) (6 ) Plan acquisition — 4 APBO at end of year $ 69 $ 69
Change in FVA (Other Post Retirement Benefit Plan Assets)	The following table summarizes changes in FVA. Year ended December 31, in millions 2017 2016 FVA at beginning of year $ 50 $ 49 Employer contributions — — Plan participants’ contributions 1 2 Benefit payments (8 ) (6 ) Actual return on plan assets 9 5 FVA at end of year $ 52 $ 50
Funded Status of Postretirement Plans Recognized in Balance Sheets	The following table summarizes the funded status of the postretirement plans, which corresponds to the amounts recognized in the balance sheets at December 31, 2017 , and December 31, 2016 . December 31, in millions 2017 2016 Funded status (a) $ (16 ) $ (19 ) Accrued postretirement benefit cost recognized (b) (16 ) (19 ) (a) The shortage of the FVA under the APBO. (b) Consists entirely of noncurrent liabilities.
Weighted-Average Rates to Determine Net Postretirement Benefit Cost	To determine net postretirement benefit cost, we assumed the following weighted-average rates. Year ended December 31, 2017 2016 2015 Discount rate 3.75 % 4.00 % 3.75 % Expected return on plan assets 4.50 4.50 4.50
Asset Target Allocations Prescribed by Trusts' Investment Policies	The following table shows the asset target allocations prescribed by the trust’s investment policy. Target Allocation Asset Class 2017 Equity securities 80 % Fixed income securities 10 Convertible securities 5 Cash equivalents 5 Total 100 %
Fair Values of Pension Plan Assets by Asset Category	The following tables show the fair values of our postretirement plan assets by asset class at December 31, 2017 , and December 31, 2016 . December 31, 2017 in millions Level 1 Level 2 Level 3 Total ASSET CLASS Mutual funds: Equity — U.S. $ 25 — — $ 25 Equity — International 10 — — 10 Fixed income — U.S. 4 — — 4 Fixed income — lnternational 3 — — 3 Common investment funds: Equity — U.S. — $ 10 — 10 Total net assets at fair value $ 42 $ 10 — $ 52 December 31, 2016 in millions Level 1 Level 2 Level 3 Total ASSET CLASS Mutual funds: Equity — U.S. $ 23 — — $ 23 Equity — International 5 — — 5 Fixed income — U.S. 5 — — 5 Common investment funds: Equity — U.S. — $ 10 — 10 Short-term investments — 7 — 7 Total net assets at fair value $ 33 $ 17 — $ 50

Short-Term Borrowings (Tables)

Short-Term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Components of Short-Term Borrowings	Selected financial information pertaining to the components of our short-term borrowings is as follows: December 31, dollars in millions 2017 2016 2015 FEDERAL FUNDS PURCHASED Balance at year end $ 3 $ 1,005 $ 20 Average during the year 128 44 195 Maximum month-end balance 2,331 1,005 678 Weighted-average rate during the year (a) .72 % .68 % .14 % Weighted-average rate at December 31 (a) — .55 .05 SECURITIES SOLD UNDER REPURCHASE AGREEMENTS Balance at year end $ 374 $ 497 $ 352 Average during the year 389 443 437 Maximum month-end balance 472 684 589 Weighted-average rate during the year (a) .08 % .04 % .00 % Weighted-average rate at December 31 (a) .08 .07 .00 OTHER SHORT-TERM BORROWINGS Balance at year end $ 634 $ 808 $ 533 Average during the year 1,140 852 572 Maximum month-end balance 1,242 872 1,122 Weighted-average rate during the year (a) 1.34 % 1.18 % 1.52 % Weighted-average rate at December 31 (a) 2.01 1.11 1.78 (a) Rates exclude the effects of interest rate swaps and caps, which modify the repricing characteristics of certain short-term borrowings. For more information about such financial instruments, see Note 9 (“ Derivatives and Hedging Activities ”).

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Components of Long-Term Debt	The following table presents the components of our long-term debt, net of unamortized discounts and adjustments related to hedging with derivative financial instruments. We use interest rate swaps and caps, which modify the repricing characteristics of certain long-term debt, to manage interest rate risk. For more information about such financial instruments, see Note 9 (“ Derivatives and Hedging Activities ”). December 31, dollars in millions 2017 2016 Senior medium-term notes due through 2021 (a) $ 2,766 $ 2,799 2.075% Subordinated notes due 2028 (b) 161 162 6.875% Subordinated notes due 2029 (b) 109 111 7.750% Subordinated notes due 2029 (b) 141 141 7.25% Subordinated notes due 2021 (c) 348 358 6.75% Senior notes due 2020 (d) 327 338 Other subordinated notes (b), (e) 69 78 Total parent company 3,921 3,987 Senior medium-term notes due through 2039 (f) 8,011 6,715 3.18% Senior remarketable notes due 2027 (g) 202 193 5.70% Subordinated notes due 2017 (h) — 207 4.625% Subordinated notes due 2018 (h) 100 102 3.40% Subordinated notes due 2026 (h) 565 567 6.95% Subordinated notes due 2028 (h) 299 299 Secured borrowing due through 2021 (i) 24 68 Federal Home Loan Bank advances due through 2036 (j) 1,106 126 Investment Fund Financing due through 2052 (k) 88 100 Obligations under Capital Leases due through 2032 (l) 17 20 Total subsidiaries 10,412 8,397 Total long-term debt $ 14,333 $ 12,384 (a) Senior medium-term notes had a weighted-average interest rate of 3.56% at December 31, 2017 , and 3.57% at December 31, 2016 . These notes had fixed interest rates at December 31, 2017 , and December 31, 2016 . These notes may not be redeemed prior to their maturity dates. (b) See Note 21 (“ Trust Preferred Securities Issued by Unconsolidated Subsidiaries ”) for a description of these notes. (c) The First Niagara subordinated debt had a weighted-average interest rate of 7.25% at December 31, 2017 , and December 31, 2016 . These notes may not be redeemed prior to their maturity dates. (d) The First Niagara senior notes had a weighted-average interest rate of 6.75% at December 31, 2017 , and December 31, 2016 . These notes may not be redeemed prior to their maturity dates. (e) The First Niagara variable rate trust preferred securities had a weighted-average interest rates of 3.022% at December 31, 2017 , and 4.612% at December 31, 2016 . These notes may be redeemed prior to their maturity dates. (f) Senior medium-term notes had weighted-average interest rates of 2.24% at December 31, 2017 , and 1.93% at December 31, 2016 . These notes are a combination of fixed and floating rates. These notes may not be redeemed prior to their maturity dates. (g) Remarketable senior medium-term notes had a fixed interest rate at December 31, 2017. These notes may not be redeemed prior to their maturity dates. (h) These notes are all obligations of KeyBank and may not be redeemed prior to their maturity dates. (i) The secured borrowing had weighted-average interest rates of 4.46% at December 31, 2017 , and 4.45% at December 31, 2016 . This borrowing is collateralized by commercial lease financing receivables, and principal reductions are based on the cash payments received from the related receivables. Additional information pertaining to these commercial lease financing receivables is included in Note 5 (“ Loans and Loans Held for Sale ”). (j) Long-term advances from the Federal Home Loan Bank had a weighted-average interest rate of 2.318% at December 31, 2017 , and 3.64% at December 31, 2016 . These advances, which had fixed interest rates, were secured by real estate loans and securities totaling $1.1 billion at December 31, 2017 , and $126 million at December 31, 2016 . (k) Investment Fund Financing had a weighted-average interest rate of 1.94% at December 31, 2017 , and December 31, 2016 . (l) These are capital leases acquired in the First Niagara merger with a maturity range from June 2019 through October 2032.
Scheduled Principal Payments on Long-Term Debt	At December 31, 2017 , scheduled principal payments on long-term debt were as follows: in millions Parent Subsidiaries Total 2018 $ 746 $ 2,325 $ 3,071 2019 — 2,048 2,048 2020 1,310 1,396 2,706 2021 1,381 1,243 2,624 2022 — 1,426 1,426 All subsequent years 483 1,975 2,458

Trust Preferred Securities Is56

Trust Preferred Securities Issued by Unconsolidated Subsidiaries (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Summary of Trust Preferred Securities, Common Stock and Related Debentures	The trust preferred securities, common stock, and related debentures are summarized as follows: dollars in millions Trust Preferred Securities, Net of Discount (a) Common Stock Principal Amount of Debentures, Net of Discount (b) Interest Rate of Trust Preferred Securities and (c) Maturity of Trust Preferred Securities and Debentures December 31, 2017 KeyCorp Capital I $ 155 $ 6 $ 161 2.750 % 2028 KeyCorp Capital II 105 4 109 6.875 2029 KeyCorp Capital III 137 4 141 7.750 2029 HNC Statutory Trust III 18 1 19 2.854 2035 Willow Grove Statutory Trust I 18 1 19 2.898 2036 HNC Statutory Trust IV 16 1 17 2.658 2037 Westbank Capital Trust II 7 — 7 3.815 2034 Westbank Capital Trust III 7 — 7 3.815 2034 Total $ 463 $ 17 $ 480 4.977 % — December 31, 2016 $ 475 $ 17 $ 492 4.845 % — (a) The trust preferred securities must be redeemed when the related debentures mature, or earlier if provided in the governing indenture. Each issue of trust preferred securities carries an interest rate identical to that of the related debenture. Certain trust preferred securities include basis adjustments related to fair value hedges totaling $55 million at December 31, 2017 , and $59 million at December 31, 2016 . See Note 9 (“Derivatives and Hedging Activities”) for an explanation of fair value hedges. (b) We have the right to redeem these debentures. If the debentures purchased by KeyCorp Capital I, HNC Statutory Trust III, Willow Grove Statutory Trust I, HNC Statutory Trust IV, Westbank Capital Trust II, or Westbank Capital Trust III are redeemed before they mature, the redemption price will be the principal amount, plus any accrued but unpaid interest. If the debentures purchased by KeyCorp Capital II or KeyCorp Capital III are redeemed before they mature, the redemption price will be the greater of: (i) the principal amount, plus any accrued but unpaid interest, or (ii) the sum of the present values of principal and interest payments discounted at the Treasury Rate (as defined in the applicable indenture), plus 20 basis points for KeyCorp Capital II or 25 basis points for KeyCorp Capital III or 50 basis points in the case of redemption upon either a tax or a capital treatment event for either KeyCorp Capital II or KeyCorp Capital III, plus any accrued but unpaid interest. The principal amount of certain debentures includes basis adjustments related to fair value hedges totaling $55 million at December 31, 2017 , and $59 million at December 31, 2016 . See Note 9 for an explanation of fair value hedges. The principal amount of debentures, net of discounts, is included in “long-term debt” on the balance sheet. (c) The interest rates for the trust preferred securities issued by KeyCorp Capital II and KeyCorp Capital III are fixed. The trust preferred securities issued by KeyCorp Capital I have a floating interest rate, equal to three-month LIBOR plus 74 basis points, that reprices quarterly. The trust preferred securities issued by HNC Statutory Trust III have a floating interest rate, equal to three-month LIBOR plus 140 basis points, that reprices quarterly. The trust preferred securities issued by Willow Grove Statutory Trust I have a floating interest rate, equal to three-month LIBOR plus 131 basis points, that reprices quarterly. The trust preferred securities issued by HNC Statutory Trust IV have a floating interest rate, equal to three-month LIBOR plus 128 basis points, that reprices quarterly. The trust preferred securities issued by Westbank Capital Trust II and Westbank Capital Trust III each have a floating interest rate, equal to three-month LIBOR plus 219 basis points, that reprices quarterly. The total interest rates are weighted-average rates.

Commitments, Contingent Liabi57

Commitments, Contingent Liabilities and Guarantees (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments to Extend Credit or Funding	The following table shows the remaining contractual amount of each class of commitment related to extending credit or funding principal investments as of December 31, 2017 , and December 31, 2016 . For loan commitments and commercial letters of credit, this amount represents our maximum possible accounting loss on the unused commitment if the borrower were to draw upon the full amount of the commitment and subsequently default on payment for the total amount of the then outstanding loan. December 31, in millions 2017 2016 Loan commitments: Commercial and other $ 40,315 $ 34,372 Commercial real estate and construction 2,774 3,034 Home equity 9,673 9,666 Credit cards 5,890 5,653 Total loan commitments 58,652 52,725 When-issued and to be announced securities commitments (a) — 34 Commercial letters of credit 231 143 Purchase card commitments 425 293 Principal investing commitments 29 37 Tax credit investment commitments 481 466 Liabilities of certain limited partnerships and other commitments — 2 Securities underwriting 9 — Total loan and other commitments $ 59,827 $ 53,700 (a) Beginning in first quarter of 2017, we now disclose amounts previously reported as “When-issued and to be announced securities commitments” in the Notional category of the “Other” line in the “Fair Values, Volume of Activity, and Gain/Loss Information Related to Derivative Instruments” table found in Note 9 (“ Derivatives and Hedging Activities “).
Guarantees	The following table shows the types of guarantees that we had outstanding at December 31, 2017 . Information pertaining to the basis for determining the liabilities recorded in connection with these guarantees is included in Note 1 (“ Summary of Significant Accounting Policies ”) under the heading “Guarantees.” December 31, 2017 Maximum Potential Undiscounted Future Payments Liability Recorded in millions Financial guarantees: Standby letters of credit $ 3,142 $ 67 Recourse agreement with FNMA 3,261 6 Residential mortgage reserve 1,362 5 Return guarantee agreement with LIHTC investors 3 3 Written put options (a) 2,080 50 Total $ 9,848 $ 131 (a) The maximum potential undiscounted future payments represent notional amounts of derivatives qualifying as guarantees.

Accumulated Other Comprehensi58

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Changes in AOCI	Our changes in AOCI for the years ended December 31, 2017 , and December 31, 2016 , are as follows: in millions Unrealized gains (losses) on securities available for sale Unrealized gains (losses) on derivative financial instruments Foreign currency translation adjustment Net pension and postretirement benefit costs Total Balance at December 31, 2015 $ (58 ) $ 20 $ (2 ) $ (365 ) $ (405 ) Other comprehensive income before reclassification, net of income taxes (127 ) 17 (1 ) 5 (106 ) Amounts reclassified from accumulated other comprehensive income, net of income taxes (a) — (51 ) — 21 (30 ) Net current-period other comprehensive income, net of income taxes (127 ) (34 ) (1 ) 26 (136 ) Balance at December 31, 2016 $ (185 ) $ (14 ) $ (3 ) $ (339 ) $ (541 ) Other comprehensive income before reclassification, net of income taxes (69 ) (48 ) 12 9 (96 ) Amounts reclassified from accumulated other comprehensive income, net of income taxes (a) (1 ) (10 ) 1 9 (1 ) Amounts reclassified from accumulated other comprehensive income resulting from new federal corporate income tax rate (b) (56 ) (14 ) (1 ) (70 ) (141 ) Net current-period other comprehensive income, net of income taxes (126 ) (72 ) 12 (52 ) (238 ) Balance at December 31, 2017 $ (311 ) $ (86 ) $ 9 $ (391 ) $ (779 ) (a) See table below for details about these reclassifications. (b) See Note 14, Income Taxes, for details about the accounting impacts resulting from the TCJ Act.
Reclassifications Out of AOCI	Our reclassifications out of AOCI for the years ended December 31, 2017 , and December 31, 2016 , are as follows: Year ended December 31, 2017 Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Statement Where Net Income is Presented in millions Unrealized gains (losses) on available for sale securities Realized gains $ 1 Other income Realized losses — Other income 1 Income (loss) from continuing operations before income taxes — Income taxes $ 1 Income (loss) from continuing operations Unrealized gains (losses) on derivative financial instruments Interest rate $ 19 Interest income — Loans Interest rate (4 ) Interest expense — Long-term debt 15 Income (loss) from continuing operations before income taxes 5 Income taxes $ 10 Income (loss) from continuing operations Foreign currency translation adjustment $ (1 ) Corporate services income (1 ) Income (loss) from continuing operations before income taxes — Income taxes $ (1 ) Income (loss) from continuing operations Net pension and postretirement benefit costs Amortization of losses $ (15 ) Personnel expense Amortization of prior service credit 1 Personnel expense (14 ) Income (loss) from continuing operations before income taxes (5 ) Income taxes $ (9 ) Income (loss) from continuing operations Year ended December 31, 2016 Amount Reclassified from Affected Line Item in the Statement Where Net Income is Presented in millions Unrealized gains (losses) on derivative financial instruments Interest rate $ 85 Interest income — Loans Interest rate (4 ) Interest expense — Long-term debt 81 Income (loss) from continuing operations before income taxes 30 Income taxes $ 51 Income (loss) from continuing operations Net pension and postretirement benefit costs Amortization of losses $ (17 ) Personnel expense Settlement loss (18 ) Personnel expense Amortization of prior service credit 1 Personnel expense (34 ) Income (loss) from continuing operations before income taxes (13 ) Income taxes $ (21 ) Income (loss) from continuing operations

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Key's and KeyBank's Actual Capital Amounts and Ratios, Minimum Capital Amounts and Ratios	At December 31, 2017 , Key and KeyBank (consolidated) had regulatory capital in excess of all current minimum risk-based capital (including all adjustments for market risk) and leverage ratio requirements as shown in the following table. Actual To Meet Minimum Capital Adequacy Requirements To Qualify as Well Capitalized Under Federal Deposit Insurance Act dollars in millions Amount Ratio Amount Ratio Amount Ratio December 31, 2017 TOTAL CAPITAL TO NET RISK-WEIGHTED ASSETS Key $ 15,345 12.92 % $ 9,505 8.00 % N/A N/A KeyBank (consolidated) 14,957 12.86 9,306 8.00 $ 11,633 10.00 % TIER 1 CAPITAL TO NET RISK-WEIGHTED ASSETS Key $ 13,083 11.01 % $ 7,129 6.00 % N/A N/A KeyBank (consolidated) 13,110 11.27 6,980 6.00 $ 6,980 6.00 % TIER 1 CAPITAL TO AVERAGE QUARTERLY TANGIBLE ASSETS Key $ 13,083 9.73 % $ 5,379 4.00 % N/A N/A KeyBank (consolidated) 13,110 9.91 5,293 4.00 $ 6,617 5.00 % December 31, 2016 TOTAL CAPITAL TO NET RISK-WEIGHTED ASSETS Key $ 15,638 12.85 % $ 9,734 8.00 % N/A N/A KeyBank (consolidated) 14,291 12.36 9,251 8.00 $ 11,564 10.00 % TIER 1 CAPITAL TO NET RISK-WEIGHTED ASSETS Key $ 13,249 10.89 % $ 7,300 6.00 % N/A N/A KeyBank (consolidated) 12,439 10.76 6,939 6.00 $ 6,939 6.00 % TIER 1 CAPITAL TO AVERAGE QUARTERLY TANGIBLE ASSETS Key $ 13,249 9.90 % $ 5,442 4.00 % N/A N/A KeyBank (consolidated) 12,439 9.46 5,353 4.00 $ 6,691 5.00 %

Line of Business Results (Table

Line of Business Results (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Financial Information of Business Groups	Year ended December 31, Key Community Bank Key Corporate Bank dollars in millions 2017 2016 2015 2017 2016 2015 SUMMARY OF OPERATIONS Net interest income (TE) $ 2,643 $ 1,953 $ 1,487 $ 1,190 $ 1,049 $ 886 Noninterest income 1,200 925 788 1,147 1,013 926 Total revenue (TE) (a) 3,843 2,878 2,275 2,337 2,062 1,812 Provision for credit losses 209 143 90 20 127 83 Depreciation and amortization expense 116 76 56 96 60 43 Other noninterest expense 2,486 2,077 1,723 1,161 1,071 945 Income (loss) from continuing operations before income taxes (TE) 1,032 582 406 1,060 804 741 Allocated income taxes (benefit) and TE adjustments 383 217 151 246 178 196 Income (loss) from continuing operations 649 365 255 814 626 545 Income (loss) from discontinued operations, net of taxes — — — — — — Net income (loss) 649 365 255 814 626 545 Less: Net income (loss) attributable to noncontrolling interests — — — — (2 ) 1 Net income (loss) attributable to Key $ 649 $ 365 $ 255 $ 814 $ 628 $ 544 AVERAGE BALANCES (b) Loans and leases $ 47,383 $ 37,620 $ 30,834 $ 37,732 $ 31,929 $ 25,865 Total assets (a) 51,433 40,300 32,948 44,521 37,801 31,541 Deposits 79,669 63,873 51,163 21,318 20,783 19,043 OTHER FINANCIAL DATA Expenditures for additions to long-lived assets (a), (b) $ 2,438 $ 1,478 $ 75 $ 559 $ 340 $ 16 Net loan charge-offs (b) 166 114 92 40 83 40 Return on average allocated equity (b) 13.59 % 10.62 % 9.42 % 28.69 % 26.80 % 28.91 % Return on average allocated equity 13.59 10.62 9.42 28.69 26.80 28.91 Average full-time equivalent employees (c) 10,924 8,936 7,520 2,407 2,244 2,100 (a) Substantially all revenue generated by our major business segments is derived from clients that reside in the United States. Substantially all long-lived assets, including premises and equipment, capitalized software, and goodwill held by our major business segments, are located in the United States. (b) From continuing operations. (c) The number of average full-time equivalent employees was not adjusted for discontinued operations. Other Segments Total Segments Reconciling Items Key 2017 2016 2015 2017 2016 2015 2017 2016 2015 2017 2016 2015 $ (23 ) $ (45 ) $ (8 ) $ 3,810 $ 2,957 $ 2,365 $ 20 $ (4 ) $ 11 $ 3,830 $ 2,953 $ 2,376 151 151 183 2,498 2,089 1,897 (20 ) (18 ) (17 ) 2,478 2,071 1,880 128 106 175 6,308 5,046 4,262 — (22 ) (6 ) 6,308 5,024 4,256 — (4 ) (8 ) 229 266 165 — — 1 229 266 166 3 4 8 215 140 107 169 163 148 384 303 255 39 35 46 3,686 3,183 2,714 28 270 (129 ) 3,714 3,453 2,585 86 71 129 2,178 1,457 1,276 (197 ) (455 ) (26 ) 1,981 1,002 1,250 (42 ) (20 ) 1 587 375 348 103 (162 ) (17 ) 690 213 331 128 91 128 1,591 1,082 928 (300 ) (293 ) (9 ) 1,291 789 919 — — — — — — 7 1 1 7 1 1 128 91 128 1,591 1,082 928 (293 ) (292 ) (8 ) 1,298 790 920 3 2 3 3 — 4 (1 ) (1 ) — 2 (1 ) 4 $ 125 $ 89 $ 125 $ 1,588 $ 1,082 $ 924 $ (292 ) $ (291 ) $ (8 ) $ 1,296 $ 791 $ 916 $ 1,225 $ 1,486 $ 1,852 $ 86,340 $ 71,035 $ 58,551 $ 25 $ 113 $ 43 $ 86,365 $ 71,148 $ 58,594 37,079 31,934 26,935 133,033 110,035 91,424 686 2,502 602 133,719 112,537 92,026 1,988 1,213 467 102,975 85,869 70,673 (29 ) 483 (43 ) 102,946 86,352 70,630 $ 19 — — $ 3,016 $ 1,818 $ 91 $ 81 $ 116 $ 49 $ 3,097 $ 1,934 $ 139 1 $ 7 $ 9 207 204 141 1 1 1 208 205 142 86.81 % 52.66 % 58.96 % 20.47 % 18.19 % 19.25 % (4.00 )% (4.36 )% (.15 )% 8.47 % 6.25 % 8.61 % 86.81 52.66 58.96 20.47 18.19 19.25 (3.91 ) (4.34 ) (.14 ) 8.51 6.25 8.62 2 5 14 13,333 11,185 9,634 5,082 4,515 3,849 18,415 15,700 13,483

