Ally Financial (ALLY) 10-K 21 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 16, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	Ally Financial Inc.
Entity Central Index Key	40,729
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		434,771,498
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 9,452,901,086

Consolidated Statement of Incom

Consolidated Statement of Income Consolidated Statement of Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Revenue and Other Income [Line Items]
Interest and Fee Income, Loans and Leases									$ 5,819	$ 5,162	$ 4,570
Interest and Fee Income, Loans and Leases Held-for-sale									0	0	40
Interest and Dividend Income, Securities, Operating, Available-for-sale									599	418	381
Interest Income, Deposits with Financial Institutions									37	14	8
Operating Leases, Income Statement, Lease Revenue									1,867	2,711	3,398
Total financing revenue and other interest income									8,322	8,305	8,397
Interest Expense [Abstract]
Interest Expense, Deposits									1,077	830	718
Interest Expense, Short-term Borrowings									127	57	49
Interest Expense, Long-term Debt									1,653	1,742	1,662
Interest Expense									2,857	2,629	2,429
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease									1,244	1,769	2,249
Net Financing Revenue	$ 1,094	$ 1,081	$ 1,067	$ 979	$ 976	$ 996	$ 984	$ 951	4,221	3,907	3,719
Other revenue [Abstract]
Insurance Services Revenue									973	945	940
Gain (Loss) on Sales of Loans, Net									68	11	45
Gain (Loss) on Extinguishment of Debt									(7)	(5)	(357)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments									102	185	155
Noninterest Income, Other Operating Income									408	394	359
Nonoperating Income (Expense)	379	381	388	396	392	388	374	376	1,544	1,530	1,142
Revenues									5,765	5,437	4,861
Provision for Loan Losses Expensed	294	314	269	271	267	258	172	220	1,148	917	707
Noninterest Expense [Abstract]
Labor and Related Expense									1,095	992	963
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									332	342	293
Other Noninterest Expense									1,683	1,605	1,505
Noninterest Expense	769	753	810	778	721	735	773	710	3,110	2,939	2,761
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	410	395	376	326	380	391	413	397	1,507	1,581	1,393
Income Tax Expense (Benefit)	231	115	122	113	134	130	56	150	581	470	496
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	179	280	254	213	246	261	357	247	926	1,111	897
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	2	2	(2)	1	2	(52)	3	3	3	(44)	392
Net Income (Loss) Attributable to Parent	$ 181	$ 282	$ 252	$ 214	$ 248	$ 209	$ 360	$ 250	$ 929	$ 1,067	$ 1,289
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.40	$ 0.62	$ 0.55	$ 0.46	$ 0.52	$ 0.54	$ 0.70	$ 0.48	$ 2.04	$ 2.25	$ (3.47)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									0.01	(0.09)	0.81
Earnings Per Share, Basic	0.41	0.63	0.55	0.46	0.53	0.43	0.71	0.49	2.05	2.15	(2.66)
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.40	0.62	0.55	0.46	0.52	0.54	0.70	0.48	2.03	2.24	(3.47)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share									0.01	(0.09)	0.81
Earnings Per Share, Diluted	0.41	0.63	0.55	0.46	0.52	0.43	0.71	0.49	2.04	2.15	(2.66)
Common Stock, Dividends, Per Share, Declared	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0	$ 0	$ 0.40	$ 0.16	$ 0
Retained Earnings [Member]
Net Income (Loss) Attributable to Parent									$ 929	$ 1,067	$ 1,289

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income Statement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Income (Loss) Attributable to Parent	$ 929	$ 1,067	$ 1,289
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	192	33	(39)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	92	147	99
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	100	(114)	(138)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period before reclassification adjustments, Net of Tax	8	3	(26)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0	(1)	22
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	8	4	(48)
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period Net of Tax	(6)	1	18
Other Comprehensive Income (Loss), Reclassification Adjustment for Net Investment Hedges Included in Net Income, Discontinued Operation, Net of Tax	0	0	(3)
Other Comprehensive Income (Loss), Net Investment Hedges, Net of Tax	(6)	1	21
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustments and Net Investment Hedges, Net of Tax	2	5	(27)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	3	0	1
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	1	(3)	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	0	(2)	1
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	(1)	1	1
Other Comprehensive Income (Loss), Net of Tax	106	(110)	(165)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	1,035	957	1,124
Retained Earnings [Member]
Net Income (Loss) Attributable to Parent	$ 929	$ 1,067	$ 1,289

Consolidated Balance Sheet & Mi

Consolidated Balance Sheet & Mini Balance Sheet - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets [Abstract]
Cash and Due from Banks	$ 844	$ 1,547
Interest-bearing Deposits in Banks and Other Financial Institutions	3,408	4,387
Cash and Cash Equivalents, at Carrying Value	4,252	5,934
Available-for-sale securities	22,821	18,926
Held-to-maturity securities	1,899	839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	108	0
Finance receivables and loans, net [Abstract]
Loans and Leases Receivable, Net of Deferred Income	122,893	118,944
Financing Receivable, Allowance for Credit Losses	1,276	1,144
Loans and Leases Receivable, Net Amount	121,617	117,800
Property Subject to or Available for Operating Lease, Net	8,741	11,470
Premiums receivable and other insurance assets	2,047	1,905
Other Assets	5,663	6,854
Assets	167,148	163,728
Liabilities and Equity [Abstract]
Noninterest-bearing deposit liabilities	108	84
Interest-bearing Deposit Liabilities	93,148	78,938
Deposits	93,256	79,022
Short-term Debt	11,413	12,673
Long-term Debt	44,226	54,128
Interest payable	375	351
Unearned Premiums	2,604	2,500
Accounts Payable and Accrued Liabilities	1,780	1,737
Liabilities	153,654	150,411
Equity [Abstract]
Common Stocks, Including Additional Paid in Capital, Net of Discount	21,245	21,166
Retained Earnings (Accumulated Deficit)	(6,406)	(7,151)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(235)	(341)
Treasury stock, Value	(1,110)	(357)
Stockholders' Equity Attributable to Parent, Total	13,494	13,317
Liabilities and Equity	167,148	163,728
Variable Interest Entity, Primary Beneficiary [Member]
Finance receivables and loans, net [Abstract]
Loans and Leases Receivable, Net of Deferred Income	20,623	24,630
Financing Receivable, Allowance for Credit Losses	136	173
Loans and Leases Receivable, Net Amount	20,487	24,457
Property Subject to or Available for Operating Lease, Net	444	1,745
Other Assets	689	1,390
Assets	21,620	27,592
Liabilities and Equity [Abstract]
Long-term Debt	10,197	13,259
Accounts Payable and Accrued Liabilities	9	12
Liabilities	$ 10,206	$ 13,271

Consolidated Balance Sheet and

Consolidated Balance Sheet and Mini Balance Sheet (Paranthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	1,100,000,000	1,100,000,000
Common Stock, Shares, Issued	489,883,553	485,707,644
Common Stock, Shares, Outstanding	437,053,936	467,000,306
Treasury Stock, Shares	52,829,617	18,707,338
Held-to-maturity Securities, Fair Value	$ 1,865	$ 789

Consolidated Statement of Chang

Consolidated Statement of Changes in Equity - USD ($) $ in Millions	Total	Common stock and paid-in capital [Member]	Preferred stock [Member]	Retained Earnings [Member]	Accumulated other comprehensive (loss) income [Member]	Treasury stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent, Total	$ 15,399	$ 21,038	$ 1,255	$ (6,828)		$ 0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(66)				$ (66)
Net Income (Loss) Attributable to Parent	1,289			1,289
Dividends, Preferred Stock, Cash	(2,571)			(2,571)
Stock Repurchased During Period, Value	(325)		(325)
Preferred Stock, Redemption Amount	(234)		(234)
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	62	62
Other Comprehensive Income (Loss), Net of Tax	(165)				(165)
Treasury Stock, Value, Acquired, Cost Method	(16)					(16)
Stock Repurchase and Redemption Premium	$ 2,364
Common Stock, Dividends, Per Share, Declared	$ 0
Stockholders' Equity Attributable to Parent, Total	$ 13,439	21,100	696	(8,110)		(16)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(231)				(231)
Net Income (Loss) Attributable to Parent	1,067			1,067
Dividends, Preferred Stock, Cash	(30)			(30)
Stock Repurchased During Period, Value	(696)		(696)
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	66	66
Other Comprehensive Income (Loss), Net of Tax	(110)				(110)
Treasury Stock, Value, Acquired, Cost Method	(341)					(341)
Dividends, Common Stock, Cash	$ (78)			(78)
Common Stock, Dividends, Per Share, Declared	$ 0.16
Stockholders' Equity Attributable to Parent, Total	$ 13,317	21,166	0	(7,151)		(357)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(341)				(341)
Net Income (Loss) Attributable to Parent	929			929
Dividends, Preferred Stock, Cash	0
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	79	79
Other Comprehensive Income (Loss), Net of Tax	106				106
Treasury Stock, Value, Acquired, Cost Method	(753)					(753)
Dividends, Common Stock, Cash	$ (184)			(184)
Common Stock, Dividends, Per Share, Declared	$ 0.40
Stockholders' Equity Attributable to Parent, Total	$ 13,494	$ 21,245	$ 0	$ (6,406)		$ (1,110)
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (235)				$ (235)

Consolidated Statement of Cash

Consolidated Statement of Cash Flows $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Originations and repayments of loans held-for-investment and other	$ (1,063)	$ (8,826)	$ (9,344)
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income (Loss) Attributable to Parent	929	1,067	1,289
Depreciation, Amortization and Accretion, Net	1,859	2,382	2,801
Provision for Loan Losses Expensed Including Discontinued Operations	1,148	917	707
Gain Loss on Sales of Loans Net Including Discontinued Operations	(68)	(11)	(45)
Availableforsale Securities Gross Realized Gain Loss Excluding Otti Including Disc Ops	(102)	(185)	(155)
Gain (Loss) on Extinguishment of Debt	7	5	357
Payments for Origination and Purchases of Loans Held-for-sale	(414)	(141)	(1,770)
Proceeds from Sale of Loans Held-for-sale	310	240	1,658
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	0	0	(452)
Increase (Decrease) in Deferred Income Taxes	534	458	565
Increase (Decrease) in Interest Payable, Net	24	1	(127)
Increase (Decrease) in Other Operating Assets	(153)	(120)	526
Increase (Decrease) in Other Operating Liabilities	(69)	(206)	(247)
Increase (Decrease) in Other Operating Assets and Liabilities, Net	74	160	4
Net Cash Provided by (Used in) Operating Activities	4,079	4,567	5,111
Net Cash (Used in) Provided by Investing Activities [Abstract]
Payments to Acquire Available-for-sale Securities	(11,234)	(16,031)	(12,250)
Proceeds from sales of available-for-sale securities	4,633	11,036	6,874
Proceeds from maturities and repayment of available-for-sale securities	2,899	3,379	4,255
Payments to Acquire Held-to-maturity Securities	(1,026)	(841)	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	68	0	0
Payments for (Proceeds from) Loans and Leases	(5,452)	(3,859)	(4,501)
Proceeds from Sale of Loans Held-for-investment	1,339	4,285	3,197
Purchases of operating lease assets	(4,052)	(3,274)	(4,685)
Disposals of operating lease assets	5,567	6,304	5,546
Payments to Acquire Interest in Subsidiaries and Affiliates	0	309	0
Proceeds from Divestiture of Businesses	0	0	1,049
Increase (Decrease) in Non marketable equity securities	(187)	(628)	(147)
Payments for (Proceeds from) Other Investing Activities	(219)	(306)	3
Net cash provided by investing activities	(8,727)	(9,070)	(10,003)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Proceeds from (Repayments of) Short-term Debt	(1,263)	4,564	1,028
Increase (Decrease) in Deposits	14,172	12,508	8,247
Proceeds from issuance of long-term debt	17,969	14,155	30,665
Repayments of long-term debt	(27,908)	(26,412)	(31,350)
Payments for Repurchase of Redeemable Preferred Stock	0	696	559
Payments for Repurchase of Common Stock	(753)	(341)	(16)
Payments of Dividends	(184)	(108)	(2,571)
Net cash (used in) provided by financing activities	2,033	3,670	5,444
Effect of exchange-rate changes on cash and cash equivalents	3	1	(4)
Supplemental Cash Flow Information [Abstract]
Interest Paid	2,829	2,647	2,632
Income Taxes Paid	51	19	96
Held-to-maturity securities received in consideration for loans sold	56	0	0
Transfer of Portfolio Loans and Leases to Held-for-sale	1,339	4,282	1,311
Proceeds from sales and repayments of mortgage loans held-for-investment originally designated as held-for-sale	36	40	68
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	4,252	5,934
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	5,269	7,881	8,713
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(2,612)	(832)	$ 548
Restricted Cash	$ 1,017	$ 1,947

Description of Business, Basis

Description of Business, Basis of Presentation, and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block]	Description of Business, Basis of Presentation, and Significant Accounting Policies Ally Financial Inc. (together with its consolidated subsidiaries unless the context requires otherwise, Ally, the Company, or we, us, or our) is a leading digital financial services company and top 25 U.S. financial holding company (FHC) based on total assets, offering diversified financial products and services for consumers, businesses, automotive dealers, and corporate clients . Ally operates with a distinctive brand, an innovative approach, and a relentless focus on our customers. We are a Delaware corporation and are registered as a bank holding company (BHC) under the Bank Holding Company Act of 1956 as amended and an FHC under the Gramm-Leach-Bliley Act of 1999 as amended . We are one of the largest full service automotive finance operations in the country with a legacy that dates back to 1919, a deep expertise in automotive lending, and a complementary automotive-focused insurance business. Our wholly-owned banking subsidiary, Ally Bank, has received numerous industry awards for its services and capabilities and is one of the largest and most respected online banks, uniquely positioned for the observed shifting trends in consumer banking preferences for digital banking . We offer mortgage lending services and a variety of deposit and other banking products, including CDs, online savings, money market and checking accounts, and IRA products. We also promote a cash back credit card. We have recently integrated a growing digital wealth management and online brokerage platform to enable consumers to have a variety of options in managing their savings and wealth. Additionally, through our corporate finance business, we primarily offer senior secured leveraged cash flow and asset-based loans to middle-market companies. Consolidation and Basis of Presentation The Consolidated Financial Statements include the accounts of the parent and its consolidated subsidiaries, of which it is deemed to possess control, after eliminating intercompany balances and transactions, and include all variable interest entities (VIEs) in which we are the primary beneficiary. Other entities in which we have invested and have the ability to exercise significant influence over operating and financial policies of the investee, but upon which we do not possess control, are accounted for by the equity method of accounting within the financial statements and they are therefore not consolidated. Refer to Note 11 for further details on our VIEs. Our accounting and reporting policies conform to accounting principles generally accepted in the United States of America (GAAP). Additionally, where applicable, the policies conform to the accounting and reporting guidelines prescribed by bank regulatory authorities. Certain reclassifications may have been made to the prior periods’ financial statements and notes to conform to the current period’s presentation, which did not have a material impact on our Consolidated Financial Statements. In the past, we have operated our international subsidiaries in a similar manner as we operate in the United States of America (U.S. or United States), subject to local laws or other circumstances that may cause us to modify our procedures accordingly. The financial statements of subsidiaries that operate outside of the United States generally are measured using the local currency as the functional currency. All assets and liabilities of foreign subsidiaries are translated into U.S. dollars at year-end exchange rates. The resulting translation adjustments are recorded in accumulated other comprehensive income until the foreign subsidiaries are sold or substantially liquidated at which point the accumulated translation adjustments are recognized directly in earnings as part of the gain or loss on sale or liquidation. Income and expense items are translated at average exchange rates prevailing during the reporting period. The majority of our international operations have ceased and are included in discontinued operations as further described in Note 3. Use of Estimates and Assumptions The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and that affect income and expenses during the reporting period and related disclosures. In developing the estimates and assumptions, management uses all available evidence; however, actual results could differ because of uncertainties associated with estimating the amounts, timing, and likelihood of possible outcomes. Our most significant estimates pertain to the allowance for loan losses, valuations of automotive lease assets and residuals, fair value of financial instruments, legal and regulatory reserves, and the determination of the provision for income taxes.
Significant Accounting Policies [Text Block]	Significant Accounting Policies Cash and Cash Equivalents Cash and cash equivalents include cash on hand, cash on deposit at other financial institutions, cash items in process of collection, and certain highly liquid investments with original maturities of three months or less from the date of purchase. The book value of cash equivalents approximates fair value because of the short maturities of these instruments and the insignificant risk they present to changes in value with respect to changes in interest rates. Certain securities with original maturities of three months or less from the date of purchase that are held as a portion of longer-term investment portfolios, primarily held by our Insurance operations, are classified as investment securities. Cash and cash equivalents with legal restrictions limiting our ability to withdraw and use the funds are considered restricted cash and restricted cash equivalents and are presented as other assets on our Consolidated Balance Sheet. Investments Our portfolio of investments includes various debt and marketable equity securities and nonmarketable equity investments. Debt and marketable equity securities are classified based on management’s intent to sell or hold the security. We classify debt securities as held-to-maturity only when we have both the intent and ability to hold the securities to maturity. We classify debt and marketable equity securities as trading when the securities are acquired for the purpose of selling or holding them for a short period of time. Securities not classified as either held-to-maturity or trading are classified as available-for-sale. Our debt and marketable equity securities include government securities, corporate bonds, asset-backed securities (ABS), mortgage-backed securities (MBS), and equity securities. Our portfolio includes securities classified as available-for-sale and held-to-maturity. Our available-for-sale securities are carried at fair value with unrealized gains and losses included in accumulated other comprehensive income or loss and are subject to impairment. Our held-to-maturity securities are carried at amortized cost and are subject to impairment. We amortize premiums and discounts on debt securities as an adjustment to investment yield generally over the stated maturity of the security. For ABS and MBS where prepayments can be reasonably estimated, amortization is adjusted for expected prepayments. Additionally, we assess our debt and marketable equity securities for potential other-than-temporary impairment. We employ a methodology that considers available evidence in evaluating potential other-than-temporary impairment of our debt and marketable equity securities classified as available-for-sale and held-to-maturity. If the cost of an investment exceeds its fair value, we evaluate, among other factors, the magnitude and duration of the decline in fair value. We also evaluate the financial health of and business outlook for the issuer, the performance of the underlying assets for interests in securitized assets, and, for securities classified as available-for-sale, our intent and ability to hold the investment through recovery of its amortized cost basis. Once a decline in fair value of a debt security is determined to be other-than-temporary, an impairment charge for the credit component is recorded to other gain (loss) on investments, net, in our Consolidated Statement of Income, and a new cost basis in the investment is established. The noncredit loss component of an available-for-sale debt security is recorded in other comprehensive income (loss) when we do not intend to sell the security and it is not more likely than not that we will have to sell the security prior to the security’s anticipated recovery. Both, the credit and noncredit loss components are recorded in earnings when we intend to sell the security or it is more likely than not that we will have to sell the security prior to the security’s anticipated recovery. Unrealized losses that we have determined to be other-than-temporary on equity securities are recorded to other gain (loss) on investments, net in our Consolidated Statement of Income. Subsequent increases and decreases to the fair value of available-for-sale debt and equity securities are included in other comprehensive income (loss), so long as they are not attributable to another other-than-temporary impairment. Realized gains and losses on investment securities are reported in other gain (loss) on investments, net, and are determined using the specific identification method. For information on our debt and marketable equity securities, refer to Note 8 . In addition to our investments in debt and marketable equity securities, we hold equity positions in other entities. These positions include Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock held to meet regulatory requirements, other equity investments that are not publicly traded and do not have a readily determinable fair value, equity investments in low income housing tax credits, and Community Reinvestment Act (CRA) equity investments, which are also not publicly traded and do not have a readily determinable fair value. Our investments in FHLB and FRB stock and other equity investments are accounted for using the cost method of accounting. Our low income housing tax credit investments are accounted for using the proportional amortization method of accounting for qualified affordable housing investments. Our obligations related to unfunded commitments for our low income housing tax credit investments are reported in other liabilities. Our CRA investments are accounted for using the equity method of accounting. Our FHLB and FRB stock and other equity investments carried at cost are included in nonmarketable equity investments in other assets. Our investments in low income housing tax credits and CRA are also included in other assets. As conditions warrant, we review our investments for impairment and will adjust the carrying value of the investment if it is deemed to be impaired. No impairment was recognized in 2017 or 2016. For more information on our nonmarketable equity investments, refer to Note 25 . Finance Receivables and Loans We initially classify finance receivables and loans as either loans held-for-sale or loans held-for-investment based on management’s assessment of our intent and ability to hold the loans for the foreseeable future or until maturity. Management’s view of the foreseeable future is based on the longest reasonably reliable net income, liquidity, and capital forecast period. Management’s intent and ability with respect to certain loans may change from time to time depending on a number of factors, for example economic, liquidity, and capital conditions. In order to reclassify loans to held-for-sale, management must have the intent to sell the loans and reasonably identify the specific loans to be sold. Loans classified as held-for-sale are presented as loans held-for-sale, net on our Consolidated Balance Sheet and are carried at the lower of their net carrying value or fair value, unless the fair value option was elected, in which case those loans are carried at fair value. We’ve elected the fair value option for conforming direct-to-consumer originations for which we have a commitment to sell. The interest rate lock commitment that we enter into for a loan originated as held-for-sale and certain forward commitments to sell the loan are considered derivative instruments, which are carried at fair value on our Consolidate Balance Sheet. We have elected the fair value option to measure our non-derivative forward commitments. Changes in the fair value of our interest rate lock commitments, derivative forward commitments, and non-derivative forward commitments, as well as changes in the carrying value of loans classified as held-for-sale, are reported through gain on mortgage and automotive loans, net in our Consolidated Statement of Comprehensive Income. Interest income on our loans classified as held-for-sale is recognized based upon the contractual rate of interest on the loan and the unpaid principal balance. We report accrued interest receivable on our loans classified as held-for-sale in other assets on the Consolidated Balance Sheet. Loans classified as held-for-investment are presented as finance receivables and loans, net on our Consolidated Balance Sheet. Finance receivables and loans are reported at their gross carrying value, which includes the principal amount outstanding, net of unamortized deferred fees and costs on originated loans, unamortized premiums and discounts on purchased loans, unamortized basis adjustments arising from the designation of finance receivables and loans as the hedged item in qualifying fair value hedge relationships, and cumulative principal charge-offs. We refer to the gross carrying value less the allowance for loan loss as the net carrying value in finance receivables and loans. Unearned rate support received from an automotive manufacturer on certain automotive loans, deferred origination fees and costs, and premiums and discounts on purchased loans, are amortized over the contractual life of the related finance receivable or loan using the effective interest method. We make various incentive payments for consumer automotive loan originations to automotive dealers and account for these payments as direct loan origination costs. Additionally, we make incentive payments to certain commercial automobile wholesale borrowers and account for these payments as a reduction to interest income in the period they are earned. Interest income on our finance receivables and loans is recognized based on the contractual rate of interest plus the amortization of deferred amounts using the effective interest method. We report accrued interest receivable on our finance receivables and loans in other assets on our Consolidated Balance Sheet. Loan commitment fees are generally deferred and amortized over the commitment period. For information on finance receivables and loans, refer to Note 9 . Our portfolio segments are based on the level at which we develop and document our methodology for determining the allowance for loan losses. Additionally, the classes of finance receivables are based on several factors including the method for monitoring and assessing credit risk, the method of measuring carrying value, and the risk characteristics of the finance receivable. Based on an evaluation of our process for developing the allowance for loan losses including the nature and extent of exposure to credit risk arising from finance receivables, we have determined our portfolio segments to be consumer automotive, consumer mortgage, and commercial. • Consumer automotive — Consists of retail automotive financing for new and used vehicles. • Consumer mortgage — Consists of the following classes of finance receivables. • Mortgage Finance — Consists of consumer first mortgages from our ongoing mortgage operations including bulk acquisitions, direct-to-consumer originations, and refinancing of high-quality jumbo mortgages and low-to-moderate income (LMI) mortgages. • Mortgage — Legacy — Consists of consumer mortgage assets originated prior to January 1, 2009, including first mortgages, subordinate-lien mortgages, and home equity mortgages. • Commercial — Consists of the following classes of finance receivables. • Commercial and Industrial • Automotive — Consists of financing operations to fund dealer purchases of new and used vehicles through wholesale floorplan financing. Additional commercial offerings include automotive dealer term loans, dealer fleet financing, and other equipment financing. • Other — Consists primarily of senior secured leveraged cash flow and asset-based loans related to our Corporate Finance business. • Commercial Real Estate — Consists of term loans to finance dealership land and buildings, and other commercial lending secured by real estate. Nonaccrual Loans Generally, we recognize loans of all classes as past due when they are 30 days delinquent on making a contractually required payment, and loans are placed on nonaccrual status when principal or interest has been delinquent for 90 days or when full collection is not expected. Interest income recognition is suspended when finance receivables and loans are placed on nonaccrual status. Additionally, amortization of premiums and discounts and deferred fees and costs ceases when finance receivables and loans are placed on nonaccrual. Exceptions include commercial real estate loans that are placed on nonaccrual status when delinquent for 60 days or when full collection is not probable, if sooner. Additionally, our policy is to generally place all loans that have been modified in troubled debt restructurings (TDRs) on nonaccrual status until the loan has been brought fully current, the collection of contractual principal and interest is reasonably assured, and six consecutive months of repayment performance is achieved. In certain cases, if a borrower has been current up to the time of the modification and repayment of the debt subsequent to the modification is reasonably assured, we may choose to continue to accrue interest on the loan. Loans on nonaccrual status are reported as nonperforming loans in Note 9 . The receivable for interest income that is accrued, but not collected, at the date finance receivables and loans are placed on nonaccrual status is reversed against interest income and subsequently recognized only to the extent it is received in cash or until it qualifies for return to accrual status. However, where there is doubt regarding the ultimate collectability of loan principal, all cash received is applied to reduce the carrying value of such loans. Generally, finance receivables and loans are restored to accrual status only when contractually current and the collection of future payments is reasonably assured. Impaired Loans Loans of all classes are considered impaired when we determine it is probable that we will be unable to collect all amounts due (both principal and interest) according to the terms of the loan agreement. For all classes of consumer loans, impaired loans include all loans that have been modified in TDRs. Commercial loans of all classes are considered impaired on an individual basis and reported as impaired when we determine it is probable that we will be unable to collect all amounts due according to the terms of the loan agreement. With the exception of certain consumer TDRs that have been returned to accruing status, for all classes of impaired loans, income recognition is consistent with that of nonaccrual loans discussed above. Impaired loans may return to accrual status as discussed in the preceding nonaccrual loan section at which time, the normal accrual of interest income resumes. For collateral dependent loans, if the recorded investment in the impaired loans exceeds the fair value of the collateral, a charge-off is recorded consistent with the TDR discussion below. Troubled Debt Restructurings When the terms of finance receivables or loans are modified, consideration must be given as to whether or not the modification results in a TDR. A modification is considered to be a TDR when both the borrower is experiencing financial difficulty and we grant a concession to the borrower. These considerations require significant judgment and vary by portfolio segment. In all cases, the cumulative impacts of all modifications are considered at the time of the most recent modification. For consumer loans of all classes, various qualitative factors are utilized for assessing the financial difficulty of the borrower. These include, but are not limited to, the borrower’s default status on any of its debts, bankruptcy and recent changes in financial circumstances (loss of job, etc.). A concession has been granted when as a result of the modification we do not expect to collect all amounts due under the original loan terms, including interest accrued at the original contract rate. Types of modifications that may be considered concessions include, but are not limited to, extensions of terms at a rate that does not constitute a market rate, a reduction, deferral or forgiveness of principal or interest owed and loans that have been discharged in a Chapter 7 Bankruptcy and have not been reaffirmed by the borrower. In addition to the modifications noted above, in our consumer automotive portfolio segment of loans we also provide extensions or deferrals of payments to borrowers whom we deem to be experiencing only temporary financial difficulty. In these cases, there are limits within our operational policies to minimize the number of times a loan can be extended, as well as limits to the length of each extension, including a cumulative cap over the life of the loan. If these limits are breached, the modification is considered a TDR as noted in the following paragraph. Before offering an extension or deferral, we evaluate the capacity of the customer to make the scheduled payments after the deferral period. During the deferral period, we continue to accrue and collect interest on the loan as part of the deferral agreement. We grant these extensions or deferrals when we expect to collect all amounts due including interest accrued at the original contract rate. A restructuring that results in only a delay in payment that is deemed to be insignificant is not a concession and the modification is not considered to be a TDR. In order to assess whether a restructuring that results in a delay in payment is insignificant, we consider the amount of the restructured payments subject to delay in conjunction with the unpaid principal balance or the collateral value of the loan, whether or not the delay is significant with respect to the frequency of payments under the original contract, or the loan’s original expected duration. In the cases where payment extensions on our automotive loan portfolio cumulatively extend beyond 90 days and are more than 10% of the original contractual term or where the cumulative payment extension is beyond 180 days, we deem the delay in payment to be more than insignificant, and as such, classify these types of modifications as TDRs. Otherwise, we believe that the modifications do not represent a concessionary modification and accordingly, they are not classified as TDRs. For commercial loans of all classes, similar qualitative factors are considered when assessing the financial difficulty of the borrower. In addition to the factors noted above, consideration is also given to the borrower’s forecasted ability to service the debt in accordance with the contractual terms, possible regulatory actions and other potential business disruptions (e.g., the loss of a significant customer or other revenue stream). Consideration of a concession is also similar for commercial loans. In addition to the factors noted above, consideration is also given to whether additional guarantees or collateral have been provided. For all loans, TDR classification typically results from our loss mitigation activities. For loans held-for-investment that are not carried at fair value and are TDRs, impairment is typically measured based on the difference between the gross carrying value of the loan and the present value of the expected future cash flows of the loan. The loan may also be measured for impairment based on the fair value of the underlying collateral less costs to sell for loans that are collateral dependent. We recognize impairment by either establishing a valuation allowance or recording a charge-off. The financial impacts of modifications that meet the definition of a TDR are reported in the period in which they are identified as TDRs. Additionally, if a loan that is classified as a TDR redefaults within twelve months of the modification, we are required to disclose the instances of redefault. For the purpose of this disclosure, we have determined that a loan is considered to have redefaulted when the loan meets the requirements for evaluation under our charge-off policy except for commercial loans where redefault is defined as 90 days past due. Impaired loans may return to accrual status as discussed in the preceding nonaccrual loan section at which time, the normal accrual of interest income resumes. Net Charge-offs We disclose the measurement of net charge-offs as the amount of gross charge-offs recognized less recoveries received. Gross charge-offs reflect the amount of the gross carry value directly written-off. Generally, we recognize recoveries when they are received and record them as an increase to the allowance for loan losses. As a general rule, consumer automotive loans are written down to estimated collateral value, less costs to sell, once a loan becomes 120 days past due. In our consumer mortgage portfolio segment, first-lien mortgages and a subset of our home equity portfolio that are secured by real estate in a first-lien position are written down to the estimated fair value of the collateral, less costs to sell, once a mortgage loan becomes 180 days past due. Consumer mortgage loans that represent second-lien positions are charged off at 180 days past due. Consumer mortgage loans within our second-lien portfolio in bankruptcy that are 60 days past due are fully charged off within 60 days of receipt of notification of filing from the bankruptcy court. Consumer automotive and first-lien consumer mortgage loans in bankruptcy that are 60 days past due are written down to their expected future cash flows, which is generally fair value of the collateral, less costs to sell, within 60 days of receipt of notification of filing from the bankruptcy court. Regardless of other timelines noted within this policy, loans are considered collateral dependent once foreclosure or repossession proceedings begin and are charged-off to the estimated fair value of the underlying collateral, less costs to sell at that time. Commercial loans are individually evaluated and where collectability of the recorded balance is in doubt are written down to the estimated fair value of the collateral less costs to sell. Generally, all commercial loans are charged-off when it becomes unlikely that the borrower is willing or able to repay the remaining balance of the loan and any underlying collateral is not sufficient to recover the outstanding principal. Collateral dependent loans are charged-off to the fair market value of collateral less costs to sell when appropriate. Noncollateral dependent loans are fully written-off. Allowance for Loan Losses The allowance for loan losses (the allowance) is management’s estimate of incurred losses in the lending portfolios. We determine the amount of the allowance required for each of our portfolio segments based on its relative risk characteristics. The evaluation of these factors for both consumer and commercial finance receivables and loans involves quantitative analysis combined with sound management judgment. Additions to the allowance are charged to current period earnings through the provision for loan losses; amounts determined to be uncollectible are charged directly against the allowance, net of amounts recovered on previously charged-off accounts. The allowance is composed of two components: specific reserves established for individual loans evaluated as impaired and portfolio-level reserves established for large groups of typically smaller balance homogeneous loans that are collectively evaluated for impairment. We evaluate the adequacy of the allowance based on the combined total of these two components. Determining the appropriateness of the allowance is complex and requires judgment by management about the effect of matters that are inherently uncertain. It is possible that others, given the same information, may at any point in time reach different reasonable conclusions. Measurement of impairment for specific reserves is generally determined on a loan-by-loan basis. Loans determined to be specifically impaired are measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate, an observable market price, or the estimated fair value of the collateral less estimated costs to sell when appropriate, whichever is determined to be the most appropriate. When these measurement values are lower than the net carrying value of that loan, impairment is recognized. Loans that are not identified as individually impaired are pooled with other loans with similar risk characteristics for evaluation of impairment for the portfolio-level allowance. For the purpose of calculating portfolio-level reserves, we have grouped our loans into three portfolio segments: consumer automotive, consumer mortgage, and commercial. The allowance consists of the combination of a quantitative assessment component based on statistical models, a retrospective evaluation of actual loss information to loss forecasts, and includes a qualitative component based on management judgment. Management takes into consideration relevant qualitative factors, including external and internal trends such as the impacts of changes in underwriting standards, collections and account management effectiveness, geographic concentrations, and economic events, among other factors, that have occurred but are not yet reflected in the quantitative assessment component. Qualitative adjustments are documented, reviewed, and approved through our established risk governance processes and follow regulatory guidance. Management also considers the need for a reserve on unfunded non-derivative loan commitments across our portfolio segments, including lines of credit and standby letters of credit, using similar procedures and methodologies used to determine the allowance for loan losses while also considering historical loss ratios and potential usage levels. The reserve for unfunded loan commitments is recorded within other liabilities on our Consolidated Balance Sheet and the related expense is reported as other noninterest expense in our Consolidated Statement of Comprehensive Income. Refer to Note 29 for information on our unfunded loan commitments. During 2017, we did not substantively change any material aspect of our overall approach used to determine the allowance for loan losses for our portfolio segments. There were no material changes in criteria or estimation techniques as compared to prior periods that impacted the determination of the current period allowance for loan losses for our portfolio segments. Refer to Note 9 for information on the allowance for loan losses. Consumer Loans Our consumer automotive and consumer mortgage portfolio segments are reviewed for impairment based on an analysis of loans that are grouped into common risk categories. We perform periodic and systematic detailed reviews of our lending portfolios to identify inherent risks and to assess the overall collectability of those portfolios. Loss models are utilized for these portfolios, which consider a variety of credit quality indicators including, but not limited to, historical loss experience, current economic conditions, credit scores, and expected loss factors by loan type. Consumer Automotive Portfolio Segment The allowance for loan losses within the consumer automotive portfolio segment is calculated using proprietary statistical models and other risk indicators applied to pools of loans with similar risk characteristics, including credit bureau score and loan-to-value ratios to arrive at an estimate of incurred losses in the portfolio. These statistical loss forecasting models are utilized to estimate incurred losses and consider a variety of factors including, but not limited to, historical loss experience, estimated defaults based on portfolio trends, and general economic and business trends. These statistical models predict forecasted losses inherent in the portfolio. The forecasted losses consider historical factors such as frequency (the number of contracts that we expect to default) and loss severity (the loss amount of contracts we expect to default). The loss severity within the consumer automotive portfolio segment is impacted by the market values of vehicles that are repossessed. Vehicle market values are affected by numerous factors including vehicle supply, the condition of the vehicle upon repossession, the overall price and volatility of gasoline or diesel fuel, consumer preference related to specific vehicle segments, and other factors. The quantitative assessment component of the allowance may be supplemented with qualitative reserves based on management’s determination that such adjustments provide a better estimate of credit losses. This qualitative assessment takes into consideration relevant internal and external factors that have occurred but are not yet reflected in the forecasted losses and may affect the performance of the portfolio. Consumer Mortgage Portfolio Segment The allowance for loan losses within the consumer mortgage portfolio segment is calculated by using proprietary statistical models based on pools of loans with similar risk characteristics, including credit score, loan-to-value, loan age, documentation type, product type, and loan purpose, to arrive at an estimate of incurred losses in the portfolio. These statistical loss forecasting models are utilized to estimate incurred losses and consider a variety of factors including, but not limited to, historical loss experience, estimated foreclosures or defaults based on portfolio trends, delinquencies, and general economic and business trends. The forecasted losses are statistically derived based on a suite of behavioral based transition models. This transition framework predicts various stages of delinquency, default, and voluntary prepayment over the course of the life of the loan. The transition probability is a function of the loan and borrower characteristics and economic variables and considers historical factors such as frequency and loss severity. When a default event is predicted, a severity model is applied to estimate future loan losses. Loss severity within the consumer mortgage portfolio segment is impacted by the market values of foreclosed properties, which is affected by numerous factors, including geographic considerations and the condition of the foreclosed property. The quantitative assessment component of the allowance may be supplemented with qualitative reserves based on management’s determination that such adjustments provide a better estimate of credit losses. This qualitative assessment takes into consideration relevant internal and external factors that have occurred but are not yet reflected in the forecasted losses and may affect the performance of the portfolio. Commercial Loans The allowance for loan losses within the commercial portfolio is composed of reserves established for specific loans evaluated as impaired and portfolio-level reserves based on nonimpaired loans grouped into pools based on similar risk characteristics and collectively evaluated. A commercial loan is considered impaired when it is probable that we will be unable to collect all amounts due according to the contractual terms of the loan agreement based on current information and events. These loans are primarily evaluated individually and are risk-rated based on borrower, collateral, and industry-specific information that management believes is relevant in determining the occurrence of a loss event and measuring impairment. Management establishes specific allowances for commercial loans determined to be individually impaired based on the present value of expected future cash flows, discounted at the loan’s effective interest rate, observable market price or the fair value of collateral, whichever is determined to be the most appropriate. Estimated costs to sell or realize the value of the collateral on a discounted basis are included in the impairment measurement, when appropriate. Loans not identified as impaired are grouped into pools based on similar risk characteristics and collectively evaluated. Our risk rating models use historical loss experience, concentrations, current economic conditions, and performance trends. The commercial historical loss experience is updated quarterly to incorporate the most recent data reflective of the current economic environment. The determination of the allowance is influenced by numerous assumptions and many factors that may materially affect estimates of loss, including volatility of loss given default, probability of default, and rating migration. In assessing the risk rati

Acquisitions Acquisitions

Acquisitions Acquisitions	12 Months Ended
	Dec. 31, 2017
Acquisitions [Abstract]
Business Combination Disclosure [Text Block]	Acquisitions On June 1, 2016 , we acquired 100% of the equity of TradeKing Group, Inc. (TradeKing), a digital wealth management company with an online broker-dealer, digital portfolio management platform, and educational content for $298 million in cash. TradeKing, which has been rebranded as Ally Invest, operates as a wholly-owned subsidiary of Ally Financial Inc. The addition of brokerage and wealth management is a natural extension of our direct online bank, creating a full suite of financial products for savings and investments. We applied the acquisition method of accounting to this transaction, which generally requires the initial recognition of assets acquired, including identifiable intangible assets, and liabilities assumed at their respective fair value. Goodwill is recognized as the excess of the acquisition price after the recognition of the net assets, including the identifiable intangible assets. Beginning in June 2016, financial information related to Ally Invest is included within Corporate and Other. The following table summarizes the allocation of cash consideration paid for TradeKing and the amounts of the identifiable assets acquired and liabilities assumed recognized at the acquisition date. ($ in millions) Purchase price Cash consideration $ 298 Allocation of purchase price to net assets acquired Intangible assets (a) 82 Cash and short-term investments (b) 50 Other assets 14 Deferred tax asset, net 4 Employee compensation and benefits (41 ) Other liabilities (4 ) Goodwill $ 193 (a) We recorded $10 million and $6 million of amortization on these intangible assets during the years ended December 31, 2017 , and 2016, respectively. (b) Includes $40 million in cash proceeds from the acquisition transaction in order to pay employee compensation and benefits that vested upon acquisition as a result of the change in control. The goodwill of $193 million arising from the acquisition consists largely of expected growth of the business as we leverage the Ally brand and our marketing capabilities to scale the acquired technology platform and expand the suite of financial products we offer to our existing growing customer base. None of the goodwill recognized is expected to be deductible for income tax purposes. Refer to Note 14 for the carrying amount of goodwill at the beginning and end of the reporting period. On August 1, 2016, we acquired assets that constitute a business from Blue Yield, an online automotive lender exchange which we rebranded as Clearlane, as we continue to expand our automotive finance offerings to include a direct-to-consumer option. We completed the acquisition for $28 million of total consideration. As a result of the purchase, we recognized $20 million of goodwill within Automotive Finance operations.

Discontinued Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]	Discontinued Operations Prior to the adoption of ASU 2014-08, which was prospectively applied only to newly identified disposals that qualify as discontinued operations beginning after January 1, 2015, we have classified operations as discontinued when operations and cash flows will be eliminated from our ongoing operations and we do not expect to retain any significant continuing involvement in their operations after the respective sale or disposal transactions. For all periods presented, the operating results for these discontinued operations have been removed from continuing operations and presented separately as discontinued operations, net of tax, in the Consolidated Statement of Income . The Notes to the Consolidated Financial Statements have been adjusted to exclude discontinued operations unless otherwise noted. Select Automotive Finance Operations During the fourth quarter of 2012, we entered into an agreement with General Motors Financial Company Inc. (GMF) to sell our 40% interest in a motor vehicle finance joint venture in China. On January 2, 2015, the sale of our interest in the motor vehicle finance joint venture in China was completed and an after-tax gain of approximately $400 million was recorded. The tax expense included in this gain was reduced by the release of the valuation allowance on our capital loss carryforward deferred tax asset that was utilized to offset capital gains stemming from this sale. The remaining activity relates to previous discontinued operations for which we continue to have minimal residual costs. Other Operations Other operations relate to previous discontinued operations in our Insurance operations and Corporate Finance operating segments, and other operations for which we continue to have wind-down, legal, and minimal operational costs. Select Financial Information Select financial information of discontinued operations is summarized below. The pretax income or loss includes direct costs to transact a sale. Year ended December 31, ($ in millions) 2017 2016 2015 Select Automotive Finance operations Pretax (loss) income (a) $ (4 ) $ (2 ) $ 452 Tax (benefit) expense (b) (5 ) 2 80 Other operations Pretax income (loss) $ 2 $ (41 ) $ 16 Tax benefit — (1 ) (4 ) (a) Includes certain treasury and other corporate activity recognized within Corporate and Other. (b) Includes certain income tax activity recognized within Corporate and Other.

Other Income, Net of Losses

Other Income, Net of Losses	12 Months Ended
	Dec. 31, 2017
Other Nonoperating Income (Expense) [Abstract]
Other Income and Other Expense Disclosure [Text Block]	Other Income, Net of Losses Details of other income, net of losses, were as follows. Year ended December 31, ($ in millions) 2017 2016 2015 Remarketing fees $ 104 $ 103 $ 101 Late charges and other administrative fees 102 98 90 Servicing fees 51 64 45 Income from equity-method investments 14 18 52 Other, net 137 111 71 Total other income, net of losses $ 408 $ 394 $ 359

Reserves for Insurance Losses a

Reserves for Insurance Losses and Loss Adjustment Expenses Reserves for Insurance Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2017
Reserves for Insurance Losses and Loss Adjustment Expenses [Abstract]
Short-Duration Insurance and Deposit Contracts [Text Block]	Reserves for Insurance Losses and Loss Adjustment Expenses The following table shows cumulative incurred claims and allocated loss adjustment expenses, net of reinsurance. For the years ended December 31, ($ in millions) December 31, 2017 ($ in millions) Accident year (a) 2012 (b) 2013 (b) 2014 (b) 2015 (b) 2016 2017 Total of incurred-but-not-reported liabilities plus expected development on reported claims (c) Cumulative number of reported claims (c) 2012 $ 435 $ 430 $ 423 $ 423 $ 423 $ 422 $ 1 772,546 2013 376 365 370 370 369 1 672,263 2014 390 389 388 388 — 525,290 2015 274 271 272 — 342,231 2016 326 327 — 475,707 2017 310 21 455,965 Total $ 2,088 (a) Due to the discontinuation of various product lines and sale of certain international operations, information prior to 2013 has been excluded from the table in order to appropriately reflect the number of years for which claims are typically outstanding. In addition, given the short tail of our insurance contracts, the table above reflects the combined presentation of all business lines. (b) Information presented for the years 2012 through 2015 is unaudited supplementary information. (c) Claims are reported on a claimant basis. Claimant is defined as one vehicle for guaranteed asset protection (GAP) products, one repair visit for vehicle service contracts (VSCs) and vehicle maintenance contracts (VMCs), one dealership for dealer inventory products, and per individual/coverage for run-off personal automotive products. The following table shows cumulative paid claims and allocated loss adjustment expenses, net of reinsurance. For the years ended December 31, ($ in millions) Accident year (a) 2012 (b) 2013 (b) 2014 (b) 2015 (b) 2016 2017 2012 $ 391 $ 412 $ 416 $ 418 $ 419 $ 421 2013 347 364 366 368 368 2014 369 388 388 388 2015 252 272 272 2016 302 327 2017 289 Total $ 2,065 All outstanding liabilities for loss and allocated loss adjustment expenses before 2012, net of reinsurance 7 Reserves for insurance losses and allocated loss adjustment expenses, net of reinsurance $ 30 (a) Due to the discontinuation of various product lines and sale of certain international operations, information prior to 2013 has been excluded from the table in order to appropriately reflect the number of years for which claims are typically outstanding. In addition, given the short tail of our insurance contracts, the table above reflects the combined presentation of all business lines. (b) Information presented for the years 2012 through 2015 is unaudited supplementary information. The following table shows the average annual percentage payout of incurred claims by age, net of reinsurance. The information presented is unaudited supplementary information. Year 1 2 3 4 5 6 Percentage payout of incurred claims 93.0 % 5.7 % 0.4 % 0.3 % 0.2 % 0.4 % The following table shows a reconciliation of the disclosures of incurred and paid claims development to the reserves for insurance losses and loss adjustment expenses. December 31, ($ in millions) 2017 2016 Reserves for insurance losses and loss adjustment expenses, net of reinsurance $ 30 $ 38 Total reinsurance recoverable on unpaid claims 108 108 Unallocated loss adjustment expenses 2 3 Total gross reserves for insurance losses and loss adjustment expenses $ 140 $ 149 The following table shows a rollforward of our reserves for insurance losses and loss adjustment expenses. ($ in millions) 2017 2016 Total gross reserves for insurance losses and loss adjustment expenses at January 1, $ 149 $ 169 Less: Reinsurance recoverable 108 120 Net reserves for insurance losses and loss adjustment expenses at January 1, 41 49 Net insurance losses and loss adjustment expenses incurred related to: Current year 332 345 Prior years (a) — (3 ) Total net insurance losses and loss adjustment expenses incurred 332 342 Net insurance losses and loss adjustment expenses paid or payable related to: Current year (309 ) (320 ) Prior years (32 ) (30 ) Total net insurance losses and loss adjustment expenses paid or payable (341 ) (350 ) Net reserves for insurance losses and loss adjustment expenses at December 31, 32 41 Plus: Reinsurance recoverable 108 108 Total gross reserves for insurance losses and loss adjustment expenses at December 31, $ 140 $ 149 (a) There have been no material adverse changes to the reserve for prior years.