Condensed Financial Informati61

Condensed Financial Information of the Parent Company (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Balance Sheets	CONDENSED BALANCE SHEETS December 31, in millions 2017 2016 ASSETS Cash and due from banks $ 2,257 $ 3,286 Short-term investments 22 70 Securities available for sale 10 10 Other investments 29 25 Loans to: Banks 250 250 Nonbank subsidiaries 31 31 Total loans 281 281 Investment in subsidiaries: Banks 15,169 14,564 Nonbank subsidiaries 885 668 Total investment in subsidiaries 16,054 15,232 Goodwill 167 167 Corporate-owned life insurance 208 207 Derivative assets 29 53 Accrued income and other assets 353 451 Total assets $ 19,410 $ 19,782 LIABILITIES Accrued expense and other liabilities $ 466 $ 553 Derivative liabilities — 2 Long-term debt due to: Subsidiaries 480 492 Unaffiliated companies 3,441 3,495 Total long-term debt 3,921 3,987 Total liabilities 4,387 4,542 SHAREHOLDERS’ EQUITY (a) 15,023 15,240 Total liabilities and shareholders’ equity $ 19,410 $ 19,782 (a) See Key’s Consolidated Statements of Changes in Equity.
Condensed Statements of Income	CONDENSED STATEMENTS OF INCOME Year ended December 31, in millions 2017 2016 2015 INCOME Dividends from subsidiaries: Bank subsidiaries $ 750 $ 625 $ 1,000 Nonbank subsidiaries — 50 1 Interest income from subsidiaries 10 10 10 Other income 9 11 20 Total income 769 696 1,031 EXPENSE Interest on long-term debt with subsidiary trusts 17 14 10 Interest on other borrowed funds 95 69 52 Personnel and other expense 46 101 73 Total expense 158 184 135 Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries 611 512 896 Income tax (expense) benefit 29 54 39 Income (loss) before equity in net income (loss) less dividends from subsidiaries 640 566 935 Equity in net income (loss) less dividends from subsidiaries 658 224 (15 ) NET INCOME (LOSS) 1,298 790 920 Less: Net income attributable to noncontrolling interests 2 (1 ) 4 NET INCOME (LOSS) ATTRIBUTABLE TO KEY $ 1,296 $ 791 $ 916 .
Condensed Statements of Cash Flows	CONDENSED STATEMENTS OF CASH FLOWS Year ended December 31, in millions 2017 2016 2015 OPERATING ACTIVITIES Net income (loss) attributable to Key $ 1,296 $ 791 $ 916 Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Deferred income taxes (benefit) 38 (24 ) 10 Stock-based compensation expense 11 12 9 Equity in net (income) loss less dividends from subsidiaries (658 ) (224 ) 15 Other intangible asset amortization — — 2 Net (increase) decrease in goodwill and other intangibles — — 86 Net (increase) decrease in other assets 82 (93 ) 29 Net increase (decrease) in other liabilities (82 ) 9 (7 ) Other operating activities, net (114 ) — (52 ) NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES 573 471 1,008 INVESTING ACTIVITIES Net (increase) decrease in securities available for sale and in short-term and other investments 47 (17 ) (38 ) Cash infusion from purchase of Cain Brothers (90 ) — — Cash used in acquisitions — (481 ) — Proceeds from sales, prepayments and maturities of securities available for sale 1 — 20 Net (increase) decrease in loans to subsidiaries — 160 (146 ) NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES (42 ) (338 ) (164 ) FINANCING ACTIVITIES Net proceeds from issuance of long-term debt — — 1,000 Payments on long-term debt — (21 ) (750 ) Repurchase of Treasury Shares (730 ) (140 ) (448 ) Net proceeds from the issuance of Common Shares and preferred stock (350 ) 1,041 22 Cash dividends paid (480 ) (335 ) (267 ) NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES (1,560 ) 545 (443 ) NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS (1,029 ) 678 401 CASH AND DUE FROM BANKS AT BEGINNING OF YEAR 3,286 2,608 2,207 CASH AND DUE FROM BANKS AT END OF YEAR $ 2,257 $ 3,286 $ 2,608

Summary of Significant Accoun62

Summary of Significant Accounting Policies - Narrative (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)SegmentstateATMBranch	Dec. 31, 2017USD ($)SegmentstateATMBranch	Jan. 01, 2018USD ($)	Dec. 31, 2016USD ($)
Accounting Policies [Line Items]
Consolidated total assets of the Company	$ 137,698,000,000	$ 137,698,000,000		$ 136,453,000,000
Number of retail branches | Branch	1,197	1,197
Number of automated teller machines | ATM	1,572	1,572
Number of states with automated teller machines | state	15	15
Number of business groups | Segment	2	2
Number of days to designate the loan as nonaccrual for commercial loan payment due period		90 days
Number of days to designate commercial loans will be charged off in full or charged down to the fair value of the underlying collateral payment due period		180 days
Number of days to designate the loan as nonaccrual for consumer payment due period		120 days
Second lien home equity loan with associated first lien due period		120 days
Number of days to designate the charge-off policy for most consumer loans taking effect, payment due period		120 days
Number of days to designate home equity and residential mortgage loans to get charged down to the fair value of the underlying collateral payment due period		180 days
Number of days to designate charge-off policy for credit card loans and similar unsecured products taking effect, payment due period		180 days
Threshold period by which amortized cost is greater than fair value to be considered as other-than-temporary		6 months
Minimum outstanding impaired commercial loans	$ 2,500,000	$ 2,500,000
Minimum percentage for an input to be significant of the total fair value of a particular asset or liability		10.00%
Threshold percentage by which amortized cost is greater than fair value to be considered as other-than-temporary		20.00%
Maximum limit for vary of market related value		10.00%
Amortization period of stock-based compensation awards		5 years
Vesting period for compensation cost		4 years
Excess tax benefits recognized pertaining to share-based payment arrangements		$ 28,000,000
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	141,000,000	$ 141,000,000
Stock Options [Member]
Accounting Policies [Line Items]
Options expiration years		10 years
Stock Options [Member] | One year after the grant date [Member]
Accounting Policies [Line Items]
Rate at which employee stock options granted to be exercisable		25.00%
Maximum [Member]
Accounting Policies [Line Items]
Nonperforming loans, collectively evaluated for impairment	$ 2,500,000	$ 2,500,000
Maximum [Member] | Stock Options [Member]
Accounting Policies [Line Items]
Options expiration years		10 years
Scenario, Forecast [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member] | Accounting Standards Update 2017-12 [Member]
Accounting Policies [Line Items]
Cumulative effect of new accounting principle in period of adoption			$ 28,000,000

Business Combination - Narrativ

Business Combination - Narrative (Details)	Aug. 01, 2016USD ($)Branch$ / sharesshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jul. 29, 2016$ / shares
Business Acquisition [Line Items]
Goodwill		$ 1,400,000,000	$ 1,386,000,000
First Niagara Bank, N.A. [Member]
Business Acquisition [Line Items]
Total consideration	$ 3,992,000,000
Number of branch locations acquired | Branch	390
Intangible assets acquired	$ 385,000,000
Goodwill	$ 1,404,000,000		1,386,000,000
Merger and acquisition integration costs		1,000,000	44,000,000
Common Stock [Member] | First Niagara Bank, N.A. [Member]
Business Acquisition [Line Items]
Shares available for issuance upon conversion of acquiree stock | shares	0.680
Cash paid upon conversion of acquiree stock	$ 2.30
Shares received by acquiree (in dollars per share) | $ / shares	$ 10.26
Closing price of acquiree stock (in dollars per share) | $ / shares				$ 11.70
Number of shares received by acquiree | shares	240,000,000
Fair value of acquiree options to purchase common stock	$ 26,000,000
Core Deposits [Member] | First Niagara Bank, N.A. [Member]
Business Acquisition [Line Items]
Intangible assets acquired		$ 356,000,000
Useful life of intangible assets		10 years
Commercial Credit Card [Member] | First Niagara Bank, N.A. [Member]
Business Acquisition [Line Items]
Useful life of intangible assets		6 years
Consumer Credit Card [Member] | First Niagara Bank, N.A. [Member]
Business Acquisition [Line Items]
Useful life of intangible assets		9 years
Key Community Bank [Member]
Business Acquisition [Line Items]
Goodwill		$ 1,100,000,000	1,109,000,000
Key Community Bank [Member] | First Niagara Bank, N.A. [Member]
Business Acquisition [Line Items]
Goodwill			1,109,000,000
Key Corporate Bank [Member]
Business Acquisition [Line Items]
Goodwill		$ 280,000,000	277,000,000
Key Corporate Bank [Member] | First Niagara Bank, N.A. [Member]
Business Acquisition [Line Items]
Goodwill			$ 277,000,000

Business Combination - Schedule

Business Combination - Schedule of Purchase Price Allocation (Details) - USD ($) $ in Millions	Aug. 01, 2016	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
LIABILITIES
Goodwill			$ 1,400	$ 1,386
First Niagara Bank, N.A. [Member]
Consideration paid:
KeyCorp common stock issued	$ 2,831
Cash payments to First Niagara stockholders	811
Exchange of First Niagara preferred stock for KeyCorp preferred stock	350
Total consideration paid	3,992
ASSETS
Cash and due from banks and short-term investments	620
Investment securities	9,012
Other investments	297
Loans	23,590	$ 23,590
Premises and equipment	245	1,467
Other intangible assets	385
Accrued income and other assets	1,467
Total assets	35,616
LIABILITIES
Deposits	28,994
Bank notes and other short-term borrowings	2,698
Accrued expense and other liabilities	490
Long-term debt	846
Total liabilities	33,028
Net identifiable assets acquired	2,588
Goodwill	$ 1,404			$ 1,386
Business Combination, Provisional Information [Abstract]
Loans		(55)
Premises and equipment, increase (decrease)		18
Unfunded lending-related commitments		65
Unfunded lending-related commitments, increase (decrease)		(2)
Deferred compensation		41
Deferred compensation, increase (decrease)		2
Scenario, Previously Reported [Member] | First Niagara Bank, N.A. [Member]
ASSETS
Loans		23,645
Premises and equipment		1,449
Business Combination, Provisional Information [Abstract]
Unfunded lending-related commitments		67
Deferred compensation		$ 39
Interest Income [Member] | First Niagara Bank, N.A. [Member]
Business Combination, Provisional Information [Abstract]
Loans			42
Provision for Credit Losses [Member] | First Niagara Bank, N.A. [Member]
Business Combination, Provisional Information [Abstract]
Loans			1
Other Noninterest Income [Member] | First Niagara Bank, N.A. [Member]
Business Combination, Provisional Information [Abstract]
Loans			(3)
Unfunded lending-related commitments, increase (decrease)			$ (4)

Business Combination - Schedu65

Business Combination - Schedule of Changes in Goodwill by Reporting Unit (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Beginning Balance	$ 2,446	$ 2,446	$ 1,060
Acquisition of First Niagara		1,400	1,386
Tax adjustment on previous fair value measurements	(19)	18
Loan adjustment on previous fair value measurements	37
Ending Balance	2,464	2,538	2,446
Key Community Bank [Member]
Goodwill [Roll Forward]
Beginning Balance	2,088	2,088	979
Acquisition of First Niagara		1,100	1,109
Tax adjustment on previous fair value measurements	(15)	15
Loan adjustment on previous fair value measurements	30
Ending Balance	2,103	2,124	2,088
Key Corporate Bank [Member]
Goodwill [Roll Forward]
Beginning Balance	358	358	81
Acquisition of First Niagara		280	277
Tax adjustment on previous fair value measurements	(4)	3
Loan adjustment on previous fair value measurements	7
Ending Balance	$ 361	$ 414	$ 358

Business Combination - Schedu66

Business Combination - Schedule of Operations Included in Consolidated Statement of Income and Unaudited Pro Forma Information (Details) - First Niagara Bank, N.A. [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net interest income (TE)	$ 3,599	$ 3,564
Noninterest income	2,231	2,206
Net income (loss) attributable to common shareholders	$ 1,161	$ 1,187

Earnings Per Common Share - Bas

Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
EARNINGS
Income (loss) from continuing operations		$ 1,291	$ 789	$ 919
Less: Net income (loss) attributable to noncontrolling interests		2	(1)	4
Income (loss) from continuing operations attributable to Key		1,289	790	915
Less: Dividends on preferred stock		70	37	23
Income (loss) from continuing operations attributable to Key common shareholders		1,219	753	892
Income (loss) from discontinued operations, net of taxes		7	1	1
Net income (loss) attributable to Key common shareholders		$ 1,226	$ 754	$ 893
WEIGHTED-AVERAGE COMMON SHARES
Weighted-average common shares outstanding (in shares)		1,072,078	927,816	836,846
Effect of convertible preferred stock (in shares)		0	0	0
Effect of common share options and other stock awards (in shares)		16,515	10,720	7,643
Weighted-average common shares and potential common shares outstanding (000) (in shares)	[1]	1,088,593	938,536	844,489
EARNINGS PER COMMON SHARE
Income (loss) from continuing operations attributable to Key common shareholders (in dollars per share)		$ 1.13	$ 0.81	$ 1.06
Income (loss) from discontinued operations, net of taxes (in dollars per share)		0.01	0	0
Net income (loss) attributable to Key common shareholders (in dollars per share)	[2]	1.14	0.81	1.06
Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution (in dollars per share)		1.12	0.80	1.05
Income (loss) from discontinued operations, net of taxes (in dollars per share)		0.01	0	0
Net income (loss) attributable to Key common shareholders (in dollars per share)	[2]	$ 1.13	$ 0.80	$ 1.05
[1]	Assumes conversion of Common Share options and other stock awards and/or convertible preferred stock, as applicable.
[2]	EPS may not foot due to rounding.

Restrictions on Cash, Dividen68

Restrictions on Cash, Dividends and Lending Activities - Narrative (Details) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Average reserve balance maintained		$ 349
Short-term investments held for discharge of obligations		2,300
KeyBank (consolidated) [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Dividends paid by non banking subsidiaries		$ 750
KeyBank (consolidated) [Member] | Subsequent Event [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Capacity to pay dividends	$ 925

Loans and Loans Held for Sale -

Loans and Loans Held for Sale - Loans by Category (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Residential — prime loans:
Total Loans	$ 86,405	$ 86,038
Collateral for secured borrowings	24	68
Payments to acquire loans held-for-investment	15,400	21,000
Net loans	85,528	85,180
Commercial Credit Card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, financial and agricultural	119	116
PCI Loans [Member]
Residential — prime loans:
Payments to acquire loans held-for-investment	738	1,000
Discontinued Operations [Member] | Education Lending [Member]
Residential — prime loans:
Net loans	1,300	1,600
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, financial and agricultural	41,859	39,768
Commercial real estate:
Commercial mortgage	14,088	15,111
Construction	1,960	2,345
Total commercial real estate loans	16,048	17,456
Commercial lease financing	4,826	4,685
Total loans	62,733	61,909
Residential — prime loans:
Total Loans	62,733	61,909
Consumer Loans [Member]
Commercial real estate:
Total loans	23,672	24,129
Residential — prime loans:
Real estate — residential mortgage	5,483	5,547
Home equity loans	12,028	12,674
Total residential — prime loans	17,511	18,221
Consumer direct loans	1,794	1,788
Credit cards	1,106	1,111
Consumer indirect loans	3,261	3,009
Total Loans	$ 23,672	$ 24,129

Loans and Loans Held for Sale70

Loans and Loans Held for Sale - Loans Held for Sale (Details) - USD ($) $ in Millions	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, financial and agricultural	$ 139		$ 19
Real estate — construction	0		1
Total loans held for sale	1,107	[1]	1,104	[1]	$ 639
Commercial Mortgage Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate - mortgage	897		1,022
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate - mortgage	71		62
Contractually required payments receivable	$ 71		$ 62
[1]	Total loans held for sale include Real estate — residential mortgage loans held for sale at fair value of $71 million at December 31, 2017, and $62 million at December 31, 2016

Loans and Loans Held for Sale71

Loans and Loans Held for Sale - Summary of Changes in Loans Held for Sale (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Loans Receivable Held-for-sale, Net, Reconciliation to Cash Flow [Roll Forward]
Balance at beginning of the period		$ 1,104	[1]	$ 639
Purchases		0		48
New originations		11,860		8,356
Transfers from (to) held to maturity, net		(63)		35
Loan sales		(11,780)		(7,979)
Loan draws (payments), net		(14)		5
Balance at end of period	[1]	1,107		1,104
Residential Mortgage [Member]
Loans Receivable Held-for-sale, Net, Reconciliation to Cash Flow [Roll Forward]
Real estate - mortgage		$ 71		$ 62
[1]	Total loans held for sale include Real estate — residential mortgage loans held for sale at fair value of $71 million at December 31, 2017, and $62 million at December 31, 2016

Loans and Loans Held for Sale72

Loans and Loans Held for Sale - Composition of Net Investment in Direct Financing Leases (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Loans Receivables [Abstract]
Direct financing lease receivables	$ 3,727	$ 3,468
Unearned income	(323)	(278)
Unguaranteed residual value	382	316
Deferred fees and costs	19	16
Net investment in direct financing leases	$ 3,805	$ 3,522

Loans and Loans Held for Sale73

Loans and Loans Held for Sale - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Minimum future lease payment to be received, 2018	$ 1,000
Minimum future lease payment to be received, 2019	860
Minimum future lease payment to be received, 2020	614
Minimum future lease payment to be received, 2021	398
Minimum future lease payment to be received, 2022	249
Minimum future lease payment to be received, subsequent years	467
Allowance related to lease financing receivables	893	$ 882	$ 824	$ 823
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to lease financing receivables	877	858	796	794
Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to lease financing receivables	735	716	656	623
Continuing Operations [Member] | Commercial Loans [Member] | Commercial Lease Financing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to lease financing receivables	$ 43	$ 42	$ 47	$ 56

Asset Quality - Financing Recei

Asset Quality - Financing Receivable Credit Quality Indicators (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 86,405	$ 86,038
Commercial Portfolio Segment Excluding PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	62,376	61,449
Commercial Portfolio Segment Excluding PCI Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	59,785	59,072
Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,400	2,044
Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	191	333
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	41,776	39,656
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,833	37,845
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,790	1,514
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	153	297
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,840	14,789
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,328	14,308
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	482	455
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	30	26
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,934	2,319
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,894	2,287
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	38	30
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	2
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,826	4,685
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,730	4,632
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	90	45
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6	8
Consumer Portfolio Segment Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	23,291	23,724
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,694	12,035
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,563	7,647
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,394	2,486
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	640	1,556
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	17,134	17,823
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,226	9,818
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,181	5,266
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,519	1,617
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	208	1,122
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,790	1,781
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	519	498
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	690	661
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	225	194
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	356	428
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,106	1,111
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	477	453
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	508	525
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	121	132
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	1
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,261	3,009
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,472	1,266
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,184	1,195
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	529	543
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	76	5
Commercial Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	357	460
Commercial Portfolio Segment, PCI [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	220	172
Commercial Portfolio Segment, PCI [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	137	288
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	83	112
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	41	12
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	42	100
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	248	322
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	153	139
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	95	183
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	26	26
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	26	21
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	5
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	381	405
Consumer Portfolio Segment, PCI [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	149	133
Consumer Portfolio Segment, PCI [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	119	129
Consumer Portfolio Segment, PCI [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	107	137
Consumer Portfolio Segment, PCI [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6	6
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	377	398
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	149	133
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	117	127
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	105	133
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6	5
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4	7
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	2
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	4
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	1
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0

Asset Quality - Aging Analysis

Asset Quality - Aging Analysis of Past Due and Current Loans (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 84,716	$ 84,057
Total Past Due and Non-performing Loans	951	1,116
Non-performing Loans	503	625
Purchased Credit Impaired	738	865
Total Loans	86,405	86,038
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	261	305
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	98	99
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	89	87
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	61,904	60,852
Total Past Due and Non-performing Loans	472	597
Non-performing Loans	191	334
Purchased Credit Impaired	357	460
Total Loans	62,733	61,909
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	41,444	39,242
Total Past Due and Non-performing Loans	332	414
Non-performing Loans	153	297
Purchased Credit Impaired	83	112
Total Loans	41,859	39,768
Commercial Loans [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	13,750	14,655
Total Past Due and Non-performing Loans	90	134
Non-performing Loans	30	26
Purchased Credit Impaired	248	322
Total Loans	14,088	15,111
Commercial Loans [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,919	2,314
Total Past Due and Non-performing Loans	15	5
Non-performing Loans	2	3
Purchased Credit Impaired	26	26
Total Loans	1,960	2,345
Commercial Loans [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,669	16,969
Total Past Due and Non-performing Loans	105	139
Non-performing Loans	32	29
Purchased Credit Impaired	274	348
Total Loans	16,048	17,456
Commercial Loans [Member] | Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,791	4,641
Total Past Due and Non-performing Loans	35	44
Non-performing Loans	6	8
Purchased Credit Impaired	0	0
Total Loans	4,826	4,685
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	164	179
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	111	58
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	26	93
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	4	0
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	30	93
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	23	28
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	60	40
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	34	28
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	13	9
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	9	0
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	22	9
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	4	3
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	57	44
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	34	31
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	21	6
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	0	2
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	21	8
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	2	5
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	22,812	23,205
Total Past Due and Non-performing Loans	479	519
Non-performing Loans	312	291
Purchased Credit Impaired	381	405
Total Loans	23,672	24,129
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,043	5,098
Total Past Due and Non-performing Loans	85	81
Non-performing Loans	58	56
Purchased Credit Impaired	355	368
Total Loans	5,483	5,547
Consumer Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	11,721	12,327
Total Past Due and Non-performing Loans	285	317
Non-performing Loans	229	223
Purchased Credit Impaired	22	30
Total Loans	12,028	12,674
Consumer Loans [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,768	1,705
Total Past Due and Non-performing Loans	22	76
Non-performing Loans	4	6
Purchased Credit Impaired	4	7
Total Loans	1,794	1,788
Consumer Loans [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,081	1,082
Total Past Due and Non-performing Loans	25	29
Non-performing Loans	2	2
Purchased Credit Impaired	0	0
Total Loans	1,106	1,111
Consumer Loans [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,199	2,993
Total Past Due and Non-performing Loans	62	16
Non-performing Loans	19	4
Purchased Credit Impaired	0	0
Total Loans	3,261	3,009
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	97	126
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	16	17
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	32	49
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	9	44
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	7	9
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	33	7
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	38	59
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	7	5
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	15	29
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	4	15
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	6
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	7	4
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	32	43
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	4	3
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	9	16
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	11
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	11	12
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	$ 3	$ 1

Asset Quality - Narrative (Deta

Asset Quality - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)SecurityLoan	Dec. 31, 2016USD ($)SecurityLoan	Dec. 31, 2015USD ($)SecurityLoan	Dec. 31, 2012USD ($)	Sep. 09, 2016Branch	Aug. 01, 2016USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of carrying amount of our commercial nonperforming loans outstanding	71.00%
Percentage of nonperforming loans outstanding face value	80.00%
Percentage of loans held for sale and other nonperforming assets	80.00%
Net reduction to interest income	$ 25	$ 26	$ 16
Commitments outstanding to lend additional funds to borrowers	2	14
Financial receivable, modifications, subsequent default, recorded investment	4
OREO	31	51
Provision (credit) for loan and lease losses	$ 237	$ 280	165
Estimated gross contractual amount receivable of PCI loans				$ 41
Estimated cash flows nonaccretable amount				11
Accretable yield				$ 5
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivable, modifications, subsequent default, recorded investment			$ 1
Number of loans | SecurityLoan	0	0	2
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivable, modifications, subsequent default, recorded investment		$ 9	$ 12
Number of loans | SecurityLoan	147	187	269
Real Estate - Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivable, modifications, subsequent default, recorded investment	$ 142	$ 141
Continuing Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision (credit) for loan and lease losses	227	267	$ 144
Continuing Operations [Member] | Purchase Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision (credit) for loan and lease losses	3	11
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income recognized on outstanding balances	9	10	6
Commercial Loans [Member] | Continuing Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision (credit) for loan and lease losses	130	179	96
Consumer Loans [Member] | Continuing Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision (credit) for loan and lease losses	97	88	48
Consumer Loans [Member] | Continuing Operations [Member] | Real Estate - Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision (credit) for loan and lease losses	(11)	2	$ (2)
First Niagara Bank, N.A. [Member] | Purchase Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractually required payments receivable						$ 22,500
Fair value of acquired receivables						22,000
Estimated cash flows not expected to be collected						500
Accretable yield						$ 172
First Niagara Financial Group, Inc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of branches sold | Branch					18
Foreclosed Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value of foreclosed residential real estate	$ 26	$ 29

Asset Quality - Breakdown of In

Asset Quality - Breakdown of Individually Impaired Loans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	$ 213	$ 306
With related allowance recorded, Recorded Investment	141	195
Recorded Investment	354	501
With no related allowance recorded, Unpaid Principal Balance	246	386
With related allowance recorded, Unpaid Principal Balance	159	207
Unpaid Principal Balance	405	593
Specific Allowance	23	38
Average Recorded Investment	428	405	$ 305
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	138	224
With related allowance recorded, Recorded Investment	10	66
With no related allowance recorded, Unpaid Principal Balance	171	304
With related allowance recorded, Unpaid Principal Balance	28	77
Specific Allowance	6	17
Average Recorded Investment	219	187	78
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	126	222
With related allowance recorded, Recorded Investment	10	62
With no related allowance recorded, Unpaid Principal Balance	153	301
With related allowance recorded, Unpaid Principal Balance	28	73
Specific Allowance	6	17
Average Recorded Investment	210	176	56
Commercial Loans [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	12	2
With related allowance recorded, Recorded Investment	0	4
With no related allowance recorded, Unpaid Principal Balance	18	3
With related allowance recorded, Unpaid Principal Balance	0	4
Specific Allowance	0	0
Average Recorded Investment	9	8	15
Commercial Loans [Member] | Commercial Real Estate: Construction [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	0
With no related allowance recorded, Unpaid Principal Balance	0
Average Recorded Investment	0	3	7
Commercial Loans [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	12	2
With related allowance recorded, Recorded Investment	0	4
With no related allowance recorded, Unpaid Principal Balance	18	3
With related allowance recorded, Unpaid Principal Balance	0	4
Specific Allowance	0	0
Average Recorded Investment	9	11	22
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	75	82
With related allowance recorded, Recorded Investment	131	129
With no related allowance recorded, Unpaid Principal Balance	75	82
With related allowance recorded, Unpaid Principal Balance	131	130
Specific Allowance	17	21
Average Recorded Investment	209	218	227
Consumer Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	56	61
With related allowance recorded, Recorded Investment	61	64
With no related allowance recorded, Unpaid Principal Balance	56	61
With related allowance recorded, Unpaid Principal Balance	61	64
Specific Allowance	9	18
Average Recorded Investment	121	125	122
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	17	20
With related allowance recorded, Recorded Investment	32	31
With no related allowance recorded, Unpaid Principal Balance	17	20
With related allowance recorded, Unpaid Principal Balance	32	31
Specific Allowance	5	2
Average Recorded Investment	50	53	55
Consumer Loans [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	2	1
With related allowance recorded, Recorded Investment	32	29
With no related allowance recorded, Unpaid Principal Balance	2	1
With related allowance recorded, Unpaid Principal Balance	32	29
Specific Allowance	3	1
Average Recorded Investment	32	34	42
Consumer Loans [Member] | Consumer Direct Loans [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	4	2
With related allowance recorded, Unpaid Principal Balance	4	3
Specific Allowance	0	0
Average Recorded Investment	3	3	4
Consumer Loans [Member] | Consumer Credit Card [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	2	3
With related allowance recorded, Unpaid Principal Balance	2	3
Specific Allowance	0	0
Average Recorded Investment	$ 3	$ 3	$ 4

Asset Quality - Post-Modificati

Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 130	$ 71	$ 83
Total loans	86,405	86,038
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	0	0	0
Forgiveness of principal	0	0	22
Extension of maturity date	12	0	21
Payment or covenant modification/deferment	46	19	0
Bankruptcy plan modification	31	18	0
Total	89	37	43
Total loans	62,733	61,909
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	13	10	19
Forgiveness of principal	0	3	4
Other	28	21	17
Total	41	34	$ 40
Total loans	$ 23,672	$ 24,129

Asset Quality - Summary of Post

Asset Quality - Summary of Post-Modification Outstanding Recorded Investment TDRs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivables, Modifications, Rollforward [Roll Forward]
Balance at beginning of the period	$ 280	$ 280
Additions	165	107
Payments	(111)	(68)
Charge-offs	(17)	(39)
Balance at end of period	$ 317	$ 280

Asset Quality - Breakdown of No

Asset Quality - Breakdown of Nonperforming TDRs by Loans Category (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)SecurityLoan	Dec. 31, 2016USD ($)SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	5,184	4,515
Pre-modification Outstanding Recorded Investment	$ 398	$ 389
Post-modification Outstanding Recorded Investment	$ 317	$ 280
Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,562	2,535
Pre-modification Outstanding Recorded Investment	$ 171	$ 196
Post-modification Outstanding Recorded Investment	$ 128	$ 139
Nonperforming [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,622	1,980
Pre-modification Outstanding Recorded Investment	$ 227	$ 193
Post-modification Outstanding Recorded Investment	$ 189	$ 141
Commercial Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	4	5
Pre-modification Outstanding Recorded Investment	$ 30	$ 30
Post-modification Outstanding Recorded Investment	$ 13	$ 16
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	4	5
Pre-modification Outstanding Recorded Investment	$ 30	$ 30
Post-modification Outstanding Recorded Investment	$ 13	$ 16
Commercial Loans [Member] | Nonperforming [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	28	25
Pre-modification Outstanding Recorded Investment	$ 125	$ 93
Post-modification Outstanding Recorded Investment	$ 98	$ 51
Commercial Loans [Member] | Nonperforming [Member] | Commercial, Financial and Agricultural [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	20	18
Pre-modification Outstanding Recorded Investment	$ 109	$ 91
Post-modification Outstanding Recorded Investment	$ 86	$ 50
Commercial Loans [Member] | Nonperforming [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	8	7
Pre-modification Outstanding Recorded Investment	$ 16	$ 2
Post-modification Outstanding Recorded Investment	$ 12	$ 1
Commercial Loans [Member] | Nonperforming [Member] | Commercial Real Estate Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	8	7
Pre-modification Outstanding Recorded Investment	$ 16	$ 2
Post-modification Outstanding Recorded Investment	$ 12	$ 1
Consumer Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,558	2,530
Pre-modification Outstanding Recorded Investment	$ 141	$ 166
Post-modification Outstanding Recorded Investment	$ 115	$ 123
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	484	477
Pre-modification Outstanding Recorded Investment	$ 31	$ 35
Post-modification Outstanding Recorded Investment	$ 31	$ 35
Consumer Loans [Member] | Home Equity Loan [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,276	1,231
Pre-modification Outstanding Recorded Investment	$ 75	$ 70
Post-modification Outstanding Recorded Investment	$ 59	$ 57
Consumer Loans [Member] | Consumer Direct Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	48	35
Pre-modification Outstanding Recorded Investment	$ 3	$ 2
Post-modification Outstanding Recorded Investment	$ 2	$ 2
Consumer Loans [Member] | Consumer Credit Card [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	430	410
Pre-modification Outstanding Recorded Investment	$ 1	$ 3
Post-modification Outstanding Recorded Investment	$ 1	$ 1
Consumer Loans [Member] | Consumer Indirect Loans [Member] | Prior-Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	320	377
Pre-modification Outstanding Recorded Investment	$ 31	$ 56
Post-modification Outstanding Recorded Investment	$ 22	$ 28
Consumer Loans [Member] | Nonperforming [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,594	1,955
Pre-modification Outstanding Recorded Investment	$ 102	$ 100
Post-modification Outstanding Recorded Investment	$ 91	$ 90
Consumer Loans [Member] | Nonperforming [Member] | Real Estate - Residential Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	308	264
Pre-modification Outstanding Recorded Investment	$ 18	$ 16
Post-modification Outstanding Recorded Investment	$ 18	$ 16
Consumer Loans [Member] | Nonperforming [Member] | Home Equity Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,025
Pre-modification Outstanding Recorded Investment	$ 64
Post-modification Outstanding Recorded Investment	$ 57
Consumer Loans [Member] | Nonperforming [Member] | Home Equity Loan [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan		1,199
Pre-modification Outstanding Recorded Investment		$ 77
Post-modification Outstanding Recorded Investment		$ 69
Consumer Loans [Member] | Nonperforming [Member] | Consumer Direct Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	114	32
Pre-modification Outstanding Recorded Investment	$ 2	$ 1
Post-modification Outstanding Recorded Investment	$ 2	$ 0
Consumer Loans [Member] | Nonperforming [Member] | Consumer Credit Card [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	322	336
Pre-modification Outstanding Recorded Investment	$ 2	$ 2
Post-modification Outstanding Recorded Investment	$ 1	$ 2
Consumer Loans [Member] | Nonperforming [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	825
Pre-modification Outstanding Recorded Investment	$ 16
Post-modification Outstanding Recorded Investment	$ 13
Consumer Loans [Member] | Nonperforming [Member] | Consumer Indirect Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan		124
Pre-modification Outstanding Recorded Investment		$ 4
Post-modification Outstanding Recorded Investment		$ 3

Asset Quality - Summary of Allo

Asset Quality - Summary of Allowance for Loan and Lease Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 882	$ 824	$ 823
Charge-offs	(328)	(289)	(238)
Recoveries	102	67	74
Provision for loan and lease losses from continuing operations	229	266	166
Ending balance	893	882	824
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	858	796	794
Charge-offs	(302)	(261)	(203)
Recoveries	94	56	61
Net loans and leases charged off	(208)	(205)	(142)
Provision for loan and lease losses from continuing operations	227	267	145
Foreign currency translation adjustment	0	0	1
Ending balance	877	858	796
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	24	28	29
Charge-offs	(26)	(28)	(35)
Recoveries	8	11	13
Ending balance	$ 16	$ 24	$ 28

Asset Quality - Changes in Allo

Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 882	$ 824	$ 823
Provision	237	280	165
Charge-offs	(328)	(289)	(238)
Recoveries	102	67	74
Ending balance	893	882	824
Provision for credit losses	229	266	166
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	858	796	794
Provision	227	267	144
Charge-offs	(302)	(261)	(203)
Recoveries	94	56	61
Ending balance	877	858	796
Provision for credit losses	2	1	21
Foreign currency translation adjustment			1
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	24	28	29
Provision	10	13	21
Charge-offs	(26)	(28)	(35)
Recoveries	8	11	13
Ending balance	16	24	28
Commercial Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	716	656	623
Provision	130	179	96
Charge-offs	(160)	(144)	(93)
Recoveries	49	25	30
Ending balance	735	716	656
Commercial Loans [Member] | Continuing Operations [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	508	450	391
Provision	114	165	120
Charge-offs	(133)	(118)	(77)
Recoveries	40	11	16
Ending balance	529	508	450
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	144	134	148
Provision	(2)	6	(16)
Charge-offs	(11)	(5)	(4)
Recoveries	2	9	6
Ending balance	133	144	134
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	22	25	28
Provision	9	4	(3)
Charge-offs	(2)	(9)	(1)
Recoveries	1	2	1
Ending balance	30	22	25
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Lease Financing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	42	47	56
Provision	9	4	(5)
Charge-offs	(14)	(12)	(11)
Recoveries	6	3	7
Ending balance	43	42	47
Consumer Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	142	140	171
Provision	97	88	48
Charge-offs	(142)	(117)	(110)
Recoveries	45	31	31
Ending balance	142	142	140
Consumer Loans [Member] | Continuing Operations [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	17	18	23
Provision	(11)	2	(2)
Charge-offs	(3)	(4)	(6)
Recoveries	4	1	3
Ending balance	7	17	18
Consumer Loans [Member] | Continuing Operations [Member] | Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	54	57	71
Provision	4	13	7
Charge-offs	(30)	(30)	(32)
Recoveries	15	14	11
Ending balance	43	54	57
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Direct Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	24	20	22
Provision	32	26	16
Charge-offs	(34)	(27)	(24)
Recoveries	6	5	6
Ending balance	28	24	20
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	38	32	33
Provision	45	37	27
Charge-offs	(44)	(35)	(30)
Recoveries	5	4	2
Ending balance	44	38	32
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	9	13	22
Provision	27	10	0
Charge-offs	(31)	(21)	(18)
Recoveries	15	7	9
Ending balance	$ 20	$ 9	$ 13

Asset Quality - Breakdown of Al

Asset Quality - Breakdown of Allowance for Loan and Lease Losses and Corresponding Loan Balances (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance, Total ALLL - Including Discontinued Operations	$ 26	$ 39
Collectively Evaluated for Impairment Allowance, Total ALLL - Including Discontinued Operations	861	838
Purchased Credit Impaired Allowance, Total ALLL - Including Discontinued Operations	6	5
Loans Outstanding, Total ALLL - Including Discontinued Operations	87,719	87,603
Individually Evaluated for Impairment Outstanding, Total ALLL - Including Discontinued Operations	375	523
Collectively Evaluated for Impairment Outstanding, Total ALLL - Including Discontinued Operations	86,606	86,215
Purchased Credit Impaired Outstanding, Total ALLL - Including Discontinued Operations	738	865
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	23	37
Collectively Evaluated for Impairment Allowance	848	816
Purchase Credit Impairment Allowance	6	5
Loans Outstanding	86,405	86,038
Individually Evaluated for Impairment Outstanding	354	501
Collectively Evaluated for Impairment Outstanding	85,313	84,672
Purchase Credit Impairment Outstanding	738	865
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	3	2
Collectively Evaluated for Impairment Allowance	13	22
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	1,314	1,565
Individually Evaluated for Impairment Outstanding	21	22
Collectively Evaluated for Impairment Outstanding	1,293	1,543
Purchase Credit Impairment Outstanding	0	0
Loans carried at fair value	2
Commercial Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	6	17
Collectively Evaluated for Impairment Allowance	724	694
Purchase Credit Impairment Allowance	5	5
Loans Outstanding	62,733	61,909
Individually Evaluated for Impairment Outstanding	148	289
Collectively Evaluated for Impairment Outstanding	62,228	61,160
Purchase Credit Impairment Outstanding	357	460
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	6	17
Collectively Evaluated for Impairment Allowance	520	486
Purchase Credit Impairment Allowance	3	5
Loans Outstanding	41,859	39,768
Individually Evaluated for Impairment Outstanding	136	284
Collectively Evaluated for Impairment Outstanding	41,640	39,372
Purchase Credit Impairment Outstanding	83	112
Commercial Loans [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	131	144
Purchase Credit Impairment Allowance	2	0
Loans Outstanding	14,088	15,111
Individually Evaluated for Impairment Outstanding	12	5
Collectively Evaluated for Impairment Outstanding	13,828	14,784
Purchase Credit Impairment Outstanding	248	322
Commercial Loans [Member] | Commercial Real Estate: Construction [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	30	22
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	1,960	2,345
Individually Evaluated for Impairment Outstanding	0	0
Collectively Evaluated for Impairment Outstanding	1,934	2,319
Purchase Credit Impairment Outstanding	26	26
Commercial Loans [Member] | Commercial Real Estate Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	161	166
Purchase Credit Impairment Allowance	2	0
Loans Outstanding	16,048	17,456
Individually Evaluated for Impairment Outstanding	12	5
Collectively Evaluated for Impairment Outstanding	15,762	17,103
Purchase Credit Impairment Outstanding	274	348
Commercial Loans [Member] | Commercial Lease Financing [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	43	42
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	4,826	4,685
Individually Evaluated for Impairment Outstanding	0	0
Collectively Evaluated for Impairment Outstanding	4,826	4,685
Purchase Credit Impairment Outstanding	0	0
Consumer Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	17	20
Collectively Evaluated for Impairment Allowance	124	122
Purchase Credit Impairment Allowance	1	0
Loans Outstanding	23,672	24,129
Individually Evaluated for Impairment Outstanding	206	212
Collectively Evaluated for Impairment Outstanding	23,085	23,512
Purchase Credit Impairment Outstanding	381	405
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	5	2
Collectively Evaluated for Impairment Allowance	2	15
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	5,483	5,547
Individually Evaluated for Impairment Outstanding	49	51
Collectively Evaluated for Impairment Outstanding	5,079	5,128
Purchase Credit Impairment Outstanding	355	368
Consumer Loans [Member] | Home Equity Loan [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	9	17
Collectively Evaluated for Impairment Allowance	33	37
Purchase Credit Impairment Allowance	1	0
Loans Outstanding	12,028	12,674
Individually Evaluated for Impairment Outstanding	117	125
Collectively Evaluated for Impairment Outstanding	11,889	12,519
Purchase Credit Impairment Outstanding	22	30
Consumer Loans [Member] | Consumer Direct Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	28	24
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	1,794	1,788
Individually Evaluated for Impairment Outstanding	4	3
Collectively Evaluated for Impairment Outstanding	1,786	1,778
Purchase Credit Impairment Outstanding	4	7
Consumer Loans [Member] | Credit Card Receivable [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	44	38
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	1,106	1,111
Individually Evaluated for Impairment Outstanding	2	3
Collectively Evaluated for Impairment Outstanding	1,104	1,108
Purchase Credit Impairment Outstanding	0	0
Consumer Loans [Member] | Consumer Indirect Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	3	1
Collectively Evaluated for Impairment Allowance	17	8
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	3,261	3,009
Individually Evaluated for Impairment Outstanding	34	30
Collectively Evaluated for Impairment Outstanding	3,227	2,979
Purchase Credit Impairment Outstanding	0	0
Education Lending [Member] | Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans carried at fair value	$ 2	$ 3

Asset Quality - Changes in Liab

Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 55	$ 56	$ 35
Provision (credit) for losses on lending-related commitments	2	(1)	21
Balance at end of period	$ 57	$ 55	$ 56

Asset Quality - PCI and Non-Imp

Asset Quality - PCI and Non-Impaired Loans Receivable (Details) - USD ($) $ in Millions	Aug. 01, 2016	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accretable yield		$ 5
First Niagara Bank, N.A. [Member] | Purchase Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractual required payments receivable	$ 1,434
Nonaccretable difference	173
Expected cash flows	1,261
Accretable yield	172
Fair value	$ 1,089

Asset Quality - Changes in Outs

Asset Quality - Changes in Outstanding Unpaid Principal Balance, Carrying Amount, and Accretable Yield for PCI Loans (Details) - Purchase Credit Impaired Loans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accretable Yield
Balance at beginning of period	$ 197	$ 5
Additions	(32)	205
Accretion	(44)	(29)
Net reclassifications from non-accretable to accretable	15	35
Payments received, net	(4)	(19)
Disposals	(1)	0
Balance at end of period	131	197
Carrying Amount	738	865	$ 11
Outstanding Unpaid Principal Balance	$ 803	$ 1,002	$ 17

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value of Direct and Indirect Investments, Related Unfunded Commitments and Financial Support Provided (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Principal Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 137
Unfunded Commitments	29
Funded Commitments	1	$ 6
Funded Other	0	13
Direct Investments [Member] | Principal Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	13
Unfunded Commitments	0
Funded Commitments	0	0
Funded Other	$ 0	13
Indirect Investments [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation period of funds	1 year
Indirect Investments [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation period of funds	8 years
Indirect Investments [Member] | Principal Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 124
Unfunded Commitments	29
Funded Commitments	1	6
Funded Other	$ 0	$ 0