Other Operating Expenses

Other Operating Expenses	12 Months Ended
	Dec. 31, 2017
Operating Expenses [Abstract]
Other Operating Income and Expense [Text Block]	Other Operating Expenses Details of other operating expenses were as follows. Year ended December 31, ($ in millions) 2017 2016 2015 Insurance commissions $ 415 $ 389 $ 378 Technology and communications 284 274 267 Lease and loan administration 159 136 126 Advertising and marketing 133 112 107 Professional services 113 103 93 Regulatory and licensing fees 113 94 79 Vehicle remarketing and repossession 110 95 78 Premises and equipment depreciation 89 84 82 Occupancy 46 51 50 Non-income taxes 21 25 29 Other 200 242 216 Total other operating expenses $ 1,683 $ 1,605 $ 1,505

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]	Investment Securities Our portfolio of securities includes bonds, equity securities, asset-backed securities, commercial and residential mortgage-backed securities, and other investments. The cost, fair value, and gross unrealized gains and losses on investment securities were as follows. 2017 2016 Amortized cost Gross unrealized Fair value Amortized cost Gross unrealized Fair December 31, ($ in millions) gains losses gains losses Available-for-sale securities Debt securities U.S. Treasury $ 1,831 $ — $ (54 ) $ 1,777 $ 1,680 $ — $ (60 ) $ 1,620 U.S. States and political subdivisions 850 11 (7 ) 854 794 7 (19 ) 782 Foreign government 153 2 (1 ) 154 157 5 — 162 Agency mortgage-backed residential 14,412 35 (156 ) 14,291 10,473 29 (212 ) 10,290 Mortgage-backed residential 2,517 11 (34 ) 2,494 2,162 5 (70 ) 2,097 Mortgage-backed commercial 541 1 (1 ) 541 537 2 (2 ) 537 Asset-backed 933 4 (1 ) 936 1,396 6 (2 ) 1,400 Corporate debt 1,262 5 (11 ) 1,256 1,452 7 (16 ) 1,443 Total debt securities (a) (b) 22,499 69 (265 ) 22,303 18,651 61 (381 ) 18,331 Equity securities 553 13 (48 ) 518 642 7 (54 ) 595 Total available-for-sale securities $ 23,052 $ 82 $ (313 ) $ 22,821 $ 19,293 $ 68 $ (435 ) $ 18,926 Held-to-maturity securities Debt securities Agency mortgage-backed residential (c) (d) $ 1,863 $ 3 $ (37 ) $ 1,829 $ 839 $ — $ (50 ) $ 789 Asset-backed retained notes 36 — — 36 — — — — Total held-to-maturity securities $ 1,899 $ 3 $ (37 ) $ 1,865 $ 839 $ — $ (50 ) $ 789 (a) Certain entities related to our Insurance operations are required to deposit securities with state regulatory authorities. These deposited securities totaled $12 million and $14 million at December 31, 2017 , and 2016, respectively. (b) Investment securities with a fair value of $7,804 million and $4,881 million at December 31, 2017 , and 2016, respectively, were pledged to secure advances from the Federal Home Loan Bank (FHLB), short-term borrowings or repurchase agreements, or for other purposes as required by contractual obligation or law. Under these agreements, we have granted the counterparty the right to sell or pledge $1,025 million and $737 million of the underlying investment securities at December 31, 2017 , and 2016, respectively. (c) Agency mortgage-backed residential debt securities are held for liquidity risk management purposes. (d) Securities with a fair value of $664 million and $87 million at December 31, 2017 , and 2016, respectively, were pledged to secure advances from the FHLB. The maturity distribution of investment securities outstanding is summarized in the following tables. Call or prepayment options may cause actual maturities to differ from contractual maturities. Total Due in one year or less Due after one year through five years Due after five years through ten years Due after ten years ($ in millions) Amount Yield Amount Yield Amount Yield Amount Yield Amount Yield December 31, 2017 Fair value of available-for-sale debt securities (a) U.S. Treasury $ 1,777 1.7 % $ — — % $ 487 1.7 % $ 1,290 1.8 % $ — — % U.S. States and political subdivisions 854 2.9 76 1.8 36 2.3 203 2.5 539 3.3 Foreign government 154 2.5 — — 80 2.5 74 2.4 — — Agency mortgage-backed residential 14,291 3.1 — — — — 3 2.9 14,288 3.1 Mortgage-backed residential 2,494 3.1 — — — — — — 2,494 3.1 Mortgage-backed commercial 541 3.2 — — 30 3.1 31 3.1 480 3.2 Asset-backed 936 3.1 — — 698 3.1 106 3.1 132 2.8 Corporate debt 1,256 2.9 140 2.6 513 2.6 564 3.2 39 4.7 Total available-for-sale debt securities $ 22,303 3.0 $ 216 2.3 $ 1,844 2.5 $ 2,271 2.3 $ 17,972 3.1 Amortized cost of available-for-sale debt securities $ 22,499 $ 217 $ 1,852 $ 2,314 $ 18,116 Amortized cost of held-to-maturity securities Agency mortgage-backed residential $ 1,863 3.1 % $ — — % $ — — % $ — — % $ 1,863 3.1 % Asset-backed retained notes 36 1.7 — — 35 1.7 1 3.0 — — Total held-to-maturity securities $ 1,899 3.1 $ — — $ 35 1.7 $ 1 3.0 $ 1,863 3.1 December 31, 2016 Fair value of available-for-sale debt securities (a) U.S. Treasury $ 1,620 1.7 % $ 2 4.6 % $ 60 1.6 % $ 1,558 1.7 % $ — — % U.S. States and political subdivisions 782 3.1 64 1.7 29 2.3 172 2.8 517 3.4 Foreign government 162 2.6 — — 58 2.8 104 2.4 — — Agency mortgage-backed residential 10,290 2.9 — — — — 29 2.6 10,261 2.9 Mortgage-backed residential 2,097 2.9 — — — — — — 2,097 2.9 Mortgage-backed commercial 537 2.6 — — — — 3 2.8 534 2.6 Asset-backed 1,400 2.8 — — 1,059 2.8 143 3.2 198 2.6 Corporate debt 1,443 2.8 72 2.2 840 2.6 489 3.2 42 4.7 Total available-for-sale debt securities $ 18,331 2.8 $ 138 2.0 $ 2,046 2.7 $ 2,498 2.2 $ 13,649 2.9 Amortized cost of available-for-sale debt securities $ 18,651 $ 138 $ 2,040 $ 2,563 $ 13,910 Amortized cost of held-to-maturity securities (b) $ 839 2.9 % $ — — % $ — — % $ — — % $ 839 2.9 % (a) Yield is calculated using the effective yield of each security at the end of the period, weighted based on the market value. The effective yield considers the contractual coupon and amortized cost, and excludes expected capital gains and losses. (b) Our held-to-maturity securities portfolio as of December 31, 2016, consisted of agency mortgage-backed residential debt securities. The balances of cash equivalents were $10 million and $291 million at December 31, 2017 , and 2016, respectively, and were composed primarily of money market accounts and short-term securities, including U.S. Treasury bills. The following table presents interest and dividends on investment securities. Year ended December 31, ($ in millions) 2017 2016 2015 Taxable interest $ 534 $ 375 $ 340 Taxable dividends 12 17 23 Interest and dividends exempt from U.S. federal income tax 22 19 18 Interest and dividends on investment securities $ 568 $ 411 $ 381 The following table presents gross gains and losses realized upon the sales of available-for-sale securities and other-than-temporary impairment. Year ended December 31, ($ in millions) 2017 2016 2015 Gross realized gains $ 106 $ 187 $ 184 Gross realized losses (a) (4 ) (2 ) (15 ) Other-than-temporary impairment — — (14 ) Other gain on investments, net $ 102 $ 185 $ 155 (a) Certain available-for-sale securities were sold at a loss in 2017, 2016, and 2015 as a result of market conditions within these respective periods (e.g., a downgrade in the rating of a debt security). Any such sales were made in accordance with our risk management policies and practices. The table below summarizes available-for-sale securities in an unrealized loss position in accumulated other comprehensive income. Based on the assessment of whether such losses were deemed to be other-than-temporary, we believe that the unrealized losses are not indicative of an other-than-temporary impairment of these securities. As of December 31, 2017 , we did not have the intent to sell the debt securities with an unrealized loss position in accumulated other comprehensive income, it is not more likely than not that we will be required to sell these securities before recovery of their amortized cost basis, and we expect to recover the entire amortized cost basis of the securities. As of December 31, 2017 , we had the ability and intent to hold equity securities with an unrealized loss position in accumulated other comprehensive income, and it is not more likely than not that we will be required to sell these securities before recovery of their amortized cost basis. As a result, we believe that the securities with an unrealized loss position in accumulated other comprehensive income are not considered to be other-than-temporarily impaired at December 31, 2017 . Refer to Note 1 for additional information related to investment securities and our methodology for evaluating potential other-than-temporary impairments. 2017 2016 Less than 12 months 12 months or longer Less than 12 months 12 months or longer December 31, ($ in millions) Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Available-for-sale securities Debt securities U.S. Treasury $ 471 $ (8 ) $ 1,305 $ (46 ) $ 1,612 $ (60 ) $ — $ — U.S. States and political subdivisions 242 (2 ) 183 (5 ) 524 (19 ) — — Foreign government 80 (1 ) 4 — 38 — — — Agency mortgage-backed residential 4,066 (19 ) 5,671 (137 ) 8,052 (196 ) 587 (16 ) Mortgage-backed residential 857 (2 ) 773 (32 ) 813 (17 ) 860 (53 ) Mortgage-backed commercial 76 (1 ) 21 — 47 (1 ) 149 (1 ) Asset-backed 220 (1 ) 91 — 375 (2 ) 127 — Corporate debt 529 (4 ) 194 (7 ) 744 (14 ) 46 (2 ) Total temporarily impaired debt securities 6,541 (38 ) 8,242 (227 ) 12,205 (309 ) 1,769 (72 ) Temporarily impaired equity securities 126 (12 ) 116 (36 ) 151 (8 ) 269 (46 ) Total temporarily impaired available-for-sale securities $ 6,667 $ (50 ) $ 8,358 $ (263 ) $ 12,356 $ (317 ) $ 2,038 $ (118 )

Finance Receivables and Loans,

Finance Receivables and Loans, Net	12 Months Ended
	Dec. 31, 2017
Loans and Leases Receivable, Net Amount [Abstract]
Loans, Notes, Trade and Other Receivables Disclosure [Text Block]	Finance Receivables and Loans, Net The composition of finance receivables and loans reported at gross carrying value was as follows. December 31, ($ in millions) 2017 2016 Consumer automotive (a) $ 68,071 $ 65,793 Consumer mortgage Mortgage Finance (b) 11,657 8,294 Mortgage — Legacy (c) 2,093 2,756 Total consumer mortgage 13,750 11,050 Total consumer 81,821 76,843 Commercial Commercial and industrial Automotive 33,025 35,041 Other 3,887 3,248 Commercial real estate 4,160 3,812 Total commercial 41,072 42,101 Total finance receivables and loans (d) $ 122,893 $ 118,944 (a) Includes $18 million and $43 million of fair value adjustment for loans in hedge accounting relationships at December 31, 2017 , and December 31, 2016 , respectively. Refer to Note 22 for additional information. (b) Includes loans originated as interest-only mortgage loans of $20 million and $30 million at December 31, 2017 , and December 31, 2016 , respectively, 35% of which are expected to start principal amortization in 2019 , and 45% in 2020 . The remainder of these loans have already exited the interest-only period. (c) Includes loans originated as interest-only mortgage loans of $496 million and $714 million at December 31, 2017 , and December 31, 2016 , respectively, 3% of which are expected to start principal amortization in 2018 . The remainder of these loans have already exited the interest-only period. (d) Totals include net increases of $551 million and $359 million at December 31, 2017 , and December 31, 2016 , respectively, for unearned income, unamortized premiums and discounts, and deferred fees and costs. The following tables present an analysis of the activity in the allowance for loan losses on finance receivables and loans. ($ in millions) Consumer automotive Consumer mortgage Commercial Total Allowance at January 1, 2017 $ 932 $ 91 $ 121 $ 1,144 Charge-offs (a) (1,344 ) (30 ) (18 ) (1,392 ) Recoveries 358 24 — 382 Net charge-offs (986 ) (6 ) (18 ) (1,010 ) Provision for loan losses 1,127 (7 ) 28 1,148 Other (b) (7 ) 1 — (6 ) Allowance at December 31, 2017 $ 1,066 $ 79 $ 131 $ 1,276 Allowance for loan losses at December 31, 2017 Individually evaluated for impairment $ 36 $ 27 $ 14 $ 77 Collectively evaluated for impairment 1,030 52 117 1,199 Finance receivables and loans at gross carrying value Ending balance $ 68,071 $ 13,750 $ 41,072 $ 122,893 Individually evaluated for impairment 430 231 72 733 Collectively evaluated for impairment 67,641 13,519 41,000 122,160 (a) Represents the amount of the gross carrying value directly written off. For consumer and commercial loans, the loss from a charge-off is measured as the difference between the gross carrying value of a loan and the fair value of the collateral, less costs to sell. Refer to Note 1 for more information regarding our charge-off policies. (b) Primarily related to the transfer of finance receivables and loans from held-for-investment to held-for-sale. ($ in millions) Consumer automotive Consumer mortgage Commercial Total Allowance at January 1, 2016 $ 834 $ 114 $ 106 $ 1,054 Charge-offs (a) (1,102 ) (39 ) (1 ) (1,142 ) Recoveries 307 32 2 341 Net charge-offs (795 ) (7 ) 1 (801 ) Provision for loan losses 919 (16 ) 14 917 Other (b) (26 ) — — (26 ) Allowance at December 31, 2016 $ 932 $ 91 $ 121 $ 1,144 Allowance for loan losses at December 31, 2016 Individually evaluated for impairment $ 28 $ 34 $ 23 $ 85 Collectively evaluated for impairment 904 57 98 1,059 Finance receivables and loans at gross carrying value Ending balance $ 65,793 $ 11,050 $ 42,101 $ 118,944 Individually evaluated for impairment 370 247 122 739 Collectively evaluated for impairment 65,423 10,803 41,979 118,205 (a) Represents the amount of the gross carrying value directly written off. For consumer and commercial loans, the loss from a charge-off is measured as the difference between the gross carrying value of a loan and the fair value of the collateral, less costs to sell. Refer to Note 1 for more information regarding our charge-off policies. (b) Primarily related to the transfer of finance receivables and loans from held-for-investment to held-for-sale. The following table presents information about significant sales of finance receivables and loans and transfers of finance receivables and loans from held-for-investment to held-for-sale. December 31, ($ in millions) 2017 2016 Consumer automotive $ 1,339 $ 4,267 Consumer mortgage 9 15 Commercial — 29 Total sales and transfers $ 1,348 $ 4,311 The following table presents information about significant purchases of finance receivables and loans. December 31, ($ in millions) 2017 2016 Consumer automotive $ 865 $ 21 Consumer mortgage 4,481 3,747 Total purchases of finance receivables and loans $ 5,346 $ 3,768 The following table presents an analysis of our past due finance receivables and loans recorded at gross carrying value. December 31, ($ in millions) 30–59 days past due 60–89 days past due 90 days or more past due Total past due Current Total finance receivables and loans 2017 Consumer automotive $ 1,994 $ 478 $ 268 $ 2,740 $ 65,331 $ 68,071 Consumer mortgage Mortgage Finance 60 11 18 89 11,568 11,657 Mortgage — Legacy 43 25 62 130 1,963 2,093 Total consumer mortgage 103 36 80 219 13,531 13,750 Total consumer 2,097 514 348 2,959 78,862 81,821 Commercial Commercial and industrial Automotive 5 — 3 8 33,017 33,025 Other — — — — 3,887 3,887 Commercial real estate — — — — 4,160 4,160 Total commercial 5 — 3 8 41,064 41,072 Total consumer and commercial $ 2,102 $ 514 $ 351 $ 2,967 $ 119,926 $ 122,893 2016 Consumer automotive $ 1,850 $ 428 $ 302 $ 2,580 $ 63,213 $ 65,793 Consumer mortgage Mortgage Finance 39 6 4 49 8,245 8,294 Mortgage — Legacy 45 18 57 120 2,636 2,756 Total consumer mortgage 84 24 61 169 10,881 11,050 Total consumer 1,934 452 363 2,749 74,094 76,843 Commercial Commercial and industrial Automotive 3 — 7 10 35,031 35,041 Other — — — — 3,248 3,248 Commercial real estate — — — — 3,812 3,812 Total commercial 3 — 7 10 42,091 42,101 Total consumer and commercial $ 1,937 $ 452 $ 370 $ 2,759 $ 116,185 $ 118,944 The following table presents the gross carrying value of our finance receivables and loans on nonaccrual status. December 31, ($ in millions) 2017 2016 Consumer automotive $ 603 $ 598 Consumer mortgage Mortgage Finance 25 10 Mortgage — Legacy 92 89 Total consumer mortgage 117 99 Total consumer 720 697 Commercial Commercial and industrial Automotive 27 33 Other 44 84 Commercial real estate 1 5 Total commercial 72 122 Total consumer and commercial finance receivables and loans $ 792 $ 819 Management performs a quarterly analysis of the consumer automotive, consumer mortgage, and commercial portfolios using a range of credit quality indicators to assess the adequacy of the allowance for loan losses based on historical and current trends. The following tables present the population of loans by quality indicators for our consumer automotive, consumer mortgage, and commercial portfolios. The following table presents performing and nonperforming credit quality indicators in accordance with our internal accounting policies for our consumer finance receivables and loans recorded at gross carrying value. Nonperforming loans include finance receivables and loans on nonaccrual status when the principal or interest has been delinquent for 90 days or when full collection is not expected. Refer to Note 1 for additional information. 2017 2016 December 31, ($ in millions) Performing Nonperforming Total Performing Nonperforming Total Consumer automotive $ 67,468 $ 603 $ 68,071 $ 65,195 $ 598 $ 65,793 Consumer mortgage Mortgage Finance 11,632 25 11,657 8,284 10 8,294 Mortgage — Legacy 2,001 92 2,093 2,667 89 2,756 Total consumer mortgage 13,633 117 13,750 10,951 99 11,050 Total consumer $ 81,101 $ 720 $ 81,821 $ 76,146 $ 697 $ 76,843 The following table presents pass and criticized credit quality indicators based on regulatory definitions for our commercial finance receivables and loans recorded at gross carrying value. 2017 2016 December 31, ($ in millions) Pass Criticized (a) Total Pass Criticized (a) Total Commercial and industrial Automotive $ 30,982 $ 2,043 $ 33,025 $ 33,160 $ 1,881 $ 35,041 Other 2,986 901 3,887 2,597 651 3,248 Commercial real estate 4,023 137 4,160 3,653 159 3,812 Total commercial $ 37,991 $ 3,081 $ 41,072 $ 39,410 $ 2,691 $ 42,101 (a) Includes loans classified as special mention, substandard, or doubtful. These classifications are based on regulatory definitions and generally represent loans within our portfolio that have a higher default risk or have already defaulted. Impaired Loans and Troubled Debt Restructurings Impaired Loans Loans are considered impaired when we determine it is probable that we will be unable to collect all amounts due according to the terms of the loan agreement. For more information on our impaired finance receivables and loans, refer to Note 1 . The following table presents information about our impaired finance receivables and loans. December 31, ($ in millions) Unpaid principal balance (a) Gross carrying value Impaired with no allowance Impaired with an allowance Allowance for impaired loans 2017 Consumer automotive $ 438 $ 430 $ 91 $ 339 $ 36 Consumer mortgage Mortgage Finance 8 8 4 4 — Mortgage — Legacy 228 223 58 165 27 Total consumer mortgage 236 231 62 169 27 Total consumer 674 661 153 508 63 Commercial Commercial and industrial Automotive 27 27 9 18 3 Other 54 44 10 34 11 Commercial real estate 1 1 — 1 — Total commercial 82 72 19 53 14 Total consumer and commercial finance receivables and loans $ 756 $ 733 $ 172 $ 561 $ 77 2016 Consumer automotive $ 407 $ 370 $ 131 $ 239 $ 28 Consumer mortgage Mortgage Finance 8 8 3 5 — Mortgage — Legacy 243 239 56 183 34 Total consumer mortgage 251 247 59 188 34 Total consumer 658 617 190 427 62 Commercial Commercial and industrial Automotive 33 33 7 26 3 Other 99 84 — 84 19 Commercial real estate 5 5 2 3 1 Total commercial 137 122 9 113 23 Total consumer and commercial finance receivables and loans $ 795 $ 739 $ 199 $ 540 $ 85 (a) Adjusted for charge-offs. The following table presents average balance and interest income for our impaired finance receivables and loans. 2017 2016 2015 Year ended December 31, ($ in millions) Average balance Interest income Average balance Interest income Average balance Interest income Consumer automotive $ 391 $ 21 $ 344 $ 17 $ 295 $ 16 Consumer mortgage Mortgage Finance 8 — 8 — 8 — Mortgage — Legacy 234 10 248 9 272 9 Total consumer mortgage 242 10 256 9 280 9 Total consumer 633 31 600 26 575 25 Commercial Commercial and industrial Automotive 49 2 35 1 33 1 Other 69 9 60 1 41 3 Commercial real estate 5 — 6 — 5 — Total commercial 123 11 101 2 79 4 Total consumer and commercial finance receivables and loans $ 756 $ 42 $ 701 $ 28 $ 654 $ 29 Troubled Debt Restructurings TDRs are loan modifications where concessions were granted to borrowers experiencing financial difficulties. For automotive loans, we may offer several types of assistance to aid our customers, including extension of the loan maturity date and rewriting the loan terms. Additionally, for mortgage loans, as part of certain programs, we offer mortgage loan modifications to qualified borrowers. These programs are in place to provide support to our mortgage customers in financial distress, including principal forgiveness, maturity extensions, delinquent interest capitalization, and changes to contractual interest rates. Total TDRs recorded at gross carrying value were $712 million and $663 million at December 31, 2017 , and December 31, 2016 , respectively. Total commitments to lend additional funds to borrowers whose terms had been modified in a TDR were $6 million and $2 million at December 31, 2017 , and December 31, 2016 , respectively. Refer to Note 1 for additional information. The following table presents information related to finance receivables and loans recorded at gross carrying value modified in connection with a TDR during the period. 2017 2016 Year ended December 31, ($ in millions) Number of loans Pre-modification gross carrying value Post-modification gross carrying value Number of loans Pre-modification gross carrying value Post-modification gross carrying value Consumer automotive 26,156 $ 380 $ 333 20,227 $ 347 $ 293 Consumer mortgage Mortgage Finance 4 1 1 7 3 3 Mortgage — Legacy 122 21 21 120 18 18 Total consumer mortgage 126 22 22 127 21 21 Total consumer 26,282 402 355 20,354 368 314 Commercial Commercial and industrial Automotive 4 16 15 1 7 7 Other — 44 44 — — — Commercial real estate 2 3 3 — — — Total commercial 6 63 62 1 7 7 Total consumer and commercial finance receivables and loans 26,288 $ 465 $ 417 20,355 $ 375 $ 321 The following table presents information about finance receivables and loans recorded at gross carrying value that have redefaulted during the reporting period and were within 12 months or less of being modified as a TDR. Redefault is when finance receivables and loans meet the requirements for evaluation under our charge-off policy (refer to Note 1 for additional information) except for commercial finance receivables and loans, where redefault is defined as 90 days past due. 2017 2016 Year ended December 31, ($ in millions) Number of loans Gross carrying value Charge-off amount Number of loans Gross carrying value Charge-off amount Consumer automotive 8,829 $ 102 $ 71 7,800 $ 94 $ 56 Consumer mortgage Mortgage Finance 1 1 — — — — Mortgage — Legacy 2 — — 4 — — Total consumer finance receivables and loans 8,832 $ 103 $ 71 7,804 $ 94 $ 56 Concentration Risk Consumer We monitor our consumer loan portfolio for concentration risk across the states in which we lend. The highest concentrations of loans are in California and Texas, which represent an aggregate of 24.7% and 24.2% of our total outstanding consumer finance receivables and loans at December 31, 2017 , and December 31, 2016 , respectively. The following table shows the percentage of total consumer finance receivables and loans recorded at gross carrying value by state concentration. 2017 (a) 2016 December 31, Consumer automotive Consumer mortgage Consumer automotive Consumer mortgage California 8.2 % 34.6 % 7.8 % 34.2 % Texas 13.2 6.5 13.6 6.6 Florida 8.5 4.8 8.2 4.4 Pennsylvania 4.6 1.5 4.7 1.5 Illinois 4.2 3.2 4.3 3.4 Georgia 4.2 2.5 4.3 2.2 North Carolina 3.7 1.8 3.6 1.6 Ohio 3.4 0.5 3.5 0.5 New York 3.0 2.2 3.2 1.9 Missouri 2.9 0.9 2.8 1.2 Other United States 44.1 41.5 44.0 42.5 Total consumer loans 100.0 % 100.0 % 100.0 % 100.0 % (a) Presentation is in descending order as a percentage of total consumer finance receivables and loans at December 31, 2017 . Commercial Real Estate The commercial real estate portfolio consists of loans issued primarily to automotive dealers. The following table shows the percentage of total commercial real estate finance receivables and loans reported at gross carrying value by state concentration. December 31, 2017 2016 Texas 15.7 % 16.1 % Florida 10.3 10.2 California 8.2 7.9 Michigan 7.7 7.6 Georgia 4.6 3.6 New Jersey 3.6 4.2 North Carolina 3.6 3.6 South Carolina 3.5 2.7 Pennsylvania 3.0 3.1 Missouri 2.4 2.5 Other United States 37.4 38.5 Total commercial real estate finance receivables and loans 100.0 % 100.0 % Commercial Criticized Exposure Finance receivables and loans classified as special mention, substandard, or doubtful are reported as criticized. These classifications are based on regulatory definitions and generally represent finance receivables and loans within our portfolio that have a higher default risk or have already defaulted. These finance receivables and loans require additional monitoring and review including specific actions to mitigate our potential loss. The following table presents the percentage of total commercial criticized finance receivables and loans reported at gross carrying value by industry concentrations. December 31, 2017 2016 Automotive 76.3 % 81.2 % Services 6.7 6.3 Health/Medical 4.9 2.3 Other 12.1 10.2 Total commercial criticized finance receivables and loans 100.0 % 100.0 %

Investment in Operating Leases,

Investment in Operating Leases, Net	12 Months Ended
	Dec. 31, 2017
Leases, Operating [Abstract]
Lessor, Operating Leases [Text Block]	Investment in Operating Leases, Net Investments in operating leases were as follows. December 31, ($ in millions) 2017 2016 Vehicles $ 10,556 $ 14,584 Accumulated depreciation (1,815 ) (3,114 ) Investment in operating leases, net $ 8,741 $ 11,470 Depreciation expense on operating lease assets includes remarketing gains and losses recognized on the sale of operating lease assets. The following summarizes the components of depreciation expense on operating lease assets. Year ended December 31, ($ in millions) 2017 2016 2015 Depreciation expense on operating lease assets (excluding remarketing gains) $ 1,368 $ 1,982 $ 2,600 Remarketing gains (124 ) (213 ) (351 ) Net depreciation expense on operating lease assets $ 1,244 $ 1,769 $ 2,249 The following table presents the future lease nonresidual rental payments due from customers for vehicles on operating leases. Year ended December 31, ($ in millions) 2018 $ 1,319 2019 839 2020 364 2021 46 2022 and thereafter 4 Total $ 2,572

Securitizations and Variable In

Securitizations and Variable Interest Entities	12 Months Ended
	Dec. 31, 2017
Securitizations And Variable Interest Entities [Abstract]
Variable Interest Entity Disclosure [Text Block]	Securitizations and Variable Interest Entities Overview We securitize, transfer, and service consumer and commercial automotive loans, and operating leases. We often securitize these loans and notes secured by operating leases (collectively referred to as financial assets) through the use of special-purpose entities (SPEs). A SPE is a legal entity that is designed to fulfill a specified limited need of the sponsor. Our principal use of SPEs is to obtain liquidity by securitizing certain of our financial assets and operating lease assets which may, or may not, be included on our Consolidated Balance Sheet . The transaction-specific SPEs involved in our securitization transactions are often considered VIEs. VIEs are entities that have either a total equity investment at risk that is insufficient to permit the entity to finance its activities without additional subordinated financial support or whose equity investors at risk lack the ability to control the entity’s activities. Securitizations In executing a securitization transaction, we typically sell pools of financial assets to a wholly-owned, bankruptcy-remote SPE, which then transfers the financial assets to a separate, transaction-specific SPE for cash, and typically, other retained interests. The securitization entity is funded through the issuance of beneficial interests, which could take the form of notes or residual interests, and can be sold to investors and/or retained by us. We typically hold retained beneficial interests in our securitizations including, but not limited to, retained notes, certificated residual interests, as well as certain noncertificated interests retained from the sale of automotive finance receivables. If sold, the beneficial interests only entitle the investors to specified cash flows generated from the underlying securitized assets. If retained, the interests provide credit enhancement to the SPE as they may absorb credit losses or other cash shortfalls and may represent a form of significant continuing economic interests. In addition to providing a source of liquidity and cost-efficient funding, securitizing these financial assets also reduces our credit exposure to the borrowers beyond any economic interest we may retain. The SPEs are limited to specific activities by their respective legal documents, but are generally allowed to acquire the financial assets, to issue beneficial interests to investors to fund the acquisition of the financial assets, and to enter into derivatives or other yield maintenance contracts to hedge or mitigate certain risks related to the financial assets or beneficial interests of the entity. A servicer, who is generally us, is appointed pursuant to the underlying legal documents to service the assets the SPE holds and the beneficial interests it issues. Servicing functions include, but are not limited to, general collection activity on current and noncurrent accounts, loss mitigation efforts including repossession and sale of collateral, as well as preparing and furnishing statements summarizing the asset and beneficial interest performance. These servicing responsibilities constitute continued involvement in the transferred financial assets. Cash flows from the securitized financial assets represent the sole source for payment of distributions on the beneficial interests issued by the SPE and for payments to the parties that perform services for the SPE, such as the servicer or the trustee. We generally hold certain conditional repurchase options specific to securitizations that allow us to repurchase assets from the securitization entity. The majority of the securitizations provide us, as servicer, with a call option that allows us to repurchase the remaining transferred financial assets or redeem outstanding beneficial interests at our discretion once the asset pool reaches a predefined level, which represents the point where servicing becomes burdensome (a clean-up call option). The repurchase price is typically the discounted securitization balance of the assets plus accrued interest when applicable. We generally have discretion regarding when or if we will exercise these options, but we would do so only when it is in our best interest. On December 24, 2016, the risk retention rules under the Dodd-Frank Wall Street Reform and Consumer Protection Act (Dodd-Frank Act) of 2010 became effective, requiring us to retain at least five percent of the credit risk of the assets underlying asset-backed securitizations. Other than our customary representation and warranty provisions, these securitizations are nonrecourse to us, thereby transferring the risk of future credit losses to the extent the beneficial interests in the securitization entities are held by third parties. Representation and warranty provisions generally require us to repurchase assets or indemnify the investor or other party for incurred losses to the extent it is determined that the assets were ineligible or were otherwise defective at the time of sale. We did not provide any non-contractual financial support to any of these entities during 2017, 2016, or 2015. Variable Interest Entities The determination of whether the assets and liabilities of the VIEs are consolidated on our balance sheet (also referred to as on-balance sheet) or not consolidated on our balance sheet (also referred to as off-balance sheet) depends on the terms of the related transaction and our continuing involvement (if any) with the VIE. We are deemed the primary beneficiary and therefore consolidate VIEs for which we have both (a) the power, through voting rights or similar rights, to direct the activities that most significantly impact the VIE’s economic performance, and (b) a variable interest (or variable interests) that (i) obligates us to absorb losses that could potentially be significant to the VIE; and/or (ii) provides us the right to receive residual returns of the VIE that could potentially be significant to the VIE. We determine whether we hold a significant variable interest in a VIE based on a consideration of both qualitative and quantitative factors regarding the nature, size, and form of our involvement with the VIE. We assess whether we are the primary beneficiary of a VIE on an ongoing basis and are generally determined to be the primary beneficiary in VIEs established for our securitization activities when we have a controlling financial interest in the VIE, primarily due to our servicing activities, and our beneficial interest in the VIE that could be potentially significant. The consolidated VIEs included on the Consolidated Balance Sheet represent separate entities with which we are involved. The third-party investors in the obligations of consolidated VIEs have legal recourse only to the assets of the VIEs and do not have such recourse to us, except for the customary representation and warranty provisions. In addition, the cash flows from the assets are restricted only to pay such liabilities. Thus, our economic exposure to loss from outstanding third-party financing related to consolidated VIEs is limited to the carrying value of the consolidated VIE assets. Generally, all assets of consolidated VIEs, presented below based upon the legal transfer of the underlying assets in order to reflect legal ownership, are restricted for the benefit of the beneficial interest holders. For additional information regarding the company’s significant accounting policies for consolidated VIEs, refer to the Securitizations and Variable Interest Entities section of Note 1 . The nature, purpose, and activities of nonconsolidated securitization entities are similar to those of our consolidated securitization entities with the primary difference being the nature and extent of our continuing involvement. Additionally, to qualify for off-balance sheet treatment, transfers of financial assets must meet appropriate sale accounting conditions. For nonconsolidated securitization entities, the transferred financial assets are removed from our balance sheet provided the conditions for sale accounting are met. The financial assets obtained from the securitization are primarily reported as cash, or retained interests (if applicable). Liabilities incurred as part of these securitization transactions, such as representation and warranty provisions, are recorded at fair value at the time of sale and are reported as accrued expenses and other liabilities on our Consolidated Balance Sheet. Upon the sale of the loans, we recognize a gain or loss on sale for the difference between the assets recognized, the assets derecognized, and the liabilities recognized as part of the transaction. The pretax gain on sales of financial assets into non-consolidated VIEs was $2 million for the year ended December 31, 2017. There were no pretax gains or losses for the year ended December 31, 2016, while there was a pretax loss of $3 million for the year ended December 31, 2015. For additional information regarding the company’s significant accounting policies for non-consolidated VIEs, refer to the Securitizations and Variable Interest Entities section of Note 1 . We provide long-term guarantee contracts to investors in certain nonconsolidated affordable housing entities and have extended a line of credit to provide liquidity. Since we do not have control over the entities or the power to make decisions, we do not consolidate the entities and our involvement is limited to the guarantee and the line of credit. We have involvement with various other nonconsolidated equity investments, including affordable housing entities and venture capital funds and loan funds. We do not consolidate these entities and our involvement is limited to our outstanding investment, additional capital committed to these funds plus any previously recognized low income housing tax credits that are subject to recapture. The following table presents our involvement in consolidated and nonconsolidated VIEs in which we hold variable interests. For additional detail related to the assets and liabilities of consolidated variable interest entities refer to the Consolidated Balance Sheet. December 31, ($ in millions) Carrying value of total assets Carrying value of total liabilities Assets sold to nonconsolidated VIEs (a) Maximum exposure to loss in nonconsolidated VIEs 2017 On-balance sheet variable interest entities Consumer automotive $ 17,597 (b) $ 7,677 (c) Commercial automotive 12,550 2,558 Off-balance sheet variable interest entities Consumer automotive 37 (d) — $ 1,964 $ 2,001 (e) Commercial other 592 (f) 248 (g) — 790 (h) Total $ 30,776 $ 10,483 $ 1,964 $ 2,791 2016 On-balance sheet variable interest entities Consumer automotive $ 20,869 (b) $ 8,557 (c) Commercial automotive 16,278 4,764 Off-balance sheet variable interest entities Consumer automotive 24 (f) — $ 2,899 $ 2,923 (e) Commercial other 460 (f) 169 (g) — 651 (h) Total $ 37,631 $ 13,490 $ 2,899 $ 3,574 (a) Asset values represent the current unpaid principal balance of outstanding consumer finance receivables and loans within the VIEs. (b) Includes $8.5 billion and $9.6 billion of assets that are not encumbered by VIE beneficial interests held by third parties at December 31, 2017 , and December 31, 2016 , respectively. Ally or consolidated affiliates hold the interests in these assets. (c) Includes $29 million and $50 million of liabilities that are not obligations to third-party beneficial interest holders at December 31, 2017 , and December 31, 2016 , respectively. (d) Represents retained notes and certificated residual interests, of which $36 million is classified as held-to-maturity securities and $1 million is classified as other assets at December 31, 2017 . These assets represent our compliance with the risk retention rules under the Dodd-Frank Act, requiring us to retain at least five percent of the credit risk of the assets underlying asset-backed securitizations , which became effective on December 24, 2016. (e) Maximum exposure to loss represents the current unpaid principal balance of outstanding loans, retained notes, certificated residual interests, as well as certain noncertificated interests retained from the sale of automotive finance receivables. This measure is based on the very unlikely event that all of our sold loans have defects that would trigger a representation and warranty provision and the underlying collateral supporting the loans becomes worthless. This required disclosure is not an indication of our expected loss. (f) Amounts are classified as other assets. (g) Amounts are classified as accrued expenses and other liabilities. (h) For certain nonconsolidated affordable housing entities, maximum exposure to loss represents the yield we guaranteed investors through long-term guarantee contracts. The amount disclosed is based on the unlikely event that the underlying properties cease generating yield to investors and the yield delivered to investors in the form of low income tax housing credits is recaptured. For nonconsolidated equity investments, maximum exposure to loss represents our outstanding investment, additional committed capital, and low income housing tax credits subject to recapture. The amount disclosed is based on the unlikely event that our committed capital is funded, our investments become worthless, and the tax credits previously delivered to us are recaptured. This required disclosure is not an indication of our expected loss. On-balance Sheet Variable Interest Entities The consolidated VIEs included on the Consolidated Balance Sheet represent separate entities with which we are involved. The third-party investors in the obligations of consolidated VIEs have legal recourse only to the assets of the VIEs and do not have such recourse to us, except for the customary representation and warranty provisions. In addition, the cash flows from the assets are restricted only to pay such liabilities. Thus, our economic exposure to loss from outstanding third-party financing related to consolidated VIEs is significantly less than the carrying value of the consolidated VIE assets. All assets of consolidated VIEs, presented below based upon the legal transfer of the underlying assets in order to reflect legal ownership, are restricted for the benefit of the beneficial interest holders. December 31, ($ in millions) 2017 2016 Assets Finance receivables and loans, net Consumer $ 8,186 $ 8,929 Commercial 12,437 15,701 Allowance for loan losses (136 ) (173 ) Total finance receivables and loans, net 20,487 24,457 Investment in operating leases, net 444 1,745 Other assets 689 1,390 Total assets $ 21,620 $ 27,592 Liabilities Long-term debt $ 10,197 $ 13,259 Accrued expenses and other liabilities 9 12 Total liabilities $ 10,206 $ 13,271 Cash Flows with Off-balance Sheet Securitization Entities The following table summarizes cash flows received and paid related to securitization entities and asset-backed financings where the transfer is accounted for as a sale and we have a continuing involvement with the transferred consumer automotive assets (e.g., servicing) that were outstanding during the years ended December 31, 2017 , 2016 , and 2015 . Additionally, this table contains information regarding cash flows received from and paid to nonconsolidated securitization entities that existed during each period. Year ended December 31, ($ in millions) 2017 2016 2015 Cash proceeds from transfers completed during the period $ 1,187 $ 1,715 $ 1,551 Cash disbursements for repurchases during the period (a) (491 ) — — Servicing fees 31 35 28 Cash flows received on retained interests in securitization entities 21 — — Other cash flows 4 8 — (a) During the second quarter of 2017, we elected to not renew a retail automotive credit conduit facility and also purchased the related retail automotive loans and settled associated retained interests. Delinquencies and Net Credit Losses The following table represents off-balance sheet securitizations and whole-loan sales where we have continuing involvement. The table presents quantitative information about delinquencies and net credit losses. Total amount Amount 60 days or more past due Net credit losses December 31, ($ in millions) 2017 2016 2017 2016 2017 2016 Off-balance sheet securitization entities Consumer automotive $ 1,964 $ 2,392 $ 16 $ 13 $ 13 $ 8 Total off-balance sheet securitization entities 1,964 2,392 16 13 13 8 Whole-loan sales (a) 1,399 3,164 4 6 3 3 Total $ 3,363 $ 5,556 $ 20 $ 19 $ 16 $ 11 (a) Whole-loan sales are not part of a securitization transaction, but represent consumer automotive pools of loans sold to third-party investors.

Servicing Activities

Servicing Activities	12 Months Ended
	Dec. 31, 2017
Servicing Asset [Abstract]
Servicing Activities [Text Block]	Servicing Activities Automotive Finance Servicing Activities We service consumer automotive contracts. Historically, we have sold a portion of our consumer automotive contracts. With respect to contracts we sell, we generally retain the right to service and earn a servicing fee for our servicing function. We have concluded that the fee we are paid for servicing consumer automotive finance receivables represents adequate compensation, and consequently, we do not recognize a servicing asset or liability. We recognized automotive servicing fee income of $51 million , $64 million , and $45 million during the years ended December 31, 2017 , 2016, and 2015, respectively. Automotive Finance Serviced Assets The current unpaid principal balance and any related unamortized deferred fees and costs of total serviced automotive finance loans and net investment in operating leases outstanding were as follows. December 31, ($ in millions) 2017 2016 On-balance sheet automotive finance loans and leases Consumer automotive $ 67,631 $ 65,646 Commercial automotive 37,058 38,853 Operating leases 8,682 11,311 Other 121 67 Off-balance sheet automotive finance loans Securitizations 1,977 2,412 Whole-loan sales 1,409 3,191 Total serviced automotive finance loans and leases $ 116,878 $ 121,480

Other Assets

Other Assets	12 Months Ended
	Dec. 31, 2017
Other Assets [Abstract]
Other Assets Disclosure [Text Block]	Other Assets The components of other assets were as follows. December 31, ($ in millions) 2017 2016 Property and equipment at cost $ 1,064 $ 901 Accumulated depreciation (608 ) (525 ) Net property and equipment 456 376 Nonmarketable equity investments (a) 1,233 1,046 Restricted cash collections for securitization trusts (b) 812 1,694 Accrued interest and rent receivables 550 476 Net deferred tax assets (c) 461 994 Goodwill (d) 240 240 Other accounts receivable 116 100 Cash reserve deposits held for securitization trusts (e) 111 184 Restricted cash and cash equivalents (f) 94 111 Fair value of derivative contracts in receivable position (g) 39 95 Cash collateral placed with counterparties 29 167 Other assets 1,522 1,371 Total other assets $ 5,663 $ 6,854 (a) Includes investments in FHLB stock of $745 million and $577 million at December 31, 2017 , and 2016, respectively; and FRB stock of $445 million and $435 million at December 31, 2017 , and 2016, respectively. (b) Represents cash collections from customer payments on securitized receivables. These funds are distributed to investors as payments on the related secured debt. (c) For further discussion regarding the impact to our deferred tax asset as a result of the Tax Act, refer to Note 23 . (d) Includes goodwill of $27 million within our Insurance operations at both December 31, 2017 , and 2016; $193 million within Corporate and Other at both December 31, 2017 , and 2016; and $20 million within Automotive Finance operations at both December 31, 2017 , and 2016. As a result of our acquisition of TradeKing, we recognized $193 million of goodwill within Corporate and Other on June 1, 2016. On August 1, 2016, we purchased assets from Blue Yield and as a result recognized $20 million of goodwill within Automotive Finance operations. No other changes to the carrying amount of goodwill were recorded during the years ended December 31, 2017, 2016, and 2015. (e) Represents credit enhancement in the form of cash reserves for various securitization transactions. (f) Primarily represents a number of arrangements with third parties where certain restrictions are placed on balances we hold due to collateral agreements associated with operational processes with a third-party bank, or letter of credit arrangements and corresponding collateral requirements. (g) For additional information on derivative instruments and hedging activities, refer to Note 22 .

Deposit Liabilities

Deposit Liabilities	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Deposit Liabilities Disclosures [Text Block]	Deposit Liabilities Deposit liabilities consisted of the following. December 31, ($ in millions) 2017 2016 Noninterest-bearing deposits $ 108 $ 84 Interest-bearing deposits Savings and money market checking accounts 49,267 46,976 Certificates of deposit 43,869 31,795 Dealer deposits 12 167 Total deposit liabilities $ 93,256 $ 79,022 At December 31, 2017 , and December 31, 2016 , certificates of deposit included $18.9 billion and $12.1 billion , respectively, of those in denominations of $100 thousand or more. At December 31, 2017 , and December 31, 2016 , certificates of deposit included $5.3 billion and $3.5 billion , respectively, of those in denominations in excess of $250 thousand federal insurance limits. The following table presents the scheduled maturity of total certificates of deposit at December 31, 2017 . ( $ in millions ) Due in 2018 $ 28,764 Due in 2019 8,613 Due in 2020 3,579 Due in 2021 1,418 Due in 2022 1,495 Total certificates of deposit $ 43,869

Debt

Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt Disclosure [Text Block]	Debt Short-term Borrowings The following table presents the composition of our short-term borrowings portfolio. 2017 2016 December 31, ($ in millions) Unsecured Secured (a) Total Unsecured Secured (a) Total Demand notes $ 3,171 $ — $ 3,171 $ 3,622 $ — $ 3,622 Federal Home Loan Bank — 7,350 7,350 — 7,875 7,875 Financial instruments sold under agreements to repurchase — 892 892 — 1,176 1,176 Total short-term borrowings $ 3,171 $ 8,242 $ 11,413 $ 3,622 $ 9,051 $ 12,673 Weighted average interest rate (b) 1.5 % 1.0 % (a) Refer to the section below titled Long-term Debt for further details on assets restricted as collateral for payment of the related debt. (b) Based on the debt outstanding and the interest rate at December 31 of each year. We periodically enter into term repurchase agreements, short-term borrowing agreements in which we sell financial instruments to one or more investors while simultaneously committing to repurchase them at a specified future date, at the stated price plus accrued interest. As of December 31, 2017 , the financial instruments sold under agreements to repurchase consisted of $892 million of agency mortgage-backed residential debt securities set to mature as follows: $73 million within the next 30 days , $521 million within 31 to 60 day s, and $298 million within 61 to 90 days . Refer to Note 8 and Note 26 for further details. Additionally, in December 2016, we sold asset-backed automotive financial instruments, which are our retained interests from certain on-balance sheet securitizations, subject to a repurchase agreement in exchange for $500 million , which was recorded as a short-term secured borrowing. The asset-backed automotive financial instruments that we sold subject to the repurchase agreement were secured by finance receivables that we have securitized. Refer to Note 11 for additional information on our securitization activities. This repurchase agreement was terminated in September 2017. The primary risk associated with these repurchase agreements is that the counterparty will be unable to perform under the terms of the contract. As the borrower, we are exposed to the excess market value of the securities pledged over the amount borrowed. Daily mark-to-market collateral management is designed to limit this risk to the initial margin. However, should a counterparty declare bankruptcy or become insolvent, we may incur additional delays and costs. In some instances, we may place or receive cash collateral with counterparties under collateral arrangements associated with our repurchase agreements. At December 31, 2017 , we placed cash collateral totaling $10 million and received cash collateral totaling $1 million . At December 31, 2016 , we placed cash collateral totaling $45 million . Long-term Debt The following tables present the composition of our long-term debt portfolio. December 31, ($ in millions) Amount Stated interest rate Weighted-average stated interest rate (a) Due date range 2017 Unsecured debt Fixed rate (b) $ 12,820 Variable rate 1 Trust preferred securities (c) 2,570 Fair value adjustment (d) 240 Total unsecured debt 15,631 1.48–8.00% 5.68 % 2018–2049 Secured debt Fixed rate 18,845 Variable rate (e) 9,782 Fair value adjustment (d) (32 ) Total secured debt (f) (g) (h) 28,595 0.63–4.50% 1.96 % 2018–2036 Total long-term debt $ 44,226 2016 Unsecured debt Fixed rate (b) $ 17,155 Variable rate 1 Trust preferred securities (c) 2,568 Fair value adjustment (d) 326 Total unsecured debt 20,050 0.68–8.00% 5.36 % 2017–2049 Secured debt Fixed rate 17,935 Variable rate 16,154 Fair value adjustment (d) (11 ) Total secured debt (f) (g) (h) 34,078 0.63–4.55% 1.53 % 2017–2035 Total long-term debt $ 54,128 (a) Based on the debt outstanding and the interest rate at December 31 of each year excluding any impacts of interest rate hedges. (b) Includes subordinated debt of $1.4 billion at both December 31, 2017 , and 2016. (c) Refer to the section below titled Trust Preferred Securities for further information. (d) Represents the fair value adjustment associated with the application of hedge accounting on certain of our long-term debt positions. Refer to Note 22 for additional information. (e) Includes $8 million of long-term debt that does not have a stated interest rate. (f) Includes $10.2 billion and $13.3 billion of VIE secured debt at December 31, 2017 , and 2016, respectively. (g) Includes $8.1 billion and $14.8 billion of debt outstanding from our automotive secured revolving credit facilities at December 31, 2017 , and 2016, respectively. (h) Includes advances from the FHLB of Pittsburgh of $10.3 billion and $6.1 billion at December 31, 2017 , and 2016, respectively. 2017 2016 December 31, ($ in millions) Unsecured Secured Total Unsecured Secured Total Long-term debt Due within one year $ 3,482 $ 7,499 $ 10,981 $ 4,274 $ 10,279 $ 14,553 Due after one year 11,909 21,128 33,037 15,450 23,810 39,260 Fair value adjustment 240 (32 ) 208 326 (11 ) 315 Total long-term debt $ 15,631 $ 28,595 $ 44,226 $ 20,050 $ 34,078 $ 54,128 To achieve the desired balance between fixed- and variable-rate debt, we utilize interest rate swap agreements. The use of these derivative financial instruments had the effect of synthetically converting $3.8 billion and $2.1 billion of our fixed-rate debt into variable-rate obligations, and $3.4 billion and $132 million of our variable-rate debt into fixed-rate obligations at December 31, 2017 , and 2016, respectively. The following table presents the scheduled remaining maturity of long-term debt at December 31, 2017 , assuming no early redemptions will occur. The actual payment of secured debt may vary based on the payment activity of the related pledged assets. ($ in millions) 2018 2019 2020 2021 2022 2023 and thereafter Fair value adjustment Total Unsecured Long-term debt $ 3,582 $ 1,681 $ 2,251 $ 637 $ 1,067 $ 7,408 $ 240 $ 16,866 Original issue discount (100 ) (39 ) (39 ) (43 ) (47 ) (967 ) — (1,235 ) Total unsecured 3,482 1,642 2,212 594 1,020 6,441 240 15,631 Secured Long-term debt 7,499 8,352 6,879 3,712 1,631 554 (32 ) 28,595 Total long-term debt $ 10,981 $ 9,994 $ 9,091 $ 4,306 $ 2,651 $ 6,995 $ 208 $ 44,226 The following summarizes assets restricted as collateral for the payment of the related debt obligation primarily arising from securitization transactions accounted for as secured borrowings and repurchase agreements. 2017 2016 December 31, ($ in millions) Total (a) Ally Bank Total (a) Ally Bank Investment securities (b) $ 8,371 $ 7,443 $ 4,895 $ 4,231 Mortgage assets held-for-investment and lending receivables 13,579 13,579 10,954 10,954 Consumer automotive finance receivables (b) 19,787 6,200 27,846 5,751 Commercial automotive finance receivables 16,567 16,472 19,487 19,280 Operating leases 457 — 2,040 913 Total assets restricted as collateral (c) (d) $ 58,761 $ 43,694 $ 65,222 $ 41,129 Secured debt $ 36,837 (e) $ 23,278 $ 43,129 (e) $ 22,149 (a) Ally Bank is a component of the total column. (b) A portion of the restricted investment securities at December 31, 2017 , and December 31, 2016 , and consumer automotive finance receivables at December 31, 2016 , were restricted under repurchase agreements. Refer to the section above titled Short-term Borrowings for information on the repurchase agreements. (c) Ally Bank has an advance agreement with the FHLB, and had assets pledged to secure borrowings that were restricted as collateral to the FHLB totaling $25.2 billion and $19.0 billion at December 31, 2017 , and December 31, 2016 , respectively. These assets were composed primarily of consumer mortgage finance receivables and loans and investment securities. Ally Bank has access to the FRB Discount Window. Ally Bank had assets pledged and restricted as collateral to the FRB totaling $2.3 billion and $2.4 billion at December 31, 2017 , and December 31, 2016 , respectively. These assets were composed of consumer automotive finance receivables and loans and operating lease assets. Availability under these programs is only for the operations of Ally Bank and cannot be used to fund the operations or liabilities of Ally or its subsidiaries. (d) Excludes restricted cash and cash reserves for securitization trusts recorded within other assets on the Consolidated Balance Sheet . Refer to Note 14 for additional information. (e) Includes $8.2 billion and $9.1 billion of short-term borrowings at December 31, 2017 , and December 31, 2016 , respectively. Trust Preferred Securities At December 31, 2017 , we have issued and outstanding approximately $2.6 billion in aggregate liquidation preference of 8.125% Fixed Rate/Floating Rate Trust Preferred Securities, Series 2 (Series 2 TRUPS). Each Series 2 TRUPS security has a liquidation amount of $25. Distributions are cumulative and are payable until redemption at the applicable coupon rate. Distributions were payable at an annual rate of 8.125% payable quarterly in arrears, through but excluding February 15, 2016. From and including February 15, 2016, to but excluding February 15, 2040, distributions will be payable at an annual rate equal to three-month London interbank offer rate plus 5.785% payable quarterly in arrears, beginning May 15, 2016. Ally has the right to defer payments of interest for a period not exceeding 20 consecutive quarters. The Series 2 TRUPS have no stated maturity date, but must be redeemed upon the redemption or maturity of the related debentures (Debentures), which mature on February 15, 2040. Ally at any time on or after February 15, 2016, may redeem the Series 2 TRUPS at a redemption price equal to 100% of the principal amount being redeemed, plus accrued and unpaid interest through the date of redemption. The Series 2 TRUPS are generally nonvoting, other than with respect to certain limited matters. During any period in which any Series 2 TRUPS remain outstanding but in which distributions on the Series 2 TRUPS have not been fully paid, none of Ally or its subsidiaries will be permitted to (i) declare or pay dividends on, make any distributions with respect to, or redeem, purchase, acquire or otherwise make a liquidation payment with respect to, any of Ally’s capital stock or make any guarantee payment with respect thereto; or (ii) make any payments of principal, interest, or premium on, or repay, repurchase or redeem, any debt securities or guarantees that rank on a parity with or junior in interest to the Debentures with certain specified exceptions in each case. Covenants and Other Requirements In secured funding transactions, there are trigger events that could cause the debt to be prepaid at an accelerated rate or could cause our usage of the credit facility to be discontinued. The triggers are generally based on the financial health and performance of the servicer as well as performance criteria for the pool of receivables, such as delinquency ratios, loss ratios, and commercial payment rates. During 2017 , there were no trigger events that resulted in the repayment of debt at an accelerated rate or impacted the usage of our credit facilities. Funding Facilities We utilize both committed credit facilities and other collateralized funding vehicles. The debt outstanding under our various funding facilities is included on our Consolidated Balance Sheet . As of December 31, 2017 , Ally Bank had exclusive access to $2.7 billion of funding capacity from committed credit facilities. Funding programs supported by the FRB and the FHLB complement Ally Bank’s private collateralized funding vehicles. The total capacity in our committed funding facilities is provided by banks through private transactions. The committed secured funding facilities can be revolving in nature and allow for additional funding during the commitment period, or they can be amortizing and not allow for any further funding after the closing date. At December 31, 2017 , all of our $11.9 billion of committed capacity was revolving. Our revolving facilities generally have an original tenor ranging from 364 days to two years. As of December 31, 2017 , we had $2.6 billion of committed funding capacity from revolving facilities with a remaining tenor greater than 364 days. Committed Funding Facilities Outstanding Unused capacity (a) Total capacity December 31, ($ in millions) 2017 2016 2017 2016 2017 2016 Bank funding Secured (b) $ 1,785 $ 3,250 $ 890 $ 350 $ 2,675 $ 3,600 Parent funding Secured 6,330 11,550 2,920 1,975 9,250 13,525 Unsecured — — — 1,250 — 1,250 Total committed facilities $ 8,115 $ 14,800 $ 3,810 $ 3,575 $ 11,925 $ 18,375 (a) Funding from committed secured facilities is available on request in the event excess collateral resides in certain facilities or the extent incremental collateral is available and contributed to the facilities. (b) Excludes off-balance sheet credit facility amounts.

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	12 Months Ended
	Dec. 31, 2017
Accounts Payable and Accrued Liabilities [Abstract]
Accounts Payable and Accrued Liabilities Disclosure [Text Block]	Accrued Expenses and Other Liabilities The components of accrued expenses and other liabilities were as follows. December 31, ($ in millions) 2017 2016 Accounts payable $ 746 $ 649 Employee compensation and benefits 248 232 Reserves for insurance losses and loss adjustment expenses 140 149 Fair value of derivative contracts in payable position (a) 41 95 Deferred revenue 32 56 Cash collateral received from counterparties 17 10 Other liabilities 556 546 Total accrued expenses and other liabilities $ 1,780 $ 1,737 (a) For additional information on derivative instruments and hedging activities, refer to Note 22 .

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Accumulated Other Comprehensive Loss The following table presents changes, net of tax, in each component of accumulated other comprehensive loss. ($ in millions) Unrealized (losses) gains on investment securities (a) Translation adjustments and net investment hedges (b) Cash flow hedges (b) Defined benefit pension plans Accumulated other comprehensive loss Balance at January 1, 2015 $ (21 ) $ 36 $ 7 $ (88 ) $ (66 ) 2015 net change (138 ) (27 ) 1 (1 ) (165 ) Balance at December 31, 2015 $ (159 ) $ 9 $ 8 $ (89 ) $ (231 ) 2016 net change (114 ) 5 — (1 ) (110 ) Balance at December 31, 2016 $ (273 ) $ 14 $ 8 $ (90 ) $ (341 ) 2017 net change 100 2 3 1 106 Balance at December 31, 2017 $ (173 ) $ 16 $ 11 $ (89 ) $ (235 ) (a) Represents the after-tax difference between the fair value and amortized cost of our available-for-sale securities portfolio. (b) For additional information on derivative instruments and hedging activities, refer to Note 22 . The following tables present the before- and after-tax changes in each component of accumulated other comprehensive (loss) income. Year ended December 31, 2017 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized gains arising during the period $ 237 $ (45 ) $ 192 Less: Net realized gains reclassified to income from continuing operations 105 (a) (13 ) (b) 92 Net change 132 (32 ) 100 Translation adjustments Net unrealized gains arising during the period 12 (4 ) 8 Net investment hedges (c) Net unrealized losses arising during the period (10 ) 4 (6 ) Cash flow hedges (c) Net unrealized gains arising during the period 5 (2 ) 3 Defined benefit pension plans Net unrealized gains arising during the period 1 — 1 Other comprehensive income $ 140 $ (34 ) $ 106 (a) Includes gains reclassified to other gain on investments, net in our Consolidated Statement of Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Consolidated Statement of Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 22 . Year ended December 31, 2016 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized gains arising during the period $ 13 $ 20 $ 33 Less: Net realized gains reclassified to income from continuing operations 185 (a) (38 ) (b) 147 Net change (172 ) 58 (114 ) Translation adjustments Net unrealized gains arising during the period 5 (2 ) 3 Less: Net realized losses reclassified to income from discontinued operations, net of tax (1 ) — (1 ) Net change 6 (2 ) 4 Net investment hedges (c) Net unrealized gains arising during the period 1 — 1 Defined benefit pension plans Net unrealized losses arising during the period (5 ) 2 (3 ) Less: Net realized losses reclassified to income from continuing operations (4 ) (d) 2 (b) (2 ) Net change (1 ) — (1 ) Other comprehensive loss $ (166 ) $ 56 $ (110 ) (a) Includes gains reclassified to other gain on investments, net in our Consolidated Statement of Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Consolidated Statement of Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 22 . (d) Includes gains reclassified to compensation and benefits expense in our Consolidated Statement of Income . Year ended December 31, 2015 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized losses arising during the period $ (65 ) $ 26 $ (39 ) Less: Net realized gains reclassified to income from continuing operations 155 (a) (56 ) (b) 99 Net change (220 ) 82 (138 ) Translation adjustments Net unrealized losses arising during the period (39 ) 13 (26 ) Less: Net realized gains reclassified to income from discontinued operations, net of tax 42 (20 ) 22 Net change (81 ) 33 (48 ) Net investment hedges (c) Net unrealized gains arising during the period 29 (11 ) 18 Less: Net realized losses reclassified to income from discontinued operations, net of tax (4 ) 1 (3 ) Net change 33 (12 ) 21 Cash flow hedges (c) Net unrealized gains arising during the period 2 (1 ) 1 Defined benefit pension plans Net unrealized gains (losses) arising during the period — — — Less: Net realized gains reclassified to income from continuing operations 1 (d) — (b) 1 Net change (1 ) — (1 ) Other comprehensive loss $ (267 ) $ 102 $ (165 ) (a) Includes gains reclassified to other gain on investments, net in our Consolidated Statement of Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Consolidated Statement of Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 22 . (d) Includes gains reclassified to compensation and benefits expense in our Consolidated Statement of Income .

Earnings per Common Share

Earnings per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Earnings per Common Share The following table presents the calculation of basic and diluted earnings per common share. Year ended December 31, ($ in millions, except per share data; shares in thousands) (a) 2017 2016 2015 Net income from continuing operations $ 926 $ 1,111 $ 897 Preferred stock dividends (b) — (30 ) (2,571 ) Net income (loss) from continuing operations attributable to common stockholders 926 1,081 (1,674 ) Income (loss) from discontinued operations, net of tax 3 (44 ) 392 Net income (loss) attributable to common stockholders $ 929 $ 1,037 $ (1,282 ) Basic weighted-average common shares outstanding (c) 453,704 481,105 482,873 Diluted weighted-average common shares outstanding (c) (d) 455,350 482,182 482,873 Basic earnings per common share Net income (loss) from continuing operations $ 2.04 $ 2.25 $ (3.47 ) Income (loss) from discontinued operations, net of tax 0.01 (0.09 ) 0.81 Net income (loss) $ 2.05 $ 2.15 $ (2.66 ) Diluted earnings per common share Net income (loss) from continuing operations $ 2.03 $ 2.24 $ (3.47 ) Income (loss) from discontinued operations, net of tax 0.01 (0.09 ) 0.81 Net income (loss) $ 2.04 $ 2.15 $ (2.66 ) (a) Figures in the table may not recalculate exactly due to rounding. Earnings per share is calculated based on unrounded numbers. (b) Preferred stock dividends for the year ended December 31, 2015, include $2,364 million recognized in connection with the partial redemption of the Series G Preferred Stock and the repurchase of the Series A Preferred Stock. These dividends represent an additional return to preferred stockholders calculated as the excess consideration paid over the carrying amount derecognized. (c) Includes shares related to share-based compensation that vested but were not yet issued for the years ended December 31, 2017 , 2016 , and 2015 . (d) Due to the antidilutive effect of the net loss from continuing operations attributable to common stockholders for the year ended December 31, 2015 , basic weighted-average common shares outstanding was used to calculate basic and diluted earnings per share.