Fair Value Measurements - Fai88

Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	$ 836,000,000	$ 867,000,000
Securities available for sale	18,139,000,000	20,212,000,000
Loans net of deferred income	86,405,000,000	86,038,000,000
Loans held for sale	0	0
Netting adjustments	(443,000,000)	(431,000,000)
Total derivative assets	669,000,000	803,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Netting adjustments	(616,000,000)	(384,000,000)
Total derivative liabilities	291,000,000	636,000,000
Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	14,660,000,000	16,408,000,000
U.S. Treasury, Agencies and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	157,000,000	184,000,000
States and Political Subdivisions [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	9,000,000	11,000,000
Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	20,000,000	20,000,000
Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,439,000,000	1,846,000,000
Other Mortgage-Backed Securities [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,854,000,000	1,743,000,000
Fair Value, Measurements, Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Commercial loans	15,000,000	18,000,000
Total trading account assets	836,000,000	867,000,000
Securities available for sale	18,139,000,000	20,212,000,000
Total other investments	144,000,000	191,000,000
Loans net of deferred income	2,000,000	0
Loans held for sale	71,000,000	62,000,000
Derivative assets	1,112,000,000	1,234,000,000
Netting adjustments	(443,000,000)	(431,000,000)
Total derivative assets	669,000,000	803,000,000
Accrued income and other assets	0	8,000,000
Total assets on a recurring basis at fair value	19,861,000,000	22,143,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Accrued expense and other liabilities	0	14,000,000
Total liabilities on a recurring basis at fair value	925,000,000	1,458,000,000
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	14,660,000,000	16,408,000,000
Fair Value, Measurements, Recurring [Member] | Trading Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	821,000,000	849,000,000
Fair Value, Measurements, Recurring [Member] | U.S. Treasury, Agencies and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	615,000,000	655,000,000
Securities available for sale	157,000,000	184,000,000
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	37,000,000	8,000,000
Securities available for sale	9,000,000	11,000,000
Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	65,000,000	73,000,000
Securities available for sale	20,000,000	20,000,000
Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale		1,846,000,000
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,854,000,000
Fair Value, Measurements, Recurring [Member] | Principal Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	13,000,000	27,000,000
Fair Value, Measurements, Recurring [Member] | Principal Indirect Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	124,000,000	158,000,000
Fair Value, Measurements, Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	137,000,000	185,000,000
Fair Value, Measurements, Recurring [Member] | Equity and Mezzanine Investments Indirect [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	7,000,000	6,000,000
Fair Value, Measurements, Recurring [Member] | Private Equity and Mezzanine Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	7,000,000	6,000,000
Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	104,000,000	113,000,000
Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,439,000,000
Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale		1,743,000,000
Fair Value, Measurements, Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	634,000,000	808,000,000
Fair Value, Measurements, Recurring [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	907,000,000	1,020,000,000
Netting adjustments	(616,000,000)	(384,000,000)
Total derivative liabilities	291,000,000	636,000,000
Fair Value, Measurements, Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	722,000,000	930,000,000
Fair Value, Measurements, Recurring [Member] | Interest Rate [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	520,000,000	737,000,000
Fair Value, Measurements, Recurring [Member] | Foreign Exchange [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	130,000,000	123,000,000
Fair Value, Measurements, Recurring [Member] | Foreign Exchange [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	124,000,000	113,000,000
Fair Value, Measurements, Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	255,000,000	176,000,000
Fair Value, Measurements, Recurring [Member] | Commodity [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	246,000,000	165,000,000
Fair Value, Measurements, Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	1,000,000	1,000,000
Fair Value, Measurements, Recurring [Member] | Credit [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	4,000,000	4,000,000
Fair Value, Measurements, Recurring [Member] | Other Credit Derivatives [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	4,000,000	4,000,000
Fair Value, Measurements, Recurring [Member] | Other Credit Derivatives [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	13,000,000	1,000,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Commercial loans	0	0
Total trading account assets	0	0
Securities available for sale	0	3,000,000
Total other investments	0	0
Loans net of deferred income	0	0
Loans held for sale	0	0
Derivative assets	100,000,000	114,000,000
Netting adjustments	0	0
Total derivative assets	100,000,000	114,000,000
Accrued income and other assets	0	0
Total assets on a recurring basis at fair value	100,000,000	117,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Accrued expense and other liabilities	0	0
Total liabilities on a recurring basis at fair value	170,000,000	294,000,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Trading Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury, Agencies and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	3,000,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale		0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Indirect Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity and Mezzanine Investments Indirect [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity and Mezzanine Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale		0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	72,000,000	192,000,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	98,000,000	102,000,000
Netting adjustments	0	0
Total derivative liabilities	98,000,000	102,000,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Exchange [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	100,000,000	114,000,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Exchange [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	98,000,000	102,000,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Credit [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Credit Derivatives [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Credit Derivatives [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Commercial loans	15,000,000	18,000,000
Total trading account assets	836,000,000	867,000,000
Securities available for sale	18,119,000,000	20,192,000,000
Total other investments	4,000,000	0
Loans net of deferred income	0	0
Loans held for sale	70,000,000	62,000,000
Derivative assets	999,000,000	1,110,000,000
Netting adjustments	0	0
Total derivative assets	999,000,000	1,110,000,000
Accrued income and other assets	0	8,000,000
Total assets on a recurring basis at fair value	20,028,000,000	22,239,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Accrued expense and other liabilities	0	14,000,000
Total liabilities on a recurring basis at fair value	1,371,000,000	1,548,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	14,660,000,000	16,408,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Trading Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	821,000,000	849,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury, Agencies and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	615,000,000	655,000,000
Securities available for sale	157,000,000	184,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	37,000,000	8,000,000
Securities available for sale	9,000,000	11,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	65,000,000	73,000,000
Securities available for sale	0	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale		1,846,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,854,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Indirect Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity and Mezzanine Investments Indirect [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	4,000,000	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity and Mezzanine Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	4,000,000	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	104,000,000	113,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,439,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale		1,743,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	562,000,000	616,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	809,000,000	918,000,000
Netting adjustments	0	0
Total derivative liabilities	809,000,000	918,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	713,000,000	923,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	520,000,000	737,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Exchange [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	30,000,000	9,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Exchange [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	26,000,000	11,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	255,000,000	176,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	246,000,000	165,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Credit [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	4,000,000	4,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Credit Derivatives [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	1,000,000	2,000,000
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Credit Derivatives [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	13,000,000	1,000,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Commercial loans	0	0
Total trading account assets	0	0
Securities available for sale	20,000,000
Total other investments	16,000,000	27,000,000
Loans net of deferred income	2,000,000	0
Loans held for sale	1,000,000	0
Derivative assets	13,000,000	10,000,000
Netting adjustments	0	0
Total derivative assets	13,000,000	10,000,000
Accrued income and other assets	0	0
Total assets on a recurring basis at fair value	52,000,000	54,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Accrued expense and other liabilities	0	0
Total liabilities on a recurring basis at fair value	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Trading Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury, Agencies and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	20,000,000	17,000,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale		0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	13,000,000	27,000,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Indirect Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	13,000,000	27,000,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity and Mezzanine Investments Indirect [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	3,000,000	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity and Mezzanine Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	3,000,000	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale		0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Netting adjustments	0	0
Total derivative liabilities	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	9,000,000	7,000,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Exchange [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Exchange [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	1,000,000	1,000,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Credit [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Credit Derivatives [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	3,000,000	2,000,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Credit Derivatives [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Estimate of Fair Value Measurement [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	836,000,000	867,000,000
Securities available for sale	18,139,000,000	20,212,000,000
Loans held for sale	1,107,000,000	1,104,000,000
Total derivative assets	669,000,000	803,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Total derivative liabilities	291,000,000	636,000,000
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	3,000,000
Loans held for sale	0	0
Total derivative assets	100,000,000	114,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Total derivative liabilities	98,000,000	102,000,000
Estimate of Fair Value Measurement [Member] | Level 2 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	836,000,000	867,000,000
Securities available for sale	18,119,000,000	20,192,000,000
Loans held for sale	70,000,000	62,000,000
Total derivative assets	999,000,000	1,110,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Total derivative liabilities	809,000,000	918,000,000
Estimate of Fair Value Measurement [Member] | Level 3 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	20,000,000	17,000,000
Loans held for sale	1,037,000,000	1,042,000,000
Total derivative assets	13,000,000	10,000,000
LIABILITIES MEASURED ON A RECURRING BASIS
Total derivative liabilities	$ 0	$ 0

Fair Value Measurements - Chang

Fair Value Measurements - Change in Fair Values of Level 3 Financial Instruments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities [Member] | Other Securities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	$ 17,000,000	$ 17,000,000
Gains (Losses) included in comprehensive income	3,000,000
Gains (Losses) Included in Earnings	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance	20,000,000	17,000,000
Unrealized Gains (Losses) Included in Earnings	0	0
Other Investments [Member] | Principal Investments Direct [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	27,000,000	50,000,000
Gains (Losses) included in comprehensive income	0
Gains (Losses) Included in Earnings	(6,000,000)	16,000,000
Purchases	0	0
Sales	(8,000,000)	(39,000,000)
Settlements	0	0
Transfers Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance	13,000,000	27,000,000
Unrealized Gains (Losses) Included in Earnings	(1,000,000)	2,000,000
Other Investments [Member] | Principal Other Indirect Investments [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	0	0
Gains (Losses) Included in Earnings		0
Purchases		0
Sales		(20,000,000)
Settlements		0
Transfers Other		0
Transfers into Level 3		20,000,000
Transfers out of Level 3		0
End of Period Balance		0
Unrealized Gains (Losses) Included in Earnings		(1,000,000)
Other Investments [Member] | Equity Investments Direct [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	0
Gains (Losses) included in comprehensive income	0
Gains (Losses) Included in Earnings	0
Purchases	0
Sales	0
Settlements	0
Transfers Other	0
Transfers into Level 3	3,000,000
Transfers out of Level 3	0
End of Period Balance	3,000,000	0
Unrealized Gains (Losses) Included in Earnings	0
Interest Rate [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	7,000,000	16,000,000
Gains (Losses) included in comprehensive income	0
Gains (Losses) Included in Earnings	(2,000,000)	4,000,000
Purchases	0	1,000,000
Sales	0	0
Settlements	0	0
Transfers Other	0	0
Transfers into Level 3	13,000,000	9,000,000
Transfers out of Level 3	(9,000,000)	(23,000,000)
End of Period Balance	9,000,000	7,000,000
Unrealized Gains (Losses) Included in Earnings	0	0
Credit [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	1,000,000	1,000,000
Gains (Losses) included in comprehensive income	0
Gains (Losses) Included in Earnings	(16,000,000)	(13,000,000)
Purchases	0	1,000,000
Sales	0	0
Settlements	16,000,000	12,000,000
Transfers Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance	1,000,000	1,000,000
Unrealized Gains (Losses) Included in Earnings	0	0
Other Credit Derivatives [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	2,000,000	0
Gains (Losses) included in comprehensive income	0
Gains (Losses) Included in Earnings	0	0
Purchases	0	5,000,000
Sales	0	0
Settlements	0	0
Transfers Other	1,000,000	3,000,000
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
End of Period Balance	3,000,000	2,000,000
Unrealized Gains (Losses) Included in Earnings	0	0
Loans Held For Sale Fair Value [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	0
Gains (Losses) included in comprehensive income	0
Gains (Losses) Included in Earnings	0
Purchases	0
Sales	(3,000,000)
Settlements	0
Transfers Other	4,000,000
Transfers into Level 3	0
Transfers out of Level 3	0
End of Period Balance	1,000,000	0
Unrealized Gains (Losses) Included in Earnings	0
Loans Held For Investment Fair Value [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning of Period Balance	0
Gains (Losses) included in comprehensive income	0
Gains (Losses) Included in Earnings	0
Purchases	0
Sales	0
Settlements	0
Transfers Other	2,000,000
Transfers into Level 3	0
Transfers out of Level 3	0
End of Period Balance	2,000,000	$ 0
Unrealized Gains (Losses) Included in Earnings	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities measured at fair value on non recurring basis	$ 0	$ 0
Loans held for sale adjusted to fair value	$ 0	0
Fair value of OREO property re-evaluated period	90 days
Fair value measurements, third party broker price opinion periodic review period	180 days
Net loans	$ 85,528,000,000	85,180,000,000
Discontinued Operations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans carried at fair value	2,000,000
Discontinued Operations [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	1,300,000,000	1,600,000,000
Loans carried at fair value	2,000,000	3,000,000
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	85,528,000,000	85,180,000,000
Carrying Amount [Member] | Discontinued Operations [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	1,300,000,000	1,500,000,000
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale adjusted to fair value	1,107,000,000	1,104,000,000
Loans carried at fair value	84,005,000,000	83,285,000,000
Estimate of Fair Value Measurement [Member] | Discontinued Operations [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	$ 1,100,000,000	$ 1,300,000,000

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
ASSETS MEASURED ON A NONRECURRING BASIS
Loans held for sale	$ 0	$ 0	$ 0
Impairment related to tax credit carryforwards impacted by TCJ Act	31,000,000
Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	9,000,000	9,000,000	11,000,000
Loans held for sale	0	0	0
Accrued income and other assets	138,000,000	138,000,000	11,000,000
Total assets on a recurring basis at fair value	147,000,000	147,000,000	22,000,000
Transfer of commercial and residential loans and leases from HFS to HTM		63,000,000	35,000,000
Nonrecurring [Member] | Level 1 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	0	0	0
Loans held for sale	0	0	0
Accrued income and other assets	0	0	0
Total assets on a recurring basis at fair value	0	0	0
Nonrecurring [Member] | Level 2 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	0	0	0
Loans held for sale	0	0	0
Accrued income and other assets	5,000,000	5,000,000	0
Total assets on a recurring basis at fair value	5,000,000	5,000,000	0
Nonrecurring [Member] | Level 3 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	9,000,000	9,000,000	11,000,000
Loans held for sale	0	0	0
Accrued income and other assets	133,000,000	133,000,000	11,000,000
Total assets on a recurring basis at fair value	142,000,000	142,000,000	$ 22,000,000
LIHTC And Historic Tax Credit Investments [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Tax credit carryforward	$ 119,000,000	$ 119,000,000

Fair Value Measurements - Quant

Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	$ 726	$ 738
Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	9	11
Level 3 [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	$ 9	11
Level 3 [Member] | Other Investments [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments		$ 27
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	0.00%	0.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	50.00%	70.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	23.00%	46.00%
Level 3 [Member] | EBITDA Multiple [Member] | Fair Value, Measurements, Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		6.30%
Level 3 [Member] | EBITDA Multiple [Member] | Fair Value, Measurements, Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		7.00%
Level 3 [Member] | EBITDA Multiple [Member] | Fair Value, Measurements, Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	6.00%	6.50%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Fair Value, Measurements, Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		6.30%
Principal Investments [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value	$ 137
Principal Investments [Member] | Direct Investments [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value	13
Principal Investments [Member] | Direct Investments [Member] | Level 3 [Member] | Other Investments [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value	$ 13

Fair Value Measurements - Fai93

Fair Value Measurements - Fair Value Disclosures of Financial Instruments (Details) - USD ($)	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
ASSETS
Trading account assets	$ 836,000,000		$ 867,000,000
Securities available for sale	18,139,000,000		20,212,000,000
Held-to-maturity securities	11,830,000,000		10,232,000,000
Held-to-maturity securities	11,565,000,000		10,007,000,000
Other investments	726,000,000		738,000,000
Loans, net of allowance, Carrying Amount	85,528,000,000		85,180,000,000
Loans held for sale, Carrying Amount	1,107,000,000	[1]	1,104,000,000	[1]	$ 639,000,000
Loans held for sale	0		0
Derivative assets	669,000,000		803,000,000
LIABILITIES
Long-term debt, Carrying Amount	14,333,000,000		12,384,000,000
Derivative liabilities	291,000,000		636,000,000
Carrying Amount [Member]
ASSETS
Cash and short-term investments	5,118,000,000		3,452,000,000
Trading account assets	836,000,000		867,000,000
Securities available for sale	18,139,000,000		20,212,000,000
Held-to-maturity securities	11,830,000,000		10,232,000,000
Other investments	726,000,000		738,000,000
Loans, net of allowance, Carrying Amount	85,528,000,000		85,180,000,000
Loans held for sale, Carrying Amount	1,107,000,000		1,104,000,000
Derivative assets	669,000,000		803,000,000
LIABILITIES
Deposits with no stated maturity	93,588,000,000		93,906,000,000
Time deposits, Carrying Amount	11,647,000,000		10,181,000,000
Short-term borrowings, Carrying Amount	1,011,000,000		2,310,000,000
Long-term debt, Carrying Amount	14,333,000,000		12,384,000,000
Derivative liabilities	291,000,000		636,000,000
Estimate of Fair Value Measurement [Member]
ASSETS
Cash and short-term investments	5,118,000,000		3,452,000,000
Trading account assets	836,000,000		867,000,000
Securities available for sale	18,139,000,000		20,212,000,000
Held-to-maturity securities	11,565,000,000		10,007,000,000
Other investments	726,000,000		733,000,000
Loans, net of allowance	84,005,000,000		83,285,000,000
Loans held for sale	1,107,000,000		1,104,000,000
Derivative assets	669,000,000		803,000,000
Derivative assets, Netting Adjustment	(443,000,000)		(431,000,000)
LIABILITIES
Deposits with no stated maturity	93,588,000,000		93,906,000,000
Time deposits	11,750,000,000		10,267,000,000
Short-term borrowings	1,011,000,000		2,310,000,000
Long-term debt	14,626,000,000		12,690,000,000
Derivative liabilities	291,000,000		636,000,000
Derivative liabilities, netting adjustment	(616,000,000)		(384,000,000)
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
ASSETS
Cash and short-term investments	5,118,000,000		3,452,000,000
Trading account assets	0		0
Securities available for sale	0		3,000,000
Held-to-maturity securities	0		0
Other investments	0		0
Loans, net of allowance	0		0
Loans held for sale	0		0
Derivative assets	100,000,000		114,000,000
LIABILITIES
Deposits with no stated maturity	0		0
Time deposits	0		0
Short-term borrowings	72,000,000		192,000,000
Long-term debt	13,407,000,000		12,386,000,000
Derivative liabilities	98,000,000		102,000,000
Estimate of Fair Value Measurement [Member] | Level 2 [Member]
ASSETS
Cash and short-term investments	0		0
Trading account assets	836,000,000		867,000,000
Securities available for sale	18,119,000,000		20,192,000,000
Held-to-maturity securities			10,007,000,000
Other investments	4,000,000		0
Loans, net of allowance	0		0
Loans held for sale	70,000,000		62,000,000
Derivative assets	999,000,000		1,110,000,000
LIABILITIES
Deposits with no stated maturity	93,588,000,000		93,906,000,000
Time deposits	11,750,000,000		10,267,000,000
Short-term borrowings	939,000,000		2,118,000,000
Long-term debt	1,219,000,000		304,000,000
Derivative liabilities	809,000,000		918,000,000
Estimate of Fair Value Measurement [Member] | Level 3 [Member]
ASSETS
Cash and short-term investments	0		0
Trading account assets	0		0
Securities available for sale	20,000,000		17,000,000
Held-to-maturity securities	0		0
Other investments	598,000,000		569,000,000
Loans, net of allowance	84,005,000,000		83,285,000,000
Loans held for sale	1,037,000,000		1,042,000,000
Derivative assets	13,000,000		10,000,000
LIABILITIES
Deposits with no stated maturity	0		0
Time deposits	0		0
Short-term borrowings	0		0
Long-term debt	0		0
Derivative liabilities	0		0
Other Investments [Member] | Estimate of Fair Value Measurement [Member]
ASSETS
Other investments, measured at NAV	124,000,000		164,000,000
Fair Value, Measurements, Recurring [Member]
ASSETS
Securities available for sale	18,139,000,000		20,212,000,000
Other investments, measured at NAV	144,000,000		191,000,000
Loans held for sale	71,000,000		62,000,000
Derivative assets	669,000,000		803,000,000
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
ASSETS
Securities available for sale	0		3,000,000
Other investments, measured at NAV	0		0
Loans held for sale	0		0
Derivative assets	100,000,000		114,000,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
ASSETS
Securities available for sale	18,119,000,000		20,192,000,000
Other investments, measured at NAV	4,000,000		0
Loans held for sale	70,000,000		62,000,000
Derivative assets	999,000,000		1,110,000,000
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
ASSETS
Securities available for sale	20,000,000
Other investments, measured at NAV	16,000,000		27,000,000
Loans held for sale	1,000,000		0
Derivative assets	13,000,000		10,000,000
Other Securities [Member]
ASSETS
Securities available for sale	20,000,000		20,000,000
Held-to-maturity securities	15,000,000		15,000,000
Held-to-maturity securities	15,000,000		15,000,000
Other Securities [Member] | Fair Value, Measurements, Recurring [Member]
ASSETS
Trading account assets	65,000,000		73,000,000
Securities available for sale	20,000,000		20,000,000
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
ASSETS
Trading account assets	0		0
Securities available for sale	0		3,000,000
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
ASSETS
Trading account assets	65,000,000		73,000,000
Securities available for sale	0		0
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
ASSETS
Trading account assets	0		0
Securities available for sale	$ 20,000,000		$ 17,000,000
[1]	Total loans held for sale include Real estate — residential mortgage loans held for sale at fair value of $71 million at December 31, 2017, and $62 million at December 31, 2016

Securities - Details of Securit

Securities - Details of Securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	$ 18,546	$ 20,507
Available for sale, Gross Unrealized Gains	16	37
Available for sale, Gross Unrealized Losses	423	332
Available for sale, Fair Value	18,139	20,212
Held to maturities, Amortized Cost	11,830	10,232
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	7	2
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	272	227
Held-to-maturity Securities, Fair Value	11,565	10,007
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	159	188
Available for sale, Gross Unrealized Gains	0	0
Available for sale, Gross Unrealized Losses	2	4
Available for sale, Fair Value	157	184
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	9	11
Available for sale, Gross Unrealized Gains	0	0
Available for sale, Gross Unrealized Losses	0	0
Available for sale, Fair Value	9	11
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	1,456	1,857
Available for sale, Gross Unrealized Gains	3	6
Available for sale, Gross Unrealized Losses	20	17
Available for sale, Fair Value	1,439	1,846
Held to maturities, Amortized Cost	574	629
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	4	5
Held-to-maturity Securities, Fair Value	571	624
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	44	49
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	17	21
Available for sale, Gross Unrealized Gains	3	0
Available for sale, Gross Unrealized Losses	0	1
Available for sale, Fair Value	20	20
Held to maturities, Amortized Cost	15	15
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	15	15
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	14,985	16,652
Available for sale, Gross Unrealized Gains	10	31
Available for sale, Gross Unrealized Losses	335	275
Available for sale, Fair Value	14,660	16,408
Held to maturities, Amortized Cost	8,055	8,404
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	1
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	224	173
Held-to-maturity Securities, Fair Value	7,831	8,232
Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	4	5
Other Mortgage-Backed Securities [Member] | Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	1,920	1,778
Available for sale, Gross Unrealized Gains	0	0
Available for sale, Gross Unrealized Losses	66	35
Available for sale, Fair Value	1,854	1,743
Held to maturities, Amortized Cost	3,186	1,184
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	6	1
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	44	49
Held-to-maturity Securities, Fair Value	$ 3,148	$ 1,136

Securities - Available for Sale

Securities - Available for Sale Securities (Unrealized Loss Position) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Gross unrealized losses	$ 272	$ 227
Fair value less than 12 months, total temporarily impaired securities	10,991	24,038
Gross unrealized losses less than 12 months, total temporarily impaired securities	125	497
Fair value 12 months or longer, total temporarily impaired securities	16,041	1,931
Gross unrealized losses 12 months or longer, total temporarily impaired securities	570	62
Fair value, total temporarily impaired securities	27,032	25,969
Gross unrealized losses, total temporarily impaired securities	695	559
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	41	182
Gross unrealized losses, less than 12 months	0	4
Fair value, 12 months or longer	116	0
Gross unrealized losses, 12 months or longer	2	0
Fair Value	157	182
Gross unrealized losses, Total	2	4
Held-to-maturity Securities, Fair Value less than 12 months	0
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	0
Held-to-maturity Securities, Fair Value 12 months or longer	0
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	0
Held-to-maturity Securities, Fair Value	0
Held-to-maturity Securities, Gross unrealized losses	0
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	0
Gross unrealized losses, less than 12 months	0
Fair value, 12 months or longer	0
Gross unrealized losses, 12 months or longer	0
Fair Value	0
Gross unrealized losses, Total	0
Held-to-maturity Securities, Fair Value less than 12 months	0
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	0
Held-to-maturity Securities, Fair Value 12 months or longer	0
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	0
Held-to-maturity Securities, Fair Value	0
Held-to-maturity Securities, Gross unrealized losses	0
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	6,153	12,345
Gross unrealized losses, less than 12 months	74	231
Fair value, 12 months or longer	7,270	1,410
Gross unrealized losses, 12 months or longer	261	44
Fair Value	13,423	13,755
Gross unrealized losses, Total	335	275
Held-to-maturity Securities, Fair Value less than 12 months	2,201	7,028
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	27	156
Held-to-maturity Securities, Fair Value 12 months or longer	5,599	518
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	197	17
Held-to-maturity Securities, Fair Value	7,800	7,546
Held-to-maturity Securities, Gross unrealized losses	224	173
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Gross unrealized losses	4	5
Residential Mortgage Backed Securities [Member] | Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	666	1,452
Gross unrealized losses, less than 12 months	7	17
Fair value, 12 months or longer	702	0
Gross unrealized losses, 12 months or longer	13	0
Fair Value	1,368	1,452
Gross unrealized losses, Total	20	17
Held-to-maturity Securities, Fair Value less than 12 months	252	547
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	1	5
Held-to-maturity Securities, Fair Value 12 months or longer	206	0
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	3	0
Held-to-maturity Securities, Fair Value	458	547
Held-to-maturity Securities, Gross unrealized losses	4	5
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	205	1,482
Gross unrealized losses, less than 12 months	4	35
Fair value, 12 months or longer	1,649	0
Gross unrealized losses, 12 months or longer	62	0
Fair Value	1,854	1,482
Gross unrealized losses, Total		35
Held-to-maturity Securities, Fair Value less than 12 months	1,470	996
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	12	49
Held-to-maturity Securities, Fair Value 12 months or longer	495	0
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	32	0
Held-to-maturity Securities, Fair Value	1,965	996
Held-to-maturity Securities, Gross unrealized losses	44	49
Commercial Mortgage Backed Securities [Member] | Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses, Total	66
Held-to-maturity Securities, Gross unrealized losses	44	49
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	0	2
Gross unrealized losses, less than 12 months	0	0
Fair value, 12 months or longer	0	3
Gross unrealized losses, 12 months or longer	0	1
Fair Value	0	5
Gross unrealized losses, Total	0	1
Held-to-maturity Securities, Fair Value less than 12 months	3	4
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	0	0
Held-to-maturity Securities, Fair Value 12 months or longer	4	0
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	0	0
Held-to-maturity Securities, Fair Value	7	4
Held-to-maturity Securities, Gross unrealized losses	0	0
Gross unrealized losses, available for sale securities		1
Gross unrealized losses, held-to-maturity securities	$ 1	$ 1