Regulatory Capital and Other Re

Regulatory Capital and Other Regulatory Matters	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Regulatory Capital Requirements under Banking Regulations [Text Block]	Regulatory Capital and Other Regulatory Matters The FRB and other U.S. banking agencies have adopted risk-based and leverage capital standards that establish minimum capital-to-asset ratios for BHCs, like Ally, and depository institutions, like Ally Bank. The risk-based capital ratios are based on a banking organization’s risk-weighted assets (RWAs), which are generally determined under the standardized approach applicable to Ally and Ally Bank by (1) assigning on-balance sheet exposures to broad risk weight categories according to the counterparty or, if relevant, the guarantor or collateral (with higher risk weights assigned to categories of exposures perceived as representing greater risk), and (2) multiplying off-balance sheet exposures by specified credit conversion factors to calculate credit equivalent amounts and assigning those credit equivalent amounts to the relevant risk weight categories. The leverage ratio, in contrast, is based on an institution’s average unweighted on-balance sheet exposures. Ally and Ally Bank are subject to capital requirements issued by U.S. banking regulators that require us to maintain risk-based and leverage capital ratios above minimum levels. As of January 1, 2015, Ally and Ally Bank became subject to the rules implementing the 2010 Basel III capital framework in the United States (U.S. Basel III), which generally reflects higher capital requirements, capital buffers, and changes to regulatory capital definitions, deductions and adjustments, relative to the predecessor requirements implementing the Basel I capital framework in the United States. Certain aspects of U.S. Basel III, including the capital buffers and certain regulatory capital deductions, are subject to a phase-in period through December 31, 2018. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary action by regulators that, if undertaken, could have a direct material effect on the Consolidated Financial Statements or the results of operations and financial condition of Ally and Ally Bank. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, we and Ally Bank must meet specific capital guidelines that involve quantitative measures of capital, assets and certain off-balance sheet items. These measures and related classifications, which are used in the calculation of our risk-based and leverage capital ratios and those of Ally Bank, are also subject to qualitative judgments by the regulators about the components of capital, the risk-weightings of assets and other exposures, and other factors. The FRB also uses these ratios and guidelines as part of the capital planning and stress testing processes. In addition, in order for Ally to maintain its status as an FHC, Ally and its bank subsidiary, Ally Bank, must remain well capitalized and well managed, as defined under applicable laws. The well capitalized standard for insured depository institutions, such as Ally Bank, reflects the capital requirements under U.S. Basel III. Under U.S. Basel III, Ally and Ally Bank must maintain a minimum Common Equity Tier 1 risk-based capital ratio of 4.5% , a minimum Tier 1 risk-based capital ratio of 6% , and a minimum total risk-based capital ratio of 8% . In addition to these minimum risk-based capital ratios, Ally and Ally Bank are also subject to a Common Equity Tier 1 capital conservation buffer of more than 2.5% , subject to a phase-in period from January 1, 2016, through December 31, 2018. Failure to maintain the full amount of the buffer would result in restrictions on the ability of Ally and Ally Bank to make capital distributions, including dividend payments and stock repurchases and redemptions, and to pay discretionary bonuses to executive officers. U.S. Basel III also subjects Ally and Ally Bank to a minimum Tier 1 leverage ratio of 4% . U.S. Basel III also revised the eligibility criteria for regulatory capital instruments and provides for the phase-out of instruments that had previously been recognized as capital but that do not satisfy these criteria. For example, subject to certain exceptions (e.g., certain debt or equity issued to the U.S. government under the Emergency Economic Stabilization Act), trust preferred and other hybrid securities were excluded from a BHC’s Tier 1 capital as of January 1, 2016. Also, subject to a phase-in schedule, certain items are deducted from Common Equity Tier 1 capital under U.S. Basel III that had not previously been deducted from regulatory capital, and certain other deductions from regulatory capital have been modified. Among other things, U.S. Basel III requires significant investments in the common stock of unconsolidated financial institutions, mortgage servicing assets, and certain deferred tax assets that exceed specified individual and aggregate thresholds to be deducted from Common Equity Tier 1 capital. U.S. Basel III also revised the standardized approach for calculating RWAs by, among other things, modifying certain risk weights and the methods for calculating RWAs for certain types of assets and exposures. Ally and Ally Bank are subject to the U.S. Basel III standardized approach for counterparty credit risk, but not to the U.S. Basel III advanced approaches for credit risk or operational risk. Ally is also not subject to the U.S. market risk capital rule, which applies only to banking organizations with significant trading assets and liabilities. On November 21, 2017, the FRB and other U.S. banking agencies finalized a rule that extends the period for applying existing capital requirements to a targeted set of items that are subject to transition provisions under U.S. Basel III. Specifically, the rule indefinitely postpones certain remaining phase-in requirements for capital deductions and adjustments for investments in unconsolidated financial institutions, mortgage servicing assets, and certain deferred tax assets, none of which have a material impact on our regulatory capital position. In addition, on September 27, 2017, the FRB and other U.S. banking agencies released a proposal to simplify certain capital requirements, including the requirements related to the above-mentioned capital deductions and adjustments. The simplification proposal primarily applies to non-advanced approaches banking organizations such as Ally and Ally Bank. We are evaluating the effect that this proposal would have on our regulatory capital position, but we do not expect this will have a material impact on our regulatory capital position. In December 2017, the Basel Committee approved revisions to the global Basel III capital framework (commonly known as Basel IV), many of which—if adopted in the United States—could heighten regulatory capital standards even more. At this time, it is not clear how all of these proposals and revisions will be harmonized and finalized in the United States. On March 7, 2016, Ally Bank received approval from the FRB to become a state member bank. Ally Bank is now regulated by the FRB through the Federal Reserve Bank of Chicago, as well as the Utah Department of Financial Institutions (UDFI). As a requirement of FRB membership, we held $445 million of FRB stock at December 31, 2017 . In addition, in connection with the application for membership in the Federal Reserve System, Ally Bank made commitments to the FRB relating to capital, liquidity, and business plan requirements. These commitments were consistent with the prior requirements under the now-terminated Capital and Liquidity Maintenance Agreement with the Federal Deposit Insurance Corporation (FDIC), including the requirement to maintain capital at a level such that Ally Bank’s Tier 1 leverage ratio was at least 15% . On August 22, 2017, banking agencies lifted the capital, liquidity, and business plan commitments that Ally Bank had made in connection with its application for membership in the Federal Reserve System, including the commitment to maintain a Tier 1 leverage ratio of at least 15% . As a result of this development, during the third quarter of 2017, Ally Bank paid a dividend of $2.9 billion to Ally Financial Inc., which was utilized to reduce less cost-efficient borrowings and further enhance our funding profile. Additionally, a $400 million dividend was paid from Ally Bank to Ally Financial Inc. during the fourth quarter of 2017. Compliance with capital requirements is a strategic priority for Ally. We expect to be in compliance with all applicable requirements within the established timeframes. The following table summarizes our capital ratios under the U.S. Basel III capital framework. December 31, 2017 December 31, 2016 Required minimum (a) Well-capitalized minimum ( $ in millions ) Amount Ratio Amount Ratio Capital ratios Common Equity Tier 1 (to risk-weighted assets) Ally Financial Inc. $ 13,237 9.53 % $ 12,978 9.37 % 4.50 % (b) Ally Bank 17,059 15.04 17,888 16.70 4.50 6.50 % Tier 1 (to risk-weighted assets) Ally Financial Inc. $ 15,628 11.25 % $ 15,147 10.93 % 6.00 % 6.00 % Ally Bank 17,059 15.04 17,888 16.70 6.00 8.00 Total (to risk-weighted assets) Ally Financial Inc. $ 17,974 12.94 % $ 17,419 12.57 % 8.00 % 10.00 % Ally Bank 17,886 15.77 18,458 17.24 8.00 10.00 Tier 1 leverage (to adjusted quarterly average assets) (c) Ally Financial Inc. $ 15,628 9.53 % $ 15,147 9.54 % 4.00 % (b) Ally Bank 17,059 12.87 17,888 15.21 4.00 (d) 5.00 % (a) In addition to the minimum risk-based capital requirements for common equity Tier 1 capital, Tier 1 capital, and total capital ratios, Ally and Ally Bank were required to maintain a minimum capital conservation buffer of 1.25% and 0.625% at December 31, 2017, and December 31, 2016, respectively, which ultimately increases to 2.5% on January 1, 2019. (b) Currently, there is no ratio component for determining whether a BHC is “well-capitalized.” (c) Federal regulatory reporting guidelines require the calculation of adjusted quarterly average assets using a daily average methodology. (d) On August 22, 2017, banking agencies lifted the capital, liquidity, and business plan commitments that Ally Bank had made in connection with its application for membership in the Federal Reserve System, including the commitment to maintain a Tier 1 leverage ratio of at least 15% . Ally Bank now manages its capital and liquidity subject to applicable regulatory requirements. At December 31, 2017 , Ally and Ally Bank were “well-capitalized” and met all applicable capital requirements to which each was subject. Capital Planning and Stress Tests As a BHC with $50 billion or more of total consolidated assets, Ally is required to conduct semi-annual company-run stress tests, is subject to an annual supervisory stress test conducted by the FRB, and must submit a proposed capital plan to the FRB. Ally’s proposed capital plan must include an assessment of our expected uses and sources of capital and a description of all planned capital actions over a nine-quarter planning horizon, including any issuance of a debt or equity capital instrument, any dividend or other capital distribution, and any similar action that the FRB determines could have an impact on Ally’s capital. The proposed capital plan must also include a discussion of how Ally, under expected and stressful conditions, will maintain capital commensurate with its risks and above the minimum regulatory capital ratios, and serve as a source of strength to Ally Bank. The FRB will either object to Ally’s proposed capital plan, in whole or in part, or provide a notice of non-objection to Ally’s proposed capital plan, and must do so before Ally may take any capital action. In addition, even if the FRB does not object to our capital plan, Ally may be precluded from or limited in paying dividends or other capital distributions without the FRB’s approval under certain circumstances—for example, when we would not meet minimum regulatory capital ratios after giving effect to the distributions. As part of the 2017 Comprehensive Capital Analysis and Review (CCAR) process, on April 5, 2017, we submitted our 2017 capital plan and stress test results to the FRB. On June 23, 2017 , we publicly disclosed summary results of the stress test under the most severe scenario in accordance with regulatory requirements. On June 28, 2017, we received a non-objection to our capital plan from the FRB, including the proposed capital actions contained in our submission. The capital actions included a 50% increase in the quarterly cash dividend on common stock from $0.08 per share to $0.12 per share, and a 9% increase in our share repurchase program, which has been authorized by the Ally Board of Directors (the Board), permitting us to repurchase up to $760 million of our common stock from time to time from the third quarter of 2017 through the second quarter of 2018. In addition, we submitted to the FRB the results of our company-run mid-cycle stress test conducted under multiple macroeconomic scenarios and disclosed the results of this stress test under the most severe scenario on October 5, 2017, in accordance with regulatory requirements. Additionally, in connection with the 2017 CCAR process, on January 10, 2018 , the Board declared a quarterly cash dividend payment of $0.13 per share on all common stock, representing a $0.01 per share increase relative to the prior quarter. The following table presents information related to our common stock for each quarter since the commencement of our common stock repurchase programs and initiation of a quarterly cash dividend on common stock. ($ in millions, except per share data; shares in thousands) 4th quarter 2017 3rd quarter 2017 2nd quarter 2017 1st quarter 2017 4th quarter 2016 3rd quarter 2016 Common stock repurchased during period (a) Approximate dollar value $ 190 $ 190 $ 204 $ 169 $ 167 $ 159 Number of shares 7,033 8,507 10,485 8,097 8,745 8,298 Number of common shares outstanding Beginning of period 443,796 452,292 462,193 467,000 475,470 483,753 End of period 437,054 443,796 452,292 462,193 467,000 475,470 Cash dividends declared per common share (b) $ 0.12 $ 0.12 $ 0.08 $ 0.08 $ 0.08 $ 0.08 (a) Includes shares of common stock withheld to cover income taxes owed by participants in our share-based incentive plans. (b) On January 10, 2018 , the Board declared a quarterly cash dividend payment of $0.13 per share on all common stock, a $0.01 per share increase relative to our prior quarterly cash dividend. Refer to Note 32 for further information regarding this common stock dividend. Our ability to make capital distributions, including our ability to pay dividends or repurchase shares of our common stock, will continue to be subject to the FRB’s review of and non-objection to the actions that we propose each year in our annual capital plan. The amount and size of any future dividends and share repurchases will depend upon our results of operations, capital levels, future opportunities, consideration and approval by the Board, and other considerations including the degree of severity of stress scenarios assigned by the FRB as part of the CCAR process. In January 2017, the FRB amended the capital planning and stress testing rules, effective for the 2017 cycle and beyond. As a result of this amendment, the FRB may no longer object to the capital plan of a large and noncomplex BHC, like Ally, on the basis of qualitative deficiencies in its capital planning process. Instead, the qualitative assessment of Ally’s capital planning process is now conducted outside of CCAR through the supervisory review process. The amendment also decreased the de minimis threshold for the amount of capital that Ally could distribute to stockholders outside of an approved capital plan without seeking prior approval of the FRB, and modified Ally’s reporting requirements to reduce unnecessary burdens. Depository Institutions Ally Bank is a member of the Federal Reserve System and is subject to regulation, supervision, and examination by the FRB and the UDFI. Ally Bank’s deposits are insured by the FDIC, and Ally Bank is required to file periodic reports with the FDIC concerning its financial condition. Total assets of Ally Bank were $137.4 billion and $123.5 billion at December 31, 2017, and 2016, respectively. Federal and Utah law place a number of conditions, restrictions, and limitations on dividends and other capital distributions that may be paid by Ally Bank to Ally. Dividends or other distributions made by Ally Bank to Ally were $3.3 billion in 2017. No dividends were paid in 2016. The FRB requires banks to maintain minimum average reserve balances. The amount of the required reserve balance for Ally Bank was $370 million and $149 million at December 31, 2017, and 2016, respectively. Ally Bank is required to satisfy regulatory net worth requirements. Failure to meet minimum capital requirements can initiate certain mandatory actions by federal, state, and foreign agencies that could have a material effect on our results of operations and financial condition. Ally Bank was in compliance with these requirements at December 31, 2017. Insurance Companies Certain of our Insurance operations are subject to certain minimum aggregate capital requirements, net asset and dividend restrictions under applicable state and foreign insurance laws, and the rules and regulations promulgated by various U.S. and foreign regulatory agencies. Under various state and foreign insurance regulations, dividend distributions may be made only from statutory unassigned surplus, with approvals required from the regulatory authorities for dividends in excess of certain statutory limitations. At December 31, 2017, the maximum dividend that could be paid by the U.S. insurance subsidiaries over the next twelve months without prior statutory approval was $87 million .

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Derivative Instruments and Hedging Activities We enter into interest rate, foreign-currency, and equity swaps, futures, forwards, and options in connection with our market risk management activities. Derivative instruments are used to manage interest rate risk relating to specific groups of assets and liabilities, including available-for-sale securities, automotive loan assets, and debt. We use foreign exchange contracts to mitigate foreign-currency risk associated with foreign-currency-denominated debt, foreign exchange transactions, and our net investment in foreign subsidiaries. In addition, we also enter into equity option contracts to manage our exposure to the equity markets. Our primary objective for utilizing derivative financial instruments is to manage interest rate risk associated with our fixed- and variable-rate assets and liabilities, foreign exchange risks related to our foreign-currency denominated assets and liabilities, and market risks related to our investment portfolio and certain of our executive share-based compensation plans. Interest Rate Risk We monitor our mix of fixed- and variable-rate assets and liabilities. We may enter into interest rate swaps, forwards, futures, options, and swaptions to achieve our desired mix of fixed- and variable-rate assets and liabilities. We execute interest rate swaps, forwards, futures, and options to modify our exposure to interest rate risk by converting certain fixed-rate instruments to a variable-rate and certain variable-rate instruments to a fixed-rate. We use a mix of both derivatives that qualify for hedge accounting treatment and economic hedges. Derivatives qualifying for hedge accounting can include receive-fixed swaps designated as fair value hedges of specific fixed-rate unsecured debt obligations, receive-fixed swaps designated as fair value hedges of specific fixed-rate FHLB advances, fair value hedges of U.S. Treasury positions within our available-for-sale portfolio, and pay-fixed swaps designated as fair value hedges of specific portfolios of fixed-rate held-for-investment retail automotive loan assets. Other derivatives qualifying for hedge accounting consist of pay-fixed swaps designated as cash flow hedges of the expected future cash flows in the form of interest payments on certain variable-rate borrowings. As of December 31, 2017 , there were no open hedges related to our held-for-investment retail automotive loan assets or U.S. Treasury positions. We may also execute economic hedges, which consist of interest rate swaps and interest rate caps held to mitigate interest rate risk associated with our debt portfolio. We may also use interest rate swaps to economically hedge our net fixed-versus-variable interest rate exposure. We enter into economic hedges in the form of short-dated, exchange-traded Eurodollar futures to hedge the interest rate exposure of our fixed-rate automotive loans, as well as forwards, options, and swaptions to economically hedge our net fixed-versus-variable interest rate exposure. We also enter into interest rate lock commitments and forward-sale commitments that are executed as part of our mortgage business that meet the accounting definition of a derivative. Foreign Exchange Risk We enter into derivative financial instrument contracts to mitigate the risk associated with variability in cash flows related to our various foreign-currency exposures. We enter into foreign-currency forwards with external counterparties as net investment hedges of foreign exchange exposure on our investments in foreign subsidiaries. Our equity is impacted by the cumulative translation adjustments resulting from the translation of foreign subsidiary results; this impact is reflected in our accumulated other comprehensive loss. We also periodically enter into foreign-currency forwards to economically hedge our foreign-denominated debt, our centralized lending program, and foreign-denominated third-party loans. These foreign currency forwards that are used as economic hedges are recorded at fair value with changes recorded as income offsetting the gains and losses on the associated foreign-currency transactions. Market Risk We enter into equity options to economically hedge our exposure to the equity markets. We purchase options to assume a long position on certain equities and write options to assume a short position. We did not hold any equity options at December 31, 2017 . Counterparty Credit Risk Derivative financial instruments contain an element of credit risk if counterparties are unable to meet the terms of the agreements. Credit risk associated with derivative financial instruments is measured as the net replacement cost should the counterparties that owe us under the contract completely fail to perform under the terms of those contracts, assuming no recoveries of underlying collateral as measured by the market value of the derivative financial instrument. To mitigate the risk of counterparty default, we maintain collateral agreements with certain counterparties. The agreements generally require both parties to post collateral in the event the fair values of the derivative financial instruments meet posting thresholds established under the agreements. In the event that either party defaults on the obligation, the secured party may seize the collateral. Generally, our collateral arrangements are bilateral such that we and the counterparty post collateral for the value of our total obligation to each other. Contractual terms provide for standard and customary exchange of collateral based on changes in the market value of the outstanding derivatives. The securing party posts additional collateral when their obligation rises or removes collateral when it falls. These payments are characterized as collateral for over-the-counter (OTC) derivatives. We execute certain derivatives such as interest rate swaps with clearinghouses, which requires us to post collateral. For these clearinghouse derivatives, these payments are recognized as settlements rather than collateral. Certain derivative instruments contain provisions that require us to either post additional collateral or immediately settle any outstanding liability balances upon the occurrence of a specified credit risk-related event. No such specified credit risk related events occurred during the years ended December 31, 2017, and 2016. We placed cash collateral totaling $20 million and securities collateral totaling $97 million at December 31, 2017 , and $122 million and $72 million at December 31, 2016 , respectively, in accounts maintained by counterparties. This amount primarily relates to collateral posted to support our derivative positions. This amount also excludes cash and securities pledged as collateral under repurchase agreements. At December 31, 2017 , and December 31, 2016 , we placed cash collateral totaling $10 million and $45 million , respectively, with counterparties under collateral arrangements associated with repurchase agreements. Refer to Note 16 for details on the repurchase agreements. The receivables for cash collateral placed are included on our Consolidated Balance Sheet in other assets. We received cash collateral from counterparties totaling $17 million and $10 million at December 31, 2017 , and December 31, 2016, respectively, primarily to support these derivative positions. This amount also excludes cash and securities pledged as collateral under repurchase agreements. At December 31, 2017 , we received cash collateral totaling $1 million from counterparties under collateral arrangements associated with repurchase agreements. Refer to Note 16 for details on the repurchase agreements. The payables for cash collateral received are included on our Consolidated Balance Sheet in accrued expenses and other liabilities. In certain circumstances, we receive or post securities as collateral with counterparties. We do not record collateral received on our Consolidated Balance Sheet unless certain conditions are met. At December 31, 2017 , and December 31, 2016 , we received noncash collateral of $2 million and $6 million , respectively. Included in these amounts is noncash collateral where we have been granted the right to sell or pledge the underlying assets. We have not sold or pledged any of the noncash collateral received under these agreements. Balance Sheet Presentation The following table summarizes the fair value amounts of derivative instruments reported on our Consolidated Balance Sheet . The fair value amounts are presented on a gross basis, are segregated by derivatives that are designated and qualifying as hedging instruments or those that are not, and are further segregated by type of contract within those two categories. Derivative contracts in a receivable and payable position exclude open trade equity on derivatives cleared through central clearing counterparties. Any associated collateral exchanged with our central clearing counterparties are treated as settlements of the derivative exposure, rather than collateral. Such payments are recognized as settlements of the derivatives contracts in a receivable and payable position on our Consolidated Balance Sheet. Notional amounts are reference amounts from which contractual obligations are derived and are not recorded on the balance sheet. In our view, derivative notional is not an accurate measure of our derivative exposure when viewed in isolation from other factors, such as market rate fluctuations and counterparty credit risk. 2017 2016 Derivative contracts in a Notional amount Derivative contracts in a Notional amount December 31, ($ in millions) receivable position (a) payable position (b) receivable position (a) payable position (b) Derivatives designated as accounting hedges Interest rate contracts Swaps $ — $ — $ 6,915 $ 19 $ 21 $ 4,731 Foreign exchange contracts Forwards — 1 136 1 — 171 Total derivatives designated as accounting hedges — 1 7,051 20 21 4,902 Derivatives not designated as accounting hedges Interest rate contracts Swaps — — — — — 137 Futures and forwards — — 23 — — — Written options 1 39 8,327 — 73 14,518 Purchased options 38 — 8,237 73 — 14,517 Total interest rate risk 39 39 16,587 73 73 29,172 Foreign exchange contracts Futures and forwards — 1 124 1 — 92 Total foreign exchange risk — 1 124 1 — 92 Equity contracts Written options — — — — 1 — Purchased options — — — 1 — — Total equity risk — — — 1 1 — Total derivatives not designated as accounting hedges 39 40 16,711 75 74 29,264 Total derivatives $ 39 $ 41 $ 23,762 $ 95 $ 95 $ 34,166 (a) Derivative contracts in a receivable position are classified as other assets on the Consolidated Balance Sheet , and include accrued interest of $0 million and $7 million at December 31, 2017 , and December 31, 2016 , respectively. (b) Derivative contracts in a liability position are classified as accrued expenses and other liabilities on the Consolidated Balance Sheet , and include accrued interest of $0 million and $1 million at December 31, 2017 , and December 31, 2016 , respectively. Statement of Income Presentation The following table summarizes the location and amounts of gains and losses on derivative instruments reported in our Consolidated Statement of Income . Year ended December 31, ($ in millions) 2017 2016 2015 Derivatives qualifying for hedge accounting Gain (loss) recognized in earnings on derivatives Interest rate contracts Interest and fees on finance receivables and loans (a) $ 1 $ (2 ) $ (9 ) Interest and dividends on investment securities 1 — — Interest on long-term debt (b) (25 ) 65 35 (Loss) gain recognized in earnings on hedged items Interest rate contracts Interest and fees on finance receivables and loans (c) (3 ) — 39 Interest and dividends on investment securities (1 ) — — Interest on long-term debt (d) 30 (70 ) (30 ) Total derivatives qualifying for hedge accounting 3 (7 ) 35 Derivatives not designated as accounting hedges Gain (loss) recognized in earnings on derivatives Interest rate contracts Gain on mortgage and automotive loans, net 1 — (2 ) Other income, net of losses (3 ) — (17 ) Total interest rate contracts (2 ) — (19 ) Foreign exchange contracts (e) Interest on long-term debt — (2 ) (139 ) Other income, net of losses (7 ) 1 12 Total foreign exchange contracts (7 ) (1 ) (127 ) Equity contracts Compensation and benefits expense — — (10 ) Total equity contracts — — (10 ) Loss recognized in earnings on derivatives $ (6 ) $ (8 ) $ (121 ) (a) Amounts exclude losses related to interest for qualifying accounting hedges of retail automotive loans held-for-investment, which are primarily offset by the fixed coupon payments of the loans. The losses were $1 million , $18 million , and $64 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively. (b) Amounts exclude gains related to interest for qualifying accounting hedges of unsecured debt, which are primarily offset by the fixed coupon payment on the long-term debt. The gains were $24 million , $40 million , and $97 million for the years ended December 31, 2017 , 2016, and 2015, respectively. Amounts also exclude gains related to interest for qualifying accounting hedges of secured debt (FHLB advances), which are primarily offset by the fixed coupon payment on the long-term debt. The gains were $3 million , $5 million , and $1 million for the years ended December 31, 2017 , 2016, and 2015, respectively. (c) Amounts exclude losses related to amortization of deferred loan basis adjustments on the de-designated hedged item of $21 million , $20 million , and $8 million for the years ended December 31, 2017 , 2016 , and 2015, respectively. (d) Amounts exclude gains related to amortization of deferred debt basis adjustments on the de-designated hedged item of $77 million , $84 million , and $73 million for the years ended December 31, 2017 , 2016 , and 2015, respectively. Amounts also exclude losses related to amortization of deferred debt basis adjustments (FHLB advances) on the de-designated hedge item of $2 million for the year ended December 31, 2017 . (e) Amounts exclude gains and losses related to the revaluation of the related foreign-denominated debt or receivable. Gains of $9 million , $0 million , and $132 million were recognized for the years ended December 31, 2017 , 2016 , and 2015, respectively. The following table summarizes derivative instruments used in cash flow and net investment hedge accounting relationships. Year ended December 31, ($ in millions) 2017 2016 2015 Cash flow hedges Interest rate contracts Gain recognized in other comprehensive loss $ 5 $ — $ 2 Net investment hedges Foreign exchange contracts Loss reclassified from accumulated other comprehensive loss to income from discontinued operations, net $ — $ — $ (4 ) (Loss) gain recognized in other comprehensive loss (a) $ (10 ) $ 1 $ 33 (a) The amounts represent the effective portion of net investment hedges. There are offsetting amounts recognized in accumulated other comprehensive loss related to the revaluation of the related net investment in foreign operations, including the tax impacts of the hedge and related net investment, as disclosed separately in Note 19 . There were gains of $12 million and $4 million for the years ended December 31, 2017 , and 2016 , respectively, and losses of $59 million for the year ended December 31, 2015.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes The significant components of income tax expense from continuing operations were as follows. Year ended December 31, ($ in millions) 2017 2016 2015 Current income tax (benefit) expense U.S. federal $ (17 ) $ — $ — Foreign 6 8 6 State and local 53 9 3 Total current expense 42 17 9 Deferred income tax expense (benefit) U.S. federal 566 423 454 Foreign — — 1 State and local (27 ) 30 32 Total deferred expense 539 453 487 Total income tax expense from continuing operations $ 581 $ 470 $ 496 A reconciliation of income tax expense from continuing operations with the amounts at the statutory U.S. federal income tax rate is shown in the following table. Year ended December 31, ($ in millions) 2017 2016 2015 Statutory U.S. federal tax expense $ 527 $ 553 $ 488 Change in tax resulting from Valuation allowance change, excluding expirations (49 ) 51 (25 ) Tax credits, excluding expirations (12 ) (15 ) (13 ) State and local income taxes, net of federal income tax benefit (a) 7 35 38 Nondeductible expenses 4 7 14 Changes in unrecognized tax expenses (benefits) (b) 1 (161 ) (5 ) Other, net (16 ) — (1 ) Total income tax expense from continuing operations exclusive of tax reform impacts 462 470 496 Tax law enactment 119 — — Total income tax expense from continuing operations inclusive of tax reform impacts $ 581 $ 470 $ 496 (a) Amount for 2017 includes state deferred tax adjustments primarily offset in the valuation allowance change caption. (b) Amount for 2016 is primarily the result of a U.S. tax reserve release in the second quarter of 2016 related to a prior-year federal return. On December 22, 2017, the Tax Act was enacted. The Tax Act makes broad and complex changes to the U.S. tax code that impact our year ended December 31, 2017, and forward, including, but not limited to (1) reducing the U.S. federal corporate tax rate from 35 percent to 21 percent; (2) allowing bonus depreciation for full expensing of qualified property; (3) eliminating the corporate alternative minimum tax (AMT) and changing how existing AMT credit carryforwards can be realized; and (4) eliminating the deduction for FDIC premiums. As a result of the Tax Act, we recorded net tax expense of $119 million due to an increase in the valuation allowance of $549 million primarily attributable to foreign tax credit carryforwards and a decrease to the value of the low income housing tax credit investments of $7 million , offset by adjustments to deferred tax assets and liabilities of $421 million and an increase to income tax receivable of $16 million due to refundable AMT credit carryforwards. As of December 31, 2017, we have completed our accounting for the income tax effects of the Tax Act enactment. While the Tax Act negatively impacted earnings in the fourth quarter of 2017, the lower corporate tax rate is expected to be a significant ongoing benefit to Ally. For the year ended December 31, 2017 , consolidated income tax expense from continuing operations was largely driven by tax attributable to pretax earnings for the year increased by the aforementioned Tax Act enactment charge, partially offset by changes to our valuation allowance balances related to capital-in-nature deferred tax assets and foreign tax credit carryforwards. For the year ended December 31, 2016 , consolidated income tax expense from continuing operations was largely driven by tax attributable to pretax earnings for the year and the establishment of a valuation allowance on capital loss carryforwards, offset by a reduction in the liability for unrecognized tax benefits that resulted from the completion of a U.S. federal audit related to a prior tax year. For the year ended December 31, 2015 , consolidated income tax expense from continuing operations was largely driven by tax attributable to pretax earnings for the year, offset by tax benefits recognized from the release of our valuation allowance on capital loss carryforwards utilized against current year capital gains. As of each reporting date, we consider existing evidence, both positive and negative, that could impact our view with regard to future realization of deferred tax assets. We continue to believe it is more likely than not that the benefit for certain foreign tax credit carryforwards, state net operating loss carryforwards, and state capital loss carryforwards will not be realized. In recognition of this risk, we continue to provide a partial valuation allowance on the deferred tax assets relating to these carryforwards. The significant components of deferred tax assets and liabilities are reflected in the following table. December 31, ($ in millions) 2017 2016 Deferred tax assets Tax credit carryforwards $ 2,002 $ 1,987 Adjustments to loan value 450 546 Tax loss carryforwards 302 936 State and local taxes 200 162 Unearned insurance premiums 85 141 Hedging transactions 49 123 Other 108 208 Gross deferred tax assets 3,196 4,103 Valuation allowance (1,123 ) (646 ) Deferred tax assets, net of valuation allowance 2,073 3,457 Deferred tax liabilities Lease transactions 1,212 1,789 Deferred acquisition costs 269 424 Debt transactions 95 161 Other 44 107 Gross deferred tax liabilities 1,620 2,481 Net deferred tax assets (a) (b) $ 453 $ 976 (a) Amounts include $461 million and $994 million of net deferred tax assets included in other assets on our Consolidated Balance Sheet for tax jurisdictions in a total net deferred tax asset position and $8 million and $18 million included in accrued expenses and other liabilities on our Consolidated Balance Sheet for tax jurisdictions in a total net deferred tax liability position at December 31, 2017 , and 2016 , respectively. (b) Amount for 2017 decreased $128 million due to the Tax Act, which is composed of adjustments to our deferred tax assets and liabilities of $421 million and an increase in the valuation allowance of $549 million primarily attributable to foreign tax credit carryforwards. The additional decrease of $395 million primarily resulted from the monetization of deferred tax assets against taxes generated from pretax earnings for the year, offset by deferred tax asset builds stemming from tax credit generation, including low income housing tax credits. The following table summarizes net deferred tax assets including related valuation allowances at December 31, 2017 . ($ in millions) Deferred tax asset (liability) Valuation allowance Net deferred tax asset (liability) Years of expiration Tax credit carryforwards Foreign tax credits $ 1,772 $ (983 ) $ 789 2018–2027 General business credits 213 — 213 2031–2037 Alternative minimum tax (AMT) credits 17 — 17 n/a Total tax credit carryforwards 2,002 (983 ) 1,019 Tax loss carryforwards Net operating losses — federal 302 — 302 2027–2036 Net operating losses — state 253 (a) (135 ) 118 2018–2037 Capital losses — state 2 (a) (2 ) — 2018–2027 Total tax loss carryforwards 557 (137 ) 420 Other net deferred tax liabilities (b) (983 ) (3 ) (986 ) n/a Net deferred tax assets $ 1,576 $ (1,123 ) (c) $ 453 (a) State net operating loss and capital loss carryforwards are included in the state and local taxes and other liabilities totals disclosed in our deferred inventory table above. (b) Other net deferred tax liabilities are composed of other liabilities and assets. A portion of these assets are subject to a valuation allowance. (c) Includes the valuation allowance impact of the Tax Act of $549 million primarily related to foreign tax credit carryforwards. This valuation allowance impact of the Tax Act is disclosed in the tax law enactment caption in the reconciliation of income tax expense table above. As part of the Tax Act, a Deemed Repatriation Transition Tax (the Transition Tax) was enacted. The Transition Tax is a tax on previously-untaxed accumulated and current earnings and profits (E&P) of certain foreign subsidiaries. To determine the amount of the Transition Tax, we had to determine, in addition to other factors, the amount of post-1986 E&P of the relevant subsidiaries, as well as the amount of non-U.S. income taxes paid on such earnings. Given our consolidated accumulated E&P deficit position, we determined there is no liability related to the Transition Tax. As of December 31, 2017 , we continue to not assert that foreign earnings are indefinitely reinvested outside of the United States. Deferred tax liabilities for incremental U.S. tax that stem from temporary differences related to investments in foreign subsidiaries or corporate joint ventures are negligible and have been recognized as of December 31, 2017. The following table provides a reconciliation of the beginning and ending amount of unrecognized tax benefits. ($ in millions) 2017 2016 2015 Balance at January 1, $ 14 $ 185 $ 191 Additions based on tax positions related to the current year — — — Additions for tax positions of prior years 3 12 7 Reductions for tax positions of prior years (1 ) — — Settlements — (182 ) (10 ) Expiration of statute of limitations (1 ) (1 ) (3 ) Balance at December 31, $ 15 $ 14 $ 185 Included in the unrecognized tax benefits balances are some items, the recognition of which would not affect the effective tax rate, such as the tax effect of certain temporary differences and the portion of gross state unrecognized tax benefits that would be offset by the tax benefit of the associated federal deduction. At December 31, 2017 , 2016 , and 2015 , the balance of unrecognized tax benefits that, if recognized, would affect our effective tax rate were $12 million , $9 million , and $177 million , respectively. We recognize accrued interest and penalties related to uncertain income tax positions in interest expense and other operating expenses, respectively. The cumulative accrued balance for interest and penalties was less than $1 million at December 31, 2017 , $1 million at December 31, 2016 , and $2 million at December 31, 2015 . For each of the years ended December 31, 2017 , 2016 , and 2015 , interest and penalties of $1 million or less were accrued. It is reasonably possible that the unrecognized tax benefits will decrease by up to $15 million over the next twelve months if certain tax matters ultimately settle with the applicable taxing jurisdiction. We file tax returns in the U.S. federal jurisdiction and various states and foreign jurisdictions. Our most significant operations remaining following our divestitures of various international operations are the United States and Canada. The oldest tax years that remain subject to examination for those jurisdictions are 2012 and 2011, respectively.

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Disclosures [Text Block]	Fair Value Fair Value Measurements For purposes of this disclosure, fair value is defined as the exchange price that would be received to sell an asset or paid to transfer a liability (exit price) in the principal or most advantageous market in an orderly transaction between market participants at the measurement date under current market conditions. Fair value is based on the assumptions we believe market participants would use when pricing an asset or liability. Additionally, entities are required to consider all aspects of nonperformance risk, including the entity’s own credit standing, when measuring the fair value of a liability. GAAP specifies a three-level hierarchy that is used when measuring and disclosing fair value. The fair value hierarchy gives the highest priority to quoted prices available in active markets (i.e., observable inputs) and the lowest priority to data lacking transparency (i.e., unobservable inputs). An instrument’s categorization within the fair value hierarchy is based on the lowest level of significant input to its valuation. The following is a description of the three hierarchy levels. Level 1 Inputs are quoted prices in active markets for identical assets or liabilities at the measurement date. Additionally, the entity must have the ability to access the active market, and the quoted prices cannot be adjusted by the entity. Level 2 Inputs are other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs include quoted prices in active markets for similar assets or liabilities; quoted prices in inactive markets for identical or similar assets or liabilities; or inputs that are observable or can be corroborated by observable market data by correlation or other means for substantially the full term of the assets or liabilities. Level 3 Unobservable inputs are supported by little or no market activity. The unobservable inputs represent management’s best assumptions of how market participants would price the assets or liabilities. Generally, Level 3 assets and liabilities are valued using pricing models, discounted cash flow methodologies, or similar techniques that require significant judgment or estimation. Transfers Transfers into or out of any hierarchy level are recognized at the end of the reporting period in which the transfer occurred. Following are descriptions of the valuation methodologies used to measure material assets and liabilities at fair value and details of the valuation models, key inputs to those models, and significant assumptions utilized. • Available-for-sale securities — All classes of available-for-sale securities are carried at fair value based on observable market prices, when available. If observable market prices are not available, our valuations are based on internally developed discounted cash flow models (an income approach) that use a market-based discount rate and consider recent market transactions, experience with similar securities, current business conditions, and analysis of the underlying collateral, as available. To estimate cash flows, we are required to utilize various significant assumptions including market observable inputs (e.g., forward interest rates) and internally developed inputs (including prepayment speeds, delinquency levels, and credit losses). • Interests retained in financial asset sales — Includes certain noncertificated interests retained from the sale of automotive finance receivables. Due to inactivity in the market, valuations are based on internally developed discounted cash flow models (an income approach) that use a market-based discount rate; therefore, we classified these assets as Level 3. The valuation considers recent market transactions, experience with similar assets, current business conditions, and analysis of the underlying collateral, as available. To estimate cash flows, we utilize various significant assumptions, including market observable inputs (e.g., forward interest rates) and internally developed inputs (e.g., prepayment speeds, delinquency levels, and credit losses). • Derivative instruments — We enter into a variety of derivative financial instruments as part of our risk management strategies. Certain of these derivatives are exchange traded, such as Eurodollar futures, options of Eurodollar futures, and equity options. To determine the fair value of these instruments, we utilize the quoted market prices for the particular derivative contracts; therefore, we classified these contracts as Level 1. We also execute OTC and centrally-cleared derivative contracts, such as interest rate swaps, swaptions, foreign-currency denominated forward contracts, prepaid equity forward contracts, caps, floors, and agency to-be-announced securities. For OTC contracts, we utilize third-party-developed valuation models that are widely accepted in the market to value these OTC derivative contracts. The specific terms of the contract and market observable inputs (such as interest rate forward curves, interpolated volatility assumptions, or equity pricing) are used in the model. We classified these OTC derivative contracts as Level 2 because all significant inputs into these models were market observable. For centrally-cleared contracts, we utilize unadjusted prices obtained from the clearing house as the basis for valuation, and they are also classified as Level 2. We also enter into interest rate lock commitments and forward-sale commitments that are executed as part of our mortgage business, certain of which meet the accounting definition of a derivative and therefore are recorded as derivatives on our Consolidated Balance Sheet . Because these derivatives are valued using internal pricing models with unobservable inputs, they are classified as Level 3. We are required to consider all aspects of nonperformance risk, including our own credit standing, when measuring fair value of a liability. We reduce credit risk on the majority of our derivatives by entering into legally enforceable agreements that enable the posting and receiving of collateral associated with the fair value of our derivative positions on an ongoing basis. In the event that we do not enter into legally enforceable agreements that enable the posting and receiving of collateral, we will consider our credit risk and the credit risk of our counterparties in the valuation of derivative instruments through a credit valuation adjustment (CVA), if warranted. The CVA calculation utilizes the credit default swap spreads of the counterparty. Recurring Fair Value The following tables display the assets and liabilities measured at fair value on a recurring basis including financial instruments elected for the fair value option. We often economically hedge the fair value change of our assets or liabilities with derivatives and other financial instruments. The tables below display the hedges separately from the hedged items; therefore, they do not directly display the impact of our risk management activities. Recurring fair value measurements December 31, 2017 ($ in millions) Level 1 Level 2 Level 3 Total Assets Investment securities Available-for-sale securities Debt securities U.S. Treasury $ 1,777 $ — $ — $ 1,777 U.S. States and political subdivisions — 854 — 854 Foreign government 8 146 — 154 Agency mortgage-backed residential — 14,291 — 14,291 Mortgage-backed residential — 2,494 — 2,494 Mortgage-backed commercial — 541 — 541 Asset-backed — 936 — 936 Corporate debt — 1,256 — 1,256 Total debt securities 1,785 20,518 — 22,303 Equity securities (a) 518 — — 518 Total available-for-sale securities 2,303 20,518 — 22,821 Mortgage loans held-for-sale (b) — — 13 13 Interests retained in financial asset sales — — 5 5 Derivative contracts in a receivable position Interest rate — 38 1 39 Total derivative contracts in a receivable position — 38 1 39 Total assets $ 2,303 $ 20,556 $ 19 $ 22,878 Liabilities Accrued expenses and other liabilities Derivative contracts in a payable position Interest rate $ — $ (39 ) $ — $ (39 ) Foreign currency — (2 ) — (2 ) Total derivative contracts in a payable position — (41 ) — (41 ) Total liabilities $ — $ (41 ) $ — $ (41 ) (a) Our investment in any one industry did not exceed 14% . (b) Carried at fair value due to fair value option elections. Recurring fair value measurements December 31, 2016 ($ in millions) Level 1 Level 2 Level 3 Total Assets Investment securities Available-for-sale securities Debt securities U.S. Treasury $ 1,620 $ — $ — $ 1,620 U.S. States and political subdivisions — 782 — 782 Foreign government 11 151 — 162 Agency mortgage-backed residential — 10,290 — 10,290 Mortgage-backed residential — 2,097 — 2,097 Mortgage-backed commercial — 537 — 537 Asset-backed — 1,400 — 1,400 Corporate debt — 1,443 — 1,443 Total debt securities 1,631 16,700 — 18,331 Equity securities (a) 595 — — 595 Total available-for-sale securities 2,226 16,700 — 18,926 Other assets Interests retained in financial asset sales — — 29 29 Derivative contracts in a receivable position Interest rate — 92 — 92 Foreign currency — 2 — 2 Other 1 — — 1 Total derivative contracts in a receivable position 1 94 — 95 Total assets $ 2,227 $ 16,794 $ 29 $ 19,050 Liabilities Accrued expenses and other liabilities Derivative contracts in a payable position Interest rate $ — $ (94 ) $ — $ (94 ) Other (1 ) — — (1 ) Total derivative contracts in a payable position (1 ) (94 ) — (95 ) Total liabilities $ (1 ) $ (94 ) $ — $ (95 ) (a) Our investment in any one industry did not exceed 14% . The following tables present the reconciliation for all Level 3 assets and liabilities measured at fair value on a recurring basis. We often economically hedge the fair value change of our assets or liabilities with derivatives and other financial instruments. The Level 3 items presented below may be hedged by derivatives and other financial instruments that are classified as Level 1 or Level 2. Thus, the following tables do not fully reflect the impact of our risk management activities. Level 3 recurring fair value measurements Net realized/unrealized gains Fair value at December 31, 2017 Net unrealized gains included in earnings still held at December 31, 2017 ($ in millions) Fair value at Jan. 1, 2017 included in earnings included in OCI Purchases Sales Issuances Settlements Assets Mortgage loans held-for-sale (a) $ — $ 2 (b) $ — $ 137 $ (126 ) $ — $ — $ 13 $ — Other assets Interests retained in financial asset sales 29 1 (c) — — 8 — (33 ) 5 — Derivative assets — 1 (b) — — — — — 1 1 Total assets $ 29 $ 4 $ — $ 137 $ (118 ) $ — $ (33 ) $ 19 $ 1 (a) Carried at fair value due to fair value option elections. (b) Reported as gain on mortgage and automotive loans, net, in the Consolidated Statement of Income (c) Reported as other income, net of losses, in the Consolidated Statement of Income . Level 3 recurring fair value measurements Fair value at Jan. 1, 2016 Net realized/unrealized gains Purchases Sales Issuances Settlements Fair value at December 31, 2016 Net unrealized gains included in earnings still held at December 31, 2016 ($ in millions) included in earnings included in OCI Assets Other assets Interests retained in financial asset sales $ 40 $ 4 (a) $ — $ — $ 9 $ — $ (24 ) $ 29 $ — Total assets $ 40 $ 4 $ — $ — $ 9 $ — $ (24 ) $ 29 $ — (a) Reported as other income, net of losses, in the Consolidated Statement of Income . Nonrecurring Fair Value We may be required to measure certain assets and liabilities at fair value from time to time. These periodic fair value measures typically result from the application of lower-of-cost or fair value accounting or certain impairment measures. These items would constitute nonrecurring fair value measures. The following tables display the assets and liabilities measured at fair value on a nonrecurring basis. Nonrecurring fair value measurements Lower-of-cost or fair value or valuation reserve allowance Total gain (loss) included in earnings for the year ended December 31, 2017 ($ in millions) Level 1 Level 2 Level 3 Total Assets Loans held-for-sale, net $ — $ — $ 77 $ 77 $ — n/m (a) Commercial finance receivables and loans, net (b) Automotive — — 20 20 (3 ) n/m (a) Other — — 22 22 (12 ) n/m (a) Total commercial finance receivables and loans, net — — 42 42 (15 ) n/m (a) Other assets Repossessed and foreclosed assets (c) — — 14 14 (1 ) n/m (a) Other — — 3 3 — n/m (a) Total assets $ — $ — $ 136 $ 136 $ (16 ) n/m n/m = not meaningful (a) We consider the applicable valuation or loan loss allowance to be the most relevant indicator of the impact on earnings caused by the fair value measurement. Accordingly, the table above excludes total gains and losses included in earnings for these items. The carrying values are inclusive of the respective valuation or loan loss allowance. (b) Represents the portion of the portfolio specifically impaired during 2017. The related valuation allowance represents the cumulative adjustment to fair value of those specific receivables. (c) The allowance provided for repossessed and foreclosed assets represents any cumulative valuation adjustment recognized to adjust the assets to fair value. Nonrecurring fair value measurements Lower-of-cost or fair value or valuation reserve allowance Total gain included in earnings for the year ended December 31, 2016 ($ in millions) Level 1 Level 2 Level 3 Total Assets Commercial finance receivables and loans, net (a) Automotive $ — $ — $ 27 $ 27 $ (4 ) n/m (b) Other — — 65 65 (19 ) n/m (b) Total commercial finance receivables and loans, net — — 92 92 (23 ) n/m (b) Other assets Repossessed and foreclosed assets (c) — — 12 12 (4 ) n/m (b) Other — — 4 4 — n/m (b) Total assets $ — $ — $ 108 $ 108 $ (27 ) n/m n/m = not meaningful (a) Represents the portion of the portfolio specifically impaired during 2016 . The related valuation allowance represents the cumulative adjustment to fair value of those specific receivables. (b) We consider the applicable valuation or loan loss allowance to be the most relevant indicator of the impact on earnings caused by the fair value measurement. Accordingly, the table above excludes total gains and losses included in earnings for these items. The carrying values are inclusive of the respective valuation or loan loss allowance. (c) The allowance provided for repossessed and foreclosed assets represents any cumulative valuation adjustment recognized to adjust the assets to fair value. Fair Value Option for Financial Assets We elected the fair value option for an insignificant amount of conforming mortgage loans held-for-sale. We elected the fair value option to mitigate earnings volatility by better matching the accounting for the assets with the related hedges. Our intent in electing fair value measurement was to mitigate a divergence between accounting losses and economic exposure for certain assets and liabilities. Fair Value of Financial Instruments The following table presents the carrying and estimated fair value of financial instruments, except for those recorded at fair value on a recurring basis presented in the previous section of this note titled Recurring Fair Value. When possible, we use quoted market prices to determine fair value. Where quoted market prices are not available, the fair value is internally derived based on appropriate valuation methodologies with respect to the amount and timing of future cash flows and estimated discount rates. However, considerable judgment is required in interpreting current market data to develop the market assumptions and inputs necessary to estimate fair value. As such, the actual amount received to sell an asset or the amount paid to settle a liability could differ from our estimates. Fair value information presented herein was based on information available at December 31, 2017 , and December 31, 2016 . Estimated fair value ($ in millions) Carrying value Level 1 Level 2 Level 3 Total December 31, 2017 Financial assets Held-to-maturity securities $ 1,899 $ — $ 1,865 $ — $ 1,865 Loans held-for-sale, net 95 — — 95 95 Finance receivables and loans, net 121,617 — — 123,302 123,302 Nonmarketable equity investments 1,233 — 1,190 49 1,239 Financial liabilities Deposit liabilities $ 93,256 $ — $ — $ 91,029 $ 91,029 Short-term borrowings 11,413 — — 11,417 11,417 Long-term debt 44,226 — 27,807 18,817 46,624 December 31, 2016 Financial assets Held-to-maturity securities $ 839 $ — $ 789 $ — $ 789 Finance receivables and loans, net 117,800 — — 118,750 118,750 Nonmarketable equity investments 1,046 — 1,012 55 1,067 Financial liabilities Deposit liabilities $ 79,022 $ — $ — $ 78,469 $ 78,469 Short-term borrowings 12,673 — — 12,675 12,675 Long-term debt 54,128 — 22,036 34,084 56,120 The following describes the methodologies and assumptions used to determine fair value for the significant classes of financial instruments. In addition to the valuation methods discussed below, we also followed guidelines for determining whether a market was not active and a transaction was not distressed. We assumed the price that would be received in an orderly transaction (including a market-based return) and not in forced liquidation or distressed sale. • Cash and cash equivalents — Included in cash and cash equivalents are highly liquid investments that are readily convertible to known amounts of cash and which are subject to an insignificant risk of change in value due to interest rate, quoted price, or penalty on withdrawal. Classified as Level 1 under the fair value hierarchy, cash and cash equivalents generally expose us to limited credit risk and are so near maturity that they present insignificant risk of changes in value because of changes in interest rates. Accordingly, the carrying value approximates the fair value of these instruments. • Held-to-maturity securities — Held-to-maturity securities, which consist of asset-backed retained notes and residential mortgage-backed debt securities issued by government agencies, are carried at amortized cost. For fair value disclosure purposes, held-to-maturity securities are classified as Level 2, with fair value based on observable market prices, when available. • Finance receivables and loans, net — With the exception of mortgage loans held-for-investment, the fair value of finance receivables and loans was based on discounted future cash flows using applicable spreads to approximate current rates applicable to each category of finance receivables and loans (an income approach using Level 3 inputs). The carrying value of commercial receivables in certain markets and certain automotive and other receivables for which interest rates reset on a short-term basis with applicable market indices are assumed to approximate fair value either because of the short-term nature or because of the interest rate adjustment feature. The fair value of commercial receivables in other markets was based on discounted future cash flows using applicable spreads to approximate current rates applicable to similar assets in those markets. The fair value of mortgage loans held-for-investment was based on a discounted cash flow basis utilizing cash flow projections from models that utilized prepayment, default, and discount rate assumptions. These valuations consider unique attributes of the loans such as geography, delinquency status, product type, and other factors. • Nonmarketable equity investments — Nonmarketable equity investments primarily include investments in FHLB and FRB stock and other equity investments carried at cost. As a member of the FHLB and FRB, Ally Bank is required to hold FHLB and FRB stock. The stock can be sold only to the FHLB and FRB upon termination of membership, or redeemed at the sole discretion of the FHLB and FRB, respectively. The fair value of FHLB and FRB stock is equal to the stock’s par value since the stock is bought, sold, and/or redeemed at par. FHLB and FRB stock is carried at cost, which generally represents the stock’s par value. • Deposit liabilities — Deposit liabilities represent certain consumer and brokered bank deposits, mortgage escrow deposits, and dealer deposits. The fair value of deposits at Level 3 was estimated by discounting projected cash flows based on discount factors derived from the forward interest rate swap curve. • Short-term borrowings and Long-term debt — Level 2 debt was valued using quoted market prices for similar instruments, when available, or other means for substantiation with observable inputs. Debt valued by discounting projected cash flows using internally derived inputs, such as prepayment speeds and discount rates, was classified as Level 3. For our credit facilities, which are floating rate in nature and where pricing occurs on a more frequent basis, the carrying amount or par value is considered to be a reasonable estimate of fair value. Based on the availability of observable inputs from an independent pricing service, as of June 30, 2017, we began using quoted market prices of similar instruments for certain of our long-term debt associated with asset-backed securitizations. Following the change in valuation technique, the corresponding financial instruments were transferred from Level 3 to Level 2 within the fair value hierarchy. • Financial instruments for which carrying value approximates fair value — Certain financial instruments that are not carried at fair value on the consolidated balance sheet are carried at amounts that approximate fair value primarily due to their short-term nature and limited credit risk. These instruments include restricted cash, cash collateral, accrued interest receivable, accrued interest payable, trade receivables and payables, and other short-term receivables and payables.

Offsetting Assets and Liabiliti

Offsetting Assets and Liabilities Offsetting Assets and Liabilities	12 Months Ended
	Dec. 31, 2017
Offsetting Assets and Liabilities [Abstract]
Offsetting Assets and Liabilities [Text Block]	Offsetting Assets and Liabilities Our derivative contracts and repurchase/reverse repurchase transactions are supported by qualifying master netting and master repurchase agreements. These agreements are legally enforceable bilateral agreements that (i) create a single legal obligation for all individual transactions covered by the agreement to the nondefaulting entity upon an event of default of the counterparty, including bankruptcy, insolvency, or similar proceeding, and (ii) provide the nondefaulting entity the right to accelerate, terminate, and close-out on a net basis all transactions under the agreement and to liquidate or set off collateral promptly upon an event of default of the counterparty. To further mitigate the risk of counterparty default related to derivative instruments, we maintain collateral agreements with certain counterparties. The agreements require both parties to maintain collateral in the event the fair values of the derivative financial instruments meet established thresholds. In the event that either party defaults on the obligation, the secured party may seize the collateral. Generally, our collateral arrangements are bilateral such that we and the counterparty post collateral for the obligation. Contractual terms provide for standard and customary exchange of collateral based on changes in the market value of the outstanding derivatives. A party posts additional collateral when their obligation rises or removes collateral when it falls, such that the net replacement cost of the nondefaulting party is covered in the event of counterparty default. In certain instances as it relates to our derivative instruments, we have the option to report derivative assets and liabilities as well as assets and liabilities associated with cash collateral received or delivered that is governed by a master netting agreement on a net basis as long as certain qualifying criteria are met. Similarly, for our repurchase/reverse repurchase transactions, we have the option to report recognized assets and liabilities subject to a master netting agreement on a net basis if certain qualifying criteria are met. At December 31, 2017 , these instruments are reported as gross assets and gross liabilities on the Consolidated Balance Sheet . The composition of offsetting derivative instruments, financial assets, and financial liabilities was as follows. Gross amounts of recognized assets/(liabilities) Gross amounts offset on the Consolidated Balance Sheet Net amounts of assets/(liabilities) presented on the Consolidated Balance Sheet Gross amounts not offset on the Consolidated Balance Sheet December 31, 2017 ($ in millions) Financial instruments Collateral (a) (b) (c) Net amount Assets Derivative assets in net asset positions $ 38 $ — $ 38 $ — $ — $ 38 Derivative assets with no offsetting arrangements 1 — 1 — — 1 Total assets (d) $ 39 $ — $ 39 $ — $ — $ 39 Liabilities Derivative liabilities in net liability positions (d) $ (41 ) $ — $ (41 ) $ — $ 1 $ (40 ) Securities sold under agreements to repurchase (e) (892 ) — (892 ) — 892 — Total liabilities $ (933 ) $ — $ (933 ) $ — $ 893 $ (40 ) (a) Financial collateral received/pledged shown as a balance based on the sum of all net asset and liability positions between Ally and each individual derivative counterparty. (b) Amounts disclosed are limited to the financial asset or liability balance and, accordingly, exclude excess collateral received or pledged and noncash collateral received. $2 million of noncash derivative collateral pledged to us was excluded at December 31, 2017 . We do not record such collateral received on our Consolidated Balance Sheet unless certain conditions are met. (c) Certain agreements grant us the right to sell or pledge the noncash assets we receive as collateral. Noncash collateral pledged to us where the agreement grants us the right to sell or pledge the underlying assets had a fair value of $2 million at December 31, 2017 . We have not sold or pledged any of the noncash collateral received under these agreements as of December 31, 2017 . (d) For additional information on derivative instruments and hedging activities, refer to Note 22 . (e) For additional information on securities sold under agreements to repurchase, refer to Note 16 . Gross amounts of recognized assets/(liabilities) Gross amounts offset on the Consolidated Balance Sheet Net amounts of assets/(liabilities) presented on the Consolidated Balance Sheet Gross amounts not offset on the Consolidated Balance Sheet December 31, 2016 ($ in millions) Financial instruments Collateral (a) (b) (c) Net amount Assets Derivative assets in net asset positions $ 87 $ — $ 87 $ (4 ) $ (9 ) $ 74 Derivative assets in net liability positions 8 — 8 (8 ) — — Total assets (d) $ 95 $ — $ 95 $ (12 ) $ (9 ) $ 74 Liabilities Derivative liabilities in net liability positions $ (91 ) $ — $ (91 ) $ 8 $ 13 $ (70 ) Derivative liabilities in net asset positions (4 ) — (4 ) 4 — — Total derivative liabilities (d) (95 ) — (95 ) 12 13 (70 ) Securities sold under agreements to repurchase (e) (676 ) — (676 ) — 676 — Total liabilities $ (771 ) $ — $ (771 ) $ 12 $ 689 $ (70 ) (a) Financial collateral received/pledged shown as a balance based on the sum of all net asset and liability positions between Ally and each individual derivative counterparty. (b) Amounts disclosed are limited to the financial asset or liability balance and, accordingly, exclude excess collateral received or pledged and noncash collateral received. $6 million of noncash derivative collateral pledged to us was excluded at December 31, 2016. We do not record such collateral received on our Consolidated Balance Sheet unless certain conditions are met. (c) Certain agreements grant us the right to sell or pledge the noncash assets we receive as collateral. Noncash collateral pledged to us where the agreement grants us the right to sell or pledge the underlying assets had a fair value of $6 million at December 31, 2016. We have not sold or pledged any of the noncash collateral received under these agreements as of December 31, 2016. (d) For additional information on derivative instruments and hedging activities, refer to Note 22 . (e) For additional information on securities sold under agreements to repurchase, refer to Note 16 .