Securities - Narrative (Details

Securities - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)MortgageLoanposition	Dec. 31, 2016USD ($)
Schedule of Available-for-sale Securities [Line Items]
Pledged available for sale and held-to-maturity securities	$ 7,000
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses	$ 335	$ 275
Number of fixed rate collateralized mortgage obligations | MortgageLoan	428
Weighted-average maturity collateralized mortgage, in years	4 years 1 month 24 days
Residential Mortgage Backed Securities [Member] | Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses	$ 20	17
Number of other mortgage-backed securities positions | position	248
Weighted-average maturity mortgage-backed securities, in years	3 years 10 months 2 days
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 35
Commercial Mortgage Backed Securities [Member] | Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses	$ 66
Number of other mortgage-backed securities positions | position	14
Weighted-average maturity mortgage-backed securities, in years	4 years 25 days

Securities - Cumulative Credit

Securities - Cumulative Credit Portion of Impairments on Debt Securities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Cumulative Impairments On Debt Securities [Roll Forward]
Cumulative Impairments on Debt Securities, Beginning Balance	$ 4
Impairment recognized in earnings	0
Cumulative Impairments on Debt Securities, Ending Balance	$ 4

Securities - Available for Sa98

Securities - Available for Sale Securities Realized Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Realized gains	$ 1	$ 0	$ 1
Realized losses	0	0	1
Net securities gains (losses)	1	0	$ 0
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Net securities gains (losses)	$ 1	$ 1

Securities - Securities by Matu

Securities - Securities by Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Amortized Cost of Securities Available for sale, Due in one year or less	$ 190
Amortized Cost of Securities Available for sale, Due after one through five years	14,990
Amortized Cost of Securities Available for sale, Due after five through ten years	3,358
Amortized Cost of Securities Available for sale, Due after ten years	8
Total Amortized Cost of Securities Available for sale	18,546
Fair Value of Securities Available for sale, Due in one year or less	190
Fair Value of Securities Available for sale, Due after one through five years	14,635
Fair Value of Securities Available for sale, Due after five through ten years	3,305
Fair Value of Securities Available for sale, Due after ten years	9
Total Fair Value of Securities Available-for-sale	18,139	$ 20,212
Amortized Cost of Held-to-Maturity Securities, Due in one year or less	56
Amortized Cost of Held-to-Maturity Securities, Due after one through five years	7,977
Amortized Cost of Held-to-Maturity Securities, Due after five through ten years	3,190
Amortized Cost of Held-to-Maturity Securities, Due after ten years	607
Held to maturities, Amortized Cost	11,830	10,232
Fair Value of Held-to-Maturity Securities, Due in one year or less	56
Fair Value of Held-to-Maturity Securities, Due after one through five years	7,776
Fair Value of Held-to-Maturity Securities, Due after five through ten years	3,142
Fair Value of Held-to-Maturity Securities, Due after ten years	591
Total Fair Value of Held-to-Maturity Securities	$ 11,565	$ 10,007

Derivatives and Hedging Acti100

Derivatives and Hedging Activities - Narrative (Details)	12 Months Ended
	Dec. 31, 2017USD ($)rating	Dec. 31, 2016USD ($)rating
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ (12,000,000)
Derivative liabilities after effects of bilateral collateral and master netting agreements	2,000,000
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	681,000,000
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	289,000,000
Reclassify of after-tax net losses on derivative instruments from AOCI	$ 39,000,000
Length of time hedge in cash flow hedge	12 months
Reclassification of net losses related to terminated cash flow hedges from AOCI to income	$ (3,000,000)
Maximum length of time over which forecasted transactions are hedged, years	11 years
Other comprehensive income unrealized gain on derivatives arising during period net of tax	$ 37,000,000
Cash collateral netted against derivative assets	(23,000,000)	$ 155,000,000
Collateral netted against derivative liabilities	150,000,000	108,000,000
Cash collateral not netted transferred with clearing organization	383,000,000	448,000,000
Cash collateral not netted transferred from clearing organization	99,000,000	59,000,000
Cash paid to settle derivatives	239,000,000
Cash received to settle derivatives	64,000,000
Increase (decrease) in derivative assets	(2,000,000)
Increase (decrease) in derivative liabilities		$ (283,000,000)
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	450,000,000
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	210,000,000
Over-collateralization on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	197,000,000
Additional collateral held in the form of securities	13,000,000
Default reserve associated with uncollateralized contracts	4,000,000
Gross exposure on derivatives after taking into account effects of master netting agreements	503,000,000
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	459,000,000
KeyBank (consolidated) [Member]
Credit Derivatives [Line Items]
Net liability position totaled	215,000,000
Derivative assets included in net liability position	188,000,000
Derivative liabilities included in net liability position	403,000,000
Cash and securities collateral posted	202,000,000
Additional collateral amount	$ 0
KeyBank (consolidated) [Member] | Unsecured Debt [Member]
Credit Derivatives [Line Items]
Number of ratings above noninvestment | rating	4	4
KeyBank (consolidated) [Member] | Maximum [Member] | Unsecured Debt [Member]
Credit Derivatives [Line Items]
Payments to terminate contracts	$ 12,000,000	$ 4,000,000
Key Corp [Member]
Credit Derivatives [Line Items]
Additional collateral amount	$ 0	$ 1,000,000

Derivatives and Hedging Acti101

Derivatives and Hedging Activities - Fair Values, Volume of Activity and Gain (Loss) Information Related to Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional Amount	$ 100,193	$ 88,288
Derivative assets, Netting adjustments	(443)	(431)
Derivative assets, Fair Value	664	782
Derivative liabilities, Netting adjustments	(616)	(384)
Derivative liabilities, Fair Value	207	539
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	26,478	24,519
Derivative assets, Fair Value	82	195
Derivative liabilities, Fair Value	50	98
Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	73,715	63,769
Derivative assets, Fair Value	1,030	1,039
Derivative liabilities, Fair Value	857	922
Interest Rate [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	26,176	24,237
Derivative assets, Fair Value	81	189
Derivative liabilities, Fair Value	46	94
Interest Rate [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	61,390	55,315
Derivative assets, Fair Value	641	741
Derivative liabilities, Fair Value	474	643
Foreign Exchange [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	302	282
Derivative assets, Fair Value	1	6
Derivative liabilities, Fair Value	4	4
Foreign Exchange [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	8,317	6,230
Derivative assets, Fair Value	129	117
Derivative liabilities, Fair Value	120	109
Commodity [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	1,687	1,474
Derivative assets, Fair Value	255	176
Derivative liabilities, Fair Value	246	165
Credit [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	315	360
Derivative assets, Fair Value	1	1
Derivative liabilities, Fair Value	4	4
Other Credit Derivatives [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,006	390
Derivative assets, Fair Value	4	4
Derivative liabilities, Fair Value	13	1
Net Derivatives [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	100,193	88,288
Derivative assets, Fair Value	669	803
Derivative liabilities, Fair Value	291	636
Counterparty And Cash Collateral Netting [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	0	0
Derivative assets, Fair Value	(5)	(21)
Derivative liabilities, Fair Value	$ (84)	$ (97)

Derivatives and Hedging Acti102

Derivatives and Hedging Activities - Pre-Tax Net Gains (Losses) on Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Net Gains (Losses) on Derivative		$ (54)	$ 1
Net Gains (Losses) on Hedged Item	$ 107		97
Other Income [Member] | Interest Rate [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) on Derivative		(103)	(95)
Net Gains (Losses) on Hedged Item		107	97
Interest Expense [Member] | Interest Rate [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) on Derivative		$ 49	$ 96

Derivatives and Hedging Acti103

Derivatives and Hedging Activities - Derivative Instrument Cash Flow Hedge Earning Recognized by Income Statement Location (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI (Effective Portion)	$ (77)	$ 28
Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion)	15	81
Net Gains (Losses) Recognized in Income (Ineffective Portion)	0	0
Interest Income [Member] | Interest Rate [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI (Effective Portion)	(59)	29
Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion)	19	85
Interest Expense [Member] | Interest Rate [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI (Effective Portion)	0	0
Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion)	(4)	(4)
Investment Banking and Debt Placement Fees [Member] | Interest Rate [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI (Effective Portion)	(1)	1
Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion)	0	0
Other Income [Member] | Interest Rate [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in Income (Ineffective Portion)	0	0
Other Income [Member] | Foreign Exchange [Member] | Net Investment Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI (Effective Portion)	(17)	(2)
Net Gains (Losses) Reclassified From OCI Into Income (Effective Portion)	0	0
Net Gains (Losses) Recognized in Income (Ineffective Portion)	$ 0	$ 0

Derivatives and Hedging Acti104

Derivatives and Hedging Activities - After-Tax Change in AOCI Resulting from Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
December 31, 2016		$ (14)
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	$ 141	141
December 31, 2017	$ (86)	(86)
Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
2017 Hedging Activity		(48)
Reclassification of Gains to Net Income		(10)
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		$ (14)

Derivatives and Hedging Acti105

Derivatives and Hedging Activities - Pre-Tax Net Gains (Losses) on Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	$ 49	$ 61	$ 53
Interest Rate [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	28	31	28
Foreign Exchange [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	41	40	36
Commodity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	6	4	5
Credit [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	(19)	(15)	(16)
Other Credit Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	(7)	1	0
Corporate Services Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	78	75	68
Corporate Services Income [Member] | Interest Rate [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	29	30	28
Corporate Services Income [Member] | Foreign Exchange [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	41	40	36
Corporate Services Income [Member] | Commodity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	6	4	5
Corporate Services Income [Member] | Credit [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	2	1	(1)
Corporate Services Income [Member] | Other Credit Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	0	0	0
Consumer Mortgage Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	(1)	1
Consumer Mortgage Income [Member] | Interest Rate [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	0	0
Consumer Mortgage Income [Member] | Foreign Exchange [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	0	0
Consumer Mortgage Income [Member] | Commodity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	0	0
Consumer Mortgage Income [Member] | Credit [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	0	0
Consumer Mortgage Income [Member] | Other Credit Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	(1)	1
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	(28)	(15)	(15)
Other Income [Member] | Interest Rate [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	(1)	1	0
Other Income [Member] | Foreign Exchange [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	0	0	0
Other Income [Member] | Commodity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	0	0	0
Other Income [Member] | Credit [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	(21)	(16)	(15)
Other Income [Member] | Other Credit Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses)	$ (6)	$ 0	$ 0

Derivatives and Hedging Acti106

Derivatives and Hedging Activities - Fair Value of Derivative Assets by Type (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Credit Derivatives [Line Items]
Derivative assets before collateral	$ 646	$ 958
Less: Related collateral	(23)	155
Total derivative assets	669	803
Interest Rate [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	401	782
Foreign Exchange [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	77	62
Commodity [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	163	110
Credit [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	1	0
Other Credit Derivatives [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	$ 4	$ 4

Derivatives and Hedging Acti107

Derivatives and Hedging Activities - Fair Value of Credit Derivatives Purchased and Sold (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Credit Derivatives [Line Items]
Purchased	$ (3)	$ (3)
Sold	0	0
Net	(3)	(3)
Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Purchased	(1)	(2)
Sold	0	0
Net	(1)	(2)
Traded Credit Default Swap Indices [Member]
Credit Derivatives [Line Items]
Purchased	(2)	(1)
Sold	0	0
Net	(2)	(1)
Other [Member]
Credit Derivatives [Line Items]
Purchased	0	0
Sold	0	0
Net	$ 0	0
Maximum [Member] | Other [Member]
Credit Derivatives [Line Items]
Sold		$ (1)

Derivatives and Hedging Acti108

Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Credit Derivatives [Line Items]
Notional Amount	$ 15	$ 4
Average Term (Years)	0 years	0 years
Payment / Performance Risk	0.00%	0.00%
Other [Member]
Credit Derivatives [Line Items]
Notional Amount	$ 15	$ 4
Average Term (Years)	3 years 29 days	6 years 5 months 27 days
Payment / Performance Risk	6.64%	17.93%

Derivatives and Hedging Acti109

Derivatives and Hedging Activities - Credit Risk Contingent Feature (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	$ 13
Moody's, A3 Rating [Member] | One Rating Downgrade [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	2	$ 2
Moody's, A3 Rating [Member] | Two Rating Downgrades [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	2	2
Moody's, A3 Rating [Member] | Three Rating Downgrades [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	2	2
Standard & Poor's, A- Rating [Member] | One Rating Downgrade [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	2	2
Standard & Poor's, A- Rating [Member] | Two Rating Downgrades [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	2	2
Standard & Poor's, A- Rating [Member] | Three Rating Downgrades [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	$ 2	$ 2

Mortgage Servicing Assets - Cha

Mortgage Servicing Assets - Changes in Carrying Amount of Mortgage Servicing Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Commercial Mortgage Backed Securities [Member]
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Balance at beginning of period	$ 356	$ 322
Servicing retained from loan sales	110	80
Purchases	36	41
Amortization	(90)	(87)
Balance at end of period	412	356
Fair value at end of period	537	459
Residential Mortgage Backed Securities [Member]
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Balance at beginning of period	28	0
Servicing retained from loan sales	7	2
Purchases	0	28
Amortization	(4)	(2)
Balance at end of period	31	28
Fair value at end of period	$ 37	$ 33

Mortgage Servicing Assets - Sch

Mortgage Servicing Assets - Schedule of Range and Weighted-Average of Significant Unobservable Inputs (Details) - Discounted Cash Flow [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Commercial Mortgage Backed Securities [Member] | Minimum [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	1.00%	1.00%
Residual cash flows discount rate (as a percent)	7.00%	7.00%
Escrow earn rate (as a percent)	0.90%	1.10%
Servicing cost	$ 150,000,000	$ 150,000,000
Loan assumption rate (as a percent)	0.00%	0.00%
Percentage late (as a percent)	0.00%	0.00%
Commercial Mortgage Backed Securities [Member] | Maximum [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	3.00%	3.00%
Residual cash flows discount rate (as a percent)	15.00%	12.00%
Escrow earn rate (as a percent)	3.10%	3.00%
Servicing cost	$ 38,500,000,000	$ 2,700,000,000
Loan assumption rate (as a percent)	3.00%	3.00%
Percentage late (as a percent)	1.30%	2.00%
Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	1.20%	1.40%
Residual cash flows discount rate (as a percent)	9.10%	8.00%
Escrow earn rate (as a percent)	2.50%	2.40%
Servicing cost	$ 1,468,000,000	$ 1,214,000,000
Loan assumption rate (as a percent)	1.22%	1.13%
Percentage late (as a percent)	0.25%	0.34%
Residential Mortgage Backed Securities [Member] | Minimum [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	8.50%	8.50%
Servicing cost	$ 76,000,000	$ 76,000,000
Prepayment speed (as a percent)	9.16%	7.79%
Residential Mortgage Backed Securities [Member] | Maximum [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	11.00%	11.00%
Servicing cost	$ 4,385,000,000	$ 3,335,000,000
Prepayment speed (as a percent)	51.52%	18.61%
Residential Mortgage Backed Securities [Member] | Weighted Average [Member]
Servicing Assets at Fair Value [Line Items]
Expected defaults/Discount rate (as a percent)	8.54%	8.55%
Servicing cost	$ 83,110,000	$ 830,400
Prepayment speed (as a percent)	10.46%	9.42%

Mortgage Servicing Assets - Nar

Mortgage Servicing Assets - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 01, 2016
Commercial Mortgage Backed Securities [Member]
Contractual fee income	$ 150	$ 139	$ 142
Amortization of mortgage servicing rights	90	$ 87	$ 94
Residential Mortgage Backed Securities [Member]
Contractual fee income	12
Amortization of mortgage servicing rights	$ 4
First Niagara Bank, N.A. [Member] | Residential Mortgage Backed Securities [Member]
Fair value of mortgage servicing asset				$ 28

Premises and Equipment - Schedu

Premises and Equipment - Schedule of Premises and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total premises and equipment	$ 2,508	$ 2,541
Less: Accumulated depreciation and amortization	(1,578)	(1,563)
Premises and equipment, net	930	978
Land
Property, Plant and Equipment [Line Items]
Total premises and equipment	138	139
Buildings and improvements
Property, Plant and Equipment [Line Items]
Total premises and equipment	$ 741	727
Buildings and improvements | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	15 years
Buildings and improvements | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	40 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total premises and equipment	$ 633	663
Leasehold improvements | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	1 year
Leasehold improvements | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	15 years
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total premises and equipment	$ 931	943
Furniture and equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	2 years
Furniture and equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	15 years
Capitalized building leases
Property, Plant and Equipment [Line Items]
Total premises and equipment	$ 27	27
Capitalized building leases | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	1 year
Capitalized building leases | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	15 years
Construction in process
Property, Plant and Equipment [Line Items]
Total premises and equipment	$ 38	$ 42

Premises and Equipment - Narrat

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]
Depreciation and amortization expense	$ 138	$ 123	$ 120

Goodwill and Other Intangibl115

Goodwill and Other Intangible Assets - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Oct. 02, 2017	Jul. 01, 2017	Jun. 30, 2017	Dec. 31, 2016	Aug. 01, 2016	Dec. 31, 2015
Goodwill And Other Intangible Asset [Line Items]
Expected deductible goodwill for tax purpose	$ 627,000,000
First Niagara Bank, N.A. [Member]
Goodwill And Other Intangible Asset [Line Items]
Intangible assets acquired						$ 385,000,000
Key Merchant Services, LLC [Member]
Goodwill And Other Intangible Asset [Line Items]
Intangible assets acquired	$ 85,000,000			$ 95,000,000
HelloWallet Holdings, LLC [Member]
Goodwill And Other Intangible Asset [Line Items]
Intangible assets acquired			$ 12,000,000
Cain Brothers & Company, LLC. [Member]
Goodwill And Other Intangible Asset [Line Items]
Intangible assets acquired		$ 30,000,000
Key Community Bank Unit [Member]
Goodwill And Other Intangible Asset [Line Items]
Estimated fair value of the Community Bank unit greater than certain percent of carrying value	48.00%
Accumulated impairment loss	$ 0				$ 0		$ 0
Key Corporate Bank [Member]
Goodwill And Other Intangible Asset [Line Items]
Estimated fair value of the Community Bank unit greater than certain percent of carrying value	39.00%
Accumulated impairment loss	$ 0				$ 0		$ 0
Core Deposits [Member] | First Niagara Bank, N.A. [Member]
Goodwill And Other Intangible Asset [Line Items]
Intangible assets acquired	$ 356,000,000
Useful life of intangible assets	10 years
Commercial Credit Card [Member] | First Niagara Bank, N.A. [Member]
Goodwill And Other Intangible Asset [Line Items]
Useful life of intangible assets	6 years
Consumer Credit Card [Member] | First Niagara Bank, N.A. [Member]
Goodwill And Other Intangible Asset [Line Items]
Useful life of intangible assets	9 years
Customer Relationships [Member] | Key Merchant Services, LLC [Member]
Goodwill And Other Intangible Asset [Line Items]
Useful life of intangible assets	10 years
Customer Relationships [Member] | Cain Brothers & Company, LLC. [Member]
Goodwill And Other Intangible Asset [Line Items]
Useful life of intangible assets	8 years
Proprietary Software [Member] | HelloWallet Holdings, LLC [Member]
Goodwill And Other Intangible Asset [Line Items]
Useful life of intangible assets	3 years
Trade Names [Member] | Cain Brothers & Company, LLC. [Member]
Goodwill And Other Intangible Asset [Line Items]
Useful life of intangible assets	3 years

Goodwill and Other Intangibl116

Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	Aug. 01, 2016	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Beginning Balance		$ 2,446	$ 2,446	$ 1,060
Fair value measurement adjustments - First Niagara acquisition		(19)	18
Additional ownership interest in Key Merchant Services			4
Goodwill, acquired during period			1,400	1,386
Ending Balance		2,464	2,538	2,446
Key Community Bank [Member]
Goodwill [Roll Forward]
Beginning Balance		2,088	2,088	979
Fair value measurement adjustments - First Niagara acquisition		(15)	15
Additional ownership interest in Key Merchant Services			4
Goodwill, acquired during period			1,100	1,109
Ending Balance		2,103	2,124	2,088
Key Corporate Bank [Member]
Goodwill [Roll Forward]
Beginning Balance		358	358	81
Fair value measurement adjustments - First Niagara acquisition		(4)	3
Additional ownership interest in Key Merchant Services			0
Goodwill, acquired during period			280	277
Ending Balance		$ 361	414	358
First Niagara Bank, N.A. [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period	$ 1,404			1,386
First Niagara Bank, N.A. [Member] | Key Community Bank [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period				1,109
First Niagara Bank, N.A. [Member] | Key Corporate Bank [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period				$ 277
HelloWallet Holdings, LLC [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period			17
HelloWallet Holdings, LLC [Member] | Key Community Bank [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period			17
HelloWallet Holdings, LLC [Member] | Key Corporate Bank [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period			0
Cain Brothers & Company, LLC. [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period			53
Cain Brothers & Company, LLC. [Member] | Key Community Bank [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period			0
Cain Brothers & Company, LLC. [Member] | Key Corporate Bank [Member]
Goodwill [Roll Forward]
Goodwill, acquired during period			$ 53

Goodwill and Other Intangibl117

Goodwill and Other Intangible Assets - Gross Carrying Amount and Accumulated Amortization of Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Gross Carrying Amount	$ 741	$ 687
Accumulated Amortization	325	303
Austin Capital Management [Member]
Goodwill [Line Items]
Gross Carrying Amount		18
Accumulated Amortization		18
Core Deposit Intangibles [Member]
Goodwill [Line Items]
Gross Carrying Amount	461	461
Accumulated Amortization	192	125
Purchased Credit Card Relationship Intangible [Member]
Goodwill [Line Items]
Gross Carrying Amount	152	152
Accumulated Amortization	126	110
Other Intangible Assets [Member]
Goodwill [Line Items]
Gross Carrying Amount	128	74
Accumulated Amortization	$ 7	$ 68

Goodwill and Other Intangibl118

Goodwill and Other Intangible Assets - Schedule of Intangible Assets Acquired (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	$ 127
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	114
Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	1
Proprietary Software [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	12
Key Merchant Services, LLC [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	85
Key Merchant Services, LLC [Member] | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	85
Key Merchant Services, LLC [Member] | Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	0
Key Merchant Services, LLC [Member] | Proprietary Software [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	0
HelloWallet Holdings, LLC [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	12
HelloWallet Holdings, LLC [Member] | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	0
HelloWallet Holdings, LLC [Member] | Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	0
HelloWallet Holdings, LLC [Member] | Proprietary Software [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	12
Cain Brothers & Company, LLC. [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	30
Cain Brothers & Company, LLC. [Member] | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	29
Cain Brothers & Company, LLC. [Member] | Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	1
Cain Brothers & Company, LLC. [Member] | Proprietary Software [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired, subject to amortization	$ 0

Goodwill and Other Intangibl119

Goodwill and Other Intangible Assets - Future Amortization Expense of Finite-Lived Intangible Assets (Details) $ in Millions	Dec. 31, 2017USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Estimated amortization expense 2018	$ 96
Estimated amortization expense 2019	79
Estimated amortization expense 2020	64
Estimated amortization expense 2021	52
Estimated amortization expense 2022	$ 42

Variable Interest Entities - Na

Variable Interest Entities - Narrative (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	$ 230,000,000	$ 230,000,000	$ 178,000,000
Total Liabilities	4,000,000	4,000,000	4,000,000
Other expense		563,000,000	505,000,000	$ 344,000,000
LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	6,003,000,000	6,003,000,000	4,814,000,000
Total Liabilities	2,943,000,000	2,943,000,000	2,003,000,000
LIHTC Investments [Member] | Qualified affordable housing projects investment [Member]
Variable Interest Entity [Line Items]
Total Liabilities	476,000,000	476,000,000	462,000,000
Accrued Income And Other Assets [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	1,300,000,000	1,300,000,000	1,200,000,000
Investments [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Amortization of investment		172,000,000	131,000,000
Tax credit of investment		171,000,000	144,000,000
Impairment expense related to tax reform	12,000,000
Other expense	3,000,000
Investments [Member] | Guaranteed Funds [Member]
Variable Interest Entity [Line Items]
Assets that can only be used to settle entities' obligations	4,000,000	4,000,000	1,000,000
Variable interest entity, liabilities	0	0	0
Fair Value, Measurements, Recurring [Member]
Variable Interest Entity [Line Items]
Total other investments	144,000,000	144,000,000	191,000,000
Principal Indirect Investments [Member] | Fair Value, Measurements, Recurring [Member]
Variable Interest Entity [Line Items]
Total other investments	$ 124,000,000	$ 124,000,000	$ 158,000,000

Variable Interest Entities - Va

Variable Interest Entities - Variable Interest Entities Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Total Assets	$ 230	$ 178
Total Liabilities	4	4
LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Total Assets	6,003	4,814
Total Liabilities	2,943	2,003
Maximum Exposure to Loss	1,561	1,465
KCC Indirect Investments [Member]
Variable Interest Entity [Line Items]
Total Assets	26,817	32,755
Total Liabilities	292	201
Maximum Exposure to Loss	$ 153	$ 195

Income Taxes - Income Taxes Inc

Income Taxes - Income Taxes Included in Income Statement (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Currently payable:
Federal	$ 334,000,000	$ 149,000,000	$ 337,000,000
State	0	19,000,000	42,000,000
Total currently payable	334,000,000	168,000,000	379,000,000
Deferred:
Federal	274,000,000	13,000,000	(69,000,000)
State	29,000,000	(2,000,000)	(7,000,000)
Total deferred	303,000,000	11,000,000	(76,000,000)
Total income tax expense (benefit)	637,000,000	179,000,000	303,000,000
Income tax (benefit) expense on securities transactions	0	0	0
Equity and gross receipts based taxes assessed in lieu of income tax recorded in noninterest expense	$ 22,000,000	$ 18,000,000	$ 16,000,000

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Assets and Liabilities Included in "Accrued Income and Other Assets" and "Accrued Expense and Other Liabilities" (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Allowance for loan and lease losses	$ 233	$ 373
Employee benefits	147	276
Net unrealized securities losses	138	146
Federal net operating losses and credits	205	130
Fair value adjustments	63	136
Non-tax accruals	89	150
State net operating losses and credits	7	15
Other	223	236
Gross deferred tax assets	1,105	1,462
Less: Valuation Allowance	15	26
Total deferred tax assets	1,090	1,436
Leasing transactions	588	728
Other	182	101
Total deferred tax liabilities	770	829
Net deferred tax assets (liabilities)	$ 320	$ 607

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Tax Cuts and Jobs Act of 2017, provisional income tax expense		$ 161,000,000
Tax Cuts and Jobs Act of 2017, provisional income tax expense, low-income housing investments		14,000,000
Tax Cuts and Jobs Act of 2017, change in tax rate, provisional income tax expense		$ 147,000,000
Effective income tax rate reconciliation, change in enacted tax rate		7.60%
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	$ 141,000,000	$ 141,000,000
Less: Valuation Allowance	15,000,000	15,000,000	$ 26,000,000
Credit carryforward	205,000,000	205,000,000	130,000,000
Deferred tax asset	1,090,000,000	1,090,000,000	1,436,000,000
Unrecognized tax benefits	39,000,000	39,000,000	53,000,000	$ 12,000,000
Net interest expenses (credits)		(1,300,000)	(400,000)	(600,000)
Recovery of penalties related to unrecognized tax benefits in income tax expense	1,000,000	1,000,000	0	$ 300,000
Accrued interest payable	4,000,000	4,000,000	3,000,000
Reduction in federal tax credit carryforward		17,200,000	10,100,000
Maximum [Member]
Income Taxes [Line Items]
Less: Valuation Allowance	15,000,000	15,000,000
Federal [Member]
Income Taxes [Line Items]
Federal net operating loss carryforwards	79,000,000	79,000,000
Credit carryforward	189,000,000	189,000,000
State [Member]
Income Taxes [Line Items]
Credit carryforward	5,000,000	5,000,000
Capital loss carryforwards	2,000,000	2,000,000
State net operating loss carryforwards	72,000,000	72,000,000
Deferred tax asset	7,000,000	7,000,000
Accrued state tax penalties	0	0	$ 1,000,000
First Niagara Bank, N.A. [Member]
Income Taxes [Line Items]
Allocated bad debt deductions for which no income taxes have been recorded	92,000,000	92,000,000
Capital Loss Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforward	$ 15,000,000	$ 15,000,000

Income Taxes - Total Income Tax

Income Taxes - Total Income Tax Expense (Benefit) and Resulting Effective Tax Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income (loss) before income taxes times 35% statutory federal tax rate	$ 675	$ 339	$ 428
Amortization of tax-advantaged investments	104	88	81
Foreign tax adjustments	1	1	(1)
Tax-exempt interest income	(37)	(25)	(18)
Corporate-owned life insurance income	(46)	(44)	(45)
State income tax, net of federal tax benefit	19	11	22
Tax credits	(218)	(208)	(155)
Tax Cuts and Jobs Act	147	0	0
Other	(8)	17	(9)
Total income tax expense (benefit)	$ 637	$ 179	$ 303
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal income tax rate	35.00%	35.00%	35.00%
Amortization of tax-advantaged investments (as a percent)	5.40%	9.00%	6.70%
Foreign tax adjustments (as a percent)	0.10%	0.10%	(0.10%)
Tax-exempt interest income (as a percent)	(1.90%)	(2.60%)	(1.50%)
Corporate-owned life insurance income (as a percent)	(2.40%)	(4.50%)	(3.60%)
State income tax, net of federal tax benefit (as a percent)	1.00%	1.10%	1.80%
Tax credits (as a percent)	(11.30%)	(21.30%)	(12.70%)
Tax Cuts and Jobs Act (as a percent)	7.60%	0.00%	0.00%
Other (as a percent)	(0.50%)	1.70%	(0.80%)
Total income tax expense (benefit) (as a percent)	33.00%	18.50%	24.80%

Income Taxes - Change in Liabil

Income Taxes - Change in Liability for Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 53	$ 12
Increase for other tax positions of prior years	3	10
Increase from Acquisitions	3	33
Decrease for payments and settlements	(4)	0
Decrease related to tax positions taken in prior years	(16)	(2)
Balance at end of year	$ 39	$ 53

Acquisition, Divestiture, an127

Acquisition, Divestiture, and Discontinued Operations - Narrative (Details) $ / shares in Units, $ in Millions	Jun. 30, 2017USD ($)	Jun. 29, 2017USD ($)	Aug. 01, 2016USD ($)	Oct. 30, 2015$ / sharesshares	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Oct. 02, 2017USD ($)	Jul. 01, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 09, 2016USD ($)Branch	Dec. 31, 2015USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill	$ 2,464				$ 2,538		$ 2,464	$ 2,538			$ 2,446		$ 1,060
Tax adjustment on previous fair value measurements							(19)	18
Cain Brothers & Company, LLC. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other intangible assets									$ 30
Goodwill									$ 53
HelloWallet Holdings, LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other intangible assets										$ 12
Goodwill										$ 17
Key Merchant Services, LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other intangible assets	95				85		95	85
Goodwill	$ 1						$ 1
Business acquisition, percentage of voting interests acquired	51.00%						51.00%
Business combination, percentage held before acquisition date		49.00%
Business combination, ownership percentage	100.00%						100.00%
Exchange of First Niagara preferred stock for KeyCorp preferred stock		$ 74				$ 69
Business combination, estimated fair value of equity interest						5
Business combination, noncash holding gain	$ 64					59
Measurement-period adjustment, intangible assets						$ 10
Reduction to goodwill, subsequent recognition of deferred tax asset					2
Tax adjustment on previous fair value measurements								4
First Niagara Financial Group, Inc. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration			$ 4,000
Acquiree shares equivalent of acquirer common stock | shares				0.680
Cash payable per acquiree common stock (in dollars per share) | $ / shares				$ 2.30
Number of branches sold | Branch												18
Loans included in divestiture												$ 439
Deposits included in divestiture												$ 1,600
Discontinued Operations [Member] | Government Guaranteed Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans included in divestiture					$ 1,300			$ 1,300			$ 1,600

Securities Financing Activit128

Securities Financing Activities - Summarized Securities Financing Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	$ 0	$ 0
Total offsetting of financial assets	0	0
Repurchase agreements	0	0
Total offsetting of financial liabilities	0	0
Counterparty And Cash Collateral Netting [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	0	0
Total offsetting of financial assets	0	0
Repurchase agreements	(370)	(494)
Total offsetting of financial liabilities	(370)	(494)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities Financing Transaction [Line Items]
Pledged Financial Instruments, Not Separately Reported, Securities	463
Liabilities associated with collateral pledged	370
Gross Amount Presented in Balance Sheet [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	3	3
Total offsetting of financial assets	3	3
Repurchase agreements	374	497
Total offsetting of financial liabilities	374	497
Netting Adjustments [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(3)	(3)
Total offsetting of financial assets	(3)	(3)
Repurchase agreements	(4)	(3)
Total offsetting of financial liabilities	$ (4)	$ (3)

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense for stock-based compensation plans	$ 104,000,000	$ 102,000,000	$ 59,000,000
Total income tax benefit recognized for stock-based compensation plans	$ 39,000,000	$ 38,000,000	$ 22,000,000
Common Shares available for future grant under compensation plans (in shares)	40,088,115
Maximum percentage of outstanding common stock that may be granted as options	6.00%
Rolling period in which a certain percentage of common stock cannot be granted as options	3 years
Exercise rate of stock options granted to employees	25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Common shares, shares issued (in shares)	1,256,702,081	1,256,702,081
Weighted-average grant-date fair value of options (in dollars per share)	$ 4.60	$ 2.14	$ 4.33
Number of options, exercised (in shares)	3,755,177
Total intrinsic value of exercised options	$ 31,000,000	$ 12,000,000	$ 14,000,000
Cash received from options exercised	25,000,000	32,000,000	22,000,000
Actual tax benefit realized for tax deductions from options exercised	$ 4,000,000	$ 2,000,000	$ 2,000,000
Mandatory deferred incentive awards, vesting rate (as a percent)	25.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares, shares issued (in shares)	3,000,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options, exercised (in shares)	3,755,177	2,849,010	2,496,965
Unrecognized compensation cost related to nonvested options expected to vest	$ 5,000,000
Weighted-average period	2 years 7 months 1 day
Expected to vest, Weighted-Average Remaining Life (Years)	10 years
Stock Options [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Stock Options [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected to vest, Weighted-Average Remaining Life (Years)	10 years
Deferred Cash Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Restricted Stock Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Equity Based Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Cash Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Deferred Compensation Plans and Other Restricted Stock Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value granted (in dollars per share)	$ 18.55	$ 11.46	$ 14.22
Deferred Compensation Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested options expected to vest	$ 37,000,000
Weighted-average period	3 years 7 months 25 days
Fair value of units/shares vested	$ 21,000,000	$ 16,000,000	$ 15,000,000
Long-Term Incentive Compensation Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested options expected to vest	$ 82,000,000
Weighted-average period	2 years 2 months 27 days
Number of performance units vested (in shares)	887,489	1,915,239
Fair value of units/shares vested	$ 76,000,000	$ 57,000,000	$ 39,000,000
Weighted-average grant-date fair value granted (in dollars per share)	$ 19.82	$ 10.49	$ 13.99
Long-Term Incentive Compensation Program [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of units/shares vested	$ 14,000,000	$ 21,000,000
Discounted Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee discount on the purchase of stock through Discounted Stock Purchase Plan	10.00%
Purchases are limited to any month	$ 10,000
Purchases are limited to any calendar year	$ 50,000
Issuance of common shares (in shares)	257,738	310,604	250,913
Weighted-average cost of common shares issued under the plan (in dollars per share)	16.61	11.04	12.55

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions Used in Options Pricing Model (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Average option life	6 years	6 years	6 years
Future dividend yield (as a percentage)	1.79%	2.86%	1.84%
Historical share price volatility (as a percentage)	0.287%	0.297%	0.382%
Weighted-average risk-free interest rate (as a percentage)	2.10%	1.30%	1.70%

Stock-Based Compensation - Acti

Stock-Based Compensation - Activity, Pricing and Other Information for Stock Options (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options Outstanding, Beginning Balance (in shares)	13,885,566
Granted, Number of Options (in shares)	1,370,069
Exercised, Number of Options (in shares)	(3,755,177)
Lapsed or canceled, Number of Options (in shares)	(1,617,841)
Number of Options Outstanding, Ending Balance (in shares)	9,882,617	13,885,566
Expected to vest, Number of Options (in shares)	3,422,790
Number of Options Exercisable, Ending Balance (in shares)	6,183,136
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price Per Option Outstanding, Beginning Balance (in dollars per share)	$ 13
Granted, Weighted-Average Exercise Price Per Option (in dollars per share)	18.96
Exercised, Weighted-Average Exercise Price Per Option (in dollars per share)	10.16
Lapsed or canceled, Weighted-Average Exercise Price Per Option (in dollars per share)	35.15
Weighted-Average Exercise Price Per Option Outstanding, Ending Balance (in dollars per share)	11.28	$ 13
Expected to vest, Weighted-Average Exercise Price Per Option (in dollars per share)	13.97
Weighted-Average Exercise Price Per Option Exercisable, Ending Balance (in dollars per share)	$ 9.63
Weighted-Average Remaining Life (Years) Outstanding	5 years 6 months	4 years 6 months
Expected to vest, Weighted-Average Remaining Life (Years)	8 years 3 months 18 days
Weighted-Average Remaining Life (Years) Exercisable	3 years 9 months 18 days
Aggregate Intrinsic Value Outstanding	$ 88	$ 101
Expected to vest, Aggregate Intrinsic Value	21
Aggregate Intrinsic Value Exercisable	$ 65

Stock-Based Compensation - A132

Stock-Based Compensation - Activity and Pricing Information for Nonvested Shares in Long-Term Incentive Compensation Program (Detail) - Long-Term Incentive Compensation Program [Member]	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Vesting Contingent on Service Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Nonvested Shares Outstanding, Beginning Balance (in shares) | shares	13,918,806
Number of Nonvested Shares, Granted (in shares) | shares	3,899,826
Number of Nonvested Shares, Vested (in shares) | shares	(5,324,226)
Number of Nonvested Shares, Forfeited (in shares) | shares	(661,450)
Number of Nonvested Shares Outstanding, Ending Balance (in shares) | shares	11,832,956
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant-Date Fair Value Outstanding, Beginning Balance (in dollars per share) | $ / shares	$ 11.78
Weighted-Average Grant-Date Fair Value, Granted (in dollars per share) | $ / shares	18.96
Weighted-Average Grant-Date Fair Value, Vested (in dollars per share) | $ / shares	11.64
Weighted-Average Grant-Date Fair Value, Forfeited (in dollars per share) | $ / shares	13.19
Weighted-Average Grant-Date Fair Value Outstanding, Ending Balance (in dollars per share) | $ / shares	$ 14.05
Vesting Contingent on Performance and Service Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Nonvested Shares Outstanding, Beginning Balance (in shares) | shares	2,765,622
Number of Nonvested Shares, Granted (in shares) | shares	2,321,041
Number of Nonvested Shares, Vested (in shares) | shares	(887,489)
Number of Nonvested Shares, Forfeited (in shares) | shares	(51,154)
Number of Nonvested Shares Outstanding, Ending Balance (in shares) | shares	4,148,020
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant-Date Fair Value Outstanding, Beginning Balance (in dollars per share) | $ / shares	$ 14.45
Weighted-Average Grant-Date Fair Value, Granted (in dollars per share) | $ / shares	19.82
Weighted-Average Grant-Date Fair Value, Vested (in dollars per share) | $ / shares	16.27
Weighted-Average Grant-Date Fair Value, Forfeited (in dollars per share) | $ / shares	20.33
Weighted-Average Grant-Date Fair Value Outstanding, Ending Balance (in dollars per share) | $ / shares	$ 17.51

Stock-Based Compensation - A133

Stock-Based Compensation - Activity and Pricing Information for Nonvested Shares Granted Under Deferred Compensation Plans and Other Restricted Stock Awards (Detail) - Deferred Compensation Plans and Other Restricted Stock Award [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Nonvested Shares Outstanding, Beginning Balance (in shares)	3,858,152
Number of Nonvested Shares, Granted (in shares)	2,347,005
Number of Nonvested Shares, Dividend Equivalents	14
Number of Nonvested Shares, Vested (in shares)	(1,684,824)
Number of Nonvested Shares, Forfeited (in shares)	(296,573)
Number of Nonvested Shares Outstanding, Ending Balance (in shares)	4,223,774	3,858,152
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant-Date Fair Value Outstanding, Beginning Balance (in dollars per share)	$ 12.22
Weighted-Average Grant Date Fair Value, Granted (in dollars per share)	18.55	$ 11.46	$ 14.22
Weighted-Average Grant Date Fair Value, Dividend Equivalents	12.54
Weighted-Average Grant-Date Fair Value, Vested (in dollars per share)	12.50
Weighted-Average Grant-Date Fair Value, Forfeited (in dollars per share)	12.14
Weighted-Average Grant-Date Fair Value Outstanding, Ending Balance (in dollars per share)	$ 15.61	$ 12.22

Employee Benefits - Narrative (

Employee Benefits - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2009benefit_plan
Defined Benefit Plan Disclosure [Line Items]
Pre-tax AOCI not yet recognized as net pension cost		$ 525,000,000	$ 550,000,000
Pre-tax accumulated other comprehensive loss expected to be recognized as net pension cost		17,000,000
Accumulated benefit obligation for all pension plans		$ 1,300,000,000	$ 1,300,000,000
Percentage increase or decrease in expected return on plan assets		0.25%
Estimated increase or decrease in net pension cost		$ 3,000,000
Percentage increase or decrease in assumed discount rate		0.25%
Estimated change in net pension cost due to discount rate		$ 2,000,000
Expected return on plan assets		6.00%	6.00%	6.25%
Expected return on plan assets on estimating 2013 pension cost		4.75%
Employer contribution to saving plan		6.00%
Annual increase to default employee contribution, percent		1.00%
Employer discretionary contribution, required service period		1 year
Employer discretionary contribution percentage		2.00%	2.50%	2.00%
Additional employer discretionary contribution amount, per full-time employee		$ 1,000
Additional employer discretionary contribution amount, per part-time employee		500
Additional employer discretionary contribution amount, salary requirement		100,000
Total expenses associated with saving plan		$ 129,000,000	$ 94,000,000	$ 79,000,000
Initial Default Percentage [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial default employee contribution, percent		2.00%
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2018		$ 115,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2019		114,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2020		115,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2021		101,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2022		99,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2023 through 2027		412,000,000
Accumulated benefit obligation for all pension plans		1,323,000,000	1,338,000,000
Defined benefit plan, net periodic benefit cost expected		$ (5,000,000)	$ 21,000,000	$ 26,000,000
Expected return on plan assets		6.00%	6.00%	6.25%
Discount rate		3.25%	3.75%
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax AOCI not yet recognized as net pension cost		$ (13,000,000)	$ (11,000,000)
Pre-tax accumulated other comprehensive loss expected to be recognized as net pension cost		1,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2018		5,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2019		5,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2020		5,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2021		5,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2022		5,000,000
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2023 through 2027		22,000,000
Defined benefit plan, net periodic benefit cost expected		$ 1,000,000	$ 0	$ 0
Expected return on plan assets		4.50%	4.50%	4.50%
Age of employees under condition one		55 years
Period of service under condition one		5 years
Age of employees under condition two		50 years
Period of service under condition two		15 years
Minimum period of service at the time of termination hired before 2001		15 years
Discount rate		3.50%	3.75%
First Niagara Bank, N.A. [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plans | benefit_plan					2
Scenario, Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost expected	$ 5,000,000
Scenario, Forecast [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost expected	$ (1,000,000)
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Employees contribution to saving plan		1.00%
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Employees contribution to saving plan		100.00%
Default employee contribution, percent		10.00%

Employee Benefits - Net Pension

Employee Benefits - Net Pension Cost and Amount Recognized in OCI for All Funded and Unfunded Plans (Details) - Pension Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	$ 48	$ 44	$ 41
Expected return on plan assets	(68)	(58)	(56)
Amortization of losses	15	17	18
Settlement loss	0	18	23
Net pension cost (benefit)	(5)	21	26
Other changes in plan assets and benefit obligations recognized in OCI:
Net (gain) loss	(10)	(9)	47
Amortization of gains	(15)	(35)	(41)
Total recognized in comprehensive income	(25)	(44)	6
Total recognized in net pension cost and comprehensive income	$ (30)	$ (23)	$ 32

Employee Benefits - Changes in

Employee Benefits - Changes in PBO Related to Pension Plans (Details) - Pension Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
PBO/APBO at beginning of year	$ 1,338	$ 1,136
Interest cost	48	44	$ 41
Actuarial losses (gains)	37	(25)
Benefit payments	(100)	(85)
Plan acquisitions	0	268
PBO/APBO at end of year	$ 1,323	$ 1,338	$ 1,136