Segment and Geographic Informat

Segment and Geographic Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment and Geographic Reporting Disclosure [Text Block]	Segment and Geographic Information Operating segments are defined as components of an enterprise that engage in business activity from which revenues are earned and expenses incurred for which discrete financial information is available that is evaluated regularly by our chief operating decision maker in deciding how to allocate resources and in assessing performance. We report our results of operations on a line-of-business basis through four operating segments: Automotive Finance operations, Insurance operations, Mortgage Finance operations, and Corporate Finance operations, with the remaining activity reported in Corporate and Other. The operating segments are determined based on the products and services offered, and reflect the manner in which financial information is currently evaluated by management. The following is a description of each of our reportable operating segments. Automotive Finance operations — One of the largest full service automotive finance operations in the United States providing automotive financing services to consumers and automotive dealers, and automotive and equipment financing services to companies and municipalities. Our automotive finance services include providing retail installment sales contracts, loans and leases, offering term loans to dealers, financing dealer floorplans and other lines of credit to dealers, warehouse lines to companies, fleet financing, providing financing to companies and municipalities for the purchase or lease of vehicles and equipment, and vehicle remarketing services. Insurance operations — A complementary automotive-focused business offering both consumer finance protection and insurance products sold primarily through the automotive dealer channel, and commercial insurance products sold directly to dealers. As part of our focus on offering dealers a broad range of consumer financial and insurance products, we provide VSCs, VMCs, and GAP products. We also underwrite select commercial insurance coverages, which primarily insure dealers’ wholesale vehicle inventory. Mortgage Finance operations — Primarily consists of the management of a held-for-investment consumer mortgage finance loan portfolio, which includes bulk purchases of high-quality jumbo and LMI mortgage loans originated by third parties. In late 2016, we introduced our direct-to-consumer mortgage offering, named Ally Home, consisting of a variety of jumbo and conforming fixed- and adjustable-rate mortgage products with the assistance of a third-party fulfillment partner. Jumbo mortgage loans are generally held on our balance sheet and are accounted for as held-for-investment. Conforming mortgage loans are generally originated as held-for-sale and then sold to the fulfillment partner . Servicing is performed by a third party and no mortgage servicing rights are created. Corporate Finance operations — Primarily provides senior secured leveraged cash flow and asset-based loans to mostly U.S.-based middle market companies. Our primary focus is on businesses owned by private equity sponsors with loans typically used for leveraged buyouts, mergers and acquisitions, debt refinancing, restructurings, and working capital. In 2017, we introduced a commercial real estate product to serve companies in the healthcare industry. Corporate and Other primarily consists of centralized corporate treasury activities such as management of the cash and corporate investment securities and loan portfolios, short- and long-term debt, retail and brokered deposit liabilities, derivative instruments, original issue discount, and the residual impacts of our corporate funds-transfer pricing (FTP) and treasury asset liability management (ALM) activities. Corporate and Other also includes certain equity investments, which primarily consist of FHLB and FRB stock, the management of our legacy mortgage portfolio, which primarily consists of loans originated prior to January 1, 2009, and reclassifications and eliminations between the reportable operating segments. Additionally, financial results related to Ally Invest are currently included within Corporate and Other. We utilize an FTP methodology for the majority of our business operations. The FTP methodology assigns charge rates and credit rates to classes of assets and liabilities based on expected duration and the benchmark rate curve plus an assumed credit spread. Matching duration allocates interest income and interest expense to these reportable segments so their respective results are insulated from interest rate risk. This methodology is consistent with our ALM practices, which includes managing interest rate risk centrally at a corporate level. The net residual impact of the FTP methodology is included within the results of Corporate and Other. The information presented in our reportable operating segments and geographic areas tables that follow are based in part on internal allocations, which involve management judgment. Financial information for our reportable operating segments is summarized as follows. Year ended December 31, ($ in millions) Automotive Finance operations Insurance operations Mortgage Finance operations Corporate Finance operations Corporate and Other Consolidated (a) 2017 Net financing revenue and other interest income $ 3,713 $ 59 $ 132 $ 167 $ 150 $ 4,221 Other revenue 355 1,059 4 45 81 1,544 Total net revenue 4,068 1,118 136 212 231 5,765 Provision for loan losses 1,134 — 8 22 (16 ) 1,148 Total noninterest expense 1,714 950 108 76 262 3,110 Income (loss) from continuing operations before income tax expense $ 1,220 $ 168 $ 20 $ 114 $ (15 ) $ 1,507 Total assets $ 114,089 $ 7,464 $ 11,708 $ 3,979 $ 29,908 $ 167,148 2016 Net financing revenue and other interest income (loss) $ 3,665 $ 61 $ 97 $ 121 $ (37 ) $ 3,907 Other revenue 306 1,036 — 26 162 1,530 Total net revenue 3,971 1,097 97 147 125 5,437 Provision for loan losses 924 — (4 ) 10 (13 ) 917 Total noninterest expense 1,667 940 67 66 199 2,939 Income (loss) from continuing operations before income tax expense $ 1,380 $ 157 $ 34 $ 71 $ (61 ) $ 1,581 Total assets $ 116,347 $ 7,172 $ 8,307 $ 3,183 $ 28,719 $ 163,728 2015 Net financing revenue and other interest income $ 3,429 $ 57 $ 57 $ 89 $ 87 $ 3,719 Other revenue (loss) 235 1,033 — 25 (151 ) 1,142 Total net revenue (loss) 3,664 1,090 57 114 (64 ) 4,861 Provision for loan losses 696 — 7 9 (5 ) 707 Total noninterest expense 1,633 879 39 55 155 2,761 Income (loss) from continuing operations before income tax expense $ 1,335 $ 211 $ 11 $ 50 $ (214 ) $ 1,393 Total assets $ 115,636 $ 7,053 $ 6,461 $ 2,677 $ 26,754 $ 158,581 (a) Net financing revenue and other interest income after the provision for loan losses totaled $3.1 billion for the year ended December 31, 2017 , and $3.0 billion for both the years ended December 31, 2016 , and 2015. Information concerning principal geographic areas was as follows. Year ended December 31, ($ in millions) Total net revenue (a) Income (loss) from continuing operations before income tax expense Net income (loss) (b) Identifiable assets (c) Long-lived assets (d) 2017 Canada $ 89 $ 42 $ 37 $ 406 $ — Europe — (1 ) (6 ) 315 — Latin America — — — 23 — Asia-Pacific — — — 2 — Total foreign (e) 89 41 31 746 — Total domestic (f) 5,676 1,466 898 166,162 9,197 Total $ 5,765 $ 1,507 $ 929 $ 166,908 $ 9,197 2016 Canada $ 90 $ 44 $ 32 $ 499 $ — Europe — — (1 ) 276 — Latin America — — (1 ) 23 — Asia-Pacific — — — 2 — Total foreign (e) 90 44 30 800 — Total domestic (f) 5,347 1,537 1,037 162,688 11,846 Total $ 5,437 $ 1,581 $ 1,067 $ 163,488 $ 11,846 2015 Canada $ 98 $ 47 $ 35 $ 514 $ — Europe 1 4 27 325 — Latin America — — (2 ) 28 — Asia-Pacific — — 452 2 — Total foreign (e) 99 51 512 869 — Total domestic (f) 4,762 1,342 777 157,685 16,506 Total $ 4,861 $ 1,393 $ 1,289 $ 158,554 $ 16,506 (a) Revenue consists of net financing revenue and other interest income and total other revenue as presented in our Consolidated Statement of Income. (b) Gain (loss) realized on sale of discontinued operations are allocated to the geographic area in which the business operated. (c) Identifiable assets consist of total assets excluding goodwill. (d) Long-lived assets consist of investments in operating leases, net, and net property and equipment. (e) Our foreign operations as of December 31, 2017, 2016, and 2015, consist of our ongoing Insurance operations in Canada and our remaining international entities in wind-down. (f) Amounts include eliminations between our domestic and foreign operations.

Parent and Guarantor Consolidat

Parent and Guarantor Consolidating Financial Statements	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Condensed Financial Statements [Text Block]	Parent and Guarantor Consolidating Financial Statements Certain of our senior notes issued by the parent are guaranteed by 100% directly owned subsidiaries of Ally (the Guarantors). As of December 31, 2017 , the Guarantors include Ally US LLC and IB Finance Holding Company, LLC (IB Finance), each of which fully and unconditionally guarantee the senior notes on a joint and several basis. The following financial statements present condensed consolidating financial data for (i) Ally Financial Inc. (on a parent company-only basis); (ii) the Guarantors; (iii) the nonguarantor subsidiaries (all other subsidiaries); and (iv) an elimination column for adjustments to arrive at (v) the information for the parent company, the Guarantors, and nonguarantors on a consolidated basis. Investments in subsidiaries are accounted for by the parent company and the Guarantors using the equity-method for this presentation. Results of operations of subsidiaries are therefore classified in the parent company’s and Guarantors’ investment in subsidiaries accounts. The elimination entries set forth in the following condensed consolidating financial statements eliminate distributed and undistributed income of subsidiaries, investments in subsidiaries, and intercompany balances and transactions between the parent, the Guarantors, and nonguarantors. Condensed Consolidating Statements of Comprehensive Income Year ended December 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Financing (loss) revenue and other interest income Interest and fees on finance receivables and loans $ (27 ) $ — $ 5,846 $ — $ 5,819 Interest and fees on finance receivables and loans — intercompany 12 — 6 (18 ) — Interest and dividends on investment securities and other earning assets — — 601 (2 ) 599 Interest on cash and cash equivalents 7 — 30 — 37 Interest-bearing cash — intercompany 4 — 7 (11 ) — Operating leases 11 — 1,856 — 1,867 Total financing revenue and other interest income 7 — 8,346 (31 ) 8,322 Interest expense Interest on deposits 3 — 1,078 (4 ) 1,077 Interest on short-term borrowings 60 — 67 — 127 Interest on long-term debt 1,101 — 552 — 1,653 Interest on intercompany debt 15 — 12 (27 ) — Total interest expense 1,179 — 1,709 (31 ) 2,857 Net depreciation expense on operating lease assets 11 — 1,233 — 1,244 Net financing revenue (1,183 ) — 5,404 — 4,221 Cash dividends from subsidiaries Bank subsidiary 3,300 3,300 — (6,600 ) — Nonbank subsidiaries 752 — — (752 ) — Other revenue Insurance premiums and service revenue earned — — 973 — 973 Gain on mortgage and automotive loans, net 40 — 28 — 68 Loss on extinguishment of debt (1 ) — (6 ) — (7 ) Other gain on investments, net — — 102 — 102 Other income, net of losses 676 — 840 (1,108 ) 408 Total other revenue 715 — 1,937 (1,108 ) 1,544 Total net revenue 3,584 3,300 7,341 (8,460 ) 5,765 Provision for loan losses 465 — 683 — 1,148 Noninterest expense Compensation and benefits expense 180 — 915 — 1,095 Insurance losses and loss adjustment expenses — — 332 — 332 Other operating expenses 899 — 1,892 (1,108 ) 1,683 Total noninterest expense 1,079 — 3,139 (1,108 ) 3,110 Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries 2,040 3,300 3,519 (7,352 ) 1,507 Income tax expense from continuing operations 337 — 244 — 581 Net income from continuing operations 1,703 3,300 3,275 (7,352 ) 926 Income (loss) from discontinued operations, net of tax 7 — (4 ) — 3 Undistributed (loss) income of subsidiaries Bank subsidiary (1,168 ) (1,168 ) — 2,336 — Nonbank subsidiaries 387 — — (387 ) — Net income 929 2,132 3,271 (5,403 ) 929 Other comprehensive income, net of tax 106 65 104 (169 ) 106 Comprehensive income $ 1,035 $ 2,197 $ 3,375 $ (5,572 ) $ 1,035 Year ended December 31, 2016 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Financing (loss) revenue and other interest income Interest and fees on finance receivables and loans $ (104 ) $ — $ 5,266 $ — $ 5,162 Interest and fees on finance receivables and loans — intercompany 11 — 8 (19 ) — Interest and dividends on investment securities and other earning assets — — 421 (3 ) 418 Interest on cash and cash equivalents 5 — 9 — 14 Interest-bearing cash — intercompany — — 9 (9 ) — Operating leases 17 — 2,694 — 2,711 Total financing (loss) revenue and other interest income (71 ) — 8,407 (31 ) 8,305 Interest expense Interest on deposits 8 — 822 — 830 Interest on short-term borrowings 40 — 17 — 57 Interest on long-term debt 1,161 — 581 — 1,742 Interest on intercompany debt 20 — 11 (31 ) — Total interest expense 1,229 — 1,431 (31 ) 2,629 Net depreciation expense on operating lease assets 14 — 1,755 — 1,769 Net financing revenue (1,314 ) — 5,221 — 3,907 Cash dividends from subsidiaries Nonbank subsidiaries 965 — — (965 ) — Other revenue Insurance premiums and service revenue earned — — 945 — 945 (Loss) gain on mortgage and automotive loans, net (11 ) — 22 — 11 Loss on extinguishment of debt (3 ) — (2 ) — (5 ) Other gain on investments, net — — 176 9 185 Other income, net of losses 1,253 — 937 (1,796 ) 394 Total other revenue 1,239 — 2,078 (1,787 ) 1,530 Total net revenue 890 — 7,299 (2,752 ) 5,437 Provision for loan losses 408 — 509 — 917 Noninterest expense Compensation and benefits expense 573 — 419 — 992 Insurance losses and loss adjustment expenses — — 342 — 342 Other operating expenses 1,261 — 2,130 (1,786 ) 1,605 Total noninterest expense 1,834 — 2,891 (1,786 ) 2,939 (Loss) income from continuing operations before income tax (benefit) expense and undistributed income (loss) of subsidiaries (1,352 ) — 3,899 (966 ) 1,581 Income tax (benefit) expense from continuing operations (279 ) (82 ) 831 — 470 Net (loss) income from continuing operations (1,073 ) 82 3,068 (966 ) 1,111 Loss from discontinued operations, net of tax (39 ) — (5 ) — (44 ) Undistributed income (loss) of subsidiaries Bank subsidiary 1,273 1,273 — (2,546 ) — Nonbank subsidiaries 906 (2 ) — (904 ) — Net income 1,067 1,353 3,063 (4,416 ) 1,067 Other comprehensive loss, net of tax (110 ) (63 ) (106 ) 169 (110 ) Comprehensive income $ 957 $ 1,290 $ 2,957 $ (4,247 ) $ 957 Year ended December 31, 2015 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Financing (loss) revenue and other interest income Interest and fees on finance receivables and loans $ (83 ) $ — $ 4,653 $ — $ 4,570 Interest and fees on finance receivables and loans — intercompany 17 — 24 (41 ) — Interest on loans held-for-sale — — 40 — 40 Interest and dividends on investment securities and other earning assets — — 381 — 381 Interest on cash and cash equivalents 1 — 7 — 8 Interest-bearing cash — intercompany — — 8 (8 ) — Operating leases 9 — 3,389 — 3,398 Total financing (loss) revenue and other interest income (56 ) — 8,502 (49 ) 8,397 Interest expense Interest on deposits 10 — 708 — 718 Interest on short-term borrowings 40 — 9 — 49 Interest on long-term debt 1,121 — 541 — 1,662 Interest on intercompany debt 32 — 17 (49 ) — Total interest expense 1,203 — 1,275 (49 ) 2,429 Net depreciation expense on operating lease assets 7 — 2,242 — 2,249 Net financing revenue (1,266 ) — 4,985 — 3,719 Cash dividends from subsidiaries Bank subsidiary 525 525 — (1,050 ) — Nonbank subsidiaries 1,123 — — (1,123 ) — Other revenue Insurance premiums and service revenue earned — — 940 — 940 (Loss) gain on mortgage and automotive loans, net (9 ) — — 54 — 45 Loss on extinguishment of debt (355 ) — (2 ) — (357 ) Other gain on investments, net — — 155 — 155 Other income, net of losses 1,373 — 1,373 (2,387 ) 359 Total other revenue 1,009 — 2,520 (2,387 ) 1,142 Total net revenue 1,391 525 7,505 (4,560 ) 4,861 Provision for loan losses 157 — 550 — 707 Noninterest expense Compensation and benefits expense 571 — 842 (450 ) 963 Insurance losses and loss adjustment expenses — — 293 — 293 Other operating expenses 1,247 — 2,195 (1,937 ) 1,505 Total noninterest expense 1,818 — 3,330 (2,387 ) 2,761 (Loss) income from continuing operations before income tax (benefit) expense and undistributed income (loss) of subsidiaries (584 ) 525 3,625 (2,173 ) 1,393 Income tax (benefit) expense from continuing operations (267 ) — 763 — 496 Net (loss) income from continuing operations (317 ) 525 2,862 (2,173 ) 897 Income from discontinued operations, net of tax 356 — 36 — 392 Undistributed income (loss) of subsidiaries Bank subsidiary 581 581 — (1,162 ) — Nonbank subsidiaries 669 (1 ) — (668 ) — Net income 1,289 1,105 2,898 (4,003 ) 1,289 Other comprehensive loss, net of tax (165 ) (43 ) (172 ) 215 (165 ) Comprehensive income $ 1,124 $ 1,062 $ 2,726 $ (3,788 ) $ 1,124 Condensed Consolidating Balance Sheet December 31, 2017 ($ in millions) Parent (a) Guarantors Nonguarantors (a) Consolidating adjustments Ally consolidated Assets Cash and cash equivalents Noninterest-bearing $ 74 $ — $ 770 $ — $ 844 Interest-bearing 5 — 3,403 — 3,408 Interest-bearing — intercompany 1,138 — 695 (1,833 ) — Total cash and cash equivalents 1,217 — 4,868 (1,833 ) 4,252 Available-for-sale securities — — 22,821 — 22,821 Held-to-maturity securities — — 1,973 (74 ) 1,899 Loans held-for-sale, net — — 108 — 108 Finance receivables and loans, net Finance receivables and loans, net 7,434 — 115,459 — 122,893 Intercompany loans to Nonbank subsidiaries 879 — 408 (1,287 ) — Allowance for loan losses (185 ) — (1,091 ) — (1,276 ) Total finance receivables and loans, net 8,128 — 114,776 (1,287 ) 121,617 Investment in operating leases, net 19 — 8,722 — 8,741 Intercompany receivables from Bank subsidiary 80 — — (80 ) — Nonbank subsidiaries 71 — 77 (148 ) — Investment in subsidiaries Bank subsidiary 16,962 16,962 — (33,924 ) — Nonbank subsidiaries 8,111 — — (8,111 ) — Premiums receivable and other insurance assets — — 2,082 (35 ) 2,047 Other assets 2,207 — 5,105 (1,649 ) 5,663 Total assets $ 36,795 $ 16,962 $ 160,532 $ (47,141 ) $ 167,148 Liabilities Deposit liabilities Noninterest-bearing $ — $ — $ 108 $ — $ 108 Interest-bearing 12 — 93,136 — 93,148 Interest-bearing — intercompany — — 1,139 (1,139 ) — Total deposit liabilities 12 — 94,383 (1,139 ) 93,256 Short-term borrowings 3,171 — 8,242 — 11,413 Long-term debt 17,966 — 26,260 — 44,226 Intercompany debt to Bank subsidiary 74 — — (74 ) — Nonbank subsidiaries 1,103 — 879 (1,982 ) — Intercompany payables to Bank subsidiary 4 — — (4 ) — Nonbank subsidiaries 132 — 127 (259 ) — Interest payable 200 — 175 — 375 Unearned insurance premiums and service revenue — — 2,604 — 2,604 Accrued expenses and other liabilities 639 — 2,790 (1,649 ) 1,780 Total liabilities 23,301 — 135,460 (5,107 ) 153,654 Total equity 13,494 16,962 25,072 (42,034 ) 13,494 Total liabilities and equity $ 36,795 $ 16,962 $ 160,532 $ (47,141 ) $ 167,148 (a) Amounts presented are based upon the legal transfer of the underlying assets to VIEs in order to reflect legal ownership. December 31, 2016 ($ in millions) Parent (a) Guarantors Nonguarantors (a) Consolidating adjustments Ally consolidated Assets Cash and cash equivalents Noninterest-bearing $ 720 $ — $ 827 $ — $ 1,547 Interest-bearing 100 — 4,287 — 4,387 Interest-bearing — intercompany — — 401 (401 ) — Total cash and cash equivalents 820 — 5,515 (401 ) 5,934 Trading securities — — 82 (82 ) — Available-for-sale securities — — 19,253 (327 ) 18,926 Held-to-maturity securities — — 839 — 839 Finance receivables and loans, net Finance receivables and loans, net 4,705 — 114,239 — 118,944 Intercompany loans to Bank subsidiary 1,125 — — (1,125 ) — Nonbank subsidiaries 1,779 — 626 (2,405 ) — Allowance for loan losses (115 ) — (1,029 ) — (1,144 ) Total finance receivables and loans, net 7,494 — 113,836 (3,530 ) 117,800 Investment in operating leases, net 42 — 11,428 — 11,470 Intercompany receivables from Bank subsidiary 299 — — (299 ) — Nonbank subsidiaries 107 — 67 (174 ) — Investment in subsidiaries Bank subsidiary 17,727 17,727 — (35,454 ) — Nonbank subsidiaries 10,318 — — (10,318 ) — Premiums receivable and other insurance assets — — 1,936 (31 ) 1,905 Other assets 4,347 — 5,085 (2,578 ) 6,854 Total assets $ 41,154 $ 17,727 $ 158,041 $ (53,194 ) $ 163,728 Liabilities Deposit liabilities Noninterest-bearing $ — $ — $ 84 $ — $ 84 Interest-bearing 167 — 78,771 — 78,938 Total deposit liabilities 167 — 78,855 — 79,022 Short-term borrowings 3,622 — 9,051 — 12,673 Long-term debt 21,798 — 32,330 — 54,128 Intercompany debt to Bank subsidiary 330 — — (330 ) — Nonbank subsidiaries 1,027 — 2,903 (3,930 ) — Intercompany payables to Nonbank subsidiaries 153 — 351 (504 ) — Interest payable 253 — 98 — 351 Unearned insurance premiums and service revenue — — 2,500 — 2,500 Accrued expenses and other liabilities 487 — 3,911 (2,661 ) 1,737 Total liabilities 27,837 — 129,999 (7,425 ) 150,411 Total equity 13,317 17,727 28,042 (45,769 ) 13,317 Total liabilities and equity $ 41,154 $ 17,727 $ 158,041 $ (53,194 ) $ 163,728 (a) Amounts presented are based upon the legal transfer of the underlying assets to VIEs in order to reflect legal ownership. Condensed Consolidating Statement of Cash Flows Year ended December 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash provided by operating activities $ 4,591 $ 3,300 $ 3,466 $ (7,278 ) $ 4,079 Investing activities Purchases of available-for-sale securities — — (11,234 ) — (11,234 ) Proceeds from sales of available-for-sale securities — — 4,633 — 4,633 Proceeds from repayments of available-for-sale securities — — 2,899 — 2,899 Purchases of held-to-maturity securities — — (1,026 ) — (1,026 ) Proceeds from repayments of held-to-maturity securities — — 68 — 68 Net change in investment securities — intercompany 7 — 291 (298 ) — Purchases of finance receivables and loans held-for-investment (35 ) — (5,417 ) — (5,452 ) Proceeds from sales of finance receivables and loans initially held-for-investment 106 — 1,233 — 1,339 Originations and repayments of finance receivables and loans held-for-investment and other, net 860 — 33 (1,956 ) (1,063 ) Net change in loans — intercompany 2,068 — 217 (2,285 ) — Purchases of operating lease assets — — (4,052 ) — (4,052 ) Disposals of operating lease assets 13 — 5,554 — 5,567 Capital contributions to subsidiaries (1,212 ) (5 ) — 1,217 — Returns of contributed capital 1,567 — — (1,567 ) — Net change in nonmarketable equity investments — — (187 ) — (187 ) Other, net (31 ) — (99 ) (89 ) (219 ) Net cash provided by (used in) investing activities 3,343 (5 ) (7,087 ) (4,978 ) (8,727 ) Financing activities Net change in short-term borrowings — third party (453 ) — (810 ) — (1,263 ) Net (decrease) increase in deposits (156 ) — 15,466 (1,138 ) 14,172 Proceeds from issuance of long-term debt — third party 354 — 15,654 1,961 17,969 Repayments of long-term debt — third party (6,111 ) — (21,797 ) — (27,908 ) Net change in debt — intercompany (225 ) — (2,074 ) 2,299 — Repurchase of common stock (753 ) — — — (753 ) Dividends paid — third party (184 ) — — — (184 ) Dividends paid and returns of contributed capital — intercompany — (3,300 ) (5,619 ) 8,919 — Capital contributions from parent — 5 1,212 (1,217 ) — Net cash (used in) provided by financing activities (7,528 ) (3,295 ) 2,032 10,824 2,033 Effect of exchange-rate changes on cash and cash equivalents — — 3 — 3 Net increase (decrease) in cash and cash equivalents and restricted cash 406 — (1,586 ) (1,432 ) (2,612 ) Cash and cash equivalents and restricted cash at beginning of year 989 — 7,293 (401 ) 7,881 Cash and cash equivalents and restricted cash at end of year $ 1,395 $ — $ 5,707 $ (1,833 ) $ 5,269 The following table provides a reconciliation of cash and cash equivalents and restricted cash from the Condensed Consolidated Balance Sheet to the Condensed Consolidated Statement of Cash Flows. December 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Cash and cash equivalents as disclosed on the Consolidated Balance Sheet $ 1,217 $ — $ 4,868 $ (1,833 ) $ 4,252 Restricted cash included in other assets on the Consolidated Balance Sheet (a) 178 — 839 — 1,017 Total cash and cash equivalents and restricted cash as disclosed in the Consolidated Statement of Cash Flows $ 1,395 $ — $ 5,707 $ (1,833 ) $ 5,269 (a) Restricted cash balances relate primarily to Ally securitization arrangements. Refer to Note 14 for additional details describing the nature of restricted cash balances. Year ended December 31, 2016 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash provided by operating activities $ 241 $ 6 $ 5,383 $ (1,063 ) $ 4,567 Investing activities Purchases of available-for-sale securities — — (16,031 ) — (16,031 ) Proceeds from sales of available-for-sale securities — — 11,036 — 11,036 Proceeds from repayments of available-for-sale securities — — 3,379 — 3,379 Purchases of held-to-maturity securities — — (841 ) — (841 ) Purchases of finance receivables and loans held-for-investment (4 ) — (3,855 ) — (3,859 ) Proceeds from sales of finance receivables and loans initially held-for-investment — — 4,285 — 4,285 Originations and repayments of finance receivables and loans held-for-investment and other, net 2,013 — (10,839 ) — (8,826 ) Net change in loans — intercompany 877 — (67 ) (810 ) — Purchases of operating lease assets — — (3,274 ) — (3,274 ) Disposals of operating lease assets 25 — 6,279 — 6,304 Acquisitions, net of cash acquired (309 ) — — — (309 ) Capital contributions to subsidiaries (3,908 ) — — 3,908 — Returns of contributed capital 3,678 8 — (3,686 ) — Net change in nonmarketable equity investments — — (628 ) — (628 ) Other, net (206 ) — (191 ) 91 (306 ) Net cash provided by (used in) investing activities 2,166 8 (10,747 ) (497 ) (9,070 ) Financing activities Net change in short-term borrowings — third party 169 — 4,395 — 4,564 Net (decrease) increase in deposits (61 ) — 12,569 — 12,508 Proceeds from issuance of long-term debt — third party 979 — 13,176 — 14,155 Repayments of long-term debt — third party (2,662 ) — (23,750 ) — (26,412 ) Net change in debt — intercompany (382 ) — (877 ) 1,259 — Redemption of preferred stock (696 ) — — — (696 ) Repurchase of common stock (341 ) — — — (341 ) Dividends paid — third party (108 ) — — — (108 ) Dividends paid and returns of contributed capital — intercompany — (14 ) (4,644 ) 4,658 — Capital contributions from parent — — 3,908 (3,908 ) — Net cash (used in) provided by financing activities (3,102 ) (14 ) 4,777 2,009 3,670 Effect of exchange-rate changes on cash and cash equivalents — — 1 — 1 Net decrease in cash and cash equivalents and restricted cash (695 ) — (586 ) 449 (832 ) Cash and cash equivalents and restricted cash at beginning of year 1,684 — 7,879 (850 ) 8,713 Cash and cash equivalents and restricted cash at end of year $ 989 $ — $ 7,293 $ (401 ) $ 7,881 The following table provides a reconciliation of cash and cash equivalents and restricted cash from the Condensed Consolidated Balance Sheet to the Condensed Consolidated Statement of Cash Flows. December 31, 2016 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Cash and cash equivalents as disclosed on the Consolidated Balance Sheet $ 820 $ — $ 5,515 $ (401 ) $ 5,934 Restricted cash included in other assets on the Consolidated Balance Sheet (a) 169 — 1,778 — 1,947 Total cash and cash equivalents and restricted cash as disclosed in the Consolidated Statement of Cash Flows $ 989 $ — $ 7,293 $ (401 ) $ 7,881 (a) Restricted cash balances relate primarily to Ally securitization arrangements. Refer to Note 14 for additional details describing the nature of restricted cash balances. Year ended December 31, 2015 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash provided by operating activities $ 370 $ 525 $ 6,390 $ (2,174 ) $ 5,111 Investing activities Purchases of available-for-sale securities — — (12,250 ) — (12,250 ) Proceeds from sales of available-for-sale securities — — 6,874 — 6,874 Proceeds from repayments of available-for-sale securities — — 4,255 — 4,255 Purchases of finance receivables and loans held-for-investment (169 ) — (4,332 ) — (4,501 ) Proceeds from sales of finance receivables and loans initially held-for-investment — — 3,197 — 3,197 Originations and repayments of finance receivables and loans held-for-investment and other, net 1,954 — (11,298 ) — (9,344 ) Net change in loans — intercompany 240 — 1,211 (1,451 ) — Purchases of operating lease assets (94 ) — (4,591 ) — (4,685 ) Disposals of operating lease assets 7 — 5,539 — 5,546 Capital contributions to subsidiaries (796 ) (1 ) — 797 — Returns of contributed capital 1,444 — — (1,444 ) — Proceeds from sale of business units, net 1,049 — — — 1,049 Net change in nonmarketable equity investments — — (147 ) — (147 ) Other, net (47 ) — 50 — 3 Net cash provided by (used in) investing activities 3,588 (1 ) (11,492 ) (2,098 ) (10,003 ) Financing activities Net change in short-term borrowings — third party 115 — 913 — 1,028 Net (decrease) increase in deposits (91 ) — 8,338 — 8,247 Proceeds from issuance of long-term debt — third party 5,428 — 25,237 — 30,665 Repayments of long-term debt — third party (5,931 ) — (25,419 ) — (31,350 ) Net change in debt — intercompany (977 ) — (240 ) 1,217 — Repurchase and redemption of preferred stock (559 ) — — — (559 ) Repurchase of common stock (16 ) — — — (16 ) Dividends paid — third party (2,571 ) — — — (2,571 ) Dividends paid and returns of contributed capital — intercompany — (525 ) (3,092 ) 3,617 — Capital contributions from parent — 1 796 (797 ) — Net cash (used in) provided by financing activities (4,602 ) (524 ) 6,533 4,037 5,444 Effect of exchange-rate changes on cash and cash equivalents — — (4 ) — (4 ) Net (decrease) increase in cash and cash equivalents and restricted cash (644 ) — 1,427 (235 ) 548 Cash and cash equivalents and restricted cash at beginning of year 2,328 — 6,452 (615 ) 8,165 Cash and cash equivalents and restricted cash at end of year $ 1,684 $ — $ 7,879 $ (850 ) $ 8,713

Contingencies and Other Risks

Contingencies and Other Risks	12 Months Ended
	Dec. 31, 2017
Loss Contingency [Abstract]
Contingencies Disclosure [Text Block]	Contingencies and Other Risks Concentration with GM and Chrysler While we are continuing to diversify our automotive finance and insurance businesses and to expand into other financial services, General Motors Company (GM) and Fiat Chrysler Automobiles US LLC (Chrysler) dealers and their retail customers continue to constitute a significant portion of our customer base. GM, Chrysler, and their captive finance companies compete forcefully with us and could take further actions that negatively impact the amount of business that we do with GM and Chrysler dealers and their customers. Further, a significant adverse change in GM’s or Chrysler’s business—including, for example, in the production or sale of GM or Chrysler vehicles, the quality or resale value of GM or Chrysler vehicles, GM’s or Chrysler’s relationships with its key suppliers, or the rate or volume of recalls of GM or Chrysler vehicles—could negatively impact our GM and Chrysler dealer and retail customer bases. Any future reductions in GM and Chrysler business that we are not able to offset could adversely affect our business and financial results. Legal Matters Ally and its subsidiaries, including Ally Bank, are or may be subject to potential liability in connection with pending or threatened legal proceedings and other matters. These legal matters may be formal or informal and include litigation and arbitration with one or more identified claimants, certified or purported class actions with yet-to-be-identified claimants, and regulatory or other governmental information-gathering requests, examinations, investigations, and enforcement proceedings. Our legal matters exist in varying stages of adjudication, arbitration, negotiation, or investigation and span our lines of business and operations. Claims may be based in law or equity—such as those arising under contracts or in tort and those involving banking, consumer-protection, securities, tax, employment, and other laws—and some can present novel legal theories and allege substantial or indeterminate damages. We accrue for a legal matter when a loss becomes probable and the amount of loss can be reasonably estimated. Accruals are evaluated each quarter and may be adjusted, upward or downward, based on our best judgment after consultation with counsel. No assurance exists that our accruals will not need to be adjusted in the future. When a probable or reasonably possible loss on a legal matter could be material to our consolidated financial condition, results of operations, or cash flows, we provide disclosure in this note as prescribed by ASC 450, Contingencies . The course and outcome of legal matters are inherently unpredictable. This is especially so when a matter is still in its early stages, the damages sought are indeterminate or unsupported, significant facts are unclear or disputed, novel questions of law or other meaningful legal uncertainties exist, a request to certify a proceeding as a class action is outstanding or granted, multiple parties are named, or regulatory or other governmental entities are involved. As a result, we often are unable to determine how or when threatened or pending legal matters will be resolved and what losses may be incurred. Actual losses may be higher or lower than any amounts accrued or estimated for those matters, possibly to a significant degree. Descriptions of our material legal matters follow. We do not believe, however, that an estimate of reasonably possible losses or a range of reasonably possible losses—whether in excess of any related accrual or where no accrual exists—can be made for any of these matters for some or all of the reasons identified in the preceding paragraph. Securities Litigation In October 2016, a purported class action—Bucks County Employees Retirement Fund v. Ally Financial Inc. et al.—was filed in the Circuit Court for Wayne County in the State of Michigan (Case No. 16-013616-CZ). This matter was removed to the U.S. District Court for the Eastern District of Michigan on November 18, 2016. The complaint alleges material misstatements and omissions in connection with Ally’s initial public offering in April 2014, including a failure to adequately disclose the severity of rising subprime automotive loan delinquency rates, deficient underwriting measures employed in the origination of subprime automotive loans, and aggressive tactics used with low-income borrowers. The request for relief includes an indeterminate amount of damages, fees, and costs and other remedies. In January 2017, another purported class action—National Shopmen Pension Fund v. Ally Financial Inc. et al.—was filed in the Circuit Court for Oakland County in the State of Michigan (Case No. 2017-156719-CB). This matter was removed to the U.S. District Court for the Eastern District of Michigan on January 30, 2017. In March 2017, a third purported class action—James McIntire v. Ally Financial Inc. et al.—was filed in the Circuit Court for Wayne County in the State of Michigan (Case No. 17-003811-CZ). This matter was removed to the U.S. District Court for the Eastern District of Michigan on March 15, 2017. The allegations and requested relief in the National Shopmen Pension Fund and James McIntire complaints are substantially similar to those included in the complaint filed by Bucks County Employees Retirement Fund. All three matters were remanded from the U.S. District Court for the Eastern District of Michigan to the state circuit courts on May 26, 2017, and have been consolidated for discovery in Wayne County Circuit Court as In re Ally Financial, Inc. Securities Litigation (Case No. 16-013616-CB). In November 2017, the plaintiffs filed a consolidated amended complaint, and the court entered an interim stay of the litigation. We intend to vigorously defend against each of these actions. Automotive Subprime Matters In October 2014, we received a document request from the SEC in connection with its investigation related to subprime automotive finance and related securitization activities. Separately, in December 2014, we received a subpoena from the U.S. Department of Justice requesting similar information. In May 2015 and December 2016, we received information requests from the New York Department of Financial Services requesting similar information. We responded timely to each of the requests. Other Contingencies Ally and its subsidiaries, including Ally Bank, are or may be subject to potential liability under various other contingent exposures, including indemnification, tax, self-insurance, and other miscellaneous contingencies. We accrue for a contingent exposure when a loss becomes probable and the amount of loss can be reasonably estimated. Accruals are evaluated each quarter and may be adjusted, upward or downward, based on our best judgment. No assurance exists that our accruals will not need to be adjusted in the future, and actual losses may be higher or lower than any amounts accrued or estimated for those exposures, possibly to a significant degree. On the basis of information currently available, we do not believe that these other contingent exposures will be material to our consolidated financial condition, results of operations, or cash flows. Refer to Note 1 for additional information related to our policy for establishing reserves for legal and regulatory matters.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events Declaration of Quarterly Dividend Payment On January 10, 2018 , the Board declared a quarterly cash dividend payment of $0.13 per share on all common stock, a $0.01 per share increase relative to our prior quarterly cash dividend. The dividend was paid on February 15, 2018 , to stockholders of record at the close of business on February 1, 2018.

Premiums Receivable and Other I

Premiums Receivable and Other Insurance Assets Premiums Receivable and Other Insurance Assets	12 Months Ended
	Dec. 31, 2017
Premiums Receivable and Other Insurance Assets [Abstract]
Premiums Receivable Note [Text Block]	Premiums Receivable and Other Insurance Assets Premiums receivable and other insurance assets consisted of the following. December 31, ($ in millions) 2017 2016 Prepaid reinsurance premiums $ 507 $ 439 Reinsurance recoverable on unpaid losses 108 108 Reinsurance recoverable on paid losses 19 20 Premiums receivable 84 80 Deferred policy acquisition costs 1,329 1,258 Total premiums receivable and other insurance assets $ 2,047 $ 1,905

Equity Equity

Equity Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	Equity Common Stock The following table presents changes in the number of shares issued and outstanding. Year ended December 31, (shares in thousands) (a) 2017 2016 2015 Common stock Total issued at January 1, 485,708 482,791 480,136 New issuances Employee benefits and compensation plans 4,176 2,917 2,655 Total issued at December 31, 489,884 485,708 482,791 Treasury balance at January 1, (18,707 ) (811 ) (41 ) Repurchase of common stock (b) (c) (34,122 ) (17,897 ) (769 ) Total treasury stock at December 31, (52,830 ) (18,707 ) (811 ) Total outstanding at December 31, 437,054 467,000 481,980 (a) Figures in the table may not recalculate exactly due to rounding. Number of shares issued, in treasury, and outstanding are calculated based on unrounded numbers. (b) Includes shares of common stock withheld to cover income taxes owed by participants in our share-based incentive plans. (c) On July 19, 2016, we announced a common stock repurchase program of up to $700 million . The program commenced in the third quarter of 2016 and expired on June 30, 2017. On June 28, 2017, we announced a common stock repurchase program of up to $760 million . The program commenced in the third quarter of 2017 and will expire on June 30, 2018.

Insurance Premiums and Service

Insurance Premiums and Service Revenue Earned Insurance Premiums and Service Revenue Earned	12 Months Ended
	Dec. 31, 2017
Insurance Premiums and Service Revenue Earned [Abstract]
Insurance Premiums and Service Revenue Earned [Text Block]	Insurance Premiums and Service Revenue Earned The following table is a summary of insurance premiums and service revenue written and earned. 2017 2016 2015 Year ended December 31, ($ in millions) Written Earned Written Earned Written Earned Insurance premiums Direct $ 384 $ 364 $ 317 $ 318 $ 313 $ 296 Assumed 2 5 3 5 2 16 Gross insurance premiums 386 369 320 323 315 312 Ceded (254 ) (188 ) (198 ) (141 ) (184 ) (125 ) Net insurance premiums 132 181 122 182 131 187 Service revenue 864 792 826 763 846 753 Insurance premiums and service revenue written and earned $ 996 $ 973 $ 948 $ 945 $ 977 $ 940

Quarterly Financial Statements

Quarterly Financial Statements (unaudited) Quarterly Financial Statements (unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information (unaudited) [Abstract]
Quarterly Financial Information [Text Block]	Quarterly Financial Statements (unaudited) ($ in millions) First quarter Second quarter Third quarter Fourth quarter 2017 Net financing revenue and other interest income $ 979 $ 1,067 $ 1,081 $ 1,094 Other revenue 396 388 381 379 Total net revenue 1,375 1,455 1,462 1,473 Provision for loan losses 271 269 314 294 Total noninterest expense 778 810 753 769 Income from continuing operations before income tax expense 326 376 395 410 Income tax expense from continuing operations (a) 113 122 115 231 Net income from continuing operations 213 254 280 179 Income (loss) from discontinued operations, net of tax 1 (2 ) 2 2 Net income $ 214 $ 252 $ 282 $ 181 Basic earnings per common share (b) Net income from continuing operations $ 0.46 $ 0.55 $ 0.62 $ 0.40 Net income 0.46 0.55 0.63 0.41 Diluted earnings per common share (b) Net income from continuing operations $ 0.46 $ 0.55 $ 0.62 $ 0.40 Net income 0.46 0.55 0.63 0.41 Cash dividends per common share $ 0.08 $ 0.08 $ 0.12 $ 0.12 2016 Net financing revenue and other interest income $ 951 $ 984 $ 996 $ 976 Other revenue 376 374 388 392 Total net revenue 1,327 1,358 1,384 1,368 Provision for loan losses 220 172 258 267 Total noninterest expense 710 773 735 721 Income from continuing operations before income tax expense 397 413 391 380 Income tax expense from continuing operations (c) 150 56 130 134 Net income from continuing operations 247 357 261 246 Income (loss) from discontinued operations, net of tax 3 3 (52 ) 2 Net income $ 250 $ 360 $ 209 $ 248 Basic earnings per common share (b) Net income from continuing operations $ 0.48 $ 0.70 $ 0.54 $ 0.52 Net income 0.49 0.71 0.43 0.53 Diluted earnings per common share (b) Net income from continuing operations $ 0.48 $ 0.70 $ 0.54 $ 0.52 Net income 0.49 0.71 0.43 0.52 Cash dividends per common share $ — $ — $ 0.08 $ 0.08 (a) Amount for the fourth quarter of 2017 includes $119 million of tax expense attributable to tax reform enacted on December 22, 2017 , as further described in Note 23 (b) Earnings per share is calculated quarterly on an independent basis, therefore the total of the amounts presented for each year above may not reconcile to the annual amounts presented in Note 20 . (c) Amount for the second quarter of 2016 includes a nonrecurring tax benefit due to a U.S. tax reserve release related to a prior-year federal return that reduced our liability for unrecognized tax benefits , as further described in Note 23 .

Share-based Compensation Plans

Share-based Compensation Plans Share-based Compensation Plans	12 Months Ended
	Dec. 31, 2017
Share-based Compensation Plans [Abstract]
Compensation and Employee Benefit Plans [Text Block]	Share-based Compensation Plans We grant Restricted Stock Units (RSUs) and Performance Share Units (PSUs) to certain employees under the Ally Financial Inc. Incentive Compensation Plans (AICPs). The AICPs allow us to grant an array of equity-based and cash incentive awards to our named executive officers and other employees. Each of our approved compensation plans and awards are designed to provide certain of our employees with an opportunity to share in the future growth of value at Ally, which is necessary to attract and retain key talent. In 2017, we received stockholder approval on amendments to our AICPs. At December 31, 2017 , we had 37,778,224 shares available for future grants of incentive-based equity remaining under the AICPs. Our share-based compensation awards generally settle in Ally common stock and are classified as equity awards under GAAP. The cost of the awards are ratably charged to compensation and benefits expense in our Consolidated Statement of Income over their applicable service period and are based on the grant date fair value of Ally common stock. PSU and RSU Awards PSUs are payable contingent upon Ally achieving certain predefined performance objectives over a two-year measurement period and a three-year service condition. The number of awards payable upon vest can range from zero to 150% of the grant amount. The PSU awards settle in the form of Ally common stock. We accrue dividend equivalents for our PSUs that are paid upon vesting and based on the number of awards payable upon vest. RSUs are awarded to employees at no cost to the recipient upon their grant. The compensation costs related to these awards are ratably charged to expense over the applicable service period. The majority of the existing RSUs settle in the form of Ally common stock. RSUs granted in 2015 generally vested ratably over a two-year period starting on the date the award was issued and converted into shares of common stock at the end of the two-year period. RSU awards granted in 2017 and 2016 generally vest one third ratably each year over a three-year period starting on the date the award was issued and are converted into shares of common stock as of the vesting date. We accrue dividend equivalents for our RSUs that are paid upon vesting. Ally has awards that vested but were not yet distributed for the years ended December 31, 2017 , 2016 , and 2015 . The following table presents the changes in outstanding non-vested PSUs and RSUs activity during 2017. (in thousands, except per share data) Number of units Weighted-average grant date fair value per share RSUs and PSUs Outstanding non-vested at January 1, 2017 5,443 $ 19.00 Granted 3,280 21.30 Vested (3,043 ) 19.84 Forfeited (88 ) 19.39 Outstanding non-vested at December 31, 2017 5,592 19.89 We recognized expense related to PSU and RSU awards of $60 million , $54 million , and $49 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively.

Guarantees and Commitments Guar

Guarantees and Commitments Guarantees and Commitments	12 Months Ended
	Dec. 31, 2017
Guarantees and Commitments [Abstract]
Guarantees [Text Block]	Guarantees and Commitments Guarantees Guarantees are defined as contracts or indemnification agreements that contingently require us to make payments to third parties based on changes in the underlying agreements with the guaranteed parties. The following summarizes our outstanding guarantees, including those of our discontinued operations, made to third parties on our Consolidated Balance Sheet , for the periods shown. 2017 2016 December 31, ($ in millions) Maximum liability Carrying value of liability Maximum liability Carrying value of liability Standby letters of credit and other guarantees $ 227 $ 8 $ 175 $ 8 Corporate Finance has exposure to standby letters of credit that represent irrevocable guarantees of payment of specified financial obligations. Third-party beneficiaries primarily accept standby letters of credit as insurance in the event of nonperformance by our borrowers. Our borrowers may request letters of credit under their revolving loan facility up to a certain sub-limit amount. Expiration dates on letters of credit range from certain ongoing commitments that will expire during the upcoming year to terms of several years for certain letters of credit. If nonperformance occurs by a borrower for which we have issued a letter of credit, we can be liable for payment of the letter of credit to the beneficiary with our recourse being a charge to the borrower’s loan facility. As many of these commitments are subject to borrowing base agreements and other restrictive covenants or may expire without being fully drawn, the contract amounts are not necessarily indicative of future cash requirements. In connection with our Ally Invest wealth management business, we introduce customer securities accounts to a clearing broker, which clears and maintains custody of all customer assets and account activity. We are responsible for obtaining from each customer such funds or securities as are required to be deposited or maintained in their accounts. As a result, we are liable for any loss, liability, damage, cost, or expense incurred or sustained by the clearing broker as a result of the failure of any customer to timely make payments or deposits of securities to satisfy their contractual obligations. In addition, customer securities activities are transacted on either a cash or margin basis. In margin transactions, we may extend credit to the customer, through our clearing broker, subject to various regulatory rules and margin lending practices, collateralized by cash and securities in the customer’s account. In connection with these activities, we also execute customer transactions involving the sale of securities not yet purchased. Such transactions may expose us to credit risk in the event the customer’s assets are not sufficient to fully cover losses, which the customer may incur. In the event the customer fails to satisfy its obligations, we will purchase or sell financial instruments in the customer’s account in order to fulfill the customer’s obligations. The maximum potential exposure under these arrangements is difficult to estimate; however, the potential for us to incur material losses pursuant to these arrangements is remote. Commitments Financing Commitments The contractual commitments were as follows. December 31, ($ in millions) 2017 2016 Unused revolving credit line commitments and other (a) $ 2,341 $ 1,995 Home equity lines of credit (b) 318 356 Commitments to provide capital to investees (c) 283 206 Construction-lending commitments (d) 144 164 Mortgage loan origination commitments (e) 95 — (a) The unused portion of revolving lines of credit reset at prevailing market rates and, as such, approximate market value. (b) We are committed to fund the remaining unused balances on home equity lines of credit. (c) We are committed to contribute capital to certain investees. The fair value of these commitments is considered in the overall valuation of the underlying assets with which they are associated. (d) The fair value of these commitments is considered in the overall valuation of the related assets. (e) Commitments with mortgage loan applicants in which the loan terms, including interest rate and price, are guaranteed for a designated period of time subject to the completion of underwriting procedures. Revolving credit line commitments contain an element of credit risk. Management reduces its credit risk for unused revolving credit line commitments by applying the same credit policies in making commitments as it does for extending loans. We typically require collateral as these commitments are drawn. Lease Commitments Future minimum rental payments required under operating leases, primarily for real property, with noncancelable lease terms expiring after December 31, 2017 , are as follows. Year ended December 31, ($ in millions) 2018 $ 35 2019 35 2020 34 2021 36 2022 33 2023 and thereafter 316 Total minimum payment required $ 489 Certain of the leases contain escalation clauses and renewal or purchase options. Rental expenses under operating leases were $46 million for the year ended December 31, 2017 , and $51 million for the years ended December 31, 2016, and 2015. Contractual Commitments We have entered into multiple agreements for information technology, voice and communication technology, and related maintenance. Many of the agreements are subject to variable price provisions, fixed or minimum price provisions, and termination or renewal provisions. Year ended December 31, ($ in millions) 2018 $ 85 2019 and 2020 36 2021 and thereafter 2 Total future payment obligations $ 123

Description of Business, Basi40

Description of Business, Basis of Presentation, and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidation, Policy [Policy Text Block]	The Consolidated Financial Statements include the accounts of the parent and its consolidated subsidiaries, of which it is deemed to possess control, after eliminating intercompany balances and transactions, and include all variable interest entities (VIEs) in which we are the primary beneficiary. Other entities in which we have invested and have the ability to exercise significant influence over operating and financial policies of the investee, but upon which we do not possess control, are accounted for by the equity method of accounting within the financial statements and they are therefore not consolidated. Refer to Note 11 for further details on our VIEs.
Basis of Accounting, Policy [Policy Text Block]	Our accounting and reporting policies conform to accounting principles generally accepted in the United States of America (GAAP). Additionally, where applicable, the policies conform to the accounting and reporting guidelines prescribed by bank regulatory authorities. Certain reclassifications may have been made to the prior periods’ financial statements and notes to conform to the current period’s presentation, which did not have a material impact on our Consolidated Financial Statements.
Use of Estimates, Policy [Policy Text Block]	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and that affect income and expenses during the reporting period and related disclosures. In developing the estimates and assumptions, management uses all available evidence; however, actual results could differ because of uncertainties associated with estimating the amounts, timing, and likelihood of possible outcomes. Our most significant estimates pertain to the allowance for loan losses, valuations of automotive lease assets and residuals, fair value of financial instruments, legal and regulatory reserves, and the determination of the provision for income taxes.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and cash equivalents include cash on hand, cash on deposit at other financial institutions, cash items in process of collection, and certain highly liquid investments with original maturities of three months or less from the date of purchase. The book value of cash equivalents approximates fair value because of the short maturities of these instruments and the insignificant risk they present to changes in value with respect to changes in interest rates. Certain securities with original maturities of three months or less from the date of purchase that are held as a portion of longer-term investment portfolios, primarily held by our Insurance operations, are classified as investment securities. Cash and cash equivalents with legal restrictions limiting our ability to withdraw and use the funds are considered restricted cash and restricted cash equivalents and are presented as other assets on our Consolidated Balance Sheet.
Investment, Policy [Policy Text Block]	Our portfolio of investments includes various debt and marketable equity securities and nonmarketable equity investments. Debt and marketable equity securities are classified based on management’s intent to sell or hold the security. We classify debt securities as held-to-maturity only when we have both the intent and ability to hold the securities to maturity. We classify debt and marketable equity securities as trading when the securities are acquired for the purpose of selling or holding them for a short period of time. Securities not classified as either held-to-maturity or trading are classified as available-for-sale. Our debt and marketable equity securities include government securities, corporate bonds, asset-backed securities (ABS), mortgage-backed securities (MBS), and equity securities. Our portfolio includes securities classified as available-for-sale and held-to-maturity. Our available-for-sale securities are carried at fair value with unrealized gains and losses included in accumulated other comprehensive income or loss and are subject to impairment. Our held-to-maturity securities are carried at amortized cost and are subject to impairment. We amortize premiums and discounts on debt securities as an adjustment to investment yield generally over the stated maturity of the security. For ABS and MBS where prepayments can be reasonably estimated, amortization is adjusted for expected prepayments. Additionally, we assess our debt and marketable equity securities for potential other-than-temporary impairment. We employ a methodology that considers available evidence in evaluating potential other-than-temporary impairment of our debt and marketable equity securities classified as available-for-sale and held-to-maturity. If the cost of an investment exceeds its fair value, we evaluate, among other factors, the magnitude and duration of the decline in fair value. We also evaluate the financial health of and business outlook for the issuer, the performance of the underlying assets for interests in securitized assets, and, for securities classified as available-for-sale, our intent and ability to hold the investment through recovery of its amortized cost basis. Once a decline in fair value of a debt security is determined to be other-than-temporary, an impairment charge for the credit component is recorded to other gain (loss) on investments, net, in our Consolidated Statement of Income, and a new cost basis in the investment is established. The noncredit loss component of an available-for-sale debt security is recorded in other comprehensive income (loss) when we do not intend to sell the security and it is not more likely than not that we will have to sell the security prior to the security’s anticipated recovery. Both, the credit and noncredit loss components are recorded in earnings when we intend to sell the security or it is more likely than not that we will have to sell the security prior to the security’s anticipated recovery. Unrealized losses that we have determined to be other-than-temporary on equity securities are recorded to other gain (loss) on investments, net in our Consolidated Statement of Income. Subsequent increases and decreases to the fair value of available-for-sale debt and equity securities are included in other comprehensive income (loss), so long as they are not attributable to another other-than-temporary impairment. Realized gains and losses on investment securities are reported in other gain (loss) on investments, net, and are determined using the specific identification method. For information on our debt and marketable equity securities, refer to Note 8 . In addition to our investments in debt and marketable equity securities, we hold equity positions in other entities. These positions include Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock held to meet regulatory requirements, other equity investments that are not publicly traded and do not have a readily determinable fair value, equity investments in low income housing tax credits, and Community Reinvestment Act (CRA) equity investments, which are also not publicly traded and do not have a readily determinable fair value. Our investments in FHLB and FRB stock and other equity investments are accounted for using the cost method of accounting. Our low income housing tax credit investments are accounted for using the proportional amortization method of accounting for qualified affordable housing investments. Our obligations related to unfunded commitments for our low income housing tax credit investments are reported in other liabilities. Our CRA investments are accounted for using the equity method of accounting. Our FHLB and FRB stock and other equity investments carried at cost are included in nonmarketable equity investments in other assets. Our investments in low income housing tax credits and CRA are also included in other assets. As conditions warrant, we review our investments for impairment and will adjust the carrying value of the investment if it is deemed to be impaired. No impairment was recognized in 2017 or 2016. For more information on our nonmarketable equity investments, refer to Note 25 .
Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block]	We initially classify finance receivables and loans as either loans held-for-sale or loans held-for-investment based on management’s assessment of our intent and ability to hold the loans for the foreseeable future or until maturity. Management’s view of the foreseeable future is based on the longest reasonably reliable net income, liquidity, and capital forecast period. Management’s intent and ability with respect to certain loans may change from time to time depending on a number of factors, for example economic, liquidity, and capital conditions. In order to reclassify loans to held-for-sale, management must have the intent to sell the loans and reasonably identify the specific loans to be sold. Loans classified as held-for-sale are presented as loans held-for-sale, net on our Consolidated Balance Sheet and are carried at the lower of their net carrying value or fair value, unless the fair value option was elected, in which case those loans are carried at fair value. We’ve elected the fair value option for conforming direct-to-consumer originations for which we have a commitment to sell. The interest rate lock commitment that we enter into for a loan originated as held-for-sale and certain forward commitments to sell the loan are considered derivative instruments, which are carried at fair value on our Consolidate Balance Sheet. We have elected the fair value option to measure our non-derivative forward commitments. Changes in the fair value of our interest rate lock commitments, derivative forward commitments, and non-derivative forward commitments, as well as changes in the carrying value of loans classified as held-for-sale, are reported through gain on mortgage and automotive loans, net in our Consolidated Statement of Comprehensive Income. Interest income on our loans classified as held-for-sale is recognized based upon the contractual rate of interest on the loan and the unpaid principal balance. We report accrued interest receivable on our loans classified as held-for-sale in other assets on the Consolidated Balance Sheet. Loans classified as held-for-investment are presented as finance receivables and loans, net on our Consolidated Balance Sheet. Finance receivables and loans are reported at their gross carrying value, which includes the principal amount outstanding, net of unamortized deferred fees and costs on originated loans, unamortized premiums and discounts on purchased loans, unamortized basis adjustments arising from the designation of finance receivables and loans as the hedged item in qualifying fair value hedge relationships, and cumulative principal charge-offs. We refer to the gross carrying value less the allowance for loan loss as the net carrying value in finance receivables and loans. Unearned rate support received from an automotive manufacturer on certain automotive loans, deferred origination fees and costs, and premiums and discounts on purchased loans, are amortized over the contractual life of the related finance receivable or loan using the effective interest method. We make various incentive payments for consumer automotive loan originations to automotive dealers and account for these payments as direct loan origination costs. Additionally, we make incentive payments to certain commercial automobile wholesale borrowers and account for these payments as a reduction to interest income in the period they are earned. Interest income on our finance receivables and loans is recognized based on the contractual rate of interest plus the amortization of deferred amounts using the effective interest method. We report accrued interest receivable on our finance receivables and loans in other assets on our Consolidated Balance Sheet. Loan commitment fees are generally deferred and amortized over the commitment period. For information on finance receivables and loans, refer to Note 9 . Our portfolio segments are based on the level at which we develop and document our methodology for determining the allowance for loan losses. Additionally, the classes of finance receivables are based on several factors including the method for monitoring and assessing credit risk, the method of measuring carrying value, and the risk characteristics of the finance receivable. Based on an evaluation of our process for developing the allowance for loan losses including the nature and extent of exposure to credit risk arising from finance receivables, we have determined our portfolio segments to be consumer automotive, consumer mortgage, and commercial. • Consumer automotive — Consists of retail automotive financing for new and used vehicles. • Consumer mortgage — Consists of the following classes of finance receivables. • Mortgage Finance — Consists of consumer first mortgages from our ongoing mortgage operations including bulk acquisitions, direct-to-consumer originations, and refinancing of high-quality jumbo mortgages and low-to-moderate income (LMI) mortgages. • Mortgage — Legacy — Consists of consumer mortgage assets originated prior to January 1, 2009, including first mortgages, subordinate-lien mortgages, and home equity mortgages. • Commercial — Consists of the following classes of finance receivables. • Commercial and Industrial • Automotive — Consists of financing operations to fund dealer purchases of new and used vehicles through wholesale floorplan financing. Additional commercial offerings include automotive dealer term loans, dealer fleet financing, and other equipment financing. • Other — Consists primarily of senior secured leveraged cash flow and asset-based loans related to our Corporate Finance business. • Commercial Real Estate — Consists of term loans to finance dealership land and buildings, and other commercial lending secured by real estate. Nonaccrual Loans Generally, we recognize loans of all classes as past due when they are 30 days delinquent on making a contractually required payment, and loans are placed on nonaccrual status when principal or interest has been delinquent for 90 days or when full collection is not expected. Interest income recognition is suspended when finance receivables and loans are placed on nonaccrual status. Additionally, amortization of premiums and discounts and deferred fees and costs ceases when finance receivables and loans are placed on nonaccrual. Exceptions include commercial real estate loans that are placed on nonaccrual status when delinquent for 60 days or when full collection is not probable, if sooner. Additionally, our policy is to generally place all loans that have been modified in troubled debt restructurings (TDRs) on nonaccrual status until the loan has been brought fully current, the collection of contractual principal and interest is reasonably assured, and six consecutive months of repayment performance is achieved. In certain cases, if a borrower has been current up to the time of the modification and repayment of the debt subsequent to the modification is reasonably assured, we may choose to continue to accrue interest on the loan. Loans on nonaccrual status are reported as nonperforming loans in Note 9 . The receivable for interest income that is accrued, but not collected, at the date finance receivables and loans are placed on nonaccrual status is reversed against interest income and subsequently recognized only to the extent it is received in cash or until it qualifies for return to accrual status. However, where there is doubt regarding the ultimate collectability of loan principal, all cash received is applied to reduce the carrying value of such loans. Generally, finance receivables and loans are restored to accrual status only when contractually current and the collection of future payments is reasonably assured. Impaired Loans Loans of all classes are considered impaired when we determine it is probable that we will be unable to collect all amounts due (both principal and interest) according to the terms of the loan agreement. For all classes of consumer loans, impaired loans include all loans that have been modified in TDRs. Commercial loans of all classes are considered impaired on an individual basis and reported as impaired when we determine it is probable that we will be unable to collect all amounts due according to the terms of the loan agreement. With the exception of certain consumer TDRs that have been returned to accruing status, for all classes of impaired loans, income recognition is consistent with that of nonaccrual loans discussed above. Impaired loans may return to accrual status as discussed in the preceding nonaccrual loan section at which time, the normal accrual of interest income resumes. For collateral dependent loans, if the recorded investment in the impaired loans exceeds the fair value of the collateral, a charge-off is recorded consistent with the TDR discussion below. Troubled Debt Restructurings When the terms of finance receivables or loans are modified, consideration must be given as to whether or not the modification results in a TDR. A modification is considered to be a TDR when both the borrower is experiencing financial difficulty and we grant a concession to the borrower. These considerations require significant judgment and vary by portfolio segment. In all cases, the cumulative impacts of all modifications are considered at the time of the most recent modification. For consumer loans of all classes, various qualitative factors are utilized for assessing the financial difficulty of the borrower. These include, but are not limited to, the borrower’s default status on any of its debts, bankruptcy and recent changes in financial circumstances (loss of job, etc.). A concession has been granted when as a result of the modification we do not expect to collect all amounts due under the original loan terms, including interest accrued at the original contract rate. Types of modifications that may be considered concessions include, but are not limited to, extensions of terms at a rate that does not constitute a market rate, a reduction, deferral or forgiveness of principal or interest owed and loans that have been discharged in a Chapter 7 Bankruptcy and have not been reaffirmed by the borrower. In addition to the modifications noted above, in our consumer automotive portfolio segment of loans we also provide extensions or deferrals of payments to borrowers whom we deem to be experiencing only temporary financial difficulty. In these cases, there are limits within our operational policies to minimize the number of times a loan can be extended, as well as limits to the length of each extension, including a cumulative cap over the life of the loan. If these limits are breached, the modification is considered a TDR as noted in the following paragraph. Before offering an extension or deferral, we evaluate the capacity of the customer to make the scheduled payments after the deferral period. During the deferral period, we continue to accrue and collect interest on the loan as part of the deferral agreement. We grant these extensions or deferrals when we expect to collect all amounts due including interest accrued at the original contract rate. A restructuring that results in only a delay in payment that is deemed to be insignificant is not a concession and the modification is not considered to be a TDR. In order to assess whether a restructuring that results in a delay in payment is insignificant, we consider the amount of the restructured payments subject to delay in conjunction with the unpaid principal balance or the collateral value of the loan, whether or not the delay is significant with respect to the frequency of payments under the original contract, or the loan’s original expected duration. In the cases where payment extensions on our automotive loan portfolio cumulatively extend beyond 90 days and are more than 10% of the original contractual term or where the cumulative payment extension is beyond 180 days, we deem the delay in payment to be more than insignificant, and as such, classify these types of modifications as TDRs. Otherwise, we believe that the modifications do not represent a concessionary modification and accordingly, they are not classified as TDRs. For commercial loans of all classes, similar qualitative factors are considered when assessing the financial difficulty of the borrower. In addition to the factors noted above, consideration is also given to the borrower’s forecasted ability to service the debt in accordance with the contractual terms, possible regulatory actions and other potential business disruptions (e.g., the loss of a significant customer or other revenue stream). Consideration of a concession is also similar for commercial loans. In addition to the factors noted above, consideration is also given to whether additional guarantees or collateral have been provided. For all loans, TDR classification typically results from our loss mitigation activities. For loans held-for-investment that are not carried at fair value and are TDRs, impairment is typically measured based on the difference between the gross carrying value of the loan and the present value of the expected future cash flows of the loan. The loan may also be measured for impairment based on the fair value of the underlying collateral less costs to sell for loans that are collateral dependent. We recognize impairment by either establishing a valuation allowance or recording a charge-off. The financial impacts of modifications that meet the definition of a TDR are reported in the period in which they are identified as TDRs. Additionally, if a loan that is classified as a TDR redefaults within twelve months of the modification, we are required to disclose the instances of redefault. For the purpose of this disclosure, we have determined that a loan is considered to have redefaulted when the loan meets the requirements for evaluation under our charge-off policy except for commercial loans where redefault is defined as 90 days past due. Impaired loans may return to accrual status as discussed in the preceding nonaccrual loan section at which time, the normal accrual of interest income resumes. Net Charge-offs We disclose the measurement of net charge-offs as the amount of gross charge-offs recognized less recoveries received. Gross charge-offs reflect the amount of the gross carry value directly written-off. Generally, we recognize recoveries when they are received and record them as an increase to the allowance for loan losses. As a general rule, consumer automotive loans are written down to estimated collateral value, less costs to sell, once a loan becomes 120 days past due. In our consumer mortgage portfolio segment, first-lien mortgages and a subset of our home equity portfolio that are secured by real estate in a first-lien position are written down to the estimated fair value of the collateral, less costs to sell, once a mortgage loan becomes 180 days past due. Consumer mortgage loans that represent second-lien positions are charged off at 180 days past due. Consumer mortgage loans within our second-lien portfolio in bankruptcy that are 60 days past due are fully charged off within 60 days of receipt of notification of filing from the bankruptcy court. Consumer automotive and first-lien consumer mortgage loans in bankruptcy that are 60 days past due are written down to their expected future cash flows, which is generally fair value of the collateral, less costs to sell, within 60 days of receipt of notification of filing from the bankruptcy court. Regardless of other timelines noted within this policy, loans are considered collateral dependent once foreclosure or repossession proceedings begin and are charged-off to the estimated fair value of the underlying collateral, less costs to sell at that time. Commercial loans are individually evaluated and where collectability of the recorded balance is in doubt are written down to the estimated fair value of the collateral less costs to sell. Generally, all commercial loans are charged-off when it becomes unlikely that the borrower is willing or able to repay the remaining balance of the loan and any underlying collateral is not sufficient to recover the outstanding principal. Collateral dependent loans are charged-off to the fair market value of collateral less costs to sell when appropriate. Noncollateral dependent loans are fully written-off.
Loans and Leases Receivable, Allowance for Loan Losses Policy [Policy Text Block]	The allowance for loan losses (the allowance) is management’s estimate of incurred losses in the lending portfolios. We determine the amount of the allowance required for each of our portfolio segments based on its relative risk characteristics. The evaluation of these factors for both consumer and commercial finance receivables and loans involves quantitative analysis combined with sound management judgment. Additions to the allowance are charged to current period earnings through the provision for loan losses; amounts determined to be uncollectible are charged directly against the allowance, net of amounts recovered on previously charged-off accounts. The allowance is composed of two components: specific reserves established for individual loans evaluated as impaired and portfolio-level reserves established for large groups of typically smaller balance homogeneous loans that are collectively evaluated for impairment. We evaluate the adequacy of the allowance based on the combined total of these two components. Determining the appropriateness of the allowance is complex and requires judgment by management about the effect of matters that are inherently uncertain. It is possible that others, given the same information, may at any point in time reach different reasonable conclusions. Measurement of impairment for specific reserves is generally determined on a loan-by-loan basis. Loans determined to be specifically impaired are measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate, an observable market price, or the estimated fair value of the collateral less estimated costs to sell when appropriate, whichever is determined to be the most appropriate. When these measurement values are lower than the net carrying value of that loan, impairment is recognized. Loans that are not identified as individually impaired are pooled with other loans with similar risk characteristics for evaluation of impairment for the portfolio-level allowance. For the purpose of calculating portfolio-level reserves, we have grouped our loans into three portfolio segments: consumer automotive, consumer mortgage, and commercial. The allowance consists of the combination of a quantitative assessment component based on statistical models, a retrospective evaluation of actual loss information to loss forecasts, and includes a qualitative component based on management judgment. Management takes into consideration relevant qualitative factors, including external and internal trends such as the impacts of changes in underwriting standards, collections and account management effectiveness, geographic concentrations, and economic events, among other factors, that have occurred but are not yet reflected in the quantitative assessment component. Qualitative adjustments are documented, reviewed, and approved through our established risk governance processes and follow regulatory guidance. Management also considers the need for a reserve on unfunded non-derivative loan commitments across our portfolio segments, including lines of credit and standby letters of credit, using similar procedures and methodologies used to determine the allowance for loan losses while also considering historical loss ratios and potential usage levels. The reserve for unfunded loan commitments is recorded within other liabilities on our Consolidated Balance Sheet and the related expense is reported as other noninterest expense in our Consolidated Statement of Comprehensive Income. Refer to Note 29 for information on our unfunded loan commitments. During 2017, we did not substantively change any material aspect of our overall approach used to determine the allowance for loan losses for our portfolio segments. There were no material changes in criteria or estimation techniques as compared to prior periods that impacted the determination of the current period allowance for loan losses for our portfolio segments. Refer to Note 9 for information on the allowance for loan losses. Consumer Loans Our consumer automotive and consumer mortgage portfolio segments are reviewed for impairment based on an analysis of loans that are grouped into common risk categories. We perform periodic and systematic detailed reviews of our lending portfolios to identify inherent risks and to assess the overall collectability of those portfolios. Loss models are utilized for these portfolios, which consider a variety of credit quality indicators including, but not limited to, historical loss experience, current economic conditions, credit scores, and expected loss factors by loan type. Consumer Automotive Portfolio Segment The allowance for loan losses within the consumer automotive portfolio segment is calculated using proprietary statistical models and other risk indicators applied to pools of loans with similar risk characteristics, including credit bureau score and loan-to-value ratios to arrive at an estimate of incurred losses in the portfolio. These statistical loss forecasting models are utilized to estimate incurred losses and consider a variety of factors including, but not limited to, historical loss experience, estimated defaults based on portfolio trends, and general economic and business trends. These statistical models predict forecasted losses inherent in the portfolio. The forecasted losses consider historical factors such as frequency (the number of contracts that we expect to default) and loss severity (the loss amount of contracts we expect to default). The loss severity within the consumer automotive portfolio segment is impacted by the market values of vehicles that are repossessed. Vehicle market values are affected by numerous factors including vehicle supply, the condition of the vehicle upon repossession, the overall price and volatility of gasoline or diesel fuel, consumer preference related to specific vehicle segments, and other factors. The quantitative assessment component of the allowance may be supplemented with qualitative reserves based on management’s determination that such adjustments provide a better estimate of credit losses. This qualitative assessment takes into consideration relevant internal and external factors that have occurred but are not yet reflected in the forecasted losses and may affect the performance of the portfolio. Consumer Mortgage Portfolio Segment The allowance for loan losses within the consumer mortgage portfolio segment is calculated by using proprietary statistical models based on pools of loans with similar risk characteristics, including credit score, loan-to-value, loan age, documentation type, product type, and loan purpose, to arrive at an estimate of incurred losses in the portfolio. These statistical loss forecasting models are utilized to estimate incurred losses and consider a variety of factors including, but not limited to, historical loss experience, estimated foreclosures or defaults based on portfolio trends, delinquencies, and general economic and business trends. The forecasted losses are statistically derived based on a suite of behavioral based transition models. This transition framework predicts various stages of delinquency, default, and voluntary prepayment over the course of the life of the loan. The transition probability is a function of the loan and borrower characteristics and economic variables and considers historical factors such as frequency and loss severity. When a default event is predicted, a severity model is applied to estimate future loan losses. Loss severity within the consumer mortgage portfolio segment is impacted by the market values of foreclosed properties, which is affected by numerous factors, including geographic considerations and the condition of the foreclosed property. The quantitative assessment component of the allowance may be supplemented with qualitative reserves based on management’s determination that such adjustments provide a better estimate of credit losses. This qualitative assessment takes into consideration relevant internal and external factors that have occurred but are not yet reflected in the forecasted losses and may affect the performance of the portfolio. Commercial Loans The allowance for loan losses within the commercial portfolio is composed of reserves established for specific loans evaluated as impaired and portfolio-level reserves based on nonimpaired loans grouped into pools based on similar risk characteristics and collectively evaluated. A commercial loan is considered impaired when it is probable that we will be unable to collect all amounts due according to the contractual terms of the loan agreement based on current information and events. These loans are primarily evaluated individually and are risk-rated based on borrower, collateral, and industry-specific information that management believes is relevant in determining the occurrence of a loss event and measuring impairment. Management establishes specific allowances for commercial loans determined to be individually impaired based on the present value of expected future cash flows, discounted at the loan’s effective interest rate, observable market price or the fair value of collateral, whichever is determined to be the most appropriate. Estimated costs to sell or realize the value of the collateral on a discounted basis are included in the impairment measurement, when appropriate. Loans not identified as impaired are grouped into pools based on similar risk characteristics and collectively evaluated. Our risk rating models use historical loss experience, concentrations, current economic conditions, and performance trends. The commercial historical loss experience is updated quarterly to incorporate the most recent data reflective of the current economic environment. The determination of the allowance is influenced by numerous assumptions and many factors that may materially affect estimates of loss, including volatility of loss given default, probability of default, and rating migration. In assessing the risk rating of a particular loan, several factors are considered including an evaluation of historical and current information involving subjective assessments and interpretations. In addition, the allowance related to the commercial portfolio segment is influenced by estimated recoveries from automotive manufacturers relative to guarantees or agreements with them to repurchase vehicles used as collateral to secure the loans. The quantitative assessment component of the allowance may be supplemented with qualitative reserves based on management’s determination that such adjustments provide a better estimate of credit losses. This qualitative assessment takes into consideration relevant internal and external factors that have occurred but are not yet reflected in the forecasted losses and may affect the performance of the portfolio.
Consolidation, Variable Interest Entity, Policy [Policy Text Block]	For all VIEs in which we are involved, we assess whether we are the primary beneficiary of the VIE on an ongoing basis. In circumstances where we have both the power to direct the activities that most significantly impact the VIEs performance and the obligation to absorb losses or the right to receive benefits of the VIE that could be significant, we would conclude that we are the primary beneficiary of the VIE, and would consolidate the VIE. In situations where we are not deemed to be the primary beneficiary of the VIE, we do not consolidate the VIE and only recognize our interests in the VIE. We are involved in securitization transactions that typically involve the use of VIEs. For information regarding the company’s securitization activities, refer to Note 11 . In the case of a consolidated VIE used for a securitization transaction, the underlying automotive finance retail contracts, wholesale loans, and automotive leases remain on our Consolidated Balance Sheet with the corresponding obligations (consisting of the beneficial interests issued by the securitization entity) reflected as debt. We recognize interest income on the finance receivables, lease income on automotive leases, and interest expense on the beneficial interests issued by the securitization entity; and we recognize loan losses on the finance receivables and loans as incurred. Consolidation of the VIE would also preclude us from recording an accounting sale on the transaction. In securitization transactions where we are not determined to be the primary beneficiary of the VIE, we must determine whether or not we achieve a sale for accounting purposes. In order to achieve a sale of finance receivables and loans for accounting purposes, the assets being transferred must be legally isolated, not be constrained by restrictions from further transfer, and be deemed to be beyond our control. We would deem the transaction to be an off-balance sheet securitization if the preceding three criteria for sale accounting are met. If we were to fail any of these three criteria for sale accounting, the transfer would be accounted for as a secured borrowing consistent with the preceding paragraph. The gain or loss recognized on off-balance sheet securitizations take into consideration any assets received as part of the transaction, including any retained interests, and servicing assets or liabilities (if applicable), which are initially recorded at fair value at the date of sale. Upon the sale of the loans, we recognize a gain or loss on sale for the difference between the assets recognized, and the assets derecognized. The financial assets obtained from off-balance sheet securitizations are primarily reported as cash, or retained interests (if applicable). Retained interests are classified as securities or as other assets depending on their form and structure. The estimate of the fair value of the retained interests and servicing requires us to exercise significant judgment about the timing and amount of future cash flows from the interests. For a discussion on fair value estimates, refer to Note 25 . Gains or losses on off-balance sheet securitizations are reported in gain on mortgage and automotive loans, net, in our Consolidated Statement of Comprehensive Income . We retain servicing rights for all of our consumer and commercial automotive loan and operating lease securitizations. We may receive servicing fees for off-balance sheet securitizations based on the securitized loan balances and certain ancillary fees, all of which are reported in servicing fees in the Consolidated Statement of Income. Typically, the fee we are paid for servicing consumer automotive finance receivables represents adequate compensation, and consequently, does not result in the recognition of a servicing asset or liability. The determination of whether the assets and liabilities of the VIEs are consolidated on our balance sheet (also referred to as on-balance sheet) or not consolidated on our balance sheet (also referred to as off-balance sheet) depends on the terms of the related transaction and our continuing involvement (if any) with the VIE. We are deemed the primary beneficiary and therefore consolidate VIEs for which we have both (a) the power, through voting rights or similar rights, to direct the activities that most significantly impact the VIE’s economic performance, and (b) a variable interest (or variable interests) that (i) obligates us to absorb losses that could potentially be significant to the VIE; and/or (ii) provides us the right to receive residual returns of the VIE that could potentially be significant to the VIE. We determine whether we hold a significant variable interest in a VIE based on a consideration of both qualitative and quantitative factors regarding the nature, size, and form of our involvement with the VIE. We assess whether we are the primary beneficiary of a VIE on an ongoing basis and are generally determined to be the primary beneficiary in VIEs established for our securitization activities when we have a controlling financial interest in the VIE, primarily due to our servicing activities, and our beneficial interest in the VIE that could be potentially significant. The consolidated VIEs included on the Consolidated Balance Sheet represent separate entities with which we are involved. The third-party investors in the obligations of consolidated VIEs have legal recourse only to the assets of the VIEs and do not have such recourse to us, except for the customary representation and warranty provisions. In addition, the cash flows from the assets are restricted only to pay such liabilities. Thus, our economic exposure to loss from outstanding third-party financing related to consolidated VIEs is limited to the carrying value of the consolidated VIE assets. Generally, all assets of consolidated VIEs, presented below based upon the legal transfer of the underlying assets in order to reflect legal ownership, are restricted for the benefit of the beneficial interest holders. For additional information regarding the company’s significant accounting policies for consolidated VIEs, refer to the Securitizations and Variable Interest Entities section of Note 1 .
Finance, Loan and Lease Receivables, Held for Investments, Foreclosed Assets Policy [Policy Text Block]	Assets securing our finance receivables and loans are classified as repossessed and foreclosed and included in other assets when physical possession of the collateral is taken, which includes the transfer of title through foreclosure or other similar proceedings. Repossessed and foreclosed assets are initially recognized at the lower of the outstanding balance at the time of repossession or foreclosure or the fair value of the asset less estimated costs to sell. Losses on the revaluation of repossessed and foreclosed assets (and generally, declines in value shortly after repossession or foreclosure) are recognized as a charge-off of the allowance for loan losses. Subsequent declines in value are charged to other operating expenses.
Revenue Recognition Leases, Operating [Policy Text Block]	Investment in operating leases, net, represents the automobiles that are underlying our automotive lease contracts and is reported at cost, less accumulated depreciation and net of impairment charges and origination fees or costs. Depreciation of vehicles is recorded on a straight-line basis to an estimated residual value over the lease term. Manufacturer support payments that we receive upfront are treated as a reduction to the cost-basis in the underlying lease asset, which has the effect of reducing depreciation expense over the life of the contract. We periodically evaluate our depreciation rate for leased vehicles based on expected residual values and adjust depreciation expense over the remaining life of the lease if deemed necessary. Income from operating lease assets that includes lease origination fees, net of lease origination costs, is recognized as operating lease revenue on a straight-line basis over the scheduled lease term. We have significant investments in the residual values of the assets in our operating lease portfolio. The residual values represent an estimate of the values of the assets at the end of the lease contracts. At contract inception, we determine pricing based on the projected residual value of the lease vehicle. This evaluation is primarily based on a proprietary model, which includes variables such as age, expected mileage, seasonality, segment factors, vehicle type, economic indicators, production cycle, automotive manufacturer incentives, and shifts in used vehicle supply. This internally-generated data is compared against third-party, independent data for reasonableness. Realization of the residual values is dependent on our future ability to market the vehicles under the prevailing market conditions. Over the life of the lease, we evaluate the adequacy of our estimate of the residual value and make adjustments to the depreciation rates to the extent the expected value of the vehicle at lease termination changes. In addition to estimating the residual value at lease termination, we also evaluate the current value of the operating lease asset and test for impairment to the extent necessary when there is an indication of impairment based on market considerations and portfolio characteristics. Impairment is determined to exist if fair value of the leased asset is less than carrying value and it is determined that the net carrying value is not recoverable. The net carrying value of a leased asset is not recoverable if it exceeds the sum of the undiscounted expected future cash flows expected to result from the lease payments and the estimated residual value upon eventual disposition. If our operating lease assets are considered to be impaired, the impairment is measured as the amount by which the carrying amount of the assets exceeds the fair value as estimated by discounted cash flows. No impairment was recognized in 2017 , 2016 , or 2015 . We accrue rental income on our operating leases when collection is reasonably assured. We generally discontinue the accrual of revenue on operating leases at the time an account is determined to be uncollectible, at the earliest of the time of repossession, within 60 days of bankruptcy notification and greater than 60 days past due, or greater than 120 days past due. When a lease vehicle is returned to us, either at the end of the lease term or through repossession, the asset is reclassified from investment in operating leases, net, to other assets and recorded at the lower-of-cost or estimated fair value, less costs to sell, on our Consolidated Balance Sheet. Any losses recognized at this time are recorded as depreciation expense. Subsequent decline in value and any gain or loss recognized at the time of sale is recognized as a remarketing gain or loss and presented as a component of depreciation expense.
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]	The net carrying values of long-lived assets (including property and equipment) are evaluated for impairment whenever events or changes in circumstances indicate that their net carrying values may not be recoverable from the estimated undiscounted future cash flows expected to result from their use and eventual disposition. Recoverability of assets to be held and used is measured by a comparison of their net carrying amount to future net undiscounted cash flows expected to be generated by the assets. If these assets are considered to be impaired, the impairment is measured as the amount by which the net carrying amount of the assets exceeds the fair value estimated using a discounted cash flow method. No material impairment was recognized in 2017 , 2016 , or 2015 . An impairment test on an asset group to be sold or otherwise disposed of is performed upon occurrence of a triggering event or when certain criteria are met (e.g., the asset is planned to be disposed of within twelve months, appropriate levels of authority have approved the sale, there is an active program to locate a buyer, etc.), which cause the disposal group to be classified as held-for-sale. Long-lived assets held-for-sale are recorded at the lower of their carrying amount or estimated fair value less cost to sell. If the net carrying value of the assets held-for-sale exceeds the fair value less cost to sell, we recognize an impairment loss based on the excess of the net carrying amount over the fair value of the assets less cost to sell. Refer to Note 3 for a discussion of discontinued operations.
Property, Plant and Equipment, Policy [Policy Text Block]	Property and equipment stated at cost, net of accumulated depreciation and amortization, are reported in other assets on our Consolidated Balance Sheet. Included in property and equipment are certain buildings, furniture and fixtures, leasehold improvements, IT hardware and software, capitalized software costs, and assets under construction. We begin depreciating these assets when they are ready for their intended use. Depreciation is recorded on a straight-line basis over the estimated useful lives of the assets, which generally ranges from three to thirty years depending on the asset class. Capitalized software is generally amortized on a straight-line basis over its useful life, which generally ranges from three to five years. Capitalized software that is not expected to provide substantive service potential or for which development costs significantly exceed the amount originally expected is considered impaired and written down to fair value. Software expenditures that are considered general, administrative, or of a maintenance nature are expensed as incurred.
Business Combinations Policy [Policy Text Block]	We account for our business acquisitions using the acquisition method of accounting. Under this method, we generally record the initial carrying values of purchased assets, including identifiable intangible assets, and assumed liabilities at fair value on the acquisition date. We recognize goodwill when the acquisition price is greater than the fair value of the net assets acquired, including identifiable intangible assets. The initial fair value of recognized assets and liabilities are subject to refinement during the measurement period, a period up to one year after the closing date of an acquisition, as information relative to acquisition date fair values becomes available. Costs directly related to business combinations are recorded as expenses as they are incurred.
Goodwill and Intangible Assets, Policy [Policy Text Block]	Goodwill and intangible assets, net of accumulated amortization, are reported in other assets. Our intangible assets primarily consist of acquired customer relationships and developed technology, and are amortized using a straight line methodology over their estimated useful lives. We review intangible assets for impairment at least annually, or whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. If it is determined the carrying amount of the asset is not recoverable, an impairment charge is recorded. Refer to Note 2 for further discussion on intangible assets. Goodwill represents the excess of the cost of an acquisition over the fair value of net assets acquired, including identifiable intangibles. We allocate goodwill to applicable reporting units based on the relative fair value of the other net assets allocated to those reporting units at the time of the acquisition. In the event we restructure our business, we may reallocate goodwill. We test goodwill for impairment annually, or more frequently if events and changes in circumstances indicate that it is more likely than not that impairment exists. Our annual goodwill impairment test is performed as of August 31 of each year. In certain situations, we may perform a qualitative assessment to test goodwill for impairment. We may also decide to bypass the qualitative assessment and perform a quantitative assessment. If we perform the qualitative assessment to test goodwill for impairment and conclude that it is more likely than not that the reporting unit’s fair value is greater than its carrying value, then the quantitative assessment is not required. However, if we perform the qualitative assessment and determine that it is more likely than not that a reporting unit’s fair value is less than its carrying value, then we must perform the quantitative assessment. The quantitative assessment uses a two-step process. The first step of the assessment requires us to compare the fair value of each of the reporting units to their respective carrying value. The fair value of the reporting units in our quantitative assessment is determined based on various analyses including discounted cash flow projections using assumptions a market participant would use. If the carrying value is less than the fair value, no impairment exists, and the second step does not need to be completed. If the carrying value is greater than the fair value or there is an indication that impairment may exist, a second step must be performed where we determine the implied value of goodwill based on the individual fair values of the reporting unit’s assets and liabilities, including unrecognized intangibles, to compute the amount of the impairment. Refer to Note 2 for further discussion on goodwill.
Revenue Recognition, Deferred Revenue [Policy Text Block]	Insurance premiums, net of premiums ceded to reinsurers, and service revenue are earned over the terms of the policies. The portion of premiums and service revenue written applicable to the unexpired terms of the policies is recorded as unearned insurance premiums or unearned service revenue. For vehicle service and maintenance contracts, premiums and service revenues are earned on a basis proportionate to the anticipated cost emergence. For other short duration contracts, premiums and service revenue are earned on a pro rata basis. For further information, refer to Note 4 .
Deferred Charges, Policy [Policy Text Block]	Certain incremental direct costs incurred to originate a policy are deferred and recorded in other assets. These costs primarily include commissions paid to dealers to originate these policies and vary with the production of business. Deferred policy acquisition costs are amortized over the terms of the related policies and service contracts on the same basis as premiums and service revenue are earned. We group costs incurred for acquiring like contracts and consider anticipated investment income in determining the recoverability of these costs.
Unpaid Policy Claims and Claims Adjustment Expense, Policy [Policy Text Block]	Reserves for insurance losses and loss adjustment expenses are reported in accrued expenses and other liabilities on our Consolidated Balance Sheet. They are established for the unpaid cost of insured events that have occurred as of a point in time. More specifically, the reserves for insurance losses and loss adjustment expenses represent the accumulation of estimates for both reported losses and those incurred, but not reported, including loss adjustment expenses relating to direct insurance and assumed reinsurance agreements. We use a combination of methods, including the chain ladder development factor, expected loss, Bornhuetter Ferguson (BF), and frequency and severity methods to determine the ultimate losses for an individual line of business as well as accident year basis depending on the maturity of the accident period and line of business specifics. Development methods are used for more mature years where expected loss, BF, and frequency and severity methods are used for less mature years. Both paid and incurred loss and loss adjustment expenses are reviewed where available and a weighted average of estimates or a single method may be considered in selecting the final estimate for an individual accident period. We did not change our methodology for developing reserves for insurance losses for the year ended December 31, 2017 . Estimates for salvage and subrogation recoverable are recognized at the time losses are incurred and netted against the provision for insurance losses and loss adjustment expenses. Reserves are established for each business at the lowest meaningful level of homogeneous data. Since the reserves are based on estimates, the ultimate liability may vary from such estimates. The estimates are regularly reviewed and adjustments, which can potentially be significant, are included in earnings in the period in which they are deemed necessary.
Legal Costs, Policy [Policy Text Block]	Reserves for legal and regulatory matters are established when those matters present loss contingencies that are both probable and estimable, with a corresponding amount recorded to other operating expense. In cases where we have an accrual for losses, it is our policy to include an estimate for probable and estimable legal expenses related to the case. If, at the time of evaluation, the loss contingency related to a legal or regulatory matter is not both probable and estimable, we do not establish a liability for the contingency. We continue to monitor legal and regulatory matters for further developments that could affect the requirement to establish a liability or that may impact the amount of a previously established liability. There may be exposure to loss in excess of any amounts recognized. For certain other matters where the risk of loss is determined to be reasonably possible, estimable, and material to the financial statements, disclosure regarding details of the matter and an estimated range of loss is required. The estimated range of possible loss does not represent our maximum loss exposure. We also disclose matters that are deemed probable or reasonably possible, material to the financial statements, but for which an estimated range of loss is not possible to determine. While we believe our reserves are adequate, the outcome of legal and regulatory proceedings is extremely difficult to predict and we may settle claims or be subject to judgments for amounts that differ from our estimates. For information regarding the nature of all material contingencies, refer to Note 30 .
Earnings Per Share, Policy [Policy Text Block]	We compute basic earnings (loss) per common share by dividing net income (loss) from continuing operations attributable to common stockholders after deducting dividends on preferred stock by the weighted-average number of common shares outstanding during the period. We compute diluted earnings (loss) per common share by dividing net income (loss) from continuing operations after deducting dividends on preferred stock by the weighted-average number of common shares outstanding during the period plus the dilution resulting from incremental shares that would have been outstanding if dilutive potential common shares had been issued (assuming it does not have the effect of antidilution), if applicable.
Derivatives, Policy [Policy Text Block]	We use derivative instruments primarily for risk management purposes. We do not use derivative instruments for speculative purposes. Certain of our derivative instruments are designated as accounting hedges in qualifying relationships, whereas other derivative instruments have not been designated as accounting hedges. In accordance with applicable accounting standards, all derivative instruments, whether designated for hedge accounting or not, are required to be recorded on the balance sheet as assets or liabilities and measured at fair value. We have elected to report the fair value of derivative assets and liabilities on a gross basis—including the fair value for the right to reclaim cash collateral or the obligation to return cash collateral—arising from instruments executed with the same counterparty under a master netting arrangement where we do not have the intent to offset. For additional information on derivative instruments and hedging activities, refer to Note 22 . At the inception of a hedge accounting relationship, we designate each qualifying hedge relationship as a hedge of the fair value of a specifically identified asset or liability (fair value hedge); as a hedge of the variability of cash flows to be received or paid, or forecasted to be received or paid, related to a recognized asset or liability (cash flow hedge); or as a hedge of the foreign-currency exposure of a net investment in a foreign operation (net investment hedge). We formally document all relationships between hedging instruments and hedged items, as well as the risk management objectives for undertaking various hedge transactions. Both at hedge inception and on an ongoing basis, we formally assess whether the derivatives that are used in hedging relationships are highly effective in offsetting changes in fair values or cash flows of hedged items. Changes in the fair value of derivative instruments qualifying as fair value hedges, along with the gain or loss on the hedged asset or liability attributable to the hedged risk, are recorded in current period earnings. For qualifying cash flow hedges, the effective portion of the change in the fair value of the derivative financial instruments is recorded in accumulated other comprehensive income, and recognized in the income statement when the hedged cash flows affect earnings. For a qualifying net investment hedge, the gain or loss is reported in accumulated other comprehensive income as part of the cumulative translation adjustment. The ineffective portions of changes in fair value, cash flow, and net investment hedges are immediately recognized in earnings, along with the portion of the change in fair value that is excluded from the assessment of hedge effectiveness, if any. Hedge accounting treatment is no longer applied if a derivative financial instrument is terminated, or if the hedge designation is removed or assessed to be no longer highly effective. For terminated fair value hedges, any changes to the hedged asset or liability remain as part of the basis of the hedged asset or liability and are recognized into income over the remaining life of the asset or liability. For terminated cash flow hedges, unless it is probable that the forecasted cash flows will not occur within a specified period, any changes in fair value of the derivative financial instrument previously recognized remain in accumulated other comprehensive income, and are reclassified into earnings in the same period that the hedged cash flows affect earnings. Any previously recognized gain or loss for a net investment hedge continues to remain in accumulated other comprehensive income until earnings are impacted by sale or liquidation of the associated foreign operation. In all instances, after hedge accounting is no longer applied, any subsequent changes in fair value of the derivative instrument will be recorded into earnings. Changes in the fair value of derivative financial instruments held for risk management purposes that are not designated as accounting hedges under GAAP are reported in current period earnings.
Income Tax, Policy [Policy Text Block]	Our income tax expense, deferred tax assets and liabilities, and reserves for unrecognized tax benefits reflect management’s best assessment of estimated future taxes to be paid. We are subject to income taxes predominantly in the United States. Significant judgments and estimates are required in determining the consolidated income tax expense. Deferred income taxes arise from temporary differences between the tax and financial statement recognition of revenue and expense. In evaluating our ability to recover our deferred tax assets within the jurisdiction from which they arise we consider all available positive and negative evidence including scheduled reversals of deferred tax liabilities, projected future taxable income, tax planning strategies and recent financial operations. In projecting future taxable income, we begin with historical results adjusted for the results of discontinued operations and changes in accounting policies and incorporate assumptions including the amount of future state, federal and foreign pretax operating income, the reversal of temporary differences, and the implementation of feasible and prudent tax planning strategies. We recognize the financial statement effects of uncertain income tax positions when it is more likely than not, based on the technical merits, that the position will be sustained upon examination. Also, we recognize accrued interest and penalties related to liabilities for uncertain income tax positions in interest expense and other operating expenses, respectively. For additional information regarding our provision for income taxes, refer to Note 23 .
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	Our compensation and benefits expenses include the cost of share-based awards. For equity classified share-based awards, compensation cost is ratably charged to expense based on the grant date fair value of the awards over the applicable service periods. For liability classified share-based awards, the associated liability is measured quarterly at fair value based on our share price and services rendered at the time of measurement until the awards are paid, with changes in fair value charged to compensation expense in the period in which the change occurs. We have made an accounting policy election to account for forfeitures of share-based awards as they occur. Refer to Note 24 for a discussion of our share-based compensation plans.
Foreign Currency Transactions and Translations Policy [Policy Text Block]	Foreign-denominated assets and liabilities resulting from foreign-currency transactions are valued using period-end foreign-exchange rates and the results of operations and cash flows are determined using approximate weighted average exchange rates for the period. Translation adjustments are related to foreign subsidiaries using local currency as their functional currency and are reported as a separate component of accumulated other comprehensive income. Translation gains or losses are reclassified to earnings upon the substantial sale or liquidation of our investments in foreign operations. We may elect to enter into foreign-currency derivatives to mitigate our exposure to changes in foreign-exchange rates. Refer to the Derivative Instruments and Hedging Activities section above for a discussion of our hedging activities of the foreign-currency exposure of a net investment in a foreign operation.
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Adopted Accounting Standards Statement of Cash Flows — Restricted Cash (ASU 2016-18) As of December 31, 2017, we elected to early-adopt Accounting Standards Update (ASU) 2016-18. The amendments in this update require that amounts classified as restricted cash and restricted cash equivalents be included within the beginning-of-period and end-of-period amounts along with cash and cash equivalents on the statement of cash flows. The amendments were applied retrospectively to all periods presented within the statement of cash flows. The implementation of this guidance resulted in a change in presentation of our Consolidated Statement of Cash Flows and additional disclosures surrounding restricted cash balances, but did not result in a change to our Consolidated Statement of Income or Consolidated Balance Sheet. Recently Issued Accounting Standards Revenue from Contracts with Customers (ASU 2014-09) In May 2014, the Financial Accounting Standards Board (FASB) issued ASU 2014-09. The purpose of this guidance is to streamline and consolidate existing revenue recognition principles in GAAP and to converge revenue recognition principles with International Financial Reporting Standards (IFRS). The core principle of the amendments 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 to receive in exchange for those goods or services. The amendments include a five step process for consideration of the core principle, guidance on the accounting treatment for costs associated with a contract, and disclosure requirements related to the revenue process. The FASB has issued several additional ASUs to clarify guidance and provide implementation support for ASU 2014-09, as well as to delay the initial required adoption date of the amendments by one year. The amendments to the revenue recognition principles can be applied upon adoption either through a full retrospective application or on a modified retrospective basis with a cumulative effect adjustment on the date of initial adoption with certain practical expedients. We will adopt the new guidance effective January 1, 2018, using the modified retrospective approach applied to all contracts with customers not completed upon adoption. A majority of our revenue streams are not within the scope of this ASU as they are governed by other accounting standards. Management has determined that certain revenue streams and contractual arrangements are in scope of this guidance, including deposit fees, revenue on certain noninsurance contracts, brokering commissions through our insurance operations, sales of off-lease vehicles, remarketing fee income through SmartAuction, and commission and fee income generated through Ally Invest. Management does not expect these amendments to impact current revenue recognition patterns for most of the in scope revenue streams and contracts. Under the current guidance, a portion of revenue earned on noninsurance contracts, which includes vehicle service contracts (VSCs), guaranteed asset protection (GAP) waiver contracts, and vehicle maintenance contracts (VMCs), is recognized at contract inception, while the remainder is recognized over the contract term on a basis proportionate to the anticipated cost emergence. In addition, certain commissions incurred to obtain a noninsurance contract are recognized as expense when incurred, and certain direct-response advertising costs are deferred and recognized as expense on the same basis as revenue. Upon adoption, all revenue associated with noninsurance contracts will be recognized over the contract term on a basis proportionate to the anticipated cost emergence. Further, commissions incurred to obtain these contracts will be capitalized and recognized as expense over the contract term and all advertising costs will be recognized as expense when incurred. Upon adoption of the amendments on January 1, 2018, we expect to recognize the cumulative effect of adoption by recording a reduction to our opening retained earnings of approximately $126 million , net of income taxes. Additionally, upon implementation we expect to expand our financial statement disclosures as required by the standard. While the adoption of the standard will defer the recognition of revenue and certain costs, over time the total revenue and expense recognized will not change as a result of the adoption of the standard. Financial Instruments — Recognition and Measurement of Financial Assets (ASU 2016-01) In January 2016, the FASB issued ASU 2016-01. The amendments in this update modify the requirements related to the measurement of certain financial instruments in the statement of financial condition and results of operations. For equity investments (other than investments accounted for using the equity method), entities must measure such instruments at fair value with changes in fair value recognized in net income. Changes in fair value for equity securities will no longer be recognized through other comprehensive income. Reporting entities may continue to elect to measure certain equity investments that do not have a readily determinable fair value at cost with adjustments for impairment and observable changes in price. In addition, for a liability (other than a derivative liability) that an entity measures at fair value, any change in fair value related to the instrument-specific credit risk, that is the entity’s own-credit, should be presented separately in other comprehensive income and not as a component of net income. The amendments are effective on January 1, 2018. The amendments must be applied on a modified retrospective basis with a cumulative effect adjustment as of the beginning of the fiscal year of initial adoption. While the amendment requiring equity investments to be measured at fair value with changes in fair value recognized in net income will create additional volatility in our Consolidated Statement of Comprehensive Income, we do not anticipate the other amendments will have a material impact to our financial statements. Upon adoption of the amendments on January 1, 2018, we expect to record a reduction to our opening retained earnings of approximately $20 million , net of income taxes, primarily as a result of transferring net unrealized losses on investment securities from accumulated other comprehensive income to accumulated deficit. Leases (ASU 2016-02) In February 2016, the FASB issued ASU 2016-02. The amendments in this update primarily replace the existing accounting requirements for operating leases for lessees. Lessee accounting requirements for finance leases, and lessor accounting requirements for operating leases and sales type and direct financing leases (sales type and direct financing leases were both previously referred to as capital leases) are largely unchanged. The amendments require the lessee of an operating lease to record a balance sheet gross-up upon lease commencement by recognizing a right-of-use asset and lease liability equal to the present value of the lease payments. The right-of-use asset and lease liability should be derecognized in a manner that effectively yields a straight line lease expense over the lease term. In addition to the changes to the lessee operating lease accounting requirements, the amendments also change the types of costs that can be capitalized related to a lease agreement for both lessees and lessors for all types of leases. The amendments also require additional disclosures for all lease types for both lessees and lessors. The amendments are effective on January 1, 2019, with early adoption permitted. The amendments must be applied on a modified retrospective basis with a cumulative adjustment to the beginning of the earliest fiscal year presented in the financial statements in the period of adoption. Management is currently evaluating the impact of these amendments. Upon adoption, we expect to record a balance sheet gross-up, reflecting our right-of-use asset and lease liability for our operating leases where we are the lessee (for example, our facility leases). We are currently reviewing our operating lease contracts where we are the lessee to determine the impact of the gross-up and the changes to capitalizable costs. We are also reviewing our leases where we are the lessor to determine the impact of the changes to capitalizable costs. We currently plan to adopt these amendments on January 1, 2019, and expect to use the modified retrospective approach as required. Financial Instruments — Credit Losses (ASU 2016-13) In June 2016, the FASB issued ASU 2016-13. The amendments in this update introduce a new accounting model to measure credit losses for financial assets measured at amortized cost . Credit losses for financial assets measured at amortized cost should be determined based on the total current expected credit losses over the life of the financial asset or group of financial assets. In effect, the financial asset or group of financial assets should be presented at the net amount expected to be collected. Credit losses will no longer be recorded under the current incurred loss model for financial assets measured at amortized cost. The amendments also modify the accounting for available-for-sale debt securities whereby credit losses will be recorded through an allowance for credit losses rather than a write-down to the security’s cost basis, which allows for reversals of credit losses when estimated credit losses decline. Credit losses for available-for-sale debt securities should be measured in a manner similar to current GAAP. The amendments are effective on January 1, 2020, with early adoption permitted as of January 1, 2019. The amendments must be applied using a modified retrospective approach with a cumulative-effect adjustment through retained earnings as of the beginning of the fiscal year upon adoption. The new accounting model for credit losses represents a significant departure from existing GAAP, and will likely materially increase the allowance for credit losses with a resulting negative adjustment to retained earnings. Management created a formal working group to govern the implementation of these amendments consisting of key stakeholders from finance, risk, and accounting and is currently evaluating the impact of the amendments. We are in the process of designing and building the models and procedures that will be used to calculate the credit loss reserves in accordance with these amendments. We currently plan to adopt these amendments on January 1, 2020, and expect to use the modified retrospective approach as required. Receivables — Nonrefundable Fees and Other Costs: Premium Amortization on Purchased Callable Debt Securities (ASU 2017-08) In March 2017, the FASB issued ASU 2017-08. The amendments in this update require premiums on purchased callable debt securities to be amortized to the security’s earliest call date. Prior to this ASU, premiums and discounts on purchased callable debt securities were generally required to be amortized to the security’s maturity date. The amendments do not require an accounting change for securities held at a discount. The amendments are effective on January 1, 2019, with early adoption permitted. The amendments must be applied using a modified retrospective approach with a cumulative-effect adjustment through retained earnings as of the beginning of the fiscal year upon adoption. While our assessment is not final, we do not expect the amendments to have a material impact to our financial statements. We currently plan to adopt these amendments on January 1, 2019, and expect to use the modified retrospective approach as required. Derivatives and Hedging — Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12) In August 2017, the FASB issued ASU 2017-12, which enhances the financial reporting of hedging relationships to better portray the economic results of an entity’s risk management activities in its financial statements and make certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP. The amendments in this update better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and presentation of hedge results. The amendments are effective on January 1, 2019, with early adoption permitted. Entities must apply the amendments to cash flow and net investment hedge relationships that exist on the date of adoption using a modified retrospective approach. All transition requirements and elections must be applied to hedging relationships existing as of the adoption date and the effect of adoption should be reflected as of the beginning of the fiscal year of adoption. The presentation and disclosure requirements must be applied prospectively. We currently plan to early-adopt these amendments on January 1, 2018, and do not expect to recognize a cumulative effect adjustment to opening retained earnings for cash flow and net investment hedging relationships that exist as of the adoption date. Accumulated Other Comprehensive Income — Reclassification of Certain Tax Effects (ASU 2018-02) In February 2018, the FASB issued ASU 2018-02. The amendments in this update provide guidance concerning the treatment of stranded income tax effects in accumulated other comprehensive income resulting from the Tax Cuts and Jobs Act of 2017 (the Tax Act). The amendments will provide entities an election to reclassify these stranded income tax effects from accumulated other comprehensive income to retained earnings. The reclassification amount will include the income tax effect resulting from the newly enacted federal corporate income tax rate and other stranded tax amounts related to the Tax Act that we elect to reclassify. The amendments will also require additional disclosures related to the election and an entity’s accounting policy for stranded income taxes. The amendments are effective on January 1, 2019, with early adoption permitted. The amendments can be applied retrospectively to each period(s) in which the amounts included in accumulated other comprehensive income are impacted by the Tax Act or at the beginning of the annual or interim period in which the amendments are adopted. Management is currently evaluating the impact and the timing of the adoption of these amendments, however we do not expect the amendments to have a material impact to our financial statements.
Accounting Standards Update 2016-18 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	As of December 31, 2017, we elected to early-adopt Accounting Standards Update (ASU) 2016-18. The amendments in this update require that amounts classified as restricted cash and restricted cash equivalents be included within the beginning-of-period and end-of-period amounts along with cash and cash equivalents on the statement of cash flows. The amendments were applied retrospectively to all periods presented within the statement of cash flows. The implementation of this guidance resulted in a change in presentation of our Consolidated Statement of Cash Flows and additional disclosures surrounding restricted cash balances, but did not result in a change to our Consolidated Statement of Income or Consolidated Balance Sheet.
Accounting Standards Update 2014-09 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	In May 2014, the Financial Accounting Standards Board (FASB) issued ASU 2014-09. The purpose of this guidance is to streamline and consolidate existing revenue recognition principles in GAAP and to converge revenue recognition principles with International Financial Reporting Standards (IFRS). The core principle of the amendments 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 to receive in exchange for those goods or services. The amendments include a five step process for consideration of the core principle, guidance on the accounting treatment for costs associated with a contract, and disclosure requirements related to the revenue process. The FASB has issued several additional ASUs to clarify guidance and provide implementation support for ASU 2014-09, as well as to delay the initial required adoption date of the amendments by one year. The amendments to the revenue recognition principles can be applied upon adoption either through a full retrospective application or on a modified retrospective basis with a cumulative effect adjustment on the date of initial adoption with certain practical expedients. We will adopt the new guidance effective January 1, 2018, using the modified retrospective approach applied to all contracts with customers not completed upon adoption. A majority of our revenue streams are not within the scope of this ASU as they are governed by other accounting standards. Management has determined that certain revenue streams and contractual arrangements are in scope of this guidance, including deposit fees, revenue on certain noninsurance contracts, brokering commissions through our insurance operations, sales of off-lease vehicles, remarketing fee income through SmartAuction, and commission and fee income generated through Ally Invest. Management does not expect these amendments to impact current revenue recognition patterns for most of the in scope revenue streams and contracts. Under the current guidance, a portion of revenue earned on noninsurance contracts, which includes vehicle service contracts (VSCs), guaranteed asset protection (GAP) waiver contracts, and vehicle maintenance contracts (VMCs), is recognized at contract inception, while the remainder is recognized over the contract term on a basis proportionate to the anticipated cost emergence. In addition, certain commissions incurred to obtain a noninsurance contract are recognized as expense when incurred, and certain direct-response advertising costs are deferred and recognized as expense on the same basis as revenue. Upon adoption, all revenue associated with noninsurance contracts will be recognized over the contract term on a basis proportionate to the anticipated cost emergence. Further, commissions incurred to obtain these contracts will be capitalized and recognized as expense over the contract term and all advertising costs will be recognized as expense when incurred. Upon adoption of the amendments on January 1, 2018, we expect to recognize the cumulative effect of adoption by recording a reduction to our opening retained earnings of approximately $126 million , net of income taxes. Additionally, upon implementation we expect to expand our financial statement disclosures as required by the standard. While the adoption of the standard will defer the recognition of revenue and certain costs, over time the total revenue and expense recognized will not change as a result of the adoption of the standard.
Accounting Standards Update 2016-01 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	In January 2016, the FASB issued ASU 2016-01. The amendments in this update modify the requirements related to the measurement of certain financial instruments in the statement of financial condition and results of operations. For equity investments (other than investments accounted for using the equity method), entities must measure such instruments at fair value with changes in fair value recognized in net income. Changes in fair value for equity securities will no longer be recognized through other comprehensive income. Reporting entities may continue to elect to measure certain equity investments that do not have a readily determinable fair value at cost with adjustments for impairment and observable changes in price. In addition, for a liability (other than a derivative liability) that an entity measures at fair value, any change in fair value related to the instrument-specific credit risk, that is the entity’s own-credit, should be presented separately in other comprehensive income and not as a component of net income. The amendments are effective on January 1, 2018. The amendments must be applied on a modified retrospective basis with a cumulative effect adjustment as of the beginning of the fiscal year of initial adoption. While the amendment requiring equity investments to be measured at fair value with changes in fair value recognized in net income will create additional volatility in our Consolidated Statement of Comprehensive Income, we do not anticipate the other amendments will have a material impact to our financial statements. Upon adoption of the amendments on January 1, 2018, we expect to record a reduction to our opening retained earnings of approximately $20 million , net of income taxes, primarily as a result of transferring net unrealized losses on investment securities from accumulated other comprehensive income to accumulated deficit.
Accounting Standards Update 2016-02 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	In February 2016, the FASB issued ASU 2016-02. The amendments in this update primarily replace the existing accounting requirements for operating leases for lessees. Lessee accounting requirements for finance leases, and lessor accounting requirements for operating leases and sales type and direct financing leases (sales type and direct financing leases were both previously referred to as capital leases) are largely unchanged. The amendments require the lessee of an operating lease to record a balance sheet gross-up upon lease commencement by recognizing a right-of-use asset and lease liability equal to the present value of the lease payments. The right-of-use asset and lease liability should be derecognized in a manner that effectively yields a straight line lease expense over the lease term. In addition to the changes to the lessee operating lease accounting requirements, the amendments also change the types of costs that can be capitalized related to a lease agreement for both lessees and lessors for all types of leases. The amendments also require additional disclosures for all lease types for both lessees and lessors. The amendments are effective on January 1, 2019, with early adoption permitted. The amendments must be applied on a modified retrospective basis with a cumulative adjustment to the beginning of the earliest fiscal year presented in the financial statements in the period of adoption. Management is currently evaluating the impact of these amendments. Upon adoption, we expect to record a balance sheet gross-up, reflecting our right-of-use asset and lease liability for our operating leases where we are the lessee (for example, our facility leases). We are currently reviewing our operating lease contracts where we are the lessee to determine the impact of the gross-up and the changes to capitalizable costs. We are also reviewing our leases where we are the lessor to determine the impact of the changes to capitalizable costs. We currently plan to adopt these amendments on January 1, 2019, and expect to use the modified retrospective approach as required.
Accounting Standards Update 2016-13 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	In June 2016, the FASB issued ASU 2016-13. The amendments in this update introduce a new accounting model to measure credit losses for financial assets measured at amortized cost . Credit losses for financial assets measured at amortized cost should be determined based on the total current expected credit losses over the life of the financial asset or group of financial assets. In effect, the financial asset or group of financial assets should be presented at the net amount expected to be collected. Credit losses will no longer be recorded under the current incurred loss model for financial assets measured at amortized cost. The amendments also modify the accounting for available-for-sale debt securities whereby credit losses will be recorded through an allowance for credit losses rather than a write-down to the security’s cost basis, which allows for reversals of credit losses when estimated credit losses decline. Credit losses for available-for-sale debt securities should be measured in a manner similar to current GAAP. The amendments are effective on January 1, 2020, with early adoption permitted as of January 1, 2019. The amendments must be applied using a modified retrospective approach with a cumulative-effect adjustment through retained earnings as of the beginning of the fiscal year upon adoption. The new accounting model for credit losses represents a significant departure from existing GAAP, and will likely materially increase the allowance for credit losses with a resulting negative adjustment to retained earnings. Management created a formal working group to govern the implementation of these amendments consisting of key stakeholders from finance, risk, and accounting and is currently evaluating the impact of the amendments. We are in the process of designing and building the models and procedures that will be used to calculate the credit loss reserves in accordance with these amendments. We currently plan to adopt these amendments on January 1, 2020, and expect to use the modified retrospective approach as required.
Accounting Standards Update 2017-08 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	In March 2017, the FASB issued ASU 2017-08. The amendments in this update require premiums on purchased callable debt securities to be amortized to the security’s earliest call date. Prior to this ASU, premiums and discounts on purchased callable debt securities were generally required to be amortized to the security’s maturity date. The amendments do not require an accounting change for securities held at a discount. The amendments are effective on January 1, 2019, with early adoption permitted. The amendments must be applied using a modified retrospective approach with a cumulative-effect adjustment through retained earnings as of the beginning of the fiscal year upon adoption. While our assessment is not final, we do not expect the amendments to have a material impact to our financial statements. We currently plan to adopt these amendments on January 1, 2019, and expect to use the modified retrospective approach as required.
Accounting Standards Update 2017-12 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	In August 2017, the FASB issued ASU 2017-12, which enhances the financial reporting of hedging relationships to better portray the economic results of an entity’s risk management activities in its financial statements and make certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP. The amendments in this update better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and presentation of hedge results. The amendments are effective on January 1, 2019, with early adoption permitted. Entities must apply the amendments to cash flow and net investment hedge relationships that exist on the date of adoption using a modified retrospective approach. All transition requirements and elections must be applied to hedging relationships existing as of the adoption date and the effect of adoption should be reflected as of the beginning of the fiscal year of adoption. The presentation and disclosure requirements must be applied prospectively. We currently plan to early-adopt these amendments on January 1, 2018, and do not expect to recognize a cumulative effect adjustment to opening retained earnings for cash flow and net investment hedging relationships that exist as of the adoption date.
Accounting Standards Update 2018-02 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	In February 2018, the FASB issued ASU 2018-02. The amendments in this update provide guidance concerning the treatment of stranded income tax effects in accumulated other comprehensive income resulting from the Tax Cuts and Jobs Act of 2017 (the Tax Act). The amendments will provide entities an election to reclassify these stranded income tax effects from accumulated other comprehensive income to retained earnings. The reclassification amount will include the income tax effect resulting from the newly enacted federal corporate income tax rate and other stranded tax amounts related to the Tax Act that we elect to reclassify. The amendments will also require additional disclosures related to the election and an entity’s accounting policy for stranded income taxes. The amendments are effective on January 1, 2019, with early adoption permitted. The amendments can be applied retrospectively to each period(s) in which the amounts included in accumulated other comprehensive income are impacted by the Tax Act or at the beginning of the annual or interim period in which the amendments are adopted. Management is currently evaluating the impact and the timing of the adoption of these amendments, however we do not expect the amendments to have a material impact to our financial statements.