Employee Benefits - Changes 137

Employee Benefits - Changes in FVA (Details) - Pension Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
FVA at beginning of year	$ 1,133	$ 869
Actual return on plan assets	115	42
Employer contributions	15	14
Benefit payments	(100)	(85)
Plan acquisitions	0	293
FVA at end of year	$ 1,163	$ 1,133

Employee Benefits - Funded Stat

Employee Benefits - Funded Status of Pension Plans Recognized in Balance Sheets (Details) - Pension Plan [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Funded status	$ (160)	$ (205)
Net prepaid pension cost recognized consists of:
Noncurrent assets	29	0
Current liabilities	(15)	(16)
Noncurrent liabilities	(174)	(189)
Net prepaid pension cost recognized	$ (160)	$ (205)

Employee Benefits - Plans ABO i

Employee Benefits - Plans ABO in Excess of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
ABO	$ 1,300	$ 1,300
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
PBO	1,323	1,338
ABO	1,323	1,338
Fair value of plan assets	$ 1,163	$ 1,133

Employee Benefits - Weighted-Av

Employee Benefits - Weighted-Average Rates to Determine Actuarial Present Value of Benefit Obligations (Details)	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.25%	3.75%

Employee Benefits - Weighted141

Employee Benefits - Weighted-Average Rates to Determine Net Pension Cost (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Discount rate	3.75%	3.75%	3.50%
Expected return on plan assets	6.00%	6.00%	6.25%

Employee Benefits - Asset Targe

Employee Benefits - Asset Target Allocations Prescribed by Pension Funds' Investment Policies (Details)	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total Target Allocation	100.00%
Equity Securities, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Target Allocation	5.00%
Equity Securities, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Target Allocation	4.00%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Target Allocation	81.00%
Real Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Target Allocation	6.00%
Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Target Allocation	4.00%

Employee Benefits - Fair Values

Employee Benefits - Fair Values of Pension Plan Assets by Asset Category (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Foreign Government Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	$ 2	$ 1
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1,163	1,133	$ 869
Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	14
Pension Plan [Member] | Equity Securities, Common, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	11	133
Pension Plan [Member] | Equity Securities, Common, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1	15
Pension Plan [Member] | Equity Securities, Preferred, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	3	2
Pension Plan [Member] | Corporate Bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	152	90
Pension Plan [Member] | Corporate Bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	61	26
Pension Plan [Member] | Government Bonds and Agency Bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	203	101
Pension Plan [Member] | State and Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	31	5
Pension Plan [Member] | Mutual Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	118
Pension Plan [Member] | Mutual Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	7	35
Pension Plan [Member] | Mutual Funds, Fixed Income, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	152
Pension Plan [Member] | Mutual Funds, Fixed Income, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	19
Pension Plan [Member] | Mutual Funds, Real Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	9
Pension Plan [Member] | Collective Investment Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	45	15
Pension Plan [Member] | Collective Investment Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	41	97
Pension Plan [Member] | Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	43
Pension Plan [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	456	79
Pension Plan [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	16	18
Pension Plan [Member] | Real Assets, Collective Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	70	95
Pension Plan [Member] | Insurance Investment Contracts and Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at NAV	14	14
Pension Plan [Member] | Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at NAV	50	52
Level 1 [Member] | Foreign Government Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	22	497
Level 1 [Member] | Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	14
Level 1 [Member] | Pension Plan [Member] | Equity Securities, Common, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	11	133
Level 1 [Member] | Pension Plan [Member] | Equity Securities, Common, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1	15
Level 1 [Member] | Pension Plan [Member] | Equity Securities, Preferred, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	3	2
Level 1 [Member] | Pension Plan [Member] | Corporate Bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | Corporate Bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | Government Bonds and Agency Bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | State and Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | Mutual Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	118
Level 1 [Member] | Pension Plan [Member] | Mutual Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	7	35
Level 1 [Member] | Pension Plan [Member] | Mutual Funds, Fixed Income, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	152
Level 1 [Member] | Pension Plan [Member] | Mutual Funds, Fixed Income, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	19
Level 1 [Member] | Pension Plan [Member] | Mutual Funds, Real Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	9
Level 1 [Member] | Pension Plan [Member] | Collective Investment Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | Collective Investment Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Pension Plan [Member] | Real Assets, Collective Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Foreign Government Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	2	1
Level 2 [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1,077	570
Level 2 [Member] | Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Equity Securities, Common, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Equity Securities, Common, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Equity Securities, Preferred, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Corporate Bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	152	90
Level 2 [Member] | Pension Plan [Member] | Corporate Bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	61	26
Level 2 [Member] | Pension Plan [Member] | Government Bonds and Agency Bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	203	101
Level 2 [Member] | Pension Plan [Member] | State and Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	31	5
Level 2 [Member] | Pension Plan [Member] | Mutual Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Mutual Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Mutual Funds, Fixed Income, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Mutual Funds, Fixed Income, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Mutual Funds, Real Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Pension Plan [Member] | Collective Investment Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	45	15
Level 2 [Member] | Pension Plan [Member] | Collective Investment Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	41	97
Level 2 [Member] | Pension Plan [Member] | Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	43
Level 2 [Member] | Pension Plan [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	456	79
Level 2 [Member] | Pension Plan [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	16	18
Level 2 [Member] | Pension Plan [Member] | Real Assets, Collective Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	70	95
Level 3 [Member] | Foreign Government Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Equity Securities, Common, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Equity Securities, Common, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Equity Securities, Preferred, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Corporate Bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Corporate Bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Government Bonds and Agency Bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | State and Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Mutual Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Mutual Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Mutual Funds, Fixed Income, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Mutual Funds, Fixed Income, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Mutual Funds, Real Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Collective Investment Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Collective Investment Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Pension Plan [Member] | Real Assets, Collective Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	$ 0	$ 0

Employee Benefits - Pre-tax AOC

Employee Benefits - Pre-tax AOCI Not Yet Recognized as Net Postretirement Benefit Cost (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total unrecognized AOCI	$ 525	$ 550
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net unrecognized losses (gains)	(12)	(9)
Net unrecognized prior service credit	(1)	(2)
Total unrecognized AOCI	$ (13)	$ (11)

Employee Benefits - Net Postret

Employee Benefits - Net Postretirement Benefit Cost and the Amount Recognized in OCI for All Funded and Unfunded Plans (Details) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost of benefits earned	$ (1)	$ (1)	$ (1)
Interest cost on APBO	(3)	(2)	(3)
Expected return on plan assets	(2)	(2)	(3)
Amortization of prior service credit	(1)	(1)	(1)
Amortization of gains	0	0	0
Net pension cost (benefit)	1	0	0
Other changes in plan assets and benefit obligations recognized in OCI:
Net (gain) loss	(4)	(4)	(6)
Amortization of prior service credit	1	1	1
Amortization of losses	0	0	0
Total recognized in comprehensive income	(3)	(3)	(5)
Total recognized in net postretirement benefit cost and comprehensive income	$ (2)	$ (3)	$ (5)

Employee Benefits - Changes 146

Employee Benefits - Changes in APBO (Details) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
PBO/APBO at beginning of year	$ 69	$ 67
Service cost	1	1	$ 1
Interest cost	3	2	3
Plan participants’ contributions	1	2
Actuarial losses (gains)	3	(1)
Benefit payments	(8)	(6)
Plan acquisitions	0	4
PBO/APBO at end of year	$ 69	$ 69	$ 67

Employee Benefits - Change in F

Employee Benefits - Change in FVA (Other Post Retirement Benefit Plan Assets) (Details) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
FVA at beginning of year	$ 50	$ 49
Employer contributions	0	0
Plan participants’ contributions	1	2
Benefit payments	(8)	(6)
Actual return on plan assets	9	5
FVA at end of year	$ 52	$ 50

Employee Benefits - Funded S148

Employee Benefits - Funded Status of Postretirement Plans Recognized in Balance Sheets (Details) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Funded status	$ (16)	$ (19)
Noncurrent liabilities	$ (16)	$ (19)

Employee Benefits - Weighted149

Employee Benefits - Weighted-Average Rates to Determine Net Postretirement Benefit Cost (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.75%	3.75%	3.50%
Expected return on plan assets	6.00%	6.00%	6.25%
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.75%	4.00%	3.75%
Expected return on plan assets	4.50%	4.50%	4.50%

Employee Benefits - Asset Ta150

Employee Benefits - Asset Target Allocations Prescribed by Trusts' Investment Policies (Details)	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	100.00%
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	100.00%
Equity Securities [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	80.00%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	81.00%
Fixed Income Securities [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	10.00%
Convertible Securities [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	5.00%
Cash Equivalents [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	5.00%

Employee Benefits - Fair Val151

Employee Benefits - Fair Values of Postretirement Plan Assets by Asset Category (Details) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	$ 52	$ 50	$ 49
Mutual Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	25	23
Mutual Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	10	5
Mutual Funds, Fixed Income, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	4	5
Mutual Funds, Fixed Income, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	3
Common Investment Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	10	10
Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		7
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	42	33
Level 1 [Member] | Mutual Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	25	23
Level 1 [Member] | Mutual Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	10	5
Level 1 [Member] | Mutual Funds, Fixed Income, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	4	5
Level 1 [Member] | Mutual Funds, Fixed Income, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	3
Level 1 [Member] | Common Investment Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		0
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	10	17
Level 2 [Member] | Mutual Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Mutual Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Mutual Funds, Fixed Income, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 2 [Member] | Mutual Funds, Fixed Income, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0
Level 2 [Member] | Common Investment Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	10	10
Level 2 [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		7
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Mutual Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Mutual Funds, Equity, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Mutual Funds, Fixed Income, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Mutual Funds, Fixed Income, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0
Level 3 [Member] | Common Investment Funds, Equity, United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	$ 0	0
Level 3 [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		$ 0

Short-Term Borrowings - Compone

Short-Term Borrowings - Components 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]
Balance at year end, Securities Sold Under Repurchase Agreements	$ 0	$ 0
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Balance at year end, Federal Funds Purchase	3	1,005	$ 20
Average during the year	128	44	195
Maximum month-end balance	$ 2,331	$ 1,005	$ 678
Weighted-average rate during the year	0.72%	0.68%	0.14%
Weighted-average rate at December 31	0.00%	0.55%	0.05%
Securities Sold under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Average during the year	$ 389	$ 443	$ 437
Maximum month-end balance	$ 472	$ 684	$ 589
Weighted-average rate during the year	0.08%	0.04%	0.00%
Weighted-average rate at December 31	0.08%	0.07%	0.00%
Balance at year end, Securities Sold Under Repurchase Agreements	$ 374	$ 497	$ 352
Other Short Term Borrowings [Member]
Short-term Debt [Line Items]
Average during the year	1,140	852	572
Maximum month-end balance	$ 1,242	$ 872	$ 1,122
Weighted-average rate during the year	1.34%	1.18%	1.52%
Weighted-average rate at December 31	2.01%	1.11%	1.78%
Balance at year end, Other Short-Term Borrowings	$ 634	$ 808	$ 533

Short-Term Borrowings - Narrati

Short-Term Borrowings - Narrative (Details) $ in Billions	Dec. 31, 2017USD ($)
Short-term Debt [Line Items]
Deposits with the Federal Reserve	$ 3.7
Federal Reserve Bank of Cleveland [Member]
Short-term Debt [Line Items]
Unused Secured borrowing capacity	23.8
Federal Home Loan Bank of Cincinnati [Member]
Short-term Debt [Line Items]
Unused Secured borrowing capacity	$ 6.6

Long-Term Debt - Components of

Long-Term Debt - Components of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	May 20, 2016
Debt Instrument [Line Items]
Total long-term debt	$ 14,333	$ 12,384
Real Estate Loans and securities pledged	1,100	126
Senior Medium-Term Notes Due Through 2021 [Member]
Debt Instrument [Line Items]
Senior medium-term notes	$ 2,766	$ 2,799
Long-term debt weighted average interest rate	3.56%	3.57%
2.075% Subordinated notes due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	2.075%
Subordinated long-term notes	$ 161	$ 162
6.875% Subordinated Notes Due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.875%
Subordinated long-term notes	$ 109	111
7.750% Subordinated Notes Due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.75%
Subordinated long-term notes	$ 141	141
7.25% Subordinated notes due 2021 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.25%		3.40%
Subordinated long-term notes	$ 348	$ 358	$ 600
Long-term debt weighted average interest rate	7.25%	7.25%
6.75% Senior Notes Due 2020 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.75%
Subordinated long-term notes	$ 327	$ 338
Long-term debt weighted average interest rate	6.75%	6.75%
Other Subordinated Notes [Member]
Debt Instrument [Line Items]
Subordinated long-term notes	$ 69	$ 78
Long-term debt weighted average interest rate	3.02%	4.61%
Senior Medium-Term Notes Due Through 2039 [Member]
Debt Instrument [Line Items]
Senior medium-term notes	$ 8,011	$ 6,715
Long-term debt weighted average interest rate	2.24%	1.93%
3.18% Senior Remarketable Notes Due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	3.18%
Subordinated long-term notes	$ 202	$ 193
5.70% Subordinated notes due 2017 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	5.70%
Subordinated long-term notes	$ 0	207
4.625% Subordinated notes due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	4.625%
Subordinated long-term notes	$ 100	102
3.40% Subordinated notes due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	3.40%
Subordinated long-term notes	$ 565	567
6.95% Subordinated notes due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.95%
Subordinated long-term notes	$ 299	299
Secured Borrowing Due Through 2052 [Member]
Debt Instrument [Line Items]
Secured borrowing due through 2021	$ 24	$ 68
Long-term debt weighted average interest rate	4.46%	4.45%
Federal Home Loan Bank [Member]
Debt Instrument [Line Items]
Federal Home Loan Bank advances due through 2036	$ 1,106	$ 126
Long-term debt weighted average interest rate	2.32%	3.64%
Investment Fund Financing [Member]
Debt Instrument [Line Items]
Investment Fund Financing due through 2052	$ 88	$ 100
Long-term debt weighted average interest rate	1.94%	1.94%
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Obligations under Capital Leases due 2032	$ 17	$ 20
Key [Member]
Debt Instrument [Line Items]
Total long-term debt	3,921	3,987
Subsidiaries [Member]
Debt Instrument [Line Items]
Total long-term debt	$ 10,412	$ 8,397

Long-Term Debt - Scheduled Prin

Long-Term Debt - Scheduled Principal Payments on Long-Term Debt (Details) $ in Millions	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
2,018	$ 3,071
2,019	2,048
2,020	2,706
2,021	2,624
2,022	1,426
All subsequent years	2,458
Key [Member]
Debt Instrument [Line Items]
2,018	746
2,019	0
2,020	1,310
2,021	1,381
2,022	0
All subsequent years	483
Subsidiaries [Member]
Debt Instrument [Line Items]
2,018	2,325
2,019	2,048
2,020	1,396
2,021	1,243
2,022	1,426
All subsequent years	$ 1,975

Long-Term Debt - Narrative (Det

Long-Term Debt - Narrative (Details) - USD ($)	Sep. 29, 2015	Sep. 15, 2015	Dec. 31, 2017	Sep. 14, 2017	Jun. 09, 2017	Dec. 31, 2016	Nov. 22, 2016	Aug. 22, 2016	May 20, 2016	Mar. 08, 2016
Debt Instrument [Line Items]
Bank note, maximum issuable amount	$ 20,000,000,000
Senior notes available for future issuance			$ 15,800,000,000
Issuance of euro medium-term notes original maturities			Nine months or more
Senior Notes [Member]
Debt Instrument [Line Items]
Original maturity of bank note			7 days
Subordinated Notes [Member]
Debt Instrument [Line Items]
Original maturity of bank note			5 years
2.35% Senior Bank Notes due March 8, 2019 [Member]
Debt Instrument [Line Items]
Issuance of senior notes										$ 1,000,000,000
Debt instrument interest rate										2.35%
7.25% Subordinated notes due 2021 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate			7.25%						3.40%
Issuance of subordinated notes			$ 348,000,000			$ 358,000,000			$ 600,000,000
1.60% Senior Bank Notes due 2019 [Member]
Debt Instrument [Line Items]
Issuance of senior notes								$ 500,000,000
Debt instrument interest rate								1.60%
2.50% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Issuance of senior notes							$ 500,000,000
Debt instrument interest rate							2.50%
Issuance of floating rate senior notes							$ 250,000,000
2.40% Senior Bank Notes Due 2022 [Member]
Debt Instrument [Line Items]
Issuance of senior notes					$ 1,000,000,000
Debt instrument interest rate					2.40%
2.30% Senior Bank Notes Due 2022 [Member]
Debt Instrument [Line Items]
Issuance of senior notes				$ 1,000,000,000
Debt instrument interest rate				2.30%
Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt term			9 months
Issuance of medium-term notes		$ 1,000,000,000
Coupon rate of medium-term notes		2.90%
Additional debt securities authorized and available for issuance under note program			$ 4,000,000,000

Trust Preferred Securities I157

Trust Preferred Securities Issued by Unconsolidated Subsidiaries - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
First Niagara Bank, N.A. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities redeemed	$ 9

Trust Preferred Securities I158

Trust Preferred Securities Issued by Unconsolidated Subsidiaries - Summary of Trust Preferred Securities, Common Stock and Related Debentures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Stock	$ 1,257	$ 1,257
Debentures adjustments related to financial instrument hedging	55	59
KeyCorp Capital I [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	155
Common Stock	6
Principal Amount of of Debentures, Net of Discount	$ 161
Interest Rate of Trust Preferred Securities and Debentures	2.75%
KeyCorp Capital II [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 105
Common Stock	4
Principal Amount of of Debentures, Net of Discount	$ 109
Interest Rate of Trust Preferred Securities and Debentures	6.875%
KeyCorp Capital III [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 137
Common Stock	4
Principal Amount of of Debentures, Net of Discount	$ 141
Interest Rate of Trust Preferred Securities and Debentures	7.75%
HNC Statutory Trust III [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 18
Common Stock	1
Principal Amount of of Debentures, Net of Discount	$ 19
Interest Rate of Trust Preferred Securities and Debentures	2.854%
Willow Grove Statutory Trust I [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 18
Common Stock	1
Principal Amount of of Debentures, Net of Discount	$ 19
Interest Rate of Trust Preferred Securities and Debentures	2.898%
HNC Statutory Trust IV [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 16
Common Stock	1
Principal Amount of of Debentures, Net of Discount	$ 17
Interest Rate of Trust Preferred Securities and Debentures	2.658%
Westbank Capital Trust II [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 7
Common Stock	0
Principal Amount of of Debentures, Net of Discount	$ 7
Interest Rate of Trust Preferred Securities and Debentures	3.815%
Westbank Capital Trust III [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 7
Common Stock	0
Principal Amount of of Debentures, Net of Discount	$ 7
Interest Rate of Trust Preferred Securities and Debentures	3.815%
Business Trusts [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 463	475
Common Stock	17	17
Principal Amount of of Debentures, Net of Discount	$ 480	$ 492
Interest Rate of Trust Preferred Securities and Debentures	4.977%	4.845%
Treasury Rate [Member] | KeyCorp Capital II [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	0.20%
Treasury Rate [Member] | KeyCorp Capital III [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	0.25%
London Interbank Offered Rate (LIBOR) [Member] | KeyCorp Capital I [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	0.74%
London Interbank Offered Rate (LIBOR) [Member] | HNC Statutory Trust III [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.40%
London Interbank Offered Rate (LIBOR) [Member] | Willow Grove Statutory Trust I [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.31%
London Interbank Offered Rate (LIBOR) [Member] | HNC Statutory Trust IV [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.28%
London Interbank Offered Rate (LIBOR) [Member] | Westbank Capital Trust II and III [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	2.19%
Debt Instrument, Redemption, Period Five [Member] | Treasury Rate [Member] | Keycorp Capital II and III [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	0.50%

Commitments, Contingent Liab159

Commitments, Contingent Liabilities and Guarantees - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments Contingencies And Guarantees [Line Items]
Rental expense under all operating leases	$ 153	$ 118	$ 122
Minimum future rental payments under noncancelable operating leases due in 2018	142
Minimum future rental payments under noncancelable operating leases due in 2019	132
Minimum future rental payments under noncancelable operating leases due in 2020	117
Minimum future rental payments under noncancelable operating leases due in 2021	101
Minimum future rental payments under noncancelable operating leases due in 2022	89
Minimum future rental payments under noncancelable operating leases, all subsequent years	381
Default guarantees, value	131
Written Put Options [Member]
Commitments Contingencies And Guarantees [Line Items]
Default guarantees, value	$ 50
Weighted average life of written put options	3 years
Standby Letters of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Remaining weighted-average life of standby letters of credit in years	2 years
Default guarantees, value	$ 67
Underwriting And Servicing Program [Member]
Commitments Contingencies And Guarantees [Line Items]
Weighted-average remaining term for outstanding commercial mortgage loans in years	7 years 10 months 24 days
Unpaid principal balance outstanding of loans sold	$ 11,600
Maximum potential amount of undiscounted future payments that could be required, percentage of principal balance of loans outstanding	28.00%
Default guarantees, value	$ 6
Residential Mortgage Reserve [Member]
Commitments Contingencies And Guarantees [Line Items]
Unpaid principal balance outstanding of loans sold	$ 4,500
Maximum potential amount of undiscounted future payments that could be required, percentage of principal balance of loans outstanding	30.00%
Weighted average loan to value ratio (as a percentage)	72.00%
Default guarantees, value	$ 5
Return Guarantee Agreement with LIHTC Investors [Member]
Commitments Contingencies And Guarantees [Line Items]
Default guarantees, value	$ 3
Compliance period of property	15 years
Default Guarantees [Member]
Commitments Contingencies And Guarantees [Line Items]
Default guarantees, value	$ 1
Minimum [Member] | Standby Letters of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Remaining actual life letters of credit in years	1 year
Minimum [Member] | Low [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment (percentage)	0.00%
Minimum [Member] | Moderate [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment (percentage)	30.00%
Minimum [Member] | High [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment (percentage)	70.00%
Maximum [Member] | Standby Letters of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Remaining actual life letters of credit in years	17 years
Maximum [Member] | Low [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment (percentage)	30.00%
Maximum [Member] | Moderate [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment (percentage)	70.00%

Commitments, Contingent Liab160

Commitments, Contingent Liabilities and Guarantees - Commitments to Extend Credit or Funding (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Total loan commitments	$ 58,652	$ 52,725
When-issued and to be announced securities commitments	0	34
Commercial letters of credit	231	143
Purchase card commitments	425	293
Principal investing commitments	29	37
Tax credit investment commitments	481	466
Liabilities of certain limited partnerships and other commitments	0	2
Securities underwriting	9	0
Total loan and other commitments	59,827	53,700
Commercial and Other [Member]
Guarantor Obligations [Line Items]
Total loan commitments	40,315	34,372
Commercial Real Estate and Construction [Member]
Guarantor Obligations [Line Items]
Total loan commitments	2,774	3,034
Home Equity [Member]
Guarantor Obligations [Line Items]
Total loan commitments	9,673	9,666
Credit Cards [Member]
Guarantor Obligations [Line Items]
Total loan commitments	$ 5,890	$ 5,653