Discontinued Operations Discont

Discontinued Operations Discontinued Operations (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Discontinued Operations, Policy [Policy Text Block]	Prior to the adoption of ASU 2014-08, which was prospectively applied only to newly identified disposals that qualify as discontinued operations beginning after January 1, 2015, we have classified operations as discontinued when operations and cash flows will be eliminated from our ongoing operations and we do not expect to retain any significant continuing involvement in their operations after the respective sale or disposal transactions. For all periods presented, the operating results for these discontinued operations have been removed from continuing operations and presented separately as discontinued operations, net of tax, in the Consolidated Statement of Income . The Notes to the Consolidated Financial Statements have been adjusted to exclude discontinued operations unless otherwise noted.

Securitizations and Variable 42

Securitizations and Variable Interest Entities Securitizations and Variable Interest Entities (Policies)	12 Months Ended
	Dec. 31, 2017
Securitization and Variable Interest Entities [Abstract]
Consolidation, Variable Interest Entity, Policy [Policy Text Block]	For all VIEs in which we are involved, we assess whether we are the primary beneficiary of the VIE on an ongoing basis. In circumstances where we have both the power to direct the activities that most significantly impact the VIEs performance and the obligation to absorb losses or the right to receive benefits of the VIE that could be significant, we would conclude that we are the primary beneficiary of the VIE, and would consolidate the VIE. In situations where we are not deemed to be the primary beneficiary of the VIE, we do not consolidate the VIE and only recognize our interests in the VIE. We are involved in securitization transactions that typically involve the use of VIEs. For information regarding the company’s securitization activities, refer to Note 11 . In the case of a consolidated VIE used for a securitization transaction, the underlying automotive finance retail contracts, wholesale loans, and automotive leases remain on our Consolidated Balance Sheet with the corresponding obligations (consisting of the beneficial interests issued by the securitization entity) reflected as debt. We recognize interest income on the finance receivables, lease income on automotive leases, and interest expense on the beneficial interests issued by the securitization entity; and we recognize loan losses on the finance receivables and loans as incurred. Consolidation of the VIE would also preclude us from recording an accounting sale on the transaction. In securitization transactions where we are not determined to be the primary beneficiary of the VIE, we must determine whether or not we achieve a sale for accounting purposes. In order to achieve a sale of finance receivables and loans for accounting purposes, the assets being transferred must be legally isolated, not be constrained by restrictions from further transfer, and be deemed to be beyond our control. We would deem the transaction to be an off-balance sheet securitization if the preceding three criteria for sale accounting are met. If we were to fail any of these three criteria for sale accounting, the transfer would be accounted for as a secured borrowing consistent with the preceding paragraph. The gain or loss recognized on off-balance sheet securitizations take into consideration any assets received as part of the transaction, including any retained interests, and servicing assets or liabilities (if applicable), which are initially recorded at fair value at the date of sale. Upon the sale of the loans, we recognize a gain or loss on sale for the difference between the assets recognized, and the assets derecognized. The financial assets obtained from off-balance sheet securitizations are primarily reported as cash, or retained interests (if applicable). Retained interests are classified as securities or as other assets depending on their form and structure. The estimate of the fair value of the retained interests and servicing requires us to exercise significant judgment about the timing and amount of future cash flows from the interests. For a discussion on fair value estimates, refer to Note 25 . Gains or losses on off-balance sheet securitizations are reported in gain on mortgage and automotive loans, net, in our Consolidated Statement of Comprehensive Income . We retain servicing rights for all of our consumer and commercial automotive loan and operating lease securitizations. We may receive servicing fees for off-balance sheet securitizations based on the securitized loan balances and certain ancillary fees, all of which are reported in servicing fees in the Consolidated Statement of Income. Typically, the fee we are paid for servicing consumer automotive finance receivables represents adequate compensation, and consequently, does not result in the recognition of a servicing asset or liability. The determination of whether the assets and liabilities of the VIEs are consolidated on our balance sheet (also referred to as on-balance sheet) or not consolidated on our balance sheet (also referred to as off-balance sheet) depends on the terms of the related transaction and our continuing involvement (if any) with the VIE. We are deemed the primary beneficiary and therefore consolidate VIEs for which we have both (a) the power, through voting rights or similar rights, to direct the activities that most significantly impact the VIE’s economic performance, and (b) a variable interest (or variable interests) that (i) obligates us to absorb losses that could potentially be significant to the VIE; and/or (ii) provides us the right to receive residual returns of the VIE that could potentially be significant to the VIE. We determine whether we hold a significant variable interest in a VIE based on a consideration of both qualitative and quantitative factors regarding the nature, size, and form of our involvement with the VIE. We assess whether we are the primary beneficiary of a VIE on an ongoing basis and are generally determined to be the primary beneficiary in VIEs established for our securitization activities when we have a controlling financial interest in the VIE, primarily due to our servicing activities, and our beneficial interest in the VIE that could be potentially significant. The consolidated VIEs included on the Consolidated Balance Sheet represent separate entities with which we are involved. The third-party investors in the obligations of consolidated VIEs have legal recourse only to the assets of the VIEs and do not have such recourse to us, except for the customary representation and warranty provisions. In addition, the cash flows from the assets are restricted only to pay such liabilities. Thus, our economic exposure to loss from outstanding third-party financing related to consolidated VIEs is limited to the carrying value of the consolidated VIE assets. Generally, all assets of consolidated VIEs, presented below based upon the legal transfer of the underlying assets in order to reflect legal ownership, are restricted for the benefit of the beneficial interest holders. For additional information regarding the company’s significant accounting policies for consolidated VIEs, refer to the Securitizations and Variable Interest Entities section of Note 1 .

Fair Value Fair Value (Policies

Fair Value Fair Value (Policies)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurement, Policy [Policy Text Block]	For purposes of this disclosure, fair value is defined as the exchange price that would be received to sell an asset or paid to transfer a liability (exit price) in the principal or most advantageous market in an orderly transaction between market participants at the measurement date under current market conditions. Fair value is based on the assumptions we believe market participants would use when pricing an asset or liability. Additionally, entities are required to consider all aspects of nonperformance risk, including the entity’s own credit standing, when measuring the fair value of a liability. GAAP specifies a three-level hierarchy that is used when measuring and disclosing fair value. The fair value hierarchy gives the highest priority to quoted prices available in active markets (i.e., observable inputs) and the lowest priority to data lacking transparency (i.e., unobservable inputs). An instrument’s categorization within the fair value hierarchy is based on the lowest level of significant input to its valuation. The following is a description of the three hierarchy levels. Level 1 Inputs are quoted prices in active markets for identical assets or liabilities at the measurement date. Additionally, the entity must have the ability to access the active market, and the quoted prices cannot be adjusted by the entity. Level 2 Inputs are other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs include quoted prices in active markets for similar assets or liabilities; quoted prices in inactive markets for identical or similar assets or liabilities; or inputs that are observable or can be corroborated by observable market data by correlation or other means for substantially the full term of the assets or liabilities. Level 3 Unobservable inputs are supported by little or no market activity. The unobservable inputs represent management’s best assumptions of how market participants would price the assets or liabilities. Generally, Level 3 assets and liabilities are valued using pricing models, discounted cash flow methodologies, or similar techniques that require significant judgment or estimation. Transfers Transfers into or out of any hierarchy level are recognized at the end of the reporting period in which the transfer occurred.

Acquisitions Acquisitions (Tabl

Acquisitions Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2017
Acquisitions [Abstract]
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	The following table summarizes the allocation of cash consideration paid for TradeKing and the amounts of the identifiable assets acquired and liabilities assumed recognized at the acquisition date. ($ in millions) Purchase price Cash consideration $ 298 Allocation of purchase price to net assets acquired Intangible assets (a) 82 Cash and short-term investments (b) 50 Other assets 14 Deferred tax asset, net 4 Employee compensation and benefits (41 ) Other liabilities (4 ) Goodwill $ 193 (a) We recorded $10 million and $6 million of amortization on these intangible assets during the years ended December 31, 2017 , and 2016, respectively. (b) Includes $40 million in cash proceeds from the acquisition transaction in order to pay employee compensation and benefits that vested upon acquisition as a result of the change in control.

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations [Table Text Block]	Select financial information of discontinued operations is summarized below. The pretax income or loss includes direct costs to transact a sale. Year ended December 31, ($ in millions) 2017 2016 2015 Select Automotive Finance operations Pretax (loss) income (a) $ (4 ) $ (2 ) $ 452 Tax (benefit) expense (b) (5 ) 2 80 Other operations Pretax income (loss) $ 2 $ (41 ) $ 16 Tax benefit — (1 ) (4 ) (a) Includes certain treasury and other corporate activity recognized within Corporate and Other. (b) Includes certain income tax activity recognized within Corporate and Other.

Other Income, Net of Losses (Ta

Other Income, Net of Losses (Tables)	12 Months Ended
	Dec. 31, 2017
Other Nonoperating Income (Expense) [Abstract]
Schedule of Other Nonoperating Income, by Component [Table Text Block]	Details of other income, net of losses, were as follows. Year ended December 31, ($ in millions) 2017 2016 2015 Remarketing fees $ 104 $ 103 $ 101 Late charges and other administrative fees 102 98 90 Servicing fees 51 64 45 Income from equity-method investments 14 18 52 Other, net 137 111 71 Total other income, net of losses $ 408 $ 394 $ 359

Reserves for Insurance Losses47

Reserves for Insurance Losses and Loss Adjustment Expenses Reserves for Insurance Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2017
Reserves for Insurance Losses and Loss Adjustment Expenses [Abstract]
Short-duration Insurance Contracts, Claims Development [Table Text Block]	The following table shows cumulative incurred claims and allocated loss adjustment expenses, net of reinsurance. For the years ended December 31, ($ in millions) December 31, 2017 ($ in millions) Accident year (a) 2012 (b) 2013 (b) 2014 (b) 2015 (b) 2016 2017 Total of incurred-but-not-reported liabilities plus expected development on reported claims (c) Cumulative number of reported claims (c) 2012 $ 435 $ 430 $ 423 $ 423 $ 423 $ 422 $ 1 772,546 2013 376 365 370 370 369 1 672,263 2014 390 389 388 388 — 525,290 2015 274 271 272 — 342,231 2016 326 327 — 475,707 2017 310 21 455,965 Total $ 2,088 (a) Due to the discontinuation of various product lines and sale of certain international operations, information prior to 2013 has been excluded from the table in order to appropriately reflect the number of years for which claims are typically outstanding. In addition, given the short tail of our insurance contracts, the table above reflects the combined presentation of all business lines. (b) Information presented for the years 2012 through 2015 is unaudited supplementary information. (c) Claims are reported on a claimant basis. Claimant is defined as one vehicle for guaranteed asset protection (GAP) products, one repair visit for vehicle service contracts (VSCs) and vehicle maintenance contracts (VMCs), one dealership for dealer inventory products, and per individual/coverage for run-off personal automotive products. The following table shows cumulative paid claims and allocated loss adjustment expenses, net of reinsurance. For the years ended December 31, ($ in millions) Accident year (a) 2012 (b) 2013 (b) 2014 (b) 2015 (b) 2016 2017 2012 $ 391 $ 412 $ 416 $ 418 $ 419 $ 421 2013 347 364 366 368 368 2014 369 388 388 388 2015 252 272 272 2016 302 327 2017 289 Total $ 2,065 All outstanding liabilities for loss and allocated loss adjustment expenses before 2012, net of reinsurance 7 Reserves for insurance losses and allocated loss adjustment expenses, net of reinsurance $ 30 (a) Due to the discontinuation of various product lines and sale of certain international operations, information prior to 2013 has been excluded from the table in order to appropriately reflect the number of years for which claims are typically outstanding. In addition, given the short tail of our insurance contracts, the table above reflects the combined presentation of all business lines. (b) Information presented for the years 2012 through 2015 is unaudited supplementary information.
Short-duration Insurance Contracts, Schedule of Historical Claims Duration [Table Text Block]	The following table shows the average annual percentage payout of incurred claims by age, net of reinsurance. The information presented is unaudited supplementary information. Year 1 2 3 4 5 6 Percentage payout of incurred claims 93.0 % 5.7 % 0.4 % 0.3 % 0.2 % 0.4 %
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table Text Block]	The following table shows a reconciliation of the disclosures of incurred and paid claims development to the reserves for insurance losses and loss adjustment expenses. December 31, ($ in millions) 2017 2016 Reserves for insurance losses and loss adjustment expenses, net of reinsurance $ 30 $ 38 Total reinsurance recoverable on unpaid claims 108 108 Unallocated loss adjustment expenses 2 3 Total gross reserves for insurance losses and loss adjustment expenses $ 140 $ 149
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	The following table shows a rollforward of our reserves for insurance losses and loss adjustment expenses. ($ in millions) 2017 2016 Total gross reserves for insurance losses and loss adjustment expenses at January 1, $ 149 $ 169 Less: Reinsurance recoverable 108 120 Net reserves for insurance losses and loss adjustment expenses at January 1, 41 49 Net insurance losses and loss adjustment expenses incurred related to: Current year 332 345 Prior years (a) — (3 ) Total net insurance losses and loss adjustment expenses incurred 332 342 Net insurance losses and loss adjustment expenses paid or payable related to: Current year (309 ) (320 ) Prior years (32 ) (30 ) Total net insurance losses and loss adjustment expenses paid or payable (341 ) (350 ) Net reserves for insurance losses and loss adjustment expenses at December 31, 32 41 Plus: Reinsurance recoverable 108 108 Total gross reserves for insurance losses and loss adjustment expenses at December 31, $ 140 $ 149 (a) There have been no material adverse changes to the reserve for prior years.

Other Operating Expenses (Table

Other Operating Expenses (Tables)	12 Months Ended
	Dec. 31, 2017
Operating Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Details of other operating expenses were as follows. Year ended December 31, ($ in millions) 2017 2016 2015 Insurance commissions $ 415 $ 389 $ 378 Technology and communications 284 274 267 Lease and loan administration 159 136 126 Advertising and marketing 133 112 107 Professional services 113 103 93 Regulatory and licensing fees 113 94 79 Vehicle remarketing and repossession 110 95 78 Premises and equipment depreciation 89 84 82 Occupancy 46 51 50 Non-income taxes 21 25 29 Other 200 242 216 Total other operating expenses $ 1,683 $ 1,605 $ 1,505

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investment [Table Text Block]	Our portfolio of securities includes bonds, equity securities, asset-backed securities, commercial and residential mortgage-backed securities, and other investments. The cost, fair value, and gross unrealized gains and losses on investment securities were as follows. 2017 2016 Amortized cost Gross unrealized Fair value Amortized cost Gross unrealized Fair December 31, ($ in millions) gains losses gains losses Available-for-sale securities Debt securities U.S. Treasury $ 1,831 $ — $ (54 ) $ 1,777 $ 1,680 $ — $ (60 ) $ 1,620 U.S. States and political subdivisions 850 11 (7 ) 854 794 7 (19 ) 782 Foreign government 153 2 (1 ) 154 157 5 — 162 Agency mortgage-backed residential 14,412 35 (156 ) 14,291 10,473 29 (212 ) 10,290 Mortgage-backed residential 2,517 11 (34 ) 2,494 2,162 5 (70 ) 2,097 Mortgage-backed commercial 541 1 (1 ) 541 537 2 (2 ) 537 Asset-backed 933 4 (1 ) 936 1,396 6 (2 ) 1,400 Corporate debt 1,262 5 (11 ) 1,256 1,452 7 (16 ) 1,443 Total debt securities (a) (b) 22,499 69 (265 ) 22,303 18,651 61 (381 ) 18,331 Equity securities 553 13 (48 ) 518 642 7 (54 ) 595 Total available-for-sale securities $ 23,052 $ 82 $ (313 ) $ 22,821 $ 19,293 $ 68 $ (435 ) $ 18,926 Held-to-maturity securities Debt securities Agency mortgage-backed residential (c) (d) $ 1,863 $ 3 $ (37 ) $ 1,829 $ 839 $ — $ (50 ) $ 789 Asset-backed retained notes 36 — — 36 — — — — Total held-to-maturity securities $ 1,899 $ 3 $ (37 ) $ 1,865 $ 839 $ — $ (50 ) $ 789 (a) Certain entities related to our Insurance operations are required to deposit securities with state regulatory authorities. These deposited securities totaled $12 million and $14 million at December 31, 2017 , and 2016, respectively. (b) Investment securities with a fair value of $7,804 million and $4,881 million at December 31, 2017 , and 2016, respectively, were pledged to secure advances from the Federal Home Loan Bank (FHLB), short-term borrowings or repurchase agreements, or for other purposes as required by contractual obligation or law. Under these agreements, we have granted the counterparty the right to sell or pledge $1,025 million and $737 million of the underlying investment securities at December 31, 2017 , and 2016, respectively. (c) Agency mortgage-backed residential debt securities are held for liquidity risk management purposes. (d) Securities with a fair value of $664 million and $87 million at December 31, 2017 , and 2016, respectively, were pledged to secure advances from the FHLB.
Investments Classified by Contractual Maturity Date [Table Text Block]	Total Due in one year or less Due after one year through five years Due after five years through ten years Due after ten years ($ in millions) Amount Yield Amount Yield Amount Yield Amount Yield Amount Yield December 31, 2017 Fair value of available-for-sale debt securities (a) U.S. Treasury $ 1,777 1.7 % $ — — % $ 487 1.7 % $ 1,290 1.8 % $ — — % U.S. States and political subdivisions 854 2.9 76 1.8 36 2.3 203 2.5 539 3.3 Foreign government 154 2.5 — — 80 2.5 74 2.4 — — Agency mortgage-backed residential 14,291 3.1 — — — — 3 2.9 14,288 3.1 Mortgage-backed residential 2,494 3.1 — — — — — — 2,494 3.1 Mortgage-backed commercial 541 3.2 — — 30 3.1 31 3.1 480 3.2 Asset-backed 936 3.1 — — 698 3.1 106 3.1 132 2.8 Corporate debt 1,256 2.9 140 2.6 513 2.6 564 3.2 39 4.7 Total available-for-sale debt securities $ 22,303 3.0 $ 216 2.3 $ 1,844 2.5 $ 2,271 2.3 $ 17,972 3.1 Amortized cost of available-for-sale debt securities $ 22,499 $ 217 $ 1,852 $ 2,314 $ 18,116 Amortized cost of held-to-maturity securities Agency mortgage-backed residential $ 1,863 3.1 % $ — — % $ — — % $ — — % $ 1,863 3.1 % Asset-backed retained notes 36 1.7 — — 35 1.7 1 3.0 — — Total held-to-maturity securities $ 1,899 3.1 $ — — $ 35 1.7 $ 1 3.0 $ 1,863 3.1 December 31, 2016 Fair value of available-for-sale debt securities (a) U.S. Treasury $ 1,620 1.7 % $ 2 4.6 % $ 60 1.6 % $ 1,558 1.7 % $ — — % U.S. States and political subdivisions 782 3.1 64 1.7 29 2.3 172 2.8 517 3.4 Foreign government 162 2.6 — — 58 2.8 104 2.4 — — Agency mortgage-backed residential 10,290 2.9 — — — — 29 2.6 10,261 2.9 Mortgage-backed residential 2,097 2.9 — — — — — — 2,097 2.9 Mortgage-backed commercial 537 2.6 — — — — 3 2.8 534 2.6 Asset-backed 1,400 2.8 — — 1,059 2.8 143 3.2 198 2.6 Corporate debt 1,443 2.8 72 2.2 840 2.6 489 3.2 42 4.7 Total available-for-sale debt securities $ 18,331 2.8 $ 138 2.0 $ 2,046 2.7 $ 2,498 2.2 $ 13,649 2.9 Amortized cost of available-for-sale debt securities $ 18,651 $ 138 $ 2,040 $ 2,563 $ 13,910 Amortized cost of held-to-maturity securities (b) $ 839 2.9 % $ — — % $ — — % $ — — % $ 839 2.9 % (a) Yield is calculated using the effective yield of each security at the end of the period, weighted based on the market value. The effective yield considers the contractual coupon and amortized cost, and excludes expected capital gains and losses. (b) Our held-to-maturity securities portfolio as of December 31, 2016, consisted of agency mortgage-backed residential debt securities.
Investment Income [Table Text Block]	The following table presents interest and dividends on investment securities. Year ended December 31, ($ in millions) 2017 2016 2015 Taxable interest $ 534 $ 375 $ 340 Taxable dividends 12 17 23 Interest and dividends exempt from U.S. federal income tax 22 19 18 Interest and dividends on investment securities $ 568 $ 411 $ 381
Schedule of Realized Gain (Loss) [Table Text Block]	The following table presents gross gains and losses realized upon the sales of available-for-sale securities and other-than-temporary impairment. Year ended December 31, ($ in millions) 2017 2016 2015 Gross realized gains $ 106 $ 187 $ 184 Gross realized losses (a) (4 ) (2 ) (15 ) Other-than-temporary impairment — — (14 ) Other gain on investments, net $ 102 $ 185 $ 155 (a) Certain available-for-sale securities were sold at a loss in 2017, 2016, and 2015 as a result of market conditions within these respective periods (e.g., a downgrade in the rating of a debt security). Any such sales were made in accordance with our risk management policies and practices.
Schedule of Unrealized Loss on Investments [Table Text Block]	The table below summarizes available-for-sale securities in an unrealized loss position in accumulated other comprehensive income. Based on the assessment of whether such losses were deemed to be other-than-temporary, we believe that the unrealized losses are not indicative of an other-than-temporary impairment of these securities. As of December 31, 2017 , we did not have the intent to sell the debt securities with an unrealized loss position in accumulated other comprehensive income, it is not more likely than not that we will be required to sell these securities before recovery of their amortized cost basis, and we expect to recover the entire amortized cost basis of the securities. As of December 31, 2017 , we had the ability and intent to hold equity securities with an unrealized loss position in accumulated other comprehensive income, and it is not more likely than not that we will be required to sell these securities before recovery of their amortized cost basis. As a result, we believe that the securities with an unrealized loss position in accumulated other comprehensive income are not considered to be other-than-temporarily impaired at December 31, 2017 . Refer to Note 1 for additional information related to investment securities and our methodology for evaluating potential other-than-temporary impairments. 2017 2016 Less than 12 months 12 months or longer Less than 12 months 12 months or longer December 31, ($ in millions) Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Available-for-sale securities Debt securities U.S. Treasury $ 471 $ (8 ) $ 1,305 $ (46 ) $ 1,612 $ (60 ) $ — $ — U.S. States and political subdivisions 242 (2 ) 183 (5 ) 524 (19 ) — — Foreign government 80 (1 ) 4 — 38 — — — Agency mortgage-backed residential 4,066 (19 ) 5,671 (137 ) 8,052 (196 ) 587 (16 ) Mortgage-backed residential 857 (2 ) 773 (32 ) 813 (17 ) 860 (53 ) Mortgage-backed commercial 76 (1 ) 21 — 47 (1 ) 149 (1 ) Asset-backed 220 (1 ) 91 — 375 (2 ) 127 — Corporate debt 529 (4 ) 194 (7 ) 744 (14 ) 46 (2 ) Total temporarily impaired debt securities 6,541 (38 ) 8,242 (227 ) 12,205 (309 ) 1,769 (72 ) Temporarily impaired equity securities 126 (12 ) 116 (36 ) 151 (8 ) 269 (46 ) Total temporarily impaired available-for-sale securities $ 6,667 $ (50 ) $ 8,358 $ (263 ) $ 12,356 $ (317 ) $ 2,038 $ (118 )

Finance Receivables and Loans50

Finance Receivables and Loans, Net (Tables)	12 Months Ended
	Dec. 31, 2017
Loans and Leases Receivable, Net Amount [Abstract]
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]	The composition of finance receivables and loans reported at gross carrying value was as follows. December 31, ($ in millions) 2017 2016 Consumer automotive (a) $ 68,071 $ 65,793 Consumer mortgage Mortgage Finance (b) 11,657 8,294 Mortgage — Legacy (c) 2,093 2,756 Total consumer mortgage 13,750 11,050 Total consumer 81,821 76,843 Commercial Commercial and industrial Automotive 33,025 35,041 Other 3,887 3,248 Commercial real estate 4,160 3,812 Total commercial 41,072 42,101 Total finance receivables and loans (d) $ 122,893 $ 118,944 (a) Includes $18 million and $43 million of fair value adjustment for loans in hedge accounting relationships at December 31, 2017 , and December 31, 2016 , respectively. Refer to Note 22 for additional information. (b) Includes loans originated as interest-only mortgage loans of $20 million and $30 million at December 31, 2017 , and December 31, 2016 , respectively, 35% of which are expected to start principal amortization in 2019 , and 45% in 2020 . The remainder of these loans have already exited the interest-only period. (c) Includes loans originated as interest-only mortgage loans of $496 million and $714 million at December 31, 2017 , and December 31, 2016 , respectively, 3% of which are expected to start principal amortization in 2018 . The remainder of these loans have already exited the interest-only period. (d) Totals include net increases of $551 million and $359 million at December 31, 2017 , and December 31, 2016 , respectively, for unearned income, unamortized premiums and discounts, and deferred fees and costs.
Allowance for Credit Losses on Financing Receivables [Table Text Block]	The following tables present an analysis of the activity in the allowance for loan losses on finance receivables and loans. ($ in millions) Consumer automotive Consumer mortgage Commercial Total Allowance at January 1, 2017 $ 932 $ 91 $ 121 $ 1,144 Charge-offs (a) (1,344 ) (30 ) (18 ) (1,392 ) Recoveries 358 24 — 382 Net charge-offs (986 ) (6 ) (18 ) (1,010 ) Provision for loan losses 1,127 (7 ) 28 1,148 Other (b) (7 ) 1 — (6 ) Allowance at December 31, 2017 $ 1,066 $ 79 $ 131 $ 1,276 Allowance for loan losses at December 31, 2017 Individually evaluated for impairment $ 36 $ 27 $ 14 $ 77 Collectively evaluated for impairment 1,030 52 117 1,199 Finance receivables and loans at gross carrying value Ending balance $ 68,071 $ 13,750 $ 41,072 $ 122,893 Individually evaluated for impairment 430 231 72 733 Collectively evaluated for impairment 67,641 13,519 41,000 122,160 (a) Represents the amount of the gross carrying value directly written off. For consumer and commercial loans, the loss from a charge-off is measured as the difference between the gross carrying value of a loan and the fair value of the collateral, less costs to sell. Refer to Note 1 for more information regarding our charge-off policies. (b) Primarily related to the transfer of finance receivables and loans from held-for-investment to held-for-sale. ($ in millions) Consumer automotive Consumer mortgage Commercial Total Allowance at January 1, 2016 $ 834 $ 114 $ 106 $ 1,054 Charge-offs (a) (1,102 ) (39 ) (1 ) (1,142 ) Recoveries 307 32 2 341 Net charge-offs (795 ) (7 ) 1 (801 ) Provision for loan losses 919 (16 ) 14 917 Other (b) (26 ) — — (26 ) Allowance at December 31, 2016 $ 932 $ 91 $ 121 $ 1,144 Allowance for loan losses at December 31, 2016 Individually evaluated for impairment $ 28 $ 34 $ 23 $ 85 Collectively evaluated for impairment 904 57 98 1,059 Finance receivables and loans at gross carrying value Ending balance $ 65,793 $ 11,050 $ 42,101 $ 118,944 Individually evaluated for impairment 370 247 122 739 Collectively evaluated for impairment 65,423 10,803 41,979 118,205 (a) Represents the amount of the gross carrying value directly written off. For consumer and commercial loans, the loss from a charge-off is measured as the difference between the gross carrying value of a loan and the fair value of the collateral, less costs to sell. Refer to Note 1 for more information regarding our charge-off policies. (b) Primarily related to the transfer of finance receivables and loans from held-for-investment to held-for-sale.
Schedule Of Sales Of Financing Receivables And Loans [Table Text Block]	The following table presents information about significant sales of finance receivables and loans and transfers of finance receivables and loans from held-for-investment to held-for-sale. December 31, ($ in millions) 2017 2016 Consumer automotive $ 1,339 $ 4,267 Consumer mortgage 9 15 Commercial — 29 Total sales and transfers $ 1,348 $ 4,311
Schedule of Purchases of Financing Receivables and Loans [Table Text Block]	The following table presents information about significant purchases of finance receivables and loans. December 31, ($ in millions) 2017 2016 Consumer automotive $ 865 $ 21 Consumer mortgage 4,481 3,747 Total purchases of finance receivables and loans $ 5,346 $ 3,768
Past Due Financing Receivables [Table Text Block]	The following table presents an analysis of our past due finance receivables and loans recorded at gross carrying value. December 31, ($ in millions) 30–59 days past due 60–89 days past due 90 days or more past due Total past due Current Total finance receivables and loans 2017 Consumer automotive $ 1,994 $ 478 $ 268 $ 2,740 $ 65,331 $ 68,071 Consumer mortgage Mortgage Finance 60 11 18 89 11,568 11,657 Mortgage — Legacy 43 25 62 130 1,963 2,093 Total consumer mortgage 103 36 80 219 13,531 13,750 Total consumer 2,097 514 348 2,959 78,862 81,821 Commercial Commercial and industrial Automotive 5 — 3 8 33,017 33,025 Other — — — — 3,887 3,887 Commercial real estate — — — — 4,160 4,160 Total commercial 5 — 3 8 41,064 41,072 Total consumer and commercial $ 2,102 $ 514 $ 351 $ 2,967 $ 119,926 $ 122,893 2016 Consumer automotive $ 1,850 $ 428 $ 302 $ 2,580 $ 63,213 $ 65,793 Consumer mortgage Mortgage Finance 39 6 4 49 8,245 8,294 Mortgage — Legacy 45 18 57 120 2,636 2,756 Total consumer mortgage 84 24 61 169 10,881 11,050 Total consumer 1,934 452 363 2,749 74,094 76,843 Commercial Commercial and industrial Automotive 3 — 7 10 35,031 35,041 Other — — — — 3,248 3,248 Commercial real estate — — — — 3,812 3,812 Total commercial 3 — 7 10 42,091 42,101 Total consumer and commercial $ 1,937 $ 452 $ 370 $ 2,759 $ 116,185 $ 118,944
Schedule of Financing Receivables, Non Accrual Status [Table Text Block]	The following table presents the gross carrying value of our finance receivables and loans on nonaccrual status. December 31, ($ in millions) 2017 2016 Consumer automotive $ 603 $ 598 Consumer mortgage Mortgage Finance 25 10 Mortgage — Legacy 92 89 Total consumer mortgage 117 99 Total consumer 720 697 Commercial Commercial and industrial Automotive 27 33 Other 44 84 Commercial real estate 1 5 Total commercial 72 122 Total consumer and commercial finance receivables and loans $ 792 $ 819
Financing Receivable Credit Quality Indicators [Table Text Block]	The following table presents performing and nonperforming credit quality indicators in accordance with our internal accounting policies for our consumer finance receivables and loans recorded at gross carrying value. Nonperforming loans include finance receivables and loans on nonaccrual status when the principal or interest has been delinquent for 90 days or when full collection is not expected. Refer to Note 1 for additional information. 2017 2016 December 31, ($ in millions) Performing Nonperforming Total Performing Nonperforming Total Consumer automotive $ 67,468 $ 603 $ 68,071 $ 65,195 $ 598 $ 65,793 Consumer mortgage Mortgage Finance 11,632 25 11,657 8,284 10 8,294 Mortgage — Legacy 2,001 92 2,093 2,667 89 2,756 Total consumer mortgage 13,633 117 13,750 10,951 99 11,050 Total consumer $ 81,101 $ 720 $ 81,821 $ 76,146 $ 697 $ 76,843
Schedule Of Pass And Criticized Credit Quality Indicators Of Finance Receivables [Table Text Block]	The following table presents pass and criticized credit quality indicators based on regulatory definitions for our commercial finance receivables and loans recorded at gross carrying value. 2017 2016 December 31, ($ in millions) Pass Criticized (a) Total Pass Criticized (a) Total Commercial and industrial Automotive $ 30,982 $ 2,043 $ 33,025 $ 33,160 $ 1,881 $ 35,041 Other 2,986 901 3,887 2,597 651 3,248 Commercial real estate 4,023 137 4,160 3,653 159 3,812 Total commercial $ 37,991 $ 3,081 $ 41,072 $ 39,410 $ 2,691 $ 42,101 (a) Includes loans classified as special mention, substandard, or doubtful. These classifications are based on regulatory definitions and generally represent loans within our portfolio that have a higher default risk or have already defaulted.
Impaired Financing Receivables [Table Text Block]	The following table presents information about our impaired finance receivables and loans. December 31, ($ in millions) Unpaid principal balance (a) Gross carrying value Impaired with no allowance Impaired with an allowance Allowance for impaired loans 2017 Consumer automotive $ 438 $ 430 $ 91 $ 339 $ 36 Consumer mortgage Mortgage Finance 8 8 4 4 — Mortgage — Legacy 228 223 58 165 27 Total consumer mortgage 236 231 62 169 27 Total consumer 674 661 153 508 63 Commercial Commercial and industrial Automotive 27 27 9 18 3 Other 54 44 10 34 11 Commercial real estate 1 1 — 1 — Total commercial 82 72 19 53 14 Total consumer and commercial finance receivables and loans $ 756 $ 733 $ 172 $ 561 $ 77 2016 Consumer automotive $ 407 $ 370 $ 131 $ 239 $ 28 Consumer mortgage Mortgage Finance 8 8 3 5 — Mortgage — Legacy 243 239 56 183 34 Total consumer mortgage 251 247 59 188 34 Total consumer 658 617 190 427 62 Commercial Commercial and industrial Automotive 33 33 7 26 3 Other 99 84 — 84 19 Commercial real estate 5 5 2 3 1 Total commercial 137 122 9 113 23 Total consumer and commercial finance receivables and loans $ 795 $ 739 $ 199 $ 540 $ 85 (a) Adjusted for charge-offs.
Schedule of Average Balance And Interest Income Of Impaired Finance Receivables [Table Text Block]	The following table presents average balance and interest income for our impaired finance receivables and loans. 2017 2016 2015 Year ended December 31, ($ in millions) Average balance Interest income Average balance Interest income Average balance Interest income Consumer automotive $ 391 $ 21 $ 344 $ 17 $ 295 $ 16 Consumer mortgage Mortgage Finance 8 — 8 — 8 — Mortgage — Legacy 234 10 248 9 272 9 Total consumer mortgage 242 10 256 9 280 9 Total consumer 633 31 600 26 575 25 Commercial Commercial and industrial Automotive 49 2 35 1 33 1 Other 69 9 60 1 41 3 Commercial real estate 5 — 6 — 5 — Total commercial 123 11 101 2 79 4 Total consumer and commercial finance receivables and loans $ 756 $ 42 $ 701 $ 28 $ 654 $ 29
Troubled Debt Restructurings on Financing Receivables [Table Text Block]	The following table presents information related to finance receivables and loans recorded at gross carrying value modified in connection with a TDR during the period. 2017 2016 Year ended December 31, ($ in millions) Number of loans Pre-modification gross carrying value Post-modification gross carrying value Number of loans Pre-modification gross carrying value Post-modification gross carrying value Consumer automotive 26,156 $ 380 $ 333 20,227 $ 347 $ 293 Consumer mortgage Mortgage Finance 4 1 1 7 3 3 Mortgage — Legacy 122 21 21 120 18 18 Total consumer mortgage 126 22 22 127 21 21 Total consumer 26,282 402 355 20,354 368 314 Commercial Commercial and industrial Automotive 4 16 15 1 7 7 Other — 44 44 — — — Commercial real estate 2 3 3 — — — Total commercial 6 63 62 1 7 7 Total consumer and commercial finance receivables and loans 26,288 $ 465 $ 417 20,355 $ 375 $ 321
Finance receivables and loans redefaulted during the period [Table Text Block]	The following table presents information about finance receivables and loans recorded at gross carrying value that have redefaulted during the reporting period and were within 12 months or less of being modified as a TDR. Redefault is when finance receivables and loans meet the requirements for evaluation under our charge-off policy (refer to Note 1 for additional information) except for commercial finance receivables and loans, where redefault is defined as 90 days past due. 2017 2016 Year ended December 31, ($ in millions) Number of loans Gross carrying value Charge-off amount Number of loans Gross carrying value Charge-off amount Consumer automotive 8,829 $ 102 $ 71 7,800 $ 94 $ 56 Consumer mortgage Mortgage Finance 1 1 — — — — Mortgage — Legacy 2 — — 4 — — Total consumer finance receivables and loans 8,832 $ 103 $ 71 7,804 $ 94 $ 56
Consumer Concentration Risk [Table Text Block]	The following table shows the percentage of total consumer finance receivables and loans recorded at gross carrying value by state concentration. 2017 (a) 2016 December 31, Consumer automotive Consumer mortgage Consumer automotive Consumer mortgage California 8.2 % 34.6 % 7.8 % 34.2 % Texas 13.2 6.5 13.6 6.6 Florida 8.5 4.8 8.2 4.4 Pennsylvania 4.6 1.5 4.7 1.5 Illinois 4.2 3.2 4.3 3.4 Georgia 4.2 2.5 4.3 2.2 North Carolina 3.7 1.8 3.6 1.6 Ohio 3.4 0.5 3.5 0.5 New York 3.0 2.2 3.2 1.9 Missouri 2.9 0.9 2.8 1.2 Other United States 44.1 41.5 44.0 42.5 Total consumer loans 100.0 % 100.0 % 100.0 % 100.0 % (a) Presentation is in descending order as a percentage of total consumer finance receivables and loans at December 31, 2017 .
Commercial Concentration Risk [Table Text Block]	The commercial real estate portfolio consists of loans issued primarily to automotive dealers. The following table shows the percentage of total commercial real estate finance receivables and loans reported at gross carrying value by state concentration. December 31, 2017 2016 Texas 15.7 % 16.1 % Florida 10.3 10.2 California 8.2 7.9 Michigan 7.7 7.6 Georgia 4.6 3.6 New Jersey 3.6 4.2 North Carolina 3.6 3.6 South Carolina 3.5 2.7 Pennsylvania 3.0 3.1 Missouri 2.4 2.5 Other United States 37.4 38.5 Total commercial real estate finance receivables and loans 100.0 % 100.0 %
Commercial Criticized Risk Exposure [Table Text Block]	The following table presents the percentage of total commercial criticized finance receivables and loans reported at gross carrying value by industry concentrations. December 31, 2017 2016 Automotive 76.3 % 81.2 % Services 6.7 6.3 Health/Medical 4.9 2.3 Other 12.1 10.2 Total commercial criticized finance receivables and loans 100.0 % 100.0 %

Investment in Operating Lease51

Investment in Operating Leases, Net (Tables)	12 Months Ended
	Dec. 31, 2017
Leases, Operating [Abstract]
Schedule of Property Subject to or Available for Operating Lease [Table Text Block]	Investments in operating leases were as follows. December 31, ($ in millions) 2017 2016 Vehicles $ 10,556 $ 14,584 Accumulated depreciation (1,815 ) (3,114 ) Investment in operating leases, net $ 8,741 $ 11,470
Depreciation Expense On Operating Lease Assets [Table Text Block]	Depreciation expense on operating lease assets includes remarketing gains and losses recognized on the sale of operating lease assets. The following summarizes the components of depreciation expense on operating lease assets. Year ended December 31, ($ in millions) 2017 2016 2015 Depreciation expense on operating lease assets (excluding remarketing gains) $ 1,368 $ 1,982 $ 2,600 Remarketing gains (124 ) (213 ) (351 ) Net depreciation expense on operating lease assets $ 1,244 $ 1,769 $ 2,249
Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block]	The following table presents the future lease nonresidual rental payments due from customers for vehicles on operating leases. Year ended December 31, ($ in millions) 2018 $ 1,319 2019 839 2020 364 2021 46 2022 and thereafter 4 Total $ 2,572

Securitizations and Variable 52

Securitizations and Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2017
Securitizations And Variable Interest Entities [Abstract]
Schedule of Variable Interest Entities [Table Text Block]	The following table presents our involvement in consolidated and nonconsolidated VIEs in which we hold variable interests. For additional detail related to the assets and liabilities of consolidated variable interest entities refer to the Consolidated Balance Sheet. December 31, ($ in millions) Carrying value of total assets Carrying value of total liabilities Assets sold to nonconsolidated VIEs (a) Maximum exposure to loss in nonconsolidated VIEs 2017 On-balance sheet variable interest entities Consumer automotive $ 17,597 (b) $ 7,677 (c) Commercial automotive 12,550 2,558 Off-balance sheet variable interest entities Consumer automotive 37 (d) — $ 1,964 $ 2,001 (e) Commercial other 592 (f) 248 (g) — 790 (h) Total $ 30,776 $ 10,483 $ 1,964 $ 2,791 2016 On-balance sheet variable interest entities Consumer automotive $ 20,869 (b) $ 8,557 (c) Commercial automotive 16,278 4,764 Off-balance sheet variable interest entities Consumer automotive 24 (f) — $ 2,899 $ 2,923 (e) Commercial other 460 (f) 169 (g) — 651 (h) Total $ 37,631 $ 13,490 $ 2,899 $ 3,574 (a) Asset values represent the current unpaid principal balance of outstanding consumer finance receivables and loans within the VIEs. (b) Includes $8.5 billion and $9.6 billion of assets that are not encumbered by VIE beneficial interests held by third parties at December 31, 2017 , and December 31, 2016 , respectively. Ally or consolidated affiliates hold the interests in these assets. (c) Includes $29 million and $50 million of liabilities that are not obligations to third-party beneficial interest holders at December 31, 2017 , and December 31, 2016 , respectively. (d) Represents retained notes and certificated residual interests, of which $36 million is classified as held-to-maturity securities and $1 million is classified as other assets at December 31, 2017 . These assets represent our compliance with the risk retention rules under the Dodd-Frank Act, requiring us to retain at least five percent of the credit risk of the assets underlying asset-backed securitizations , which became effective on December 24, 2016. (e) Maximum exposure to loss represents the current unpaid principal balance of outstanding loans, retained notes, certificated residual interests, as well as certain noncertificated interests retained from the sale of automotive finance receivables. This measure is based on the very unlikely event that all of our sold loans have defects that would trigger a representation and warranty provision and the underlying collateral supporting the loans becomes worthless. This required disclosure is not an indication of our expected loss. (f) Amounts are classified as other assets. (g) Amounts are classified as accrued expenses and other liabilities. (h) For certain nonconsolidated affordable housing entities, maximum exposure to loss represents the yield we guaranteed investors through long-term guarantee contracts. The amount disclosed is based on the unlikely event that the underlying properties cease generating yield to investors and the yield delivered to investors in the form of low income tax housing credits is recaptured. For nonconsolidated equity investments, maximum exposure to loss represents our outstanding investment, additional committed capital, and low income housing tax credits subject to recapture. The amount disclosed is based on the unlikely event that our committed capital is funded, our investments become worthless, and the tax credits previously delivered to us are recaptured. This required disclosure is not an indication of our expected loss.
On-Balance Sheet Variable Interest Entities [Table Text Block]	The consolidated VIEs included on the Consolidated Balance Sheet represent separate entities with which we are involved. The third-party investors in the obligations of consolidated VIEs have legal recourse only to the assets of the VIEs and do not have such recourse to us, except for the customary representation and warranty provisions. In addition, the cash flows from the assets are restricted only to pay such liabilities. Thus, our economic exposure to loss from outstanding third-party financing related to consolidated VIEs is significantly less than the carrying value of the consolidated VIE assets. All assets of consolidated VIEs, presented below based upon the legal transfer of the underlying assets in order to reflect legal ownership, are restricted for the benefit of the beneficial interest holders. December 31, ($ in millions) 2017 2016 Assets Finance receivables and loans, net Consumer $ 8,186 $ 8,929 Commercial 12,437 15,701 Allowance for loan losses (136 ) (173 ) Total finance receivables and loans, net 20,487 24,457 Investment in operating leases, net 444 1,745 Other assets 689 1,390 Total assets $ 21,620 $ 27,592 Liabilities Long-term debt $ 10,197 $ 13,259 Accrued expenses and other liabilities 9 12 Total liabilities $ 10,206 $ 13,271
Schedule Of Cash Flow Received And Paid To Nonconsolidated Securitization Entities [Table Text Block]	The following table summarizes cash flows received and paid related to securitization entities and asset-backed financings where the transfer is accounted for as a sale and we have a continuing involvement with the transferred consumer automotive assets (e.g., servicing) that were outstanding during the years ended December 31, 2017 , 2016 , and 2015 . Additionally, this table contains information regarding cash flows received from and paid to nonconsolidated securitization entities that existed during each period. Year ended December 31, ($ in millions) 2017 2016 2015 Cash proceeds from transfers completed during the period $ 1,187 $ 1,715 $ 1,551 Cash disbursements for repurchases during the period (a) (491 ) — — Servicing fees 31 35 28 Cash flows received on retained interests in securitization entities 21 — — Other cash flows 4 8 — (a) During the second quarter of 2017, we elected to not renew a retail automotive credit conduit facility and also purchased the related retail automotive loans and settled associated retained interests.
Schedule of Quantitative Information and Net Credit Losses about Securitized and Other Financial Assets Managed Together [Table Text Block]	The following table represents off-balance sheet securitizations and whole-loan sales where we have continuing involvement. The table presents quantitative information about delinquencies and net credit losses. Total amount Amount 60 days or more past due Net credit losses December 31, ($ in millions) 2017 2016 2017 2016 2017 2016 Off-balance sheet securitization entities Consumer automotive $ 1,964 $ 2,392 $ 16 $ 13 $ 13 $ 8 Total off-balance sheet securitization entities 1,964 2,392 16 13 13 8 Whole-loan sales (a) 1,399 3,164 4 6 3 3 Total $ 3,363 $ 5,556 $ 20 $ 19 $ 16 $ 11 (a) Whole-loan sales are not part of a securitization transaction, but represent consumer automotive pools of loans sold to third-party investors.

Servicing Activities (Tables)

Servicing Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Servicing Asset [Abstract]
Schedule Of Total Serviced Automobile Loans Outstanding [Table Text Block]	The current unpaid principal balance and any related unamortized deferred fees and costs of total serviced automotive finance loans and net investment in operating leases outstanding were as follows. December 31, ($ in millions) 2017 2016 On-balance sheet automotive finance loans and leases Consumer automotive $ 67,631 $ 65,646 Commercial automotive 37,058 38,853 Operating leases 8,682 11,311 Other 121 67 Off-balance sheet automotive finance loans Securitizations 1,977 2,412 Whole-loan sales 1,409 3,191 Total serviced automotive finance loans and leases $ 116,878 $ 121,480

Other Assets (Tables)

Other Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Other Assets [Abstract]
Schedule of Other Assets [Table Text Block]	The components of other assets were as follows. December 31, ($ in millions) 2017 2016 Property and equipment at cost $ 1,064 $ 901 Accumulated depreciation (608 ) (525 ) Net property and equipment 456 376 Nonmarketable equity investments (a) 1,233 1,046 Restricted cash collections for securitization trusts (b) 812 1,694 Accrued interest and rent receivables 550 476 Net deferred tax assets (c) 461 994 Goodwill (d) 240 240 Other accounts receivable 116 100 Cash reserve deposits held for securitization trusts (e) 111 184 Restricted cash and cash equivalents (f) 94 111 Fair value of derivative contracts in receivable position (g) 39 95 Cash collateral placed with counterparties 29 167 Other assets 1,522 1,371 Total other assets $ 5,663 $ 6,854 (a) Includes investments in FHLB stock of $745 million and $577 million at December 31, 2017 , and 2016, respectively; and FRB stock of $445 million and $435 million at December 31, 2017 , and 2016, respectively. (b) Represents cash collections from customer payments on securitized receivables. These funds are distributed to investors as payments on the related secured debt. (c) For further discussion regarding the impact to our deferred tax asset as a result of the Tax Act, refer to Note 23 . (d) Includes goodwill of $27 million within our Insurance operations at both December 31, 2017 , and 2016; $193 million within Corporate and Other at both December 31, 2017 , and 2016; and $20 million within Automotive Finance operations at both December 31, 2017 , and 2016. As a result of our acquisition of TradeKing, we recognized $193 million of goodwill within Corporate and Other on June 1, 2016. On August 1, 2016, we purchased assets from Blue Yield and as a result recognized $20 million of goodwill within Automotive Finance operations. No other changes to the carrying amount of goodwill were recorded during the years ended December 31, 2017, 2016, and 2015. (e) Represents credit enhancement in the form of cash reserves for various securitization transactions. (f) Primarily represents a number of arrangements with third parties where certain restrictions are placed on balances we hold due to collateral agreements associated with operational processes with a third-party bank, or letter of credit arrangements and corresponding collateral requirements. (g) For additional information on derivative instruments and hedging activities, refer to Note 22 .

Deposit Liabilities (Tables)

Deposit Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Deposit Liabilities, Type [Table Text Block]	Deposit liabilities consisted of the following. December 31, ($ in millions) 2017 2016 Noninterest-bearing deposits $ 108 $ 84 Interest-bearing deposits Savings and money market checking accounts 49,267 46,976 Certificates of deposit 43,869 31,795 Dealer deposits 12 167 Total deposit liabilities $ 93,256 $ 79,022
Time Deposit Maturities [Table Text Block]	The following table presents the scheduled maturity of total certificates of deposit at December 31, 2017 . ( $ in millions ) Due in 2018 $ 28,764 Due in 2019 8,613 Due in 2020 3,579 Due in 2021 1,418 Due in 2022 1,495 Total certificates of deposit $ 43,869

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Short-term Debt [Table Text Block]	The following table presents the composition of our short-term borrowings portfolio. 2017 2016 December 31, ($ in millions) Unsecured Secured (a) Total Unsecured Secured (a) Total Demand notes $ 3,171 $ — $ 3,171 $ 3,622 $ — $ 3,622 Federal Home Loan Bank — 7,350 7,350 — 7,875 7,875 Financial instruments sold under agreements to repurchase — 892 892 — 1,176 1,176 Total short-term borrowings $ 3,171 $ 8,242 $ 11,413 $ 3,622 $ 9,051 $ 12,673 Weighted average interest rate (b) 1.5 % 1.0 % (a) Refer to the section below titled Long-term Debt for further details on assets restricted as collateral for payment of the related debt. (b) Based on the debt outstanding and the interest rate at December 31 of each year.
Long-term Debt [Text Block]	The following tables present the composition of our long-term debt portfolio. December 31, ($ in millions) Amount Stated interest rate Weighted-average stated interest rate (a) Due date range 2017 Unsecured debt Fixed rate (b) $ 12,820 Variable rate 1 Trust preferred securities (c) 2,570 Fair value adjustment (d) 240 Total unsecured debt 15,631 1.48–8.00% 5.68 % 2018–2049 Secured debt Fixed rate 18,845 Variable rate (e) 9,782 Fair value adjustment (d) (32 ) Total secured debt (f) (g) (h) 28,595 0.63–4.50% 1.96 % 2018–2036 Total long-term debt $ 44,226 2016 Unsecured debt Fixed rate (b) $ 17,155 Variable rate 1 Trust preferred securities (c) 2,568 Fair value adjustment (d) 326 Total unsecured debt 20,050 0.68–8.00% 5.36 % 2017–2049 Secured debt Fixed rate 17,935 Variable rate 16,154 Fair value adjustment (d) (11 ) Total secured debt (f) (g) (h) 34,078 0.63–4.55% 1.53 % 2017–2035 Total long-term debt $ 54,128 (a) Based on the debt outstanding and the interest rate at December 31 of each year excluding any impacts of interest rate hedges. (b) Includes subordinated debt of $1.4 billion at both December 31, 2017 , and 2016. (c) Refer to the section below titled Trust Preferred Securities for further information. (d) Represents the fair value adjustment associated with the application of hedge accounting on certain of our long-term debt positions. Refer to Note 22 for additional information. (e) Includes $8 million of long-term debt that does not have a stated interest rate. (f) Includes $10.2 billion and $13.3 billion of VIE secured debt at December 31, 2017 , and 2016, respectively. (g) Includes $8.1 billion and $14.8 billion of debt outstanding from our automotive secured revolving credit facilities at December 31, 2017 , and 2016, respectively. (h) Includes advances from the FHLB of Pittsburgh of $10.3 billion and $6.1 billion at December 31, 2017 , and 2016, respectively.
Schedule of Debt [Table Text Block]	2017 2016 December 31, ($ in millions) Unsecured Secured Total Unsecured Secured Total Long-term debt Due within one year $ 3,482 $ 7,499 $ 10,981 $ 4,274 $ 10,279 $ 14,553 Due after one year 11,909 21,128 33,037 15,450 23,810 39,260 Fair value adjustment 240 (32 ) 208 326 (11 ) 315 Total long-term debt $ 15,631 $ 28,595 $ 44,226 $ 20,050 $ 34,078 $ 54,128
Scheduled of Maturities of Long-term Debt [Table Text Block]	The following table presents the scheduled remaining maturity of long-term debt at December 31, 2017 , assuming no early redemptions will occur. The actual payment of secured debt may vary based on the payment activity of the related pledged assets. ($ in millions) 2018 2019 2020 2021 2022 2023 and thereafter Fair value adjustment Total Unsecured Long-term debt $ 3,582 $ 1,681 $ 2,251 $ 637 $ 1,067 $ 7,408 $ 240 $ 16,866 Original issue discount (100 ) (39 ) (39 ) (43 ) (47 ) (967 ) — (1,235 ) Total unsecured 3,482 1,642 2,212 594 1,020 6,441 240 15,631 Secured Long-term debt 7,499 8,352 6,879 3,712 1,631 554 (32 ) 28,595 Total long-term debt $ 10,981 $ 9,994 $ 9,091 $ 4,306 $ 2,651 $ 6,995 $ 208 $ 44,226
Pledged assets for the payment of the related secured borrowings and repurchase agreements [Table Text Block]	The following summarizes assets restricted as collateral for the payment of the related debt obligation primarily arising from securitization transactions accounted for as secured borrowings and repurchase agreements. 2017 2016 December 31, ($ in millions) Total (a) Ally Bank Total (a) Ally Bank Investment securities (b) $ 8,371 $ 7,443 $ 4,895 $ 4,231 Mortgage assets held-for-investment and lending receivables 13,579 13,579 10,954 10,954 Consumer automotive finance receivables (b) 19,787 6,200 27,846 5,751 Commercial automotive finance receivables 16,567 16,472 19,487 19,280 Operating leases 457 — 2,040 913 Total assets restricted as collateral (c) (d) $ 58,761 $ 43,694 $ 65,222 $ 41,129 Secured debt $ 36,837 (e) $ 23,278 $ 43,129 (e) $ 22,149 (a) Ally Bank is a component of the total column. (b) A portion of the restricted investment securities at December 31, 2017 , and December 31, 2016 , and consumer automotive finance receivables at December 31, 2016 , were restricted under repurchase agreements. Refer to the section above titled Short-term Borrowings for information on the repurchase agreements. (c) Ally Bank has an advance agreement with the FHLB, and had assets pledged to secure borrowings that were restricted as collateral to the FHLB totaling $25.2 billion and $19.0 billion at December 31, 2017 , and December 31, 2016 , respectively. These assets were composed primarily of consumer mortgage finance receivables and loans and investment securities. Ally Bank has access to the FRB Discount Window. Ally Bank had assets pledged and restricted as collateral to the FRB totaling $2.3 billion and $2.4 billion at December 31, 2017 , and December 31, 2016 , respectively. These assets were composed of consumer automotive finance receivables and loans and operating lease assets. Availability under these programs is only for the operations of Ally Bank and cannot be used to fund the operations or liabilities of Ally or its subsidiaries. (d) Excludes restricted cash and cash reserves for securitization trusts recorded within other assets on the Consolidated Balance Sheet . Refer to Note 14 for additional information. (e) Includes $8.2 billion and $9.1 billion of short-term borrowings at December 31, 2017 , and December 31, 2016 , respectively
Schedule Of Committed Funding Facilities [Table Text Block]	Committed Funding Facilities Outstanding Unused capacity (a) Total capacity December 31, ($ in millions) 2017 2016 2017 2016 2017 2016 Bank funding Secured (b) $ 1,785 $ 3,250 $ 890 $ 350 $ 2,675 $ 3,600 Parent funding Secured 6,330 11,550 2,920 1,975 9,250 13,525 Unsecured — — — 1,250 — 1,250 Total committed facilities $ 8,115 $ 14,800 $ 3,810 $ 3,575 $ 11,925 $ 18,375 (a) Funding from committed secured facilities is available on request in the event excess collateral resides in certain facilities or the extent incremental collateral is available and contributed to the facilities. (b) Excludes off-balance sheet credit facility amounts.

Accrued Expenses and Other Li57

Accrued Expenses and Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Accounts Payable and Accrued Liabilities [Abstract]
Schedule of Accrued Liabilities [Table Text Block]	The components of accrued expenses and other liabilities were as follows. December 31, ($ in millions) 2017 2016 Accounts payable $ 746 $ 649 Employee compensation and benefits 248 232 Reserves for insurance losses and loss adjustment expenses 140 149 Fair value of derivative contracts in payable position (a) 41 95 Deferred revenue 32 56 Cash collateral received from counterparties 17 10 Other liabilities 556 546 Total accrued expenses and other liabilities $ 1,780 $ 1,737 (a) For additional information on derivative instruments and hedging activities, refer to Note 22 .

Accumulated Other Comprehensi58

Accumulated Other Comprehensive Loss (Tables)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table presents changes, net of tax, in each component of accumulated other comprehensive loss. ($ in millions) Unrealized (losses) gains on investment securities (a) Translation adjustments and net investment hedges (b) Cash flow hedges (b) Defined benefit pension plans Accumulated other comprehensive loss Balance at January 1, 2015 $ (21 ) $ 36 $ 7 $ (88 ) $ (66 ) 2015 net change (138 ) (27 ) 1 (1 ) (165 ) Balance at December 31, 2015 $ (159 ) $ 9 $ 8 $ (89 ) $ (231 ) 2016 net change (114 ) 5 — (1 ) (110 ) Balance at December 31, 2016 $ (273 ) $ 14 $ 8 $ (90 ) $ (341 ) 2017 net change 100 2 3 1 106 Balance at December 31, 2017 $ (173 ) $ 16 $ 11 $ (89 ) $ (235 ) (a) Represents the after-tax difference between the fair value and amortized cost of our available-for-sale securities portfolio. (b) For additional information on derivative instruments and hedging activities, refer to Note 22 .
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	The following tables present the before- and after-tax changes in each component of accumulated other comprehensive (loss) income. Year ended December 31, 2017 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized gains arising during the period $ 237 $ (45 ) $ 192 Less: Net realized gains reclassified to income from continuing operations 105 (a) (13 ) (b) 92 Net change 132 (32 ) 100 Translation adjustments Net unrealized gains arising during the period 12 (4 ) 8 Net investment hedges (c) Net unrealized losses arising during the period (10 ) 4 (6 ) Cash flow hedges (c) Net unrealized gains arising during the period 5 (2 ) 3 Defined benefit pension plans Net unrealized gains arising during the period 1 — 1 Other comprehensive income $ 140 $ (34 ) $ 106 (a) Includes gains reclassified to other gain on investments, net in our Consolidated Statement of Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Consolidated Statement of Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 22 . Year ended December 31, 2016 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized gains arising during the period $ 13 $ 20 $ 33 Less: Net realized gains reclassified to income from continuing operations 185 (a) (38 ) (b) 147 Net change (172 ) 58 (114 ) Translation adjustments Net unrealized gains arising during the period 5 (2 ) 3 Less: Net realized losses reclassified to income from discontinued operations, net of tax (1 ) — (1 ) Net change 6 (2 ) 4 Net investment hedges (c) Net unrealized gains arising during the period 1 — 1 Defined benefit pension plans Net unrealized losses arising during the period (5 ) 2 (3 ) Less: Net realized losses reclassified to income from continuing operations (4 ) (d) 2 (b) (2 ) Net change (1 ) — (1 ) Other comprehensive loss $ (166 ) $ 56 $ (110 ) (a) Includes gains reclassified to other gain on investments, net in our Consolidated Statement of Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Consolidated Statement of Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 22 . (d) Includes gains reclassified to compensation and benefits expense in our Consolidated Statement of Income . Year ended December 31, 2015 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized losses arising during the period $ (65 ) $ 26 $ (39 ) Less: Net realized gains reclassified to income from continuing operations 155 (a) (56 ) (b) 99 Net change (220 ) 82 (138 ) Translation adjustments Net unrealized losses arising during the period (39 ) 13 (26 ) Less: Net realized gains reclassified to income from discontinued operations, net of tax 42 (20 ) 22 Net change (81 ) 33 (48 ) Net investment hedges (c) Net unrealized gains arising during the period 29 (11 ) 18 Less: Net realized losses reclassified to income from discontinued operations, net of tax (4 ) 1 (3 ) Net change 33 (12 ) 21 Cash flow hedges (c) Net unrealized gains arising during the period 2 (1 ) 1 Defined benefit pension plans Net unrealized gains (losses) arising during the period — — — Less: Net realized gains reclassified to income from continuing operations 1 (d) — (b) 1 Net change (1 ) — (1 ) Other comprehensive loss $ (267 ) $ 102 $ (165 ) (a) Includes gains reclassified to other gain on investments, net in our Consolidated Statement of Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Consolidated Statement of Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 22 . (d) Includes gains reclassified to compensation and benefits expense in our Consolidated Statement of Income .

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table presents the calculation of basic and diluted earnings per common share. Year ended December 31, ($ in millions, except per share data; shares in thousands) (a) 2017 2016 2015 Net income from continuing operations $ 926 $ 1,111 $ 897 Preferred stock dividends (b) — (30 ) (2,571 ) Net income (loss) from continuing operations attributable to common stockholders 926 1,081 (1,674 ) Income (loss) from discontinued operations, net of tax 3 (44 ) 392 Net income (loss) attributable to common stockholders $ 929 $ 1,037 $ (1,282 ) Basic weighted-average common shares outstanding (c) 453,704 481,105 482,873 Diluted weighted-average common shares outstanding (c) (d) 455,350 482,182 482,873 Basic earnings per common share Net income (loss) from continuing operations $ 2.04 $ 2.25 $ (3.47 ) Income (loss) from discontinued operations, net of tax 0.01 (0.09 ) 0.81 Net income (loss) $ 2.05 $ 2.15 $ (2.66 ) Diluted earnings per common share Net income (loss) from continuing operations $ 2.03 $ 2.24 $ (3.47 ) Income (loss) from discontinued operations, net of tax 0.01 (0.09 ) 0.81 Net income (loss) $ 2.04 $ 2.15 $ (2.66 ) (a) Figures in the table may not recalculate exactly due to rounding. Earnings per share is calculated based on unrounded numbers. (b) Preferred stock dividends for the year ended December 31, 2015, include $2,364 million recognized in connection with the partial redemption of the Series G Preferred Stock and the repurchase of the Series A Preferred Stock. These dividends represent an additional return to preferred stockholders calculated as the excess consideration paid over the carrying amount derecognized. (c) Includes shares related to share-based compensation that vested but were not yet issued for the years ended December 31, 2017 , 2016 , and 2015 . (d) Due to the antidilutive effect of the net loss from continuing operations attributable to common stockholders for the year ended December 31, 2015 , basic weighted-average common shares outstanding was used to calculate basic and diluted earnings per share.

Regulatory Capital and Other 60

Regulatory Capital and Other Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block]	The following table summarizes our capital ratios under the U.S. Basel III capital framework. December 31, 2017 December 31, 2016 Required minimum (a) Well-capitalized minimum ( $ in millions ) Amount Ratio Amount Ratio Capital ratios Common Equity Tier 1 (to risk-weighted assets) Ally Financial Inc. $ 13,237 9.53 % $ 12,978 9.37 % 4.50 % (b) Ally Bank 17,059 15.04 17,888 16.70 4.50 6.50 % Tier 1 (to risk-weighted assets) Ally Financial Inc. $ 15,628 11.25 % $ 15,147 10.93 % 6.00 % 6.00 % Ally Bank 17,059 15.04 17,888 16.70 6.00 8.00 Total (to risk-weighted assets) Ally Financial Inc. $ 17,974 12.94 % $ 17,419 12.57 % 8.00 % 10.00 % Ally Bank 17,886 15.77 18,458 17.24 8.00 10.00 Tier 1 leverage (to adjusted quarterly average assets) (c) Ally Financial Inc. $ 15,628 9.53 % $ 15,147 9.54 % 4.00 % (b) Ally Bank 17,059 12.87 17,888 15.21 4.00 (d) 5.00 % (a) In addition to the minimum risk-based capital requirements for common equity Tier 1 capital, Tier 1 capital, and total capital ratios, Ally and Ally Bank were required to maintain a minimum capital conservation buffer of 1.25% and 0.625% at December 31, 2017, and December 31, 2016, respectively, which ultimately increases to 2.5% on January 1, 2019. (b) Currently, there is no ratio component for determining whether a BHC is “well-capitalized.” (c) Federal regulatory reporting guidelines require the calculation of adjusted quarterly average assets using a daily average methodology. (d) On August 22, 2017, banking agencies lifted the capital, liquidity, and business plan commitments that Ally Bank had made in connection with its application for membership in the Federal Reserve System, including the commitment to maintain a Tier 1 leverage ratio of at least 15% . Ally Bank now manages its capital and liquidity subject to applicable regulatory requirements.
Schedule of Common Share Repurchase Activity [Table Text Block]	The following table presents information related to our common stock for each quarter since the commencement of our common stock repurchase programs and initiation of a quarterly cash dividend on common stock. ($ in millions, except per share data; shares in thousands) 4th quarter 2017 3rd quarter 2017 2nd quarter 2017 1st quarter 2017 4th quarter 2016 3rd quarter 2016 Common stock repurchased during period (a) Approximate dollar value $ 190 $ 190 $ 204 $ 169 $ 167 $ 159 Number of shares 7,033 8,507 10,485 8,097 8,745 8,298 Number of common shares outstanding Beginning of period 443,796 452,292 462,193 467,000 475,470 483,753 End of period 437,054 443,796 452,292 462,193 467,000 475,470 Cash dividends declared per common share (b) $ 0.12 $ 0.12 $ 0.08 $ 0.08 $ 0.08 $ 0.08 (a) Includes shares of common stock withheld to cover income taxes owed by participants in our share-based incentive plans. (b) On January 10, 2018 , the Board declared a quarterly cash dividend payment of $0.13 per share on all common stock, a $0.01 per share increase relative to our prior quarterly cash dividend. Refer to Note 32 for further information regarding this common stock dividend.

Derivative Instruments and He61

Derivative Instruments and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position [Table Text Block]	The following table summarizes the fair value amounts of derivative instruments reported on our Consolidated Balance Sheet . The fair value amounts are presented on a gross basis, are segregated by derivatives that are designated and qualifying as hedging instruments or those that are not, and are further segregated by type of contract within those two categories. Derivative contracts in a receivable and payable position exclude open trade equity on derivatives cleared through central clearing counterparties. Any associated collateral exchanged with our central clearing counterparties are treated as settlements of the derivative exposure, rather than collateral. Such payments are recognized as settlements of the derivatives contracts in a receivable and payable position on our Consolidated Balance Sheet. Notional amounts are reference amounts from which contractual obligations are derived and are not recorded on the balance sheet. In our view, derivative notional is not an accurate measure of our derivative exposure when viewed in isolation from other factors, such as market rate fluctuations and counterparty credit risk. 2017 2016 Derivative contracts in a Notional amount Derivative contracts in a Notional amount December 31, ($ in millions) receivable position (a) payable position (b) receivable position (a) payable position (b) Derivatives designated as accounting hedges Interest rate contracts Swaps $ — $ — $ 6,915 $ 19 $ 21 $ 4,731 Foreign exchange contracts Forwards — 1 136 1 — 171 Total derivatives designated as accounting hedges — 1 7,051 20 21 4,902 Derivatives not designated as accounting hedges Interest rate contracts Swaps — — — — — 137 Futures and forwards — — 23 — — — Written options 1 39 8,327 — 73 14,518 Purchased options 38 — 8,237 73 — 14,517 Total interest rate risk 39 39 16,587 73 73 29,172 Foreign exchange contracts Futures and forwards — 1 124 1 — 92 Total foreign exchange risk — 1 124 1 — 92 Equity contracts Written options — — — — 1 — Purchased options — — — 1 — — Total equity risk — — — 1 1 — Total derivatives not designated as accounting hedges 39 40 16,711 75 74 29,264 Total derivatives $ 39 $ 41 $ 23,762 $ 95 $ 95 $ 34,166 (a) Derivative contracts in a receivable position are classified as other assets on the Consolidated Balance Sheet , and include accrued interest of $0 million and $7 million at December 31, 2017 , and December 31, 2016 , respectively. (b) Derivative contracts in a liability position are classified as accrued expenses and other liabilities on the Consolidated Balance Sheet , and include accrued interest of $0 million and $1 million at December 31, 2017 , and December 31, 2016 , respectively.
Derivative Instruments, Gain (Loss) [Table Text Block]	The following table summarizes the location and amounts of gains and losses on derivative instruments reported in our Consolidated Statement of Income . Year ended December 31, ($ in millions) 2017 2016 2015 Derivatives qualifying for hedge accounting Gain (loss) recognized in earnings on derivatives Interest rate contracts Interest and fees on finance receivables and loans (a) $ 1 $ (2 ) $ (9 ) Interest and dividends on investment securities 1 — — Interest on long-term debt (b) (25 ) 65 35 (Loss) gain recognized in earnings on hedged items Interest rate contracts Interest and fees on finance receivables and loans (c) (3 ) — 39 Interest and dividends on investment securities (1 ) — — Interest on long-term debt (d) 30 (70 ) (30 ) Total derivatives qualifying for hedge accounting 3 (7 ) 35 Derivatives not designated as accounting hedges Gain (loss) recognized in earnings on derivatives Interest rate contracts Gain on mortgage and automotive loans, net 1 — (2 ) Other income, net of losses (3 ) — (17 ) Total interest rate contracts (2 ) — (19 ) Foreign exchange contracts (e) Interest on long-term debt — (2 ) (139 ) Other income, net of losses (7 ) 1 12 Total foreign exchange contracts (7 ) (1 ) (127 ) Equity contracts Compensation and benefits expense — — (10 ) Total equity contracts — — (10 ) Loss recognized in earnings on derivatives $ (6 ) $ (8 ) $ (121 ) (a) Amounts exclude losses related to interest for qualifying accounting hedges of retail automotive loans held-for-investment, which are primarily offset by the fixed coupon payments of the loans. The losses were $1 million , $18 million , and $64 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively. (b) Amounts exclude gains related to interest for qualifying accounting hedges of unsecured debt, which are primarily offset by the fixed coupon payment on the long-term debt. The gains were $24 million , $40 million , and $97 million for the years ended December 31, 2017 , 2016, and 2015, respectively. Amounts also exclude gains related to interest for qualifying accounting hedges of secured debt (FHLB advances), which are primarily offset by the fixed coupon payment on the long-term debt. The gains were $3 million , $5 million , and $1 million for the years ended December 31, 2017 , 2016, and 2015, respectively. (c) Amounts exclude losses related to amortization of deferred loan basis adjustments on the de-designated hedged item of $21 million , $20 million , and $8 million for the years ended December 31, 2017 , 2016 , and 2015, respectively. (d) Amounts exclude gains related to amortization of deferred debt basis adjustments on the de-designated hedged item of $77 million , $84 million , and $73 million for the years ended December 31, 2017 , 2016 , and 2015, respectively. Amounts also exclude losses related to amortization of deferred debt basis adjustments (FHLB advances) on the de-designated hedge item of $2 million for the year ended December 31, 2017 . (e) Amounts exclude gains and losses related to the revaluation of the related foreign-denominated debt or receivable. Gains of $9 million , $0 million , and $132 million were recognized for the years ended December 31, 2017 , 2016 , and 2015, respectively.
Schedule of Derivative Instruments, Effect on Other Comprehensive Income [Table Text Block]	The following table summarizes derivative instruments used in cash flow and net investment hedge accounting relationships. Year ended December 31, ($ in millions) 2017 2016 2015 Cash flow hedges Interest rate contracts Gain recognized in other comprehensive loss $ 5 $ — $ 2 Net investment hedges Foreign exchange contracts Loss reclassified from accumulated other comprehensive loss to income from discontinued operations, net $ — $ — $ (4 ) (Loss) gain recognized in other comprehensive loss (a) $ (10 ) $ 1 $ 33 (a) The amounts represent the effective portion of net investment hedges. There are offsetting amounts recognized in accumulated other comprehensive loss related to the revaluation of the related net investment in foreign operations, including the tax impacts of the hedge and related net investment, as disclosed separately in Note 19 . There were gains of $12 million and $4 million for the years ended December 31, 2017 , and 2016 , respectively, and losses of $59 million for the year ended December 31, 2015.

Income Taxes Income Taxes (Tabl

Income Taxes Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The significant components of income tax expense from continuing operations were as follows. Year ended December 31, ($ in millions) 2017 2016 2015 Current income tax (benefit) expense U.S. federal $ (17 ) $ — $ — Foreign 6 8 6 State and local 53 9 3 Total current expense 42 17 9 Deferred income tax expense (benefit) U.S. federal 566 423 454 Foreign — — 1 State and local (27 ) 30 32 Total deferred expense 539 453 487 Total income tax expense from continuing operations $ 581 $ 470 $ 496
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	A reconciliation of income tax expense from continuing operations with the amounts at the statutory U.S. federal income tax rate is shown in the following table. Year ended December 31, ($ in millions) 2017 2016 2015 Statutory U.S. federal tax expense $ 527 $ 553 $ 488 Change in tax resulting from Valuation allowance change, excluding expirations (49 ) 51 (25 ) Tax credits, excluding expirations (12 ) (15 ) (13 ) State and local income taxes, net of federal income tax benefit (a) 7 35 38 Nondeductible expenses 4 7 14 Changes in unrecognized tax expenses (benefits) (b) 1 (161 ) (5 ) Other, net (16 ) — (1 ) Total income tax expense from continuing operations exclusive of tax reform impacts 462 470 496 Tax law enactment 119 — — Total income tax expense from continuing operations inclusive of tax reform impacts $ 581 $ 470 $ 496 (a) Amount for 2017 includes state deferred tax adjustments primarily offset in the valuation allowance change caption. (b) Amount for 2016 is primarily the result of a U.S. tax reserve release in the second quarter of 2016 related to a prior-year federal return.
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The significant components of deferred tax assets and liabilities are reflected in the following table. December 31, ($ in millions) 2017 2016 Deferred tax assets Tax credit carryforwards $ 2,002 $ 1,987 Adjustments to loan value 450 546 Tax loss carryforwards 302 936 State and local taxes 200 162 Unearned insurance premiums 85 141 Hedging transactions 49 123 Other 108 208 Gross deferred tax assets 3,196 4,103 Valuation allowance (1,123 ) (646 ) Deferred tax assets, net of valuation allowance 2,073 3,457 Deferred tax liabilities Lease transactions 1,212 1,789 Deferred acquisition costs 269 424 Debt transactions 95 161 Other 44 107 Gross deferred tax liabilities 1,620 2,481 Net deferred tax assets (a) (b) $ 453 $ 976 (a) Amounts include $461 million and $994 million of net deferred tax assets included in other assets on our Consolidated Balance Sheet for tax jurisdictions in a total net deferred tax asset position and $8 million and $18 million included in accrued expenses and other liabilities on our Consolidated Balance Sheet for tax jurisdictions in a total net deferred tax liability position at December 31, 2017 , and 2016 , respectively. (b) Amount for 2017 decreased $128 million due to the Tax Act, which is composed of adjustments to our deferred tax assets and liabilities of $421 million and an increase in the valuation allowance of $549 million primarily attributable to foreign tax credit carryforwards. The additional decrease of $395 million primarily resulted from the monetization of deferred tax assets against taxes generated from pretax earnings for the year, offset by deferred tax asset builds stemming from tax credit generation, including low income housing tax credits.
Schedule of Deferred Tax Assets and Related Valuation Allowances Recognized for the Net Operating and Other Loss Carryforwards and Tax Credit Carryforwards [Table Text Block]	The significant components of deferred tax assets and liabilities are reflected in the following table. December 31, ($ in millions) 2017 2016 Deferred tax assets Tax credit carryforwards $ 2,002 $ 1,987 Adjustments to loan value 450 546 Tax loss carryforwards 302 936 State and local taxes 200 162 Unearned insurance premiums 85 141 Hedging transactions 49 123 Other 108 208 Gross deferred tax assets 3,196 4,103 Valuation allowance (1,123 ) (646 ) Deferred tax assets, net of valuation allowance 2,073 3,457 Deferred tax liabilities Lease transactions 1,212 1,789 Deferred acquisition costs 269 424 Debt transactions 95 161 Other 44 107 Gross deferred tax liabilities 1,620 2,481 Net deferred tax assets (a) (b) $ 453 $ 976 (a) Amounts include $461 million and $994 million of net deferred tax assets included in other assets on our Consolidated Balance Sheet for tax jurisdictions in a total net deferred tax asset position and $8 million and $18 million included in accrued expenses and other liabilities on our Consolidated Balance Sheet for tax jurisdictions in a total net deferred tax liability position at December 31, 2017 , and 2016 , respectively. (b) Amount for 2017 decreased $128 million due to the Tax Act, which is composed of adjustments to our deferred tax assets and liabilities of $421 million and an increase in the valuation allowance of $549 million primarily attributable to foreign tax credit carryforwards. The additional decrease of $395 million primarily resulted from the monetization of deferred tax assets against taxes generated from pretax earnings for the year, offset by deferred tax asset builds stemming from tax credit generation, including low income housing tax credits. The following table summarizes net deferred tax assets including related valuation allowances at December 31, 2017 . ($ in millions) Deferred tax asset (liability) Valuation allowance Net deferred tax asset (liability) Years of expiration Tax credit carryforwards Foreign tax credits $ 1,772 $ (983 ) $ 789 2018–2027 General business credits 213 — 213 2031–2037 Alternative minimum tax (AMT) credits 17 — 17 n/a Total tax credit carryforwards 2,002 (983 ) 1,019 Tax loss carryforwards Net operating losses — federal 302 — 302 2027–2036 Net operating losses — state 253 (a) (135 ) 118 2018–2037 Capital losses — state 2 (a) (2 ) — 2018–2027 Total tax loss carryforwards 557 (137 ) 420 Other net deferred tax liabilities (b) (983 ) (3 ) (986 ) n/a Net deferred tax assets $ 1,576 $ (1,123 ) (c) $ 453 (a) State net operating loss and capital loss carryforwards are included in the state and local taxes and other liabilities totals disclosed in our deferred inventory table above. (b) Other net deferred tax liabilities are composed of other liabilities and assets. A portion of these assets are subject to a valuation allowance. (c) Includes the valuation allowance impact of the Tax Act of $549 million primarily related to foreign tax credit carryforwards. This valuation allowance impact of the Tax Act is disclosed in the tax law enactment caption in the reconciliation of income tax expense table above.
Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]	The following table provides a reconciliation of the beginning and ending amount of unrecognized tax benefits. ($ in millions) 2017 2016 2015 Balance at January 1, $ 14 $ 185 $ 191 Additions based on tax positions related to the current year — — — Additions for tax positions of prior years 3 12 7 Reductions for tax positions of prior years (1 ) — — Settlements — (182 ) (10 ) Expiration of statute of limitations (1 ) (1 ) (3 ) Balance at December 31, $ 15 $ 14 $ 185

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on a Recurring Basis [Table Text Block]	The following tables display the assets and liabilities measured at fair value on a recurring basis including financial instruments elected for the fair value option. We often economically hedge the fair value change of our assets or liabilities with derivatives and other financial instruments. The tables below display the hedges separately from the hedged items; therefore, they do not directly display the impact of our risk management activities. Recurring fair value measurements December 31, 2017 ($ in millions) Level 1 Level 2 Level 3 Total Assets Investment securities Available-for-sale securities Debt securities U.S. Treasury $ 1,777 $ — $ — $ 1,777 U.S. States and political subdivisions — 854 — 854 Foreign government 8 146 — 154 Agency mortgage-backed residential — 14,291 — 14,291 Mortgage-backed residential — 2,494 — 2,494 Mortgage-backed commercial — 541 — 541 Asset-backed — 936 — 936 Corporate debt — 1,256 — 1,256 Total debt securities 1,785 20,518 — 22,303 Equity securities (a) 518 — — 518 Total available-for-sale securities 2,303 20,518 — 22,821 Mortgage loans held-for-sale (b) — — 13 13 Interests retained in financial asset sales — — 5 5 Derivative contracts in a receivable position Interest rate — 38 1 39 Total derivative contracts in a receivable position — 38 1 39 Total assets $ 2,303 $ 20,556 $ 19 $ 22,878 Liabilities Accrued expenses and other liabilities Derivative contracts in a payable position Interest rate $ — $ (39 ) $ — $ (39 ) Foreign currency — (2 ) — (2 ) Total derivative contracts in a payable position — (41 ) — (41 ) Total liabilities $ — $ (41 ) $ — $ (41 ) (a) Our investment in any one industry did not exceed 14% . (b) Carried at fair value due to fair value option elections. Recurring fair value measurements December 31, 2016 ($ in millions) Level 1 Level 2 Level 3 Total Assets Investment securities Available-for-sale securities Debt securities U.S. Treasury $ 1,620 $ — $ — $ 1,620 U.S. States and political subdivisions — 782 — 782 Foreign government 11 151 — 162 Agency mortgage-backed residential — 10,290 — 10,290 Mortgage-backed residential — 2,097 — 2,097 Mortgage-backed commercial — 537 — 537 Asset-backed — 1,400 — 1,400 Corporate debt — 1,443 — 1,443 Total debt securities 1,631 16,700 — 18,331 Equity securities (a) 595 — — 595 Total available-for-sale securities 2,226 16,700 — 18,926 Other assets Interests retained in financial asset sales — — 29 29 Derivative contracts in a receivable position Interest rate — 92 — 92 Foreign currency — 2 — 2 Other 1 — — 1 Total derivative contracts in a receivable position 1 94 — 95 Total assets $ 2,227 $ 16,794 $ 29 $ 19,050 Liabilities Accrued expenses and other liabilities Derivative contracts in a payable position Interest rate $ — $ (94 ) $ — $ (94 ) Other (1 ) — — (1 ) Total derivative contracts in a payable position (1 ) (94 ) — (95 ) Total liabilities $ (1 ) $ (94 ) $ — $ (95 ) (a) Our investment in any one industry did not exceed 14% .
Fair Value, Assets Measured on a Recurring Basis, Unobservable Input Reconciliation [Table Text Block]	The following tables present the reconciliation for all Level 3 assets and liabilities measured at fair value on a recurring basis. We often economically hedge the fair value change of our assets or liabilities with derivatives and other financial instruments. The Level 3 items presented below may be hedged by derivatives and other financial instruments that are classified as Level 1 or Level 2. Thus, the following tables do not fully reflect the impact of our risk management activities. Level 3 recurring fair value measurements Net realized/unrealized gains Fair value at December 31, 2017 Net unrealized gains included in earnings still held at December 31, 2017 ($ in millions) Fair value at Jan. 1, 2017 included in earnings included in OCI Purchases Sales Issuances Settlements Assets Mortgage loans held-for-sale (a) $ — $ 2 (b) $ — $ 137 $ (126 ) $ — $ — $ 13 $ — Other assets Interests retained in financial asset sales 29 1 (c) — — 8 — (33 ) 5 — Derivative assets — 1 (b) — — — — — 1 1 Total assets $ 29 $ 4 $ — $ 137 $ (118 ) $ — $ (33 ) $ 19 $ 1 (a) Carried at fair value due to fair value option elections. (b) Reported as gain on mortgage and automotive loans, net, in the Consolidated Statement of Income (c) Reported as other income, net of losses, in the Consolidated Statement of Income . Level 3 recurring fair value measurements Fair value at Jan. 1, 2016 Net realized/unrealized gains Purchases Sales Issuances Settlements Fair value at December 31, 2016 Net unrealized gains included in earnings still held at December 31, 2016 ($ in millions) included in earnings included in OCI Assets Other assets Interests retained in financial asset sales $ 40 $ 4 (a) $ — $ — $ 9 $ — $ (24 ) $ 29 $ — Total assets $ 40 $ 4 $ — $ — $ 9 $ — $ (24 ) $ 29 $ — (a) Reported as other income, net of losses, in the Consolidated Statement of Income .
Fair Value Measurements - Nonrecurring Basis [Table Text Block]	The following tables display the assets and liabilities measured at fair value on a nonrecurring basis. Nonrecurring fair value measurements Lower-of-cost or fair value or valuation reserve allowance Total gain (loss) included in earnings for the year ended December 31, 2017 ($ in millions) Level 1 Level 2 Level 3 Total Assets Loans held-for-sale, net $ — $ — $ 77 $ 77 $ — n/m (a) Commercial finance receivables and loans, net (b) Automotive — — 20 20 (3 ) n/m (a) Other — — 22 22 (12 ) n/m (a) Total commercial finance receivables and loans, net — — 42 42 (15 ) n/m (a) Other assets Repossessed and foreclosed assets (c) — — 14 14 (1 ) n/m (a) Other — — 3 3 — n/m (a) Total assets $ — $ — $ 136 $ 136 $ (16 ) n/m n/m = not meaningful (a) We consider the applicable valuation or loan loss allowance to be the most relevant indicator of the impact on earnings caused by the fair value measurement. Accordingly, the table above excludes total gains and losses included in earnings for these items. The carrying values are inclusive of the respective valuation or loan loss allowance. (b) Represents the portion of the portfolio specifically impaired during 2017. The related valuation allowance represents the cumulative adjustment to fair value of those specific receivables. (c) The allowance provided for repossessed and foreclosed assets represents any cumulative valuation adjustment recognized to adjust the assets to fair value. Nonrecurring fair value measurements Lower-of-cost or fair value or valuation reserve allowance Total gain included in earnings for the year ended December 31, 2016 ($ in millions) Level 1 Level 2 Level 3 Total Assets Commercial finance receivables and loans, net (a) Automotive $ — $ — $ 27 $ 27 $ (4 ) n/m (b) Other — — 65 65 (19 ) n/m (b) Total commercial finance receivables and loans, net — — 92 92 (23 ) n/m (b) Other assets Repossessed and foreclosed assets (c) — — 12 12 (4 ) n/m (b) Other — — 4 4 — n/m (b) Total assets $ — $ — $ 108 $ 108 $ (27 ) n/m n/m = not meaningful (a) Represents the portion of the portfolio specifically impaired during 2016 . The related valuation allowance represents the cumulative adjustment to fair value of those specific receivables. (b) We consider the applicable valuation or loan loss allowance to be the most relevant indicator of the impact on earnings caused by the fair value measurement. Accordingly, the table above excludes total gains and losses included in earnings for these items. The carrying values are inclusive of the respective valuation or loan loss allowance. (c) The allowance provided for repossessed and foreclosed assets represents any cumulative valuation adjustment recognized to adjust the assets to fair value.
Financial Instruments Disclosure [Table Text Block]	The following table presents the carrying and estimated fair value of financial instruments, except for those recorded at fair value on a recurring basis presented in the previous section of this note titled Recurring Fair Value. When possible, we use quoted market prices to determine fair value. Where quoted market prices are not available, the fair value is internally derived based on appropriate valuation methodologies with respect to the amount and timing of future cash flows and estimated discount rates. However, considerable judgment is required in interpreting current market data to develop the market assumptions and inputs necessary to estimate fair value. As such, the actual amount received to sell an asset or the amount paid to settle a liability could differ from our estimates. Fair value information presented herein was based on information available at December 31, 2017 , and December 31, 2016 . Estimated fair value ($ in millions) Carrying value Level 1 Level 2 Level 3 Total December 31, 2017 Financial assets Held-to-maturity securities $ 1,899 $ — $ 1,865 $ — $ 1,865 Loans held-for-sale, net 95 — — 95 95 Finance receivables and loans, net 121,617 — — 123,302 123,302 Nonmarketable equity investments 1,233 — 1,190 49 1,239 Financial liabilities Deposit liabilities $ 93,256 $ — $ — $ 91,029 $ 91,029 Short-term borrowings 11,413 — — 11,417 11,417 Long-term debt 44,226 — 27,807 18,817 46,624 December 31, 2016 Financial assets Held-to-maturity securities $ 839 $ — $ 789 $ — $ 789 Finance receivables and loans, net 117,800 — — 118,750 118,750 Nonmarketable equity investments 1,046 — 1,012 55 1,067 Financial liabilities Deposit liabilities $ 79,022 $ — $ — $ 78,469 $ 78,469 Short-term borrowings 12,673 — — 12,675 12,675 Long-term debt 54,128 — 22,036 34,084 56,120

Offsetting Assets and Liabili64

Offsetting Assets and Liabilities Offsetting Assets and Liabilities (Assets) (Tables)	12 Months Ended
	Dec. 31, 2017
Offsetting Assets and Liabilities [Abstract]
Offsetting Assets and liabilities [Table Text Block]	The composition of offsetting derivative instruments, financial assets, and financial liabilities was as follows. Gross amounts of recognized assets/(liabilities) Gross amounts offset on the Consolidated Balance Sheet Net amounts of assets/(liabilities) presented on the Consolidated Balance Sheet Gross amounts not offset on the Consolidated Balance Sheet December 31, 2017 ($ in millions) Financial instruments Collateral (a) (b) (c) Net amount Assets Derivative assets in net asset positions $ 38 $ — $ 38 $ — $ — $ 38 Derivative assets with no offsetting arrangements 1 — 1 — — 1 Total assets (d) $ 39 $ — $ 39 $ — $ — $ 39 Liabilities Derivative liabilities in net liability positions (d) $ (41 ) $ — $ (41 ) $ — $ 1 $ (40 ) Securities sold under agreements to repurchase (e) (892 ) — (892 ) — 892 — Total liabilities $ (933 ) $ — $ (933 ) $ — $ 893 $ (40 ) (a) Financial collateral received/pledged shown as a balance based on the sum of all net asset and liability positions between Ally and each individual derivative counterparty. (b) Amounts disclosed are limited to the financial asset or liability balance and, accordingly, exclude excess collateral received or pledged and noncash collateral received. $2 million of noncash derivative collateral pledged to us was excluded at December 31, 2017 . We do not record such collateral received on our Consolidated Balance Sheet unless certain conditions are met. (c) Certain agreements grant us the right to sell or pledge the noncash assets we receive as collateral. Noncash collateral pledged to us where the agreement grants us the right to sell or pledge the underlying assets had a fair value of $2 million at December 31, 2017 . We have not sold or pledged any of the noncash collateral received under these agreements as of December 31, 2017 . (d) For additional information on derivative instruments and hedging activities, refer to Note 22 . (e) For additional information on securities sold under agreements to repurchase, refer to Note 16 . Gross amounts of recognized assets/(liabilities) Gross amounts offset on the Consolidated Balance Sheet Net amounts of assets/(liabilities) presented on the Consolidated Balance Sheet Gross amounts not offset on the Consolidated Balance Sheet December 31, 2016 ($ in millions) Financial instruments Collateral (a) (b) (c) Net amount Assets Derivative assets in net asset positions $ 87 $ — $ 87 $ (4 ) $ (9 ) $ 74 Derivative assets in net liability positions 8 — 8 (8 ) — — Total assets (d) $ 95 $ — $ 95 $ (12 ) $ (9 ) $ 74 Liabilities Derivative liabilities in net liability positions $ (91 ) $ — $ (91 ) $ 8 $ 13 $ (70 ) Derivative liabilities in net asset positions (4 ) — (4 ) 4 — — Total derivative liabilities (d) (95 ) — (95 ) 12 13 (70 ) Securities sold under agreements to repurchase (e) (676 ) — (676 ) — 676 — Total liabilities $ (771 ) $ — $ (771 ) $ 12 $ 689 $ (70 ) (a) Financial collateral received/pledged shown as a balance based on the sum of all net asset and liability positions between Ally and each individual derivative counterparty. (b) Amounts disclosed are limited to the financial asset or liability balance and, accordingly, exclude excess collateral received or pledged and noncash collateral received. $6 million of noncash derivative collateral pledged to us was excluded at December 31, 2016. We do not record such collateral received on our Consolidated Balance Sheet unless certain conditions are met. (c) Certain agreements grant us the right to sell or pledge the noncash assets we receive as collateral. Noncash collateral pledged to us where the agreement grants us the right to sell or pledge the underlying assets had a fair value of $6 million at December 31, 2016. We have not sold or pledged any of the noncash collateral received under these agreements as of December 31, 2016. (d) For additional information on derivative instruments and hedging activities, refer to Note 22 . (e) For additional information on securities sold under agreements to repurchase, refer to Note 16 .

Segment and Geographic Inform65

Segment and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Financial information for our reportable operating segments is summarized as follows. Year ended December 31, ($ in millions) Automotive Finance operations Insurance operations Mortgage Finance operations Corporate Finance operations Corporate and Other Consolidated (a) 2017 Net financing revenue and other interest income $ 3,713 $ 59 $ 132 $ 167 $ 150 $ 4,221 Other revenue 355 1,059 4 45 81 1,544 Total net revenue 4,068 1,118 136 212 231 5,765 Provision for loan losses 1,134 — 8 22 (16 ) 1,148 Total noninterest expense 1,714 950 108 76 262 3,110 Income (loss) from continuing operations before income tax expense $ 1,220 $ 168 $ 20 $ 114 $ (15 ) $ 1,507 Total assets $ 114,089 $ 7,464 $ 11,708 $ 3,979 $ 29,908 $ 167,148 2016 Net financing revenue and other interest income (loss) $ 3,665 $ 61 $ 97 $ 121 $ (37 ) $ 3,907 Other revenue 306 1,036 — 26 162 1,530 Total net revenue 3,971 1,097 97 147 125 5,437 Provision for loan losses 924 — (4 ) 10 (13 ) 917 Total noninterest expense 1,667 940 67 66 199 2,939 Income (loss) from continuing operations before income tax expense $ 1,380 $ 157 $ 34 $ 71 $ (61 ) $ 1,581 Total assets $ 116,347 $ 7,172 $ 8,307 $ 3,183 $ 28,719 $ 163,728 2015 Net financing revenue and other interest income $ 3,429 $ 57 $ 57 $ 89 $ 87 $ 3,719 Other revenue (loss) 235 1,033 — 25 (151 ) 1,142 Total net revenue (loss) 3,664 1,090 57 114 (64 ) 4,861 Provision for loan losses 696 — 7 9 (5 ) 707 Total noninterest expense 1,633 879 39 55 155 2,761 Income (loss) from continuing operations before income tax expense $ 1,335 $ 211 $ 11 $ 50 $ (214 ) $ 1,393 Total assets $ 115,636 $ 7,053 $ 6,461 $ 2,677 $ 26,754 $ 158,581 (a) Net financing revenue and other interest income after the provision for loan losses totaled $3.1 billion for the year ended December 31, 2017 , and $3.0 billion for both the years ended December 31, 2016 , and 2015.
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]	Information concerning principal geographic areas was as follows. Year ended December 31, ($ in millions) Total net revenue (a) Income (loss) from continuing operations before income tax expense Net income (loss) (b) Identifiable assets (c) Long-lived assets (d) 2017 Canada $ 89 $ 42 $ 37 $ 406 $ — Europe — (1 ) (6 ) 315 — Latin America — — — 23 — Asia-Pacific — — — 2 — Total foreign (e) 89 41 31 746 — Total domestic (f) 5,676 1,466 898 166,162 9,197 Total $ 5,765 $ 1,507 $ 929 $ 166,908 $ 9,197 2016 Canada $ 90 $ 44 $ 32 $ 499 $ — Europe — — (1 ) 276 — Latin America — — (1 ) 23 — Asia-Pacific — — — 2 — Total foreign (e) 90 44 30 800 — Total domestic (f) 5,347 1,537 1,037 162,688 11,846 Total $ 5,437 $ 1,581 $ 1,067 $ 163,488 $ 11,846 2015 Canada $ 98 $ 47 $ 35 $ 514 $ — Europe 1 4 27 325 — Latin America — — (2 ) 28 — Asia-Pacific — — 452 2 — Total foreign (e) 99 51 512 869 — Total domestic (f) 4,762 1,342 777 157,685 16,506 Total $ 4,861 $ 1,393 $ 1,289 $ 158,554 $ 16,506 (a) Revenue consists of net financing revenue and other interest income and total other revenue as presented in our Consolidated Statement of Income. (b) Gain (loss) realized on sale of discontinued operations are allocated to the geographic area in which the business operated. (c) Identifiable assets consist of total assets excluding goodwill. (d) Long-lived assets consist of investments in operating leases, net, and net property and equipment. (e) Our foreign operations as of December 31, 2017, 2016, and 2015, consist of our ongoing Insurance operations in Canada and our remaining international entities in wind-down. (f) Amounts include eliminations between our domestic and foreign operations.