Commitments, Contingent Liab161

Commitments, Contingent Liabilities and Guarantees - Guarantees (Details) $ in Millions	Dec. 31, 2017USD ($)
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	$ 9,848
Liability Recorded	131
Written Put Options [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	2,080
Liability Recorded	50
Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	3,142
Liability Recorded	67
Recourse Agreement with FNMA [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	3,261
Liability Recorded	6
Residential Mortgage Reserve [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	1,362
Liability Recorded	5
Return Guarantee Agreement with LIHTC Investors [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	3
Liability Recorded	$ 3

Accumulated Other Comprehens162

Accumulated Other Comprehensive Income - Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		$ 15,240
Amounts reclassified from accumulated other comprehensive income resulting from new federal corporate income tax rate (b)	$ 141	141
Total other comprehensive income (loss), net of tax		(238)	$ (136)	$ (49)
Ending Balance	15,025	15,025	15,240
Unrealized Gains (Losses) on Securities Available for Sale [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		(185)	(58)
Other comprehensive income before reclassification, net of income taxes		(69)	(127)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)		(1)	0
Amounts reclassified from accumulated other comprehensive income resulting from new federal corporate income tax rate (b)		(56)
Total other comprehensive income (loss), net of tax		(126)	(127)
Ending Balance	(311)	(311)	(185)	(58)
Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		(14)	20
Other comprehensive income before reclassification, net of income taxes		(48)	17
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)		(10)	(51)
Amounts reclassified from accumulated other comprehensive income resulting from new federal corporate income tax rate (b)		(14)
Total other comprehensive income (loss), net of tax		(72)	(34)
Ending Balance	(86)	(86)	(14)	20
Foreign Currency Translation Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		(3)	(2)
Other comprehensive income before reclassification, net of income taxes		12	(1)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)		1	0
Amounts reclassified from accumulated other comprehensive income resulting from new federal corporate income tax rate (b)		(1)
Total other comprehensive income (loss), net of tax		12	(1)
Ending Balance	9	9	(3)	(2)
Net Pension and Postretirement Benefit Costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		(339)	(365)
Other comprehensive income before reclassification, net of income taxes		9	5
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)		9	21
Amounts reclassified from accumulated other comprehensive income resulting from new federal corporate income tax rate (b)		(70)
Total other comprehensive income (loss), net of tax		(52)	26
Ending Balance	(391)	(391)	(339)	(365)
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		(541)	(405)	(356)
Other comprehensive income before reclassification, net of income taxes		(96)	(106)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)		(1)	(30)
Amounts reclassified from accumulated other comprehensive income resulting from new federal corporate income tax rate (b)		(141)
Total other comprehensive income (loss), net of tax		(238)	(136)	(49)
Ending Balance	$ (779)	$ (779)	$ (541)	$ (405)

Accumulated Other Comprehens163

Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains	$ 1	$ 0	$ 1
Realized losses	0	0	1
Interest income — Loans	3,677	2,773	2,149
Interest expense — Long-term debt	(319)	(218)	(160)
Personnel expense	(2,273)	(2,073)	(1,652)
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	1,981	1,002	1,250
Income taxes	637	179	303
Income (loss) from continuing operations	1,291	789	$ 919
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	1
Income taxes	0
Income (loss) from continuing operations	1
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	15	81
Income taxes	5	30
Income (loss) from continuing operations	10	51
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Financial Instruments [Member] | Interest Rate [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	19	85
Interest expense — Long-term debt	(4)	(4)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign Currency Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	(1)
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	(1)
Income taxes	0
Income (loss) from continuing operations	(1)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	(14)	(34)
Income taxes	(5)	(13)
Income (loss) from continuing operations	(9)	(21)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Amortization of Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	(15)	(17)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Settlement Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense		(18)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Amortization Of Prior Service Credit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	1	$ 1
Other Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains	1
Realized losses	$ 0

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details)	Feb. 15, 2017USD ($)$ / shares	Jun. 30, 2018$ / shares	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2017$ / shares	Jun. 30, 2017$ / sharesshares	Mar. 31, 2017USD ($)$ / shares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / shares	Mar. 20, 2017shares	Dec. 12, 2016	Sep. 09, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends declared per common share (in dollars per share)			$ 0.105	$ 0.095	$ 0.095	$ 0.085	$ 0.38	$ 0.33	$ 0.290
Common stock issued upon conversion (in shares) | shares										7.0922
Preferred stock | $			$ 1,025,000,000				$ 1,025,000,000	$ 1,665,000,000
Dividends payable | $							(480,000,000)	$ (335,000,000)	$ (267,000,000)
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock, dividend rate, percentage								7.75%
Preferred stock | $								$ 290,000,000
Preferred stock, par value (in dollars per share)								$ 1
Preferred stock, liquidation preference (in dollars per share)								$ 100
Preferred stock, shares authorized (in shares) | shares								7,475,000
Preferred stock, shares outstanding (in shares) | shares								2,900,234
Dividend payable (in dollars per share)						$ 1.9375
Dividends payable | $						$ (6,000,000)
Series C Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock | $								$ 350,000,000
Preferred stock, par value (in dollars per share)								$ 1
Preferred stock, liquidation preference (in dollars per share)	$ 25
Preferred stock, shares authorized (in shares) | shares								14,000,000
Dividend payable (in dollars per share)	$ 0.539063
Dividends payable | $	$ (7,000,000)
Depository Shares [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Shares issued | $							$ 525,000,000
Series D Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock, par value (in dollars per share)			$ 1				$ 1
Preferred stock, liquidation preference (in dollars per share)			$ 25,000				$ 25,000
Preferred stock, shares authorized (in shares) | shares			21,000				21,000
Preferred stock, shares outstanding (in shares) | shares			21,000				21,000
Dividend payable (in dollars per share)			$ 50				$ 50
Dividends payable | $			$ (26,000,000)
Depository receipt ratio												0.04
Depository Shares, Series E [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Shares issued | $							$ 500,000,000
Series E Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock, par value (in dollars per share)			$ 1				$ 1
Preferred stock, liquidation preference (in dollars per share)			$ 1,000				$ 1,000
Preferred stock, shares authorized (in shares) | shares			500,000				500,000
Preferred stock, shares outstanding (in shares) | shares					500,000
Dividend payable (in dollars per share)			$ 1.544012				$ 1.544012
Dividends payable | $			$ (31,000,000)
Depository receipt ratio											0.025
2017 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Stock repurchase program authorized amount (in shares) | $			$ 800,000,000				$ 800,000,000
Repurchase of common stock | $							476,000,000
2016 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Repurchase of common stock | $							$ 254,000,000
Scenario, Forecast [Member] | 2017 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Proposed increase in cash dividends declared on common shares (in dollars per share)		$ 0.120

Shareholders' Equity - Key's an

Shareholders' Equity - Key's and KeyBank's Actual Capital Amounts and Ratios, Minimum Capital Amounts and Ratios (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Key [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Net Risk-Weighted Assets, Actual Amount	$ 15,345	$ 15,638
Tier 1 Capital to Average Quarterly Tangible Assets, Amount	13,083	13,249
Tier 1 Capital to Net Risk-Weighted Assets, Actual Amount	$ 13,083	$ 13,249
Total Capital to Net Risk-Weighted Assets, Actual Ratio	12.92%	12.85%
Tier 1 Capital to Net Risk-Weighted Assets, Actual Ratio	11.01%	10.89%
Tier 1 Capital to Average Quarterly Tangible Assets, Actual Ratio	9.73%	9.90%
Total Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Amount	$ 9,505	$ 9,734
Tier 1 Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Amount	7,129	7,300
Tier 1 Capital to Average Quarterly Tangible Assets to Meet Minimum Capital Adequacy Requirements, Amount	$ 5,379	$ 5,442
Total Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Ratio	8.00%	8.00%
Tier 1 Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Ratio	6.00%	6.00%
Tier 1 Capital to Average Quarterly Tangible Assets to Meet Minimum Capital Adequacy Requirements, Ratio	4.00%	4.00%
KeyBank (consolidated) [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Net Risk-Weighted Assets, Actual Amount	$ 14,957	$ 14,291
Tier 1 Capital to Average Quarterly Tangible Assets, Amount	13,110	12,439
Tier 1 Capital to Net Risk-Weighted Assets, Actual Amount	$ 13,110	$ 12,439
Total Capital to Net Risk-Weighted Assets, Actual Ratio	12.86%	12.36%
Tier 1 Capital to Net Risk-Weighted Assets, Actual Ratio	11.27%	10.76%
Tier 1 Capital to Average Quarterly Tangible Assets, Actual Ratio	9.91%	9.46%
Total Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Amount	$ 9,306	$ 9,251
Tier 1 Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Amount	6,980	6,939
Tier 1 Capital to Average Quarterly Tangible Assets to Meet Minimum Capital Adequacy Requirements, Amount	$ 5,293	$ 5,353
Total Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Ratio	8.00%	8.00%
Tier 1 Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Ratio	6.00%	6.00%
Tier 1 Capital to Average Quarterly Tangible Assets to Meet Minimum Capital Adequacy Requirements, Ratio	4.00%	4.00%
Total Capital to Net Risk-Weighted Assets, to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Amount	$ 11,633	$ 11,564
Tier 1 Capital to Net Risk-Weighted Assets, to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Amount	6,980	6,939
Tier 1 Capital to Average Quarterly Tangible Assets to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Amount	$ 6,617	$ 6,691
Total Capital to Net Risk-Weighted Assets, to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Ratio	10.00%	10.00%
Tier 1 Capital to Net Risk-Weighted Assets, to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Ratio	6.00%	6.00%
Tier 1 Capital to Average Quarterly Tangible Assets to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Ratio	5.00%	5.00%

Line of Business Results - Narr

Line of Business Results - Narrative (Details)	12 Months Ended
	Dec. 31, 2017Branchindustry_sector	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Number of state branch network | Branch	15
Number of business units | industry_sector	7
Federal income tax rate	35.00%	35.00%	35.00%
State income tax rate	2.20%

Line of Business Results - Fina

Line of Business Results - Financial Information of Business Groups (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)employee	Dec. 31, 2016USD ($)employee	Dec. 31, 2015USD ($)employee
Segment Reporting Information [Line Items]
Net interest income (TE)	$ 3,830	$ 2,953	$ 2,376
Noninterest income	2,478	2,071	1,880
Total revenue (TE)	6,308	5,024	4,256
Provision for credit losses	229	266	166
Depreciation and amortization expense	384	303	255
Other noninterest expense	3,714	3,453	2,585
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,981	1,002	1,250
Allocated income taxes (benefit) and TE adjustments	690	213	331
INCOME (LOSS) FROM CONTINUING OPERATIONS	1,291	789	919
Income (loss) from discontinued operations, net of taxes	7	1	1
NET INCOME (LOSS)	1,298	790	920
Less: Net income (loss) attributable to noncontrolling interests	2	(1)	4
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	1,296	791	916
AVERAGE BALANCES
Loans and leases	86,365	71,148	58,594
Total assets	133,719	112,537	92,026
Deposits	102,946	86,352	70,630
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	3,097	1,934	139
Net loan charge-offs	$ 208	$ 205	$ 142
Return on average allocated equity, continuing operations (as a percentage)	8.47%	6.25%	8.61%
Return on average allocated equity (as a percentage)	8.51%	6.25%	8.62%
Average full-time equivalent employees | employee	18,415	15,700	13,483
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	$ 3,810	$ 2,957	$ 2,365
Noninterest income	2,498	2,089	1,897
Total revenue (TE)	6,308	5,046	4,262
Provision for credit losses	229	266	165
Depreciation and amortization expense	215	140	107
Other noninterest expense	3,686	3,183	2,714
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	2,178	1,457	1,276
Allocated income taxes (benefit) and TE adjustments	587	375	348
INCOME (LOSS) FROM CONTINUING OPERATIONS	1,591	1,082	928
Income (loss) from discontinued operations, net of taxes	0	0	0
NET INCOME (LOSS)	1,591	1,082	928
Less: Net income (loss) attributable to noncontrolling interests	3	0	4
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	1,588	1,082	924
AVERAGE BALANCES
Loans and leases	86,340	71,035	58,551
Total assets	133,033	110,035	91,424
Deposits	102,975	85,869	70,673
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	3,016	1,818	91
Net loan charge-offs	$ 207	$ 204	$ 141
Return on average allocated equity, continuing operations (as a percentage)	20.47%	18.19%	19.25%
Return on average allocated equity (as a percentage)	20.47%	18.19%	19.25%
Average full-time equivalent employees | employee	13,333	11,185	9,634
Operating Segments [Member] | Key Community Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	$ 2,643	$ 1,953	$ 1,487
Noninterest income	1,200	925	788
Total revenue (TE)	3,843	2,878	2,275
Provision for credit losses	209	143	90
Depreciation and amortization expense	116	76	56
Other noninterest expense	2,486	2,077	1,723
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,032	582	406
Allocated income taxes (benefit) and TE adjustments	383	217	151
INCOME (LOSS) FROM CONTINUING OPERATIONS	649	365	255
Income (loss) from discontinued operations, net of taxes	0	0	0
NET INCOME (LOSS)	649	365	255
Less: Net income (loss) attributable to noncontrolling interests	0	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	649	365	255
AVERAGE BALANCES
Loans and leases	47,383	37,620	30,834
Total assets	51,433	40,300	32,948
Deposits	79,669	63,873	51,163
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	2,438	1,478	75
Net loan charge-offs	$ 166	$ 114	$ 92
Return on average allocated equity, continuing operations (as a percentage)	13.59%	10.62%	9.42%
Return on average allocated equity (as a percentage)	13.59%	10.62%	9.42%
Average full-time equivalent employees | employee	10,924	8,936	7,520
Operating Segments [Member] | Key Corporate Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	$ 1,190	$ 1,049	$ 886
Noninterest income	1,147	1,013	926
Total revenue (TE)	2,337	2,062	1,812
Provision for credit losses	20	127	83
Depreciation and amortization expense	96	60	43
Other noninterest expense	1,161	1,071	945
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,060	804	741
Allocated income taxes (benefit) and TE adjustments	246	178	196
INCOME (LOSS) FROM CONTINUING OPERATIONS	814	626	545
Income (loss) from discontinued operations, net of taxes	0	0	0
NET INCOME (LOSS)	814	626	545
Less: Net income (loss) attributable to noncontrolling interests	0	(2)	1
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	814	628	544
AVERAGE BALANCES
Loans and leases	37,732	31,929	25,865
Total assets	44,521	37,801	31,541
Deposits	21,318	20,783	19,043
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	559	340	16
Net loan charge-offs	$ 40	$ 83	$ 40
Return on average allocated equity, continuing operations (as a percentage)	28.69%	26.80%	28.91%
Return on average allocated equity (as a percentage)	28.69%	26.80%	28.91%
Average full-time equivalent employees | employee	2,407	2,244	2,100
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	$ (23)	$ (45)	$ (8)
Noninterest income	151	151	183
Total revenue (TE)	128	106	175
Provision for credit losses	0	(4)	(8)
Depreciation and amortization expense	3	4	8
Other noninterest expense	39	35	46
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	86	71	129
Allocated income taxes (benefit) and TE adjustments	(42)	(20)	1
INCOME (LOSS) FROM CONTINUING OPERATIONS	128	91	128
Income (loss) from discontinued operations, net of taxes	0	0	0
NET INCOME (LOSS)	128	91	128
Less: Net income (loss) attributable to noncontrolling interests	3	2	3
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	125	89	125
AVERAGE BALANCES
Loans and leases	1,225	1,486	1,852
Total assets	37,079	31,934	26,935
Deposits	1,988	1,213	467
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	19	0	0
Net loan charge-offs	$ 1	$ 7	$ 9
Return on average allocated equity, continuing operations (as a percentage)	86.81%	52.66%	58.96%
Return on average allocated equity (as a percentage)	86.81%	52.66%	58.96%
Average full-time equivalent employees | employee	2	5	14
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	$ 20	$ (4)	$ 11
Noninterest income	(20)	(18)	(17)
Total revenue (TE)	0	(22)	(6)
Provision for credit losses	0	0	1
Depreciation and amortization expense	169	163	148
Other noninterest expense	28	270	(129)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(197)	(455)	(26)
Allocated income taxes (benefit) and TE adjustments	103	(162)	(17)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(300)	(293)	(9)
Income (loss) from discontinued operations, net of taxes	7	1	1
NET INCOME (LOSS)	(293)	(292)	(8)
Less: Net income (loss) attributable to noncontrolling interests	(1)	(1)	0
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	(292)	(291)	(8)
AVERAGE BALANCES
Loans and leases	25	113	43
Total assets	686	2,502	602
Deposits	(29)	483	(43)
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	81	116	49
Net loan charge-offs	$ 1	$ 1	$ 1
Return on average allocated equity, continuing operations (as a percentage)	(4.00%)	(4.36%)	(0.15%)
Return on average allocated equity (as a percentage)	(3.91%)	(4.34%)	(0.14%)
Average full-time equivalent employees | employee	5,082	4,515	3,849

Condensed Financial Informat168

Condensed Financial Information of the Parent Company - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Cash and due from banks	$ 671		$ 677	$ 607	$ 653
Short-term investments	4,447		2,775
Securities available for sale	18,139		20,212
Other investments	726		738
Total loans	85,528		85,180
Goodwill	2,538	$ 2,464	2,446	1,060
Other intangible assets	416		384
Corporate-owned life insurance	4,132		4,068
Derivative assets	669		803
Accrued income and other assets	3,568		3,864
Total assets	137,698		136,453
Accrued expense and other liabilities	1,803		1,796
Derivative liabilities	291		636
Total long-term debt	14,333		12,384
Total liabilities	122,673		121,213
SHAREHOLDERS' EQUITY	15,023		15,240
Total liabilities and equity	137,698		136,453
Key [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and due from banks	2,257		3,286	$ 2,608	$ 2,207
Short-term investments	22		70
Securities available for sale	10		10
Other investments	29		25
Total loans	281		281
Total investment in subsidiaries	16,054		15,232
Goodwill	167		167
Corporate-owned life insurance	208		207
Derivative assets	29		53
Accrued income and other assets	353		451
Total assets	19,410		19,782
Accrued expense and other liabilities	466		553
Derivative liabilities	0		2
Long term debt due to Subsidiaries	480		492
Total long-term debt	3,921		3,987
Total liabilities	4,387		4,542
SHAREHOLDERS' EQUITY	15,023		15,240
Total liabilities and equity	19,410		19,782
Key [Member] | Banks [Member]
Condensed Financial Statements, Captions [Line Items]
Total loans	250		250
Investment in subsidiaries	15,169		14,564
Key [Member] | Nonbank Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total loans	31		31
Investment in subsidiaries	885		668
Key [Member] | Unaffiliated Companies [Member]
Condensed Financial Statements, Captions [Line Items]
Total long-term debt	$ 3,441		$ 3,495

Condensed Financial Informat169

Condensed Financial Information of the Parent Company - Condensed Statements of Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Other income	[1]	$ 146	$ 94	$ 54
Total interest income		4,390	3,319	2,622
Interest on long-term debt with subsidiary trusts		319	218	160
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries		1,981	1,002	1,250
Income tax (expense) benefit		(637)	(179)	(303)
NET INCOME (LOSS)		1,298	790	920
Less: Net income attributable to noncontrolling interests		2	(1)	4
NET INCOME (LOSS) ATTRIBUTABLE TO KEY		1,296	791	916
Key [Member]
Condensed Financial Statements, Captions [Line Items]
Interest income from subsidiaries		10	10	10
Other income		9	11	20
Total interest income		769	696	1,031
Interest on long-term debt with subsidiary trusts		17	14	10
Interest on other borrowed funds		95	69	52
Personnel and other expense		46	101	73
Total expense		158	184	135
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries		611	512	896
Income tax (expense) benefit		29	54	39
Income (loss) before equity in net income (loss) less dividends from subsidiaries		640	566	935
Equity in net income (loss) less dividends from subsidiaries		658	224	(15)
NET INCOME (LOSS)		1,298	790	920
Less: Net income attributable to noncontrolling interests		2	(1)	4
NET INCOME (LOSS) ATTRIBUTABLE TO KEY		1,296	791	916
Key [Member] | Banks [Member]
Condensed Financial Statements, Captions [Line Items]
Bank/Nonbank subsidiaries		750	625	1,000
Key [Member] | Nonbank Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Bank/Nonbank subsidiaries		$ 0	$ 50	$ 1
[1]	Net securities gains (losses) totaled less than $1 million for each of the years ended December 31, 2017, 2016, and 2015. For 2017, 2016, and 2015, we did not have any impairment losses related to securities.

Condensed Financial Informat170

Condensed Financial Information of the Parent Company - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES
Net income (loss) attributable to Key	$ 1,296	$ 791	$ 916
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Deferred income taxes (benefit)	303	11	(76)
Stock-based compensation expense	100	99	58
Other operating activities, net	(594)	195	(151)
NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES	1,815	1,689	1,131
INVESTING ACTIVITIES
Net decrease (increase) in short-term investments, excluding acquisitions	(1,672)	(68)	1,562
Purchases of securities available for sale	(3,002)	(5,718)	(4,090)
Cash used in acquisitions	(144)	(481)	0
Proceeds from sales, prepayments and maturities of securities available for sale	3,999	4,241	3,098
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	(2,239)	(6,457)	(2,023)
FINANCING ACTIVITIES
Net proceeds from issuance of long-term debt	2,852	2,827	3,756
Payments on long-term debt	(748)	(1,308)	(1,172)
Repurchase of Treasury Shares	(664)	(140)	(448)
Cash dividends paid	(480)	(335)	(267)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	418	4,838	846
NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS	(6)	70	(46)
CASH AND DUE FROM BANKS AT BEGINNING OF YEAR	677	607	653
CASH AND DUE FROM BANKS AT END OF YEAR	671	677	607
Key [Member]
OPERATING ACTIVITIES
Net income (loss) attributable to Key	1,296	791	916
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Deferred income taxes (benefit)	38	(24)	10
Stock-based compensation expense	11	12	9
Equity in net (income) loss less dividends from subsidiaries	(658)	(224)	15
Other intangible asset amortization	0	0	2
Net (increase) decrease in goodwill and other intangibles	0	0	86
Net (increase) decrease in other assets	82	(93)	29
Net increase (decrease) in other liabilities	(82)	9	(7)
Other operating activities, net	(114)	0	(52)
NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES	573	471	1,008
INVESTING ACTIVITIES
Net decrease (increase) in short-term investments, excluding acquisitions	47	(17)	(38)
Cash infusion from purchase of Cain Brothers	(90)	0	0
Cash used in acquisitions	0	(481)	0
Proceeds from sales, prepayments and maturities of securities available for sale	1	0	20
Net (increase) decrease in loans to subsidiaries	0	160	(146)
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	(42)	(338)	(164)
FINANCING ACTIVITIES
Net proceeds from issuance of long-term debt	0	0	1,000
Payments on long-term debt	0	(21)	(750)
Repurchase of Treasury Shares	(730)	(140)	(448)
Net proceeds from the issuance of Common Shares and preferred stock	(350)	1,041	22
Cash dividends paid	(480)	(335)	(267)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	(1,560)	545	(443)
NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS	(1,029)	678	401
CASH AND DUE FROM BANKS AT BEGINNING OF YEAR	3,286	2,608	2,207
CASH AND DUE FROM BANKS AT END OF YEAR	$ 2,257	$ 3,286	$ 2,608

Condensed Financial Informat171

Condensed Financial Information of the Parent Company - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Cash Flows [Abstract]
Interest paid	$ 120	$ 114	$ 112