Parent and Guarantor Consolid66

Parent and Guarantor Consolidating Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Condensed Income Statement [Table Text Block]	Condensed Consolidating Statements of Comprehensive Income Year ended December 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Financing (loss) revenue and other interest income Interest and fees on finance receivables and loans $ (27 ) $ — $ 5,846 $ — $ 5,819 Interest and fees on finance receivables and loans — intercompany 12 — 6 (18 ) — Interest and dividends on investment securities and other earning assets — — 601 (2 ) 599 Interest on cash and cash equivalents 7 — 30 — 37 Interest-bearing cash — intercompany 4 — 7 (11 ) — Operating leases 11 — 1,856 — 1,867 Total financing revenue and other interest income 7 — 8,346 (31 ) 8,322 Interest expense Interest on deposits 3 — 1,078 (4 ) 1,077 Interest on short-term borrowings 60 — 67 — 127 Interest on long-term debt 1,101 — 552 — 1,653 Interest on intercompany debt 15 — 12 (27 ) — Total interest expense 1,179 — 1,709 (31 ) 2,857 Net depreciation expense on operating lease assets 11 — 1,233 — 1,244 Net financing revenue (1,183 ) — 5,404 — 4,221 Cash dividends from subsidiaries Bank subsidiary 3,300 3,300 — (6,600 ) — Nonbank subsidiaries 752 — — (752 ) — Other revenue Insurance premiums and service revenue earned — — 973 — 973 Gain on mortgage and automotive loans, net 40 — 28 — 68 Loss on extinguishment of debt (1 ) — (6 ) — (7 ) Other gain on investments, net — — 102 — 102 Other income, net of losses 676 — 840 (1,108 ) 408 Total other revenue 715 — 1,937 (1,108 ) 1,544 Total net revenue 3,584 3,300 7,341 (8,460 ) 5,765 Provision for loan losses 465 — 683 — 1,148 Noninterest expense Compensation and benefits expense 180 — 915 — 1,095 Insurance losses and loss adjustment expenses — — 332 — 332 Other operating expenses 899 — 1,892 (1,108 ) 1,683 Total noninterest expense 1,079 — 3,139 (1,108 ) 3,110 Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries 2,040 3,300 3,519 (7,352 ) 1,507 Income tax expense from continuing operations 337 — 244 — 581 Net income from continuing operations 1,703 3,300 3,275 (7,352 ) 926 Income (loss) from discontinued operations, net of tax 7 — (4 ) — 3 Undistributed (loss) income of subsidiaries Bank subsidiary (1,168 ) (1,168 ) — 2,336 — Nonbank subsidiaries 387 — — (387 ) — Net income 929 2,132 3,271 (5,403 ) 929 Other comprehensive income, net of tax 106 65 104 (169 ) 106 Comprehensive income $ 1,035 $ 2,197 $ 3,375 $ (5,572 ) $ 1,035 Year ended December 31, 2016 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Financing (loss) revenue and other interest income Interest and fees on finance receivables and loans $ (104 ) $ — $ 5,266 $ — $ 5,162 Interest and fees on finance receivables and loans — intercompany 11 — 8 (19 ) — Interest and dividends on investment securities and other earning assets — — 421 (3 ) 418 Interest on cash and cash equivalents 5 — 9 — 14 Interest-bearing cash — intercompany — — 9 (9 ) — Operating leases 17 — 2,694 — 2,711 Total financing (loss) revenue and other interest income (71 ) — 8,407 (31 ) 8,305 Interest expense Interest on deposits 8 — 822 — 830 Interest on short-term borrowings 40 — 17 — 57 Interest on long-term debt 1,161 — 581 — 1,742 Interest on intercompany debt 20 — 11 (31 ) — Total interest expense 1,229 — 1,431 (31 ) 2,629 Net depreciation expense on operating lease assets 14 — 1,755 — 1,769 Net financing revenue (1,314 ) — 5,221 — 3,907 Cash dividends from subsidiaries Nonbank subsidiaries 965 — — (965 ) — Other revenue Insurance premiums and service revenue earned — — 945 — 945 (Loss) gain on mortgage and automotive loans, net (11 ) — 22 — 11 Loss on extinguishment of debt (3 ) — (2 ) — (5 ) Other gain on investments, net — — 176 9 185 Other income, net of losses 1,253 — 937 (1,796 ) 394 Total other revenue 1,239 — 2,078 (1,787 ) 1,530 Total net revenue 890 — 7,299 (2,752 ) 5,437 Provision for loan losses 408 — 509 — 917 Noninterest expense Compensation and benefits expense 573 — 419 — 992 Insurance losses and loss adjustment expenses — — 342 — 342 Other operating expenses 1,261 — 2,130 (1,786 ) 1,605 Total noninterest expense 1,834 — 2,891 (1,786 ) 2,939 (Loss) income from continuing operations before income tax (benefit) expense and undistributed income (loss) of subsidiaries (1,352 ) — 3,899 (966 ) 1,581 Income tax (benefit) expense from continuing operations (279 ) (82 ) 831 — 470 Net (loss) income from continuing operations (1,073 ) 82 3,068 (966 ) 1,111 Loss from discontinued operations, net of tax (39 ) — (5 ) — (44 ) Undistributed income (loss) of subsidiaries Bank subsidiary 1,273 1,273 — (2,546 ) — Nonbank subsidiaries 906 (2 ) — (904 ) — Net income 1,067 1,353 3,063 (4,416 ) 1,067 Other comprehensive loss, net of tax (110 ) (63 ) (106 ) 169 (110 ) Comprehensive income $ 957 $ 1,290 $ 2,957 $ (4,247 ) $ 957 Year ended December 31, 2015 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Financing (loss) revenue and other interest income Interest and fees on finance receivables and loans $ (83 ) $ — $ 4,653 $ — $ 4,570 Interest and fees on finance receivables and loans — intercompany 17 — 24 (41 ) — Interest on loans held-for-sale — — 40 — 40 Interest and dividends on investment securities and other earning assets — — 381 — 381 Interest on cash and cash equivalents 1 — 7 — 8 Interest-bearing cash — intercompany — — 8 (8 ) — Operating leases 9 — 3,389 — 3,398 Total financing (loss) revenue and other interest income (56 ) — 8,502 (49 ) 8,397 Interest expense Interest on deposits 10 — 708 — 718 Interest on short-term borrowings 40 — 9 — 49 Interest on long-term debt 1,121 — 541 — 1,662 Interest on intercompany debt 32 — 17 (49 ) — Total interest expense 1,203 — 1,275 (49 ) 2,429 Net depreciation expense on operating lease assets 7 — 2,242 — 2,249 Net financing revenue (1,266 ) — 4,985 — 3,719 Cash dividends from subsidiaries Bank subsidiary 525 525 — (1,050 ) — Nonbank subsidiaries 1,123 — — (1,123 ) — Other revenue Insurance premiums and service revenue earned — — 940 — 940 (Loss) gain on mortgage and automotive loans, net (9 ) — — 54 — 45 Loss on extinguishment of debt (355 ) — (2 ) — (357 ) Other gain on investments, net — — 155 — 155 Other income, net of losses 1,373 — 1,373 (2,387 ) 359 Total other revenue 1,009 — 2,520 (2,387 ) 1,142 Total net revenue 1,391 525 7,505 (4,560 ) 4,861 Provision for loan losses 157 — 550 — 707 Noninterest expense Compensation and benefits expense 571 — 842 (450 ) 963 Insurance losses and loss adjustment expenses — — 293 — 293 Other operating expenses 1,247 — 2,195 (1,937 ) 1,505 Total noninterest expense 1,818 — 3,330 (2,387 ) 2,761 (Loss) income from continuing operations before income tax (benefit) expense and undistributed income (loss) of subsidiaries (584 ) 525 3,625 (2,173 ) 1,393 Income tax (benefit) expense from continuing operations (267 ) — 763 — 496 Net (loss) income from continuing operations (317 ) 525 2,862 (2,173 ) 897 Income from discontinued operations, net of tax 356 — 36 — 392 Undistributed income (loss) of subsidiaries Bank subsidiary 581 581 — (1,162 ) — Nonbank subsidiaries 669 (1 ) — (668 ) — Net income 1,289 1,105 2,898 (4,003 ) 1,289 Other comprehensive loss, net of tax (165 ) (43 ) (172 ) 215 (165 ) Comprehensive income $ 1,124 $ 1,062 $ 2,726 $ (3,788 ) $ 1,124
Condensed Balance Sheet [Table Text Block]	Condensed Consolidating Balance Sheet December 31, 2017 ($ in millions) Parent (a) Guarantors Nonguarantors (a) Consolidating adjustments Ally consolidated Assets Cash and cash equivalents Noninterest-bearing $ 74 $ — $ 770 $ — $ 844 Interest-bearing 5 — 3,403 — 3,408 Interest-bearing — intercompany 1,138 — 695 (1,833 ) — Total cash and cash equivalents 1,217 — 4,868 (1,833 ) 4,252 Available-for-sale securities — — 22,821 — 22,821 Held-to-maturity securities — — 1,973 (74 ) 1,899 Loans held-for-sale, net — — 108 — 108 Finance receivables and loans, net Finance receivables and loans, net 7,434 — 115,459 — 122,893 Intercompany loans to Nonbank subsidiaries 879 — 408 (1,287 ) — Allowance for loan losses (185 ) — (1,091 ) — (1,276 ) Total finance receivables and loans, net 8,128 — 114,776 (1,287 ) 121,617 Investment in operating leases, net 19 — 8,722 — 8,741 Intercompany receivables from Bank subsidiary 80 — — (80 ) — Nonbank subsidiaries 71 — 77 (148 ) — Investment in subsidiaries Bank subsidiary 16,962 16,962 — (33,924 ) — Nonbank subsidiaries 8,111 — — (8,111 ) — Premiums receivable and other insurance assets — — 2,082 (35 ) 2,047 Other assets 2,207 — 5,105 (1,649 ) 5,663 Total assets $ 36,795 $ 16,962 $ 160,532 $ (47,141 ) $ 167,148 Liabilities Deposit liabilities Noninterest-bearing $ — $ — $ 108 $ — $ 108 Interest-bearing 12 — 93,136 — 93,148 Interest-bearing — intercompany — — 1,139 (1,139 ) — Total deposit liabilities 12 — 94,383 (1,139 ) 93,256 Short-term borrowings 3,171 — 8,242 — 11,413 Long-term debt 17,966 — 26,260 — 44,226 Intercompany debt to Bank subsidiary 74 — — (74 ) — Nonbank subsidiaries 1,103 — 879 (1,982 ) — Intercompany payables to Bank subsidiary 4 — — (4 ) — Nonbank subsidiaries 132 — 127 (259 ) — Interest payable 200 — 175 — 375 Unearned insurance premiums and service revenue — — 2,604 — 2,604 Accrued expenses and other liabilities 639 — 2,790 (1,649 ) 1,780 Total liabilities 23,301 — 135,460 (5,107 ) 153,654 Total equity 13,494 16,962 25,072 (42,034 ) 13,494 Total liabilities and equity $ 36,795 $ 16,962 $ 160,532 $ (47,141 ) $ 167,148 (a) Amounts presented are based upon the legal transfer of the underlying assets to VIEs in order to reflect legal ownership. December 31, 2016 ($ in millions) Parent (a) Guarantors Nonguarantors (a) Consolidating adjustments Ally consolidated Assets Cash and cash equivalents Noninterest-bearing $ 720 $ — $ 827 $ — $ 1,547 Interest-bearing 100 — 4,287 — 4,387 Interest-bearing — intercompany — — 401 (401 ) — Total cash and cash equivalents 820 — 5,515 (401 ) 5,934 Trading securities — — 82 (82 ) — Available-for-sale securities — — 19,253 (327 ) 18,926 Held-to-maturity securities — — 839 — 839 Finance receivables and loans, net Finance receivables and loans, net 4,705 — 114,239 — 118,944 Intercompany loans to Bank subsidiary 1,125 — — (1,125 ) — Nonbank subsidiaries 1,779 — 626 (2,405 ) — Allowance for loan losses (115 ) — (1,029 ) — (1,144 ) Total finance receivables and loans, net 7,494 — 113,836 (3,530 ) 117,800 Investment in operating leases, net 42 — 11,428 — 11,470 Intercompany receivables from Bank subsidiary 299 — — (299 ) — Nonbank subsidiaries 107 — 67 (174 ) — Investment in subsidiaries Bank subsidiary 17,727 17,727 — (35,454 ) — Nonbank subsidiaries 10,318 — — (10,318 ) — Premiums receivable and other insurance assets — — 1,936 (31 ) 1,905 Other assets 4,347 — 5,085 (2,578 ) 6,854 Total assets $ 41,154 $ 17,727 $ 158,041 $ (53,194 ) $ 163,728 Liabilities Deposit liabilities Noninterest-bearing $ — $ — $ 84 $ — $ 84 Interest-bearing 167 — 78,771 — 78,938 Total deposit liabilities 167 — 78,855 — 79,022 Short-term borrowings 3,622 — 9,051 — 12,673 Long-term debt 21,798 — 32,330 — 54,128 Intercompany debt to Bank subsidiary 330 — — (330 ) — Nonbank subsidiaries 1,027 — 2,903 (3,930 ) — Intercompany payables to Nonbank subsidiaries 153 — 351 (504 ) — Interest payable 253 — 98 — 351 Unearned insurance premiums and service revenue — — 2,500 — 2,500 Accrued expenses and other liabilities 487 — 3,911 (2,661 ) 1,737 Total liabilities 27,837 — 129,999 (7,425 ) 150,411 Total equity 13,317 17,727 28,042 (45,769 ) 13,317 Total liabilities and equity $ 41,154 $ 17,727 $ 158,041 $ (53,194 ) $ 163,728 (a) Amounts presented are based upon the legal transfer of the underlying assets to VIEs in order to reflect legal ownership.
Condensed Cash Flow Statement [Table Text Block]	Condensed Consolidating Statement of Cash Flows Year ended December 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash provided by operating activities $ 4,591 $ 3,300 $ 3,466 $ (7,278 ) $ 4,079 Investing activities Purchases of available-for-sale securities — — (11,234 ) — (11,234 ) Proceeds from sales of available-for-sale securities — — 4,633 — 4,633 Proceeds from repayments of available-for-sale securities — — 2,899 — 2,899 Purchases of held-to-maturity securities — — (1,026 ) — (1,026 ) Proceeds from repayments of held-to-maturity securities — — 68 — 68 Net change in investment securities — intercompany 7 — 291 (298 ) — Purchases of finance receivables and loans held-for-investment (35 ) — (5,417 ) — (5,452 ) Proceeds from sales of finance receivables and loans initially held-for-investment 106 — 1,233 — 1,339 Originations and repayments of finance receivables and loans held-for-investment and other, net 860 — 33 (1,956 ) (1,063 ) Net change in loans — intercompany 2,068 — 217 (2,285 ) — Purchases of operating lease assets — — (4,052 ) — (4,052 ) Disposals of operating lease assets 13 — 5,554 — 5,567 Capital contributions to subsidiaries (1,212 ) (5 ) — 1,217 — Returns of contributed capital 1,567 — — (1,567 ) — Net change in nonmarketable equity investments — — (187 ) — (187 ) Other, net (31 ) — (99 ) (89 ) (219 ) Net cash provided by (used in) investing activities 3,343 (5 ) (7,087 ) (4,978 ) (8,727 ) Financing activities Net change in short-term borrowings — third party (453 ) — (810 ) — (1,263 ) Net (decrease) increase in deposits (156 ) — 15,466 (1,138 ) 14,172 Proceeds from issuance of long-term debt — third party 354 — 15,654 1,961 17,969 Repayments of long-term debt — third party (6,111 ) — (21,797 ) — (27,908 ) Net change in debt — intercompany (225 ) — (2,074 ) 2,299 — Repurchase of common stock (753 ) — — — (753 ) Dividends paid — third party (184 ) — — — (184 ) Dividends paid and returns of contributed capital — intercompany — (3,300 ) (5,619 ) 8,919 — Capital contributions from parent — 5 1,212 (1,217 ) — Net cash (used in) provided by financing activities (7,528 ) (3,295 ) 2,032 10,824 2,033 Effect of exchange-rate changes on cash and cash equivalents — — 3 — 3 Net increase (decrease) in cash and cash equivalents and restricted cash 406 — (1,586 ) (1,432 ) (2,612 ) Cash and cash equivalents and restricted cash at beginning of year 989 — 7,293 (401 ) 7,881 Cash and cash equivalents and restricted cash at end of year $ 1,395 $ — $ 5,707 $ (1,833 ) $ 5,269 The following table provides a reconciliation of cash and cash equivalents and restricted cash from the Condensed Consolidated Balance Sheet to the Condensed Consolidated Statement of Cash Flows. December 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Cash and cash equivalents as disclosed on the Consolidated Balance Sheet $ 1,217 $ — $ 4,868 $ (1,833 ) $ 4,252 Restricted cash included in other assets on the Consolidated Balance Sheet (a) 178 — 839 — 1,017 Total cash and cash equivalents and restricted cash as disclosed in the Consolidated Statement of Cash Flows $ 1,395 $ — $ 5,707 $ (1,833 ) $ 5,269 (a) Restricted cash balances relate primarily to Ally securitization arrangements. Refer to Note 14 for additional details describing the nature of restricted cash balances. Year ended December 31, 2016 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash provided by operating activities $ 241 $ 6 $ 5,383 $ (1,063 ) $ 4,567 Investing activities Purchases of available-for-sale securities — — (16,031 ) — (16,031 ) Proceeds from sales of available-for-sale securities — — 11,036 — 11,036 Proceeds from repayments of available-for-sale securities — — 3,379 — 3,379 Purchases of held-to-maturity securities — — (841 ) — (841 ) Purchases of finance receivables and loans held-for-investment (4 ) — (3,855 ) — (3,859 ) Proceeds from sales of finance receivables and loans initially held-for-investment — — 4,285 — 4,285 Originations and repayments of finance receivables and loans held-for-investment and other, net 2,013 — (10,839 ) — (8,826 ) Net change in loans — intercompany 877 — (67 ) (810 ) — Purchases of operating lease assets — — (3,274 ) — (3,274 ) Disposals of operating lease assets 25 — 6,279 — 6,304 Acquisitions, net of cash acquired (309 ) — — — (309 ) Capital contributions to subsidiaries (3,908 ) — — 3,908 — Returns of contributed capital 3,678 8 — (3,686 ) — Net change in nonmarketable equity investments — — (628 ) — (628 ) Other, net (206 ) — (191 ) 91 (306 ) Net cash provided by (used in) investing activities 2,166 8 (10,747 ) (497 ) (9,070 ) Financing activities Net change in short-term borrowings — third party 169 — 4,395 — 4,564 Net (decrease) increase in deposits (61 ) — 12,569 — 12,508 Proceeds from issuance of long-term debt — third party 979 — 13,176 — 14,155 Repayments of long-term debt — third party (2,662 ) — (23,750 ) — (26,412 ) Net change in debt — intercompany (382 ) — (877 ) 1,259 — Redemption of preferred stock (696 ) — — — (696 ) Repurchase of common stock (341 ) — — — (341 ) Dividends paid — third party (108 ) — — — (108 ) Dividends paid and returns of contributed capital — intercompany — (14 ) (4,644 ) 4,658 — Capital contributions from parent — — 3,908 (3,908 ) — Net cash (used in) provided by financing activities (3,102 ) (14 ) 4,777 2,009 3,670 Effect of exchange-rate changes on cash and cash equivalents — — 1 — 1 Net decrease in cash and cash equivalents and restricted cash (695 ) — (586 ) 449 (832 ) Cash and cash equivalents and restricted cash at beginning of year 1,684 — 7,879 (850 ) 8,713 Cash and cash equivalents and restricted cash at end of year $ 989 $ — $ 7,293 $ (401 ) $ 7,881 The following table provides a reconciliation of cash and cash equivalents and restricted cash from the Condensed Consolidated Balance Sheet to the Condensed Consolidated Statement of Cash Flows. December 31, 2016 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Cash and cash equivalents as disclosed on the Consolidated Balance Sheet $ 820 $ — $ 5,515 $ (401 ) $ 5,934 Restricted cash included in other assets on the Consolidated Balance Sheet (a) 169 — 1,778 — 1,947 Total cash and cash equivalents and restricted cash as disclosed in the Consolidated Statement of Cash Flows $ 989 $ — $ 7,293 $ (401 ) $ 7,881 (a) Restricted cash balances relate primarily to Ally securitization arrangements. Refer to Note 14 for additional details describing the nature of restricted cash balances. Year ended December 31, 2015 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash provided by operating activities $ 370 $ 525 $ 6,390 $ (2,174 ) $ 5,111 Investing activities Purchases of available-for-sale securities — — (12,250 ) — (12,250 ) Proceeds from sales of available-for-sale securities — — 6,874 — 6,874 Proceeds from repayments of available-for-sale securities — — 4,255 — 4,255 Purchases of finance receivables and loans held-for-investment (169 ) — (4,332 ) — (4,501 ) Proceeds from sales of finance receivables and loans initially held-for-investment — — 3,197 — 3,197 Originations and repayments of finance receivables and loans held-for-investment and other, net 1,954 — (11,298 ) — (9,344 ) Net change in loans — intercompany 240 — 1,211 (1,451 ) — Purchases of operating lease assets (94 ) — (4,591 ) — (4,685 ) Disposals of operating lease assets 7 — 5,539 — 5,546 Capital contributions to subsidiaries (796 ) (1 ) — 797 — Returns of contributed capital 1,444 — — (1,444 ) — Proceeds from sale of business units, net 1,049 — — — 1,049 Net change in nonmarketable equity investments — — (147 ) — (147 ) Other, net (47 ) — 50 — 3 Net cash provided by (used in) investing activities 3,588 (1 ) (11,492 ) (2,098 ) (10,003 ) Financing activities Net change in short-term borrowings — third party 115 — 913 — 1,028 Net (decrease) increase in deposits (91 ) — 8,338 — 8,247 Proceeds from issuance of long-term debt — third party 5,428 — 25,237 — 30,665 Repayments of long-term debt — third party (5,931 ) — (25,419 ) — (31,350 ) Net change in debt — intercompany (977 ) — (240 ) 1,217 — Repurchase and redemption of preferred stock (559 ) — — — (559 ) Repurchase of common stock (16 ) — — — (16 ) Dividends paid — third party (2,571 ) — — — (2,571 ) Dividends paid and returns of contributed capital — intercompany — (525 ) (3,092 ) 3,617 — Capital contributions from parent — 1 796 (797 ) — Net cash (used in) provided by financing activities (4,602 ) (524 ) 6,533 4,037 5,444 Effect of exchange-rate changes on cash and cash equivalents — — (4 ) — (4 ) Net (decrease) increase in cash and cash equivalents and restricted cash (644 ) — 1,427 (235 ) 548 Cash and cash equivalents and restricted cash at beginning of year 2,328 — 6,452 (615 ) 8,165 Cash and cash equivalents and restricted cash at end of year $ 1,684 $ — $ 7,879 $ (850 ) $ 8,713

Premiums Receivable and Other67

Premiums Receivable and Other Insurance Assets Premiums Receivable and Other Insurance Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Premiums Receivable and Other Insurance Assets [Abstract]
Premiums Receivable and Other Insurance Assets [Table Text Block]	Premiums receivable and other insurance assets consisted of the following. December 31, ($ in millions) 2017 2016 Prepaid reinsurance premiums $ 507 $ 439 Reinsurance recoverable on unpaid losses 108 108 Reinsurance recoverable on paid losses 19 20 Premiums receivable 84 80 Deferred policy acquisition costs 1,329 1,258 Total premiums receivable and other insurance assets $ 2,047 $ 1,905

Equity Equity (Tables)

Equity Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Stockholders Equity [Table Text Block]	The following table presents changes in the number of shares issued and outstanding. Year ended December 31, (shares in thousands) (a) 2017 2016 2015 Common stock Total issued at January 1, 485,708 482,791 480,136 New issuances Employee benefits and compensation plans 4,176 2,917 2,655 Total issued at December 31, 489,884 485,708 482,791 Treasury balance at January 1, (18,707 ) (811 ) (41 ) Repurchase of common stock (b) (c) (34,122 ) (17,897 ) (769 ) Total treasury stock at December 31, (52,830 ) (18,707 ) (811 ) Total outstanding at December 31, 437,054 467,000 481,980 (a) Figures in the table may not recalculate exactly due to rounding. Number of shares issued, in treasury, and outstanding are calculated based on unrounded numbers. (b) Includes shares of common stock withheld to cover income taxes owed by participants in our share-based incentive plans. (c) On July 19, 2016, we announced a common stock repurchase program of up to $700 million . The program commenced in the third quarter of 2016 and expired on June 30, 2017. On June 28, 2017, we announced a common stock repurchase program of up to $760 million . The program commenced in the third quarter of 2017 and will expire on June 30, 2018.

Insurance Premiums and Servic69

Insurance Premiums and Service Revenue Earned Insurance Premiums and Service Revenue Earned (Tables)	12 Months Ended
	Dec. 31, 2017
Insurance Premiums and Service Revenue Earned [Abstract]
Insurance Premiums and Service Revenue Earned [Table Text Block]	The following table is a summary of insurance premiums and service revenue written and earned. 2017 2016 2015 Year ended December 31, ($ in millions) Written Earned Written Earned Written Earned Insurance premiums Direct $ 384 $ 364 $ 317 $ 318 $ 313 $ 296 Assumed 2 5 3 5 2 16 Gross insurance premiums 386 369 320 323 315 312 Ceded (254 ) (188 ) (198 ) (141 ) (184 ) (125 ) Net insurance premiums 132 181 122 182 131 187 Service revenue 864 792 826 763 846 753 Insurance premiums and service revenue written and earned $ 996 $ 973 $ 948 $ 945 $ 977 $ 940

Quarterly Financial Statement70

Quarterly Financial Statements (unaudited) Quarterly Financial Statements (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information (unaudited) [Abstract]
Quarterly Financial Information [Table Text Block]	($ in millions) First quarter Second quarter Third quarter Fourth quarter 2017 Net financing revenue and other interest income $ 979 $ 1,067 $ 1,081 $ 1,094 Other revenue 396 388 381 379 Total net revenue 1,375 1,455 1,462 1,473 Provision for loan losses 271 269 314 294 Total noninterest expense 778 810 753 769 Income from continuing operations before income tax expense 326 376 395 410 Income tax expense from continuing operations (a) 113 122 115 231 Net income from continuing operations 213 254 280 179 Income (loss) from discontinued operations, net of tax 1 (2 ) 2 2 Net income $ 214 $ 252 $ 282 $ 181 Basic earnings per common share (b) Net income from continuing operations $ 0.46 $ 0.55 $ 0.62 $ 0.40 Net income 0.46 0.55 0.63 0.41 Diluted earnings per common share (b) Net income from continuing operations $ 0.46 $ 0.55 $ 0.62 $ 0.40 Net income 0.46 0.55 0.63 0.41 Cash dividends per common share $ 0.08 $ 0.08 $ 0.12 $ 0.12 2016 Net financing revenue and other interest income $ 951 $ 984 $ 996 $ 976 Other revenue 376 374 388 392 Total net revenue 1,327 1,358 1,384 1,368 Provision for loan losses 220 172 258 267 Total noninterest expense 710 773 735 721 Income from continuing operations before income tax expense 397 413 391 380 Income tax expense from continuing operations (c) 150 56 130 134 Net income from continuing operations 247 357 261 246 Income (loss) from discontinued operations, net of tax 3 3 (52 ) 2 Net income $ 250 $ 360 $ 209 $ 248 Basic earnings per common share (b) Net income from continuing operations $ 0.48 $ 0.70 $ 0.54 $ 0.52 Net income 0.49 0.71 0.43 0.53 Diluted earnings per common share (b) Net income from continuing operations $ 0.48 $ 0.70 $ 0.54 $ 0.52 Net income 0.49 0.71 0.43 0.52 Cash dividends per common share $ — $ — $ 0.08 $ 0.08 (a) Amount for the fourth quarter of 2017 includes $119 million of tax expense attributable to tax reform enacted on December 22, 2017 , as further described in Note 23 (b) Earnings per share is calculated quarterly on an independent basis, therefore the total of the amounts presented for each year above may not reconcile to the annual amounts presented in Note 20 . (c) Amount for the second quarter of 2016 includes a nonrecurring tax benefit due to a U.S. tax reserve release related to a prior-year federal return that reduced our liability for unrecognized tax benefits , as further described in Note 23 .

Share-based Compensation Plan71

Share-based Compensation Plans Share-based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Share-based Compensation Plans [Abstract]
Shares-based Compensation Arrangements by Share-based Payment Award, Performance-Based Units and Restricted Stock Units [Table Text Block]	The following table presents the changes in outstanding non-vested PSUs and RSUs activity during 2017. (in thousands, except per share data) Number of units Weighted-average grant date fair value per share RSUs and PSUs Outstanding non-vested at January 1, 2017 5,443 $ 19.00 Granted 3,280 21.30 Vested (3,043 ) 19.84 Forfeited (88 ) 19.39 Outstanding non-vested at December 31, 2017 5,592 19.89

Guarantees and Commitments Gu72

Guarantees and Commitments Guarantees and Commitments (Tables)	12 Months Ended
	Dec. 31, 2017
Guarantees and Commitments [Abstract]
Schedule of Guarantor Obligations [Table Text Block]	Guarantees are defined as contracts or indemnification agreements that contingently require us to make payments to third parties based on changes in the underlying agreements with the guaranteed parties. The following summarizes our outstanding guarantees, including those of our discontinued operations, made to third parties on our Consolidated Balance Sheet , for the periods shown. 2017 2016 December 31, ($ in millions) Maximum liability Carrying value of liability Maximum liability Carrying value of liability Standby letters of credit and other guarantees $ 227 $ 8 $ 175 $ 8
Financing Commitments [Table Text Block]	The contractual commitments were as follows. December 31, ($ in millions) 2017 2016 Unused revolving credit line commitments and other (a) $ 2,341 $ 1,995 Home equity lines of credit (b) 318 356 Commitments to provide capital to investees (c) 283 206 Construction-lending commitments (d) 144 164 Mortgage loan origination commitments (e) 95 — (a) The unused portion of revolving lines of credit reset at prevailing market rates and, as such, approximate market value. (b) We are committed to fund the remaining unused balances on home equity lines of credit. (c) We are committed to contribute capital to certain investees. The fair value of these commitments is considered in the overall valuation of the underlying assets with which they are associated. (d) The fair value of these commitments is considered in the overall valuation of the related assets. (e) Commitments with mortgage loan applicants in which the loan terms, including interest rate and price, are guaranteed for a designated period of time subject to the completion of underwriting procedures.
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	Future minimum rental payments required under operating leases, primarily for real property, with noncancelable lease terms expiring after December 31, 2017 , are as follows. Year ended December 31, ($ in millions) 2018 $ 35 2019 35 2020 34 2021 36 2022 33 2023 and thereafter 316 Total minimum payment required $ 489
Long-term Purchase Commitment [Table Text Block]	We have entered into multiple agreements for information technology, voice and communication technology, and related maintenance. Many of the agreements are subject to variable price provisions, fixed or minimum price provisions, and termination or renewal provisions. Year ended December 31, ($ in millions) 2018 $ 85 2019 and 2020 36 2021 and thereafter 2 Total future payment obligations $ 123

Description of Business, Basi73

Description of Business, Basis of Presentation, and Significant Accounting Policies Description of Business, Basis of Presentation, and Significant Accounting Policies (Recently Issued Accounting Standards) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Accounting Standards Update 2014-09 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 126
Accounting Standards Update 2016-01 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 20

Acquisitions Acquisitions (Deta

Acquisitions Acquisitions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Aug. 01, 2016	Jun. 01, 2016
Business Acquisition [Line Items]
Business Acquisition Cash Paid			$ 28	$ 298
Goodwill	$ 240	$ 240
Amortization of Intangible Assets	10	6
Other Intangible Assets [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill				82
Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents				50
Other Assets [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill				14
Deferred Tax Asset [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill				4
Employee compensation and benefits [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents				40
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities				(41)
Other Liabilities [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities				(4)
Corporate and Other [Member]
Business Acquisition [Line Items]
Goodwill	193	193		$ 193
Automotive Finance Operations [Member]
Business Acquisition [Line Items]
Goodwill	$ 20	$ 20	$ 20

Discontinued Operations (Detail

Discontinued Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity Method Investment, Realized Gain (Loss) on Disposal			$ 400
Automotive Finance Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sold Interest in Joint Venture			40.00%
Disposal Group, Including Discontinued Operation, Operating Income (Loss)	$ (4)	$ (2)	$ 452
Discontinued Operation, Tax Effect of Discontinued Operation	(5)	2	80
Other Segments [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Operating Income (Loss)	2	(41)	16
Discontinued Operation, Tax Effect of Discontinued Operation	$ 0	$ (1)	$ (4)

Other Income, Net of Losses (Sc

Other Income, Net of Losses (Schedule of Other Income, Net of Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Nonoperating Income (Expense) [Abstract]
Remarketing Fees	$ 104	$ 103	$ 101
Fees and Commissions, Other	102	98	90
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	51	64	45
Income (Loss) from Equity Method Investments	14	18	52
Other Income	137	111	71
Noninterest Income, Other Operating Income	$ 408	$ 394	$ 359

Reserves for Insurance Losses77

Reserves for Insurance Losses and Loss Adjustment Expenses Reserves for Insurance Losses and Loss Adjustment Expenses (Short-duration Insurance Contracts) (Details) number in Millions, $ in Millions	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,088
Short-duration Insurance Cotnracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Separately Presented	2,065
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	7
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	30	$ 38
Short-duration Insurance Contracts, Accident Year 2012 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	422	423	$ 423	$ 423	$ 430	$ 435
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 1
Short-duration Insurance Contracts, Number of Reported Claims	772,546
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 421	419	418	416	412	$ 391
Short-duration Insurance Contracts, Accident Year 2013 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	369	370	370	365	376
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 1
Short-duration Insurance Contracts, Number of Reported Claims	672,263
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 368	368	366	364	$ 347
Short-duration Insurance Contracts, Accident Year 2014 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	388	388	389	390
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contracts, Number of Reported Claims	525,290
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 388	388	388	$ 369
Short-duration Insurance Contracts, Accident Year 2015 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	272	271	274
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contracts, Number of Reported Claims	342,231
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 272	272	$ 252
Short-duration Insurance Contracts, Accident Year 2016 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	327	326
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contracts, Number of Reported Claims	475,707
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 327	$ 302
Short-duration Insurance Contracts, Accident Year 2017 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	310
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 21
Short-duration Insurance Contracts, Number of Reported Claims	455,965
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 289

Reserves for Insurance Losses78

Reserves for Insurance Losses and Loss Adjustment Expenses Reserves for Insurance Losses and Loss Adjustment Expenses (Short-duration Contracts, Schedule of Historical Claims Duration) (Details)	Dec. 31, 2017
Reserves for Insurance Losses and Loss Adjustment Expenses (Short-duration Contracts, Schedule of Historical Claims Duration) [Abstract]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	93.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	5.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	0.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	0.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	0.40%

Reserves for Insurance Losses79

Reserves for Insurance Losses and Loss Adjustment Expenses Reserves for Insurance Losses and Loss Adjustment Expenses (Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserves for Insurance Losses and Loss Adjustment Expenses (Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability) [Abstract]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	$ 30	$ 38
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments	108	108	$ 120
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense	2	3
Liability for Claims and Claims Adjustment Expense	$ 140	$ 149	$ 169

Reserves for Insurance Losses80

Reserves for Insurance Losses and Loss Adjustment Expenses Reserves for Insurance Losses and Loss Adjustment Expenses (Schedule of Liability for Unpaid Claims and Claims Adjustment Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Claims and Claims Adjustment Expenses (Rollforward) [Abstract]
Liability for Claims and Claims Adjustment Expense	$ 149	$ 169
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments	108	108	$ 120
Liability for Unpaid Claims and Claims Adjustment Expense, Net	41	49
Supplemental Information for Property, Casualty Insurance Underwriters, Reserves for Unpaid Claims and Claims Adjustment Expense	332	345
Prior Year Claims and Claims Adjustment Expense	0	(3)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	332	342	293
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	(309)	(320)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	(32)	(30)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	(341)	(350)
Liability for Unpaid Claims and Claims Adjustment Expense, Net	32	41	49
Liability for Claims and Claims Adjustment Expense	$ 140	$ 149	$ 169

Other Operating Expenses (Sched

Other Operating Expenses (Schedule Of Other Operating Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Expenses [Abstract]
Insurance Commissions	$ 415	$ 389	$ 378
Communications and Information Technology	284	274	267
Lease And Loan Administration	159	136	126
Marketing and Advertising Expense	133	112	107
Professional Fees	113	103	93
Federal Deposit Insurance Corporation Premium Expense	113	94	79
Vehicle remarketing and repossession	110	95	78
Depreciation, Nonproduction	89	84	82
Occupancy, Net	46	51	50
Taxes, Miscellaneous	21	25	29
Other Cost and Expense, Operating	200	242	216
Other Noninterest Expense	$ 1,683	$ 1,605	$ 1,505

Investment Securities (Investme

Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 23,052	$ 19,293
Available-for-sale Securities, Gross Unrealized Gains	82	68
Available-for-sale Securities, Gross Unrealized Losses	(313)	(435)
Available-for-sale securities	22,821	18,926
Held-to-maturity securities	1,899	839
Held-to-maturity Securities, Fair Value	1,865	789
Deposit Assets	12	14
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	1,025	737
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	22,499	18,651
Available-for-sale Debt Securities Gross Unrealized Gain	69	61
Available-for-sale Debt Securities, Gross Unrealized Loss	(265)	(381)
Available-for-sale Securities, Debt Securities	22,303	18,331
US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,831	1,680
Available-for-sale Debt Securities Gross Unrealized Gain	0	0
Available-for-sale Debt Securities, Gross Unrealized Loss	(54)	(60)
Available-for-sale Securities, Debt Securities	1,777	1,620
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	850	794
Available-for-sale Debt Securities Gross Unrealized Gain	11	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(7)	(19)
Available-for-sale Securities, Debt Securities	854	782
Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	153	157
Available-for-sale Debt Securities Gross Unrealized Gain	2	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	0
Available-for-sale Securities, Debt Securities	154	162
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	14,412	10,473
Available-for-sale Debt Securities Gross Unrealized Gain	35	29
Available-for-sale Debt Securities, Gross Unrealized Loss	(156)	(212)
Available-for-sale Securities, Debt Securities	14,291	10,290
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	1,863	839
Held-to-maturity Securities, Unrecognized Holding Gain	3	0
Held-to-maturity Securities, Unrecognized Holding Loss	(37)	(50)
Held-to-maturity Securities, Fair Value	1,829	789
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,517	2,162
Available-for-sale Debt Securities Gross Unrealized Gain	11	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(34)	(70)
Available-for-sale Securities, Debt Securities	2,494	2,097
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	541	537
Available-for-sale Debt Securities Gross Unrealized Gain	1	2
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	(2)
Available-for-sale Securities, Debt Securities	541	537
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	933	1,396
Available-for-sale Debt Securities Gross Unrealized Gain	4	6
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	(2)
Available-for-sale Securities, Debt Securities	936	1,400
Asset-backed Securities [Member] | Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	36	0
Held-to-maturity Securities, Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	36	0
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,262	1,452
Available-for-sale Debt Securities Gross Unrealized Gain	5	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(11)	(16)
Available-for-sale Securities, Debt Securities	1,256	1,443
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	553	642
Available-for-sale Equity Securities, Gross Unrealized Gain	13	7
Available-for-sale Equity Securities, Gross Unrealized Loss	(48)	(54)
Available-for-sale Securities, Equity Securities	518	595
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	1,899	839
Held-to-maturity Securities, Unrecognized Holding Gain	3	0
Held-to-maturity Securities, Unrecognized Holding Loss	(37)	(50)
Held-to-maturity Securities, Fair Value	1,865	789
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Fair Value	664	87
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	$ 7,804	$ 4,881

Investment Securities (Invest83

Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment		$ 839
Held-to-Maturity Debt Securities, Yield		2.90%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount		$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield		0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount		$ 0
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield		0.00%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount		$ 0
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield		0.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount		$ 839
Held-to-Maturity Securities, Due After Ten Years, Yield		2.90%
Cash Equivalents, at Carrying Value	$ 10	$ 291
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 22,303	$ 18,331
Available-for-sale debt securities, Yield	3.00%	2.80%
Available-for-sale debt securities, Due in one year or less, Amount	$ 216	$ 138
Available-for-sale debt securities, Due in one year or less, Yield	2.30%	2.00%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 1,844	$ 2,046
Available-for-sale debt securities, Due after one year through five years, Yield	2.50%	2.70%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 2,271	$ 2,498
Available-for-sale debt securities, Due after five years through ten years, Yield	2.30%	2.20%
Available-for-sale debt securities, Due after ten years, Amount	$ 17,972	$ 13,649
Available-for-sale debt securities, Due after ten years, Yield	3.10%	2.90%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 22,499	$ 18,651
Amortized cost of available-for-sale debt securities, Due in one year or less, Amount	217	138
Amortized cost of available-for-sale debt securities, Due after one year through five years, Amount	1,852	2,040
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	2,314	2,563
Amortized cost of available-for-sale debt securities, Due after ten years, Amount	18,116	13,910
US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 1,777	$ 1,620
Available-for-sale debt securities, Yield	1.70%	1.70%
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 2
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	4.60%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 487	$ 60
Available-for-sale debt securities, Due after one year through five years, Yield	1.70%	1.60%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 1,290	$ 1,558
Available-for-sale debt securities, Due after five years through ten years, Yield	1.80%	1.70%
Available-for-sale debt securities, Due after ten years, Amount	$ 0	$ 0
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,831	$ 1,680
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 854	$ 782
Available-for-sale debt securities, Yield	2.90%	3.10%
Available-for-sale debt securities, Due in one year or less, Amount	$ 76	$ 64
Available-for-sale debt securities, Due in one year or less, Yield	1.80%	1.70%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 36	$ 29
Available-for-sale debt securities, Due after one year through five years, Yield	2.30%	2.30%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 203	$ 172
Available-for-sale debt securities, Due after five years through ten years, Yield	2.50%	2.80%
Available-for-sale debt securities, Due after ten years, Amount	$ 539	$ 517
Available-for-sale debt securities, Due after ten years, Yield	3.30%	3.40%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 850	$ 794
Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 154	$ 162
Available-for-sale debt securities, Yield	2.50%	2.60%
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 0
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 80	$ 58
Available-for-sale debt securities, Due after one year through five years, Yield	2.50%	2.80%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 74	$ 104
Available-for-sale debt securities, Due after five years through ten years, Yield	2.40%	2.40%
Available-for-sale debt securities, Due after ten years, Amount	$ 0	$ 0
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 153	$ 157
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 14,291	$ 10,290
Available-for-sale debt securities, Yield	3.10%	2.90%
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 0
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 0	$ 0
Available-for-sale debt securities, Due after one year through five years, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 3	$ 29
Available-for-sale debt securities, Due after five years through ten years, Yield	2.90%	2.60%
Available-for-sale debt securities, Due after ten years, Amount	$ 14,288	$ 10,261
Available-for-sale debt securities, Due after ten years, Yield	3.10%	2.90%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 14,412	$ 10,473
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 2,494	$ 2,097
Available-for-sale debt securities, Yield	3.10%	2.90%
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 0
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 0	$ 0
Available-for-sale debt securities, Due after one year through five years, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 0	$ 0
Available-for-sale debt securities, Due after five years through ten years, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after ten years, Amount	$ 2,494	$ 2,097
Available-for-sale debt securities, Due after ten years, Yield	3.10%	2.90%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 2,517	$ 2,162
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 541	$ 537
Available-for-sale debt securities, Yield	3.20%	2.60%
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 0
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 30	$ 0
Available-for-sale debt securities, Due after one year through five years, Yield	3.10%	0.00%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 31	$ 3
Available-for-sale debt securities, Due after five years through ten years, Yield	3.10%	2.80%
Available-for-sale debt securities, Due after ten years, Amount	$ 480	$ 534
Available-for-sale debt securities, Due after ten years, Yield	3.20%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 541	$ 537
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 936	$ 1,400
Available-for-sale debt securities, Yield	3.10%	2.80%
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 0
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 698	$ 1,059
Available-for-sale debt securities, Due after one year through five years, Yield	3.10%	2.80%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 106	$ 143
Available-for-sale debt securities, Due after five years through ten years, Yield	3.10%	3.20%
Available-for-sale debt securities, Due after ten years, Amount	$ 132	$ 198
Available-for-sale debt securities, Due after ten years, Yield	2.80%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 933	$ 1,396
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 1,256	$ 1,443
Available-for-sale debt securities, Yield	2.90%	2.80%
Available-for-sale debt securities, Due in one year or less, Amount	$ 140	$ 72
Available-for-sale debt securities, Due in one year or less, Yield	2.60%	2.20%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 513	$ 840
Available-for-sale debt securities, Due after one year through five years, Yield	2.60%	2.60%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 564	$ 489
Available-for-sale debt securities, Due after five years through ten years, Yield	3.20%	3.20%
Available-for-sale debt securities, Due after ten years, Amount	$ 39	$ 42
Available-for-sale debt securities, Due after ten years, Yield	4.70%	4.70%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,262	$ 1,452
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 1,899
Held-to-Maturity Debt Securities, Yield	3.10%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 35
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	1.70%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 1
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	3.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 1,863
Held-to-Maturity Securities, Due After Ten Years, Yield	3.10%
Held-to-maturity Securities [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 1,863
Held-to-Maturity Debt Securities, Yield	3.10%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 1,863
Held-to-Maturity Securities, Due After Ten Years, Yield	3.10%
Held-to-maturity Securities [Member] | Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 36
Held-to-Maturity Debt Securities, Yield	1.70%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 35
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	1.70%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 1
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	3.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 0
Held-to-Maturity Securities, Due After Ten Years, Yield	0.00%

Investment Securities (Invest84

Investment Securities (Investment Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Taxable interest	$ 534	$ 375	$ 340
Taxable dividends	12	17	23
Interest and dividends exempt from U.S. federal income tax	22	19	18
Interest and Dividend Income, Securities, Operating, Available-for-sale	599	418	381
Excludes Other Earning Assets [Member]
Interest and Dividend Income, Securities, Operating, Available-for-sale	$ 568	$ 411	$ 381

Investment Securities (Schedule

Investment Securities (Schedule Of Realized Gain (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Gross Realized Gains	$ 106	$ 187	$ 184
Available-for-sale Securities, Gross Realized Losses	(4)	(2)	(15)
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	(14)
Available-for-sale Securities, Gross Realized Gain (Loss)	$ 102	$ 185	$ 155

Investment Securities (Schedu86

Investment Securities (Schedule of Unrealized Loss on Investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	$ 6,667	$ 12,356
Available-for-sale Securities, Unrealized Loss Less than 12 months	(50)	(317)
Available-for-sale Securities, Fair value 12 months or longer	8,358	2,038
Available-for-sale Securities, Unrealized Loss 12 months or longer	(263)	(118)
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	6,541	12,205
Available-for-sale Securities, Unrealized Loss Less than 12 months	(38)	(309)
Available-for-sale Securities, Fair value 12 months or longer	8,242	1,769
Available-for-sale Securities, Unrealized Loss 12 months or longer	(227)	(72)
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	471	1,612
Available-for-sale Securities, Unrealized Loss Less than 12 months	(8)	(60)
Available-for-sale Securities, Fair value 12 months or longer	1,305	0
Available-for-sale Securities, Unrealized Loss 12 months or longer	(46)	0
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	242	524
Available-for-sale Securities, Unrealized Loss Less than 12 months	(2)	(19)
Available-for-sale Securities, Fair value 12 months or longer	183	0
Available-for-sale Securities, Unrealized Loss 12 months or longer	(5)	0
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	80	38
Available-for-sale Securities, Unrealized Loss Less than 12 months	(1)	0
Available-for-sale Securities, Fair value 12 months or longer	4	0
Available-for-sale Securities, Unrealized Loss 12 months or longer	0	0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	4,066	8,052
Available-for-sale Securities, Unrealized Loss Less than 12 months	(19)	(196)
Available-for-sale Securities, Fair value 12 months or longer	5,671	587
Available-for-sale Securities, Unrealized Loss 12 months or longer	(137)	(16)
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	857	813
Available-for-sale Securities, Unrealized Loss Less than 12 months	(2)	(17)
Available-for-sale Securities, Fair value 12 months or longer	773	860
Available-for-sale Securities, Unrealized Loss 12 months or longer	(32)	(53)
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	76	47
Available-for-sale Securities, Unrealized Loss Less than 12 months	(1)	(1)
Available-for-sale Securities, Fair value 12 months or longer	21	149
Available-for-sale Securities, Unrealized Loss 12 months or longer	0	(1)
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	220	375
Available-for-sale Securities, Unrealized Loss Less than 12 months	(1)	(2)
Available-for-sale Securities, Fair value 12 months or longer	91	127
Available-for-sale Securities, Unrealized Loss 12 months or longer	0	0
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	529	744
Available-for-sale Securities, Unrealized Loss Less than 12 months	(4)	(14)
Available-for-sale Securities, Fair value 12 months or longer	194	46
Available-for-sale Securities, Unrealized Loss 12 months or longer	(7)	(2)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	126	151
Available-for-sale Securities, Unrealized Loss Less than 12 months	(12)	(8)
Available-for-sale Securities, Fair value 12 months or longer	116	269
Available-for-sale Securities, Unrealized Loss 12 months or longer	$ (36)	$ (46)

Finance Receivables and Loans87

Finance Receivables and Loans, Net (Schedule of Accounts, Notes, Loans and Financing Receivables) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 122,893	$ 118,944
Derivative, Amount of Hedged Item	208	315
Loans and Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	551	359
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	81,821	76,843
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	68,071	65,793
Consumer Portfolio Segment [Member] | Automobile Loan [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derivative, Amount of Hedged Item	18	43
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	13,750	11,050
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	11,657	8,294
Held For Investment Mortgage Finance Receivables Interest Only Mortgage Loans	$ 20	30
Consumer Portfolio Segment [Member] | Mortgage Finance [Member] | Two years and six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	35.00%
Consumer Portfolio Segment [Member] | Mortgage Finance [Member] | Three years and six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	45.00%
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 2,093	2,756
Held For Investment Mortgage Finance Receivables Interest Only Mortgage Loans	$ 496	714
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member] | One year and six months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	3.00%
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 41,072	42,101
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	33,025	35,041
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	3,887	3,248
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 4,160	$ 3,812

Finance Receivables and Loans88

Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses				$ 1,144				$ 1,054	$ 1,144	$ 1,054
Allowance for Loan and Lease Losses, Write-offs									(1,392)	(1,142)
Allowance for Loan and Lease Loss, Recovery of Bad Debts									382	341
Allowance for Loan and Lease Losses Write-offs, Net									(1,010)	(801)
Provision for Loan Losses Expensed	$ 294	$ 314	$ 269	271	$ 267	$ 258	$ 172	220	1,148	917	$ 707
Allowance for Loan and Lease Losses, Adjustments, Other									6	26
Financing Receivable, Allowance for Credit Losses	1,276				1,144				1,276	1,144	1,054
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	77				85				77	85
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,199				1,059				1,199	1,059
Loans and Leases Receivable, Gross	122,893				118,944				122,893	118,944
Financing Receivable, Individually Evaluated for Impairment	733				739				733	739
Financing Receivable, Collectively Evaluated for Impairment	122,160				118,205				122,160	118,205
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses				932				834	932	834
Allowance for Loan and Lease Losses, Write-offs									(1,344)	(1,102)
Allowance for Loan and Lease Loss, Recovery of Bad Debts									358	307
Allowance for Loan and Lease Losses Write-offs, Net									(986)	(795)
Provision for Loan Losses Expensed									1,127	919
Allowance for Loan and Lease Losses, Adjustments, Other									7	26
Financing Receivable, Allowance for Credit Losses	1,066				932				1,066	932	834
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	36				28				36	28
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,030				904				1,030	904
Loans and Leases Receivable, Gross	68,071				65,793				68,071	65,793
Financing Receivable, Individually Evaluated for Impairment	430				370				430	370
Financing Receivable, Collectively Evaluated for Impairment	67,641				65,423				67,641	65,423
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses				91				114	91	114
Allowance for Loan and Lease Losses, Write-offs									(30)	(39)
Allowance for Loan and Lease Loss, Recovery of Bad Debts									24	32
Allowance for Loan and Lease Losses Write-offs, Net									(6)	(7)
Provision for Loan Losses Expensed									(7)	(16)
Allowance for Loan and Lease Losses, Adjustments, Other									(1)	0
Financing Receivable, Allowance for Credit Losses	79				91				79	91	114
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	27				34				27	34
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	52				57				52	57
Loans and Leases Receivable, Gross	13,750				11,050				13,750	11,050
Financing Receivable, Individually Evaluated for Impairment	231				247				231	247
Financing Receivable, Collectively Evaluated for Impairment	13,519				10,803				13,519	10,803
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses				$ 121				$ 106	121	106
Allowance for Loan and Lease Losses, Write-offs									(18)	(1)
Allowance for Loan and Lease Loss, Recovery of Bad Debts									0	2
Allowance for Loan and Lease Losses Write-offs, Net									(18)	1
Provision for Loan Losses Expensed									28	14
Allowance for Loan and Lease Losses, Adjustments, Other									0	0
Financing Receivable, Allowance for Credit Losses	131				121				131	121	$ 106
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	14				23				14	23
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	117				98				117	98
Loans and Leases Receivable, Gross	41,072				42,101				41,072	42,101
Financing Receivable, Individually Evaluated for Impairment	72				122				72	122
Financing Receivable, Collectively Evaluated for Impairment	$ 41,000				$ 41,979				$ 41,000	$ 41,979

Finance Receivables and Loans89

Finance Receivables and Loans, Net (Schedule of Sales of Financing Receivables and Loans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Sales and Transfers	$ 1,348	$ 4,311
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Sales and Transfers	1,339	4,267
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Sales and Transfers	9	15
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Sales and Transfers	$ 0	$ 29

Finance Receivables and Loans90

Finance Receivables and Loans, Net Finance Receivables and Loans, Net (Schedule of Purchases of Financing Receivables and Loans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Purchases	$ 5,346	$ 3,768
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Purchases	865	21
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Purchases	$ 4,481	$ 3,747

Finance Receivables and Loans91

Finance Receivables and Loans, Net (Past Due Financing Receivables and Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 2,967	$ 2,759
Financing Receivable, Recorded Investment, Current	119,926	116,185
Loans and Leases Receivable, Gross	122,893	118,944
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,959	2,749
Financing Receivable, Recorded Investment, Current	78,862	74,094
Loans and Leases Receivable, Gross	81,821	76,843
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,740	2,580
Financing Receivable, Recorded Investment, Current	65,331	63,213
Loans and Leases Receivable, Gross	68,071	65,793
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	219	169
Financing Receivable, Recorded Investment, Current	13,531	10,881
Loans and Leases Receivable, Gross	13,750	11,050
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	89	49
Financing Receivable, Recorded Investment, Current	11,568	8,245
Loans and Leases Receivable, Gross	11,657	8,294
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	130	120
Financing Receivable, Recorded Investment, Current	1,963	2,636
Loans and Leases Receivable, Gross	2,093	2,756
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	8	10
Financing Receivable, Recorded Investment, Current	41,064	42,091
Loans and Leases Receivable, Gross	41,072	42,101
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	8	10
Financing Receivable, Recorded Investment, Current	33,017	35,031
Loans and Leases Receivable, Gross	33,025	35,041
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivable, Recorded Investment, Current	3,887	3,248
Loans and Leases Receivable, Gross	3,887	3,248
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivable, Recorded Investment, Current	4,160	3,812
Loans and Leases Receivable, Gross	4,160	3,812
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,102	1,937
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,097	1,934
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,994	1,850
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	103	84
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	60	39
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	43	45
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	5	3
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	5	3
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	514	452
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	514	452
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	478	428
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	36	24
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	11	6
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	25	18
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	351	370
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	348	363
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	268	302
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	80	61
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	18	4
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	62	57
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	3	7
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	3	7
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 0	$ 0

Finance Receivables and Loans92

Finance Receivables and Loans, Net (Schedule of Financing Receivables, Non Accrual Status) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 792	$ 819
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	720	697
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	603	598
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	117	99
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	25	10
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	92	89
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	72	122
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	27	33
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	44	84
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 1	$ 5

Finance Receivables and Loans93

Finance Receivables and Loans, Net (Financing Receivable Credit Quality Indicators) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 122,893	$ 118,944
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	81,821	76,843
Consumer Portfolio Segment [Member] | Consumer Loan [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	81,101	76,146
Consumer Portfolio Segment [Member] | Consumer Loan [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	720	697
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	68,071	65,793
Consumer Portfolio Segment [Member] | Automobile Loan [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	67,468	65,195
Consumer Portfolio Segment [Member] | Automobile Loan [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	603	598
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	13,750	11,050
Consumer Portfolio Segment [Member] | Residential Mortgage [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	13,633	10,951
Consumer Portfolio Segment [Member] | Residential Mortgage [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	117	99
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	11,657	8,294
Consumer Portfolio Segment [Member] | Mortgage Finance [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	11,632	8,284
Consumer Portfolio Segment [Member] | Mortgage Finance [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	25	10
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,093	2,756
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,001	2,667
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 92	$ 89

Finance Receivables and Loans94

Finance Receivables and Loans, Net (Schedule of Pass And Criticized Credit Quality Indicators of Finance Receivables) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 122,893	$ 118,944
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	41,072	42,101
Commercial Portfolio Segment [Member] | Commercial Loan [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	37,991	39,410
Commercial Portfolio Segment [Member] | Commercial Loan [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	3,081	2,691
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	33,025	35,041
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	30,982	33,160
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,043	1,881
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	3,887	3,248
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,986	2,597
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	901	651
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,160	3,812
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,023	3,653
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 137	$ 159

Finance Receivables and Loans95

Finance Receivables and Loans, Net (Impaired Financing Receivables) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 756	$ 795
Impaired Financing Receivable, Recorded Investment	733	739
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	172	199
Impaired Financing Receivable, with Related Allowance, Recorded Investment	561	540
Impaired Financing Receivable, Related Allowance	77	85
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	674	658
Impaired Financing Receivable, Recorded Investment	661	617
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	153	190
Impaired Financing Receivable, with Related Allowance, Recorded Investment	508	427
Impaired Financing Receivable, Related Allowance	63	62
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	438	407
Impaired Financing Receivable, Recorded Investment	430	370
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	91	131
Impaired Financing Receivable, with Related Allowance, Recorded Investment	339	239
Impaired Financing Receivable, Related Allowance	36	28
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	236	251
Impaired Financing Receivable, Recorded Investment	231	247
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	62	59
Impaired Financing Receivable, with Related Allowance, Recorded Investment	169	188
Impaired Financing Receivable, Related Allowance	27	34
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	8	8
Impaired Financing Receivable, Recorded Investment	8	8
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4	3
Impaired Financing Receivable, with Related Allowance, Recorded Investment	4	5
Impaired Financing Receivable, Related Allowance	0	0
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	228	243
Impaired Financing Receivable, Recorded Investment	223	239
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	58	56
Impaired Financing Receivable, with Related Allowance, Recorded Investment	165	183
Impaired Financing Receivable, Related Allowance	27	34
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	82	137
Impaired Financing Receivable, Recorded Investment	72	122
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	19	9
Impaired Financing Receivable, with Related Allowance, Recorded Investment	53	113
Impaired Financing Receivable, Related Allowance	14	23
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	27	33
Impaired Financing Receivable, Recorded Investment	27	33
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	9	7
Impaired Financing Receivable, with Related Allowance, Recorded Investment	18	26
Impaired Financing Receivable, Related Allowance	3	3
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	54	99
Impaired Financing Receivable, Recorded Investment	44	84
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	10	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	34	84
Impaired Financing Receivable, Related Allowance	11	19
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	1	5
Impaired Financing Receivable, Recorded Investment	1	5
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	2
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1	3
Impaired Financing Receivable, Related Allowance	$ 0	$ 1

Finance Receivables and Loans96

Finance Receivables and Loans, Net (Schedule of Average Balance and Interest Income of Impaired Finance Receivables) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 756	$ 701	$ 654
Impaired Financing Receivable, Interest Income, Accrual Method	42	28	29
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	633	600	575
Impaired Financing Receivable, Interest Income, Accrual Method	31	26	25
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	391	344	295
Impaired Financing Receivable, Interest Income, Accrual Method	21	17	16
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	242	256	280
Impaired Financing Receivable, Interest Income, Accrual Method	10	9	9
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	8	8	8
Impaired Financing Receivable, Interest Income, Accrual Method	0	0	0
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	234	248	272
Impaired Financing Receivable, Interest Income, Accrual Method	10	9	9
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	123	101	79
Impaired Financing Receivable, Interest Income, Accrual Method	11	2	4
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	49	35	33
Impaired Financing Receivable, Interest Income, Accrual Method	2	1	1
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	69	60	41
Impaired Financing Receivable, Interest Income, Accrual Method	9	1	3
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	5	6	5
Impaired Financing Receivable, Interest Income, Accrual Method	$ 0	$ 0	$ 0

Finance Receivables and Loans97

Finance Receivables and Loans, Net (Troubled Debt Restructurings) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 712	$ 663
Financing Receivable, Modifications, Number of Contracts	26,288	20,355
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 465	$ 375
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 417	$ 321
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	26,282	20,354
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 402	$ 368
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 355	$ 314
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	26,156	20,227
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 380	$ 347
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 333	$ 293
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	126	127
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 22	$ 21
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 22	$ 21
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	4	7
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 1	$ 3
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 1	$ 3
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	122	120
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 21	$ 18
Financing Receivable, Modifications, Post-Modification Recorded Investment	21	18
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Loans and Leases Receivable, Impaired, Commitment to Lend	$ 6	$ 2
Financing Receivable, Modifications, Number of Contracts	6	1
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 63	$ 7
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 62	$ 7
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	4	1
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 16	$ 7
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 15	$ 7
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	0	0
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 44	$ 0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 44	$ 0
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	2	0
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 3	$ 0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 3	$ 0

Finance Receivables and Loans98

Finance Receivables and Loans, Net (Finance receivables and loans redefaulted during the period) (Details) - Consumer Portfolio Segment [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	8,832	7,804
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 103	$ 94
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	$ 71	$ 56
Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	8,829	7,800
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 102	$ 94
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	$ 71	$ 56
Mortgage Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	1	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 1	$ 0
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	$ 0	$ 0
Mortgage - Legacy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	2	4
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	$ 0	$ 0

Finance Receivables and Loans99

Finance Receivables and Loans, Net Finance Receivables and Loans, Net (Consumer Concentration Risk by State and Foreign Geographic)(Details) - Consumer Portfolio Segment [Member]	Dec. 31, 2017	Dec. 31, 2016
Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	100.00%	100.00%
Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	100.00%	100.00%
CALIFORNIA AND TEXAS
Concentration Risk [Line Items]
Consumer Concentration Risk	24.70%	24.20%
CALIFORNIA | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	8.20%	7.80%
CALIFORNIA | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	34.60%	34.20%
TEXAS | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	13.20%	13.60%
TEXAS | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	6.50%	6.60%
FLORIDA | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	8.50%	8.20%
FLORIDA | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	4.80%	4.40%
PENNSYLVANIA | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	4.60%	4.70%
PENNSYLVANIA | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	1.50%	1.50%
ILLINOIS | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	4.20%	4.30%
ILLINOIS | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	3.20%	3.40%
GEORGIA | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	4.20%	4.30%
GEORGIA | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	2.50%	2.20%
NORTH CAROLINA | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	3.70%	3.60%
NORTH CAROLINA | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	1.80%	1.60%
OHIO | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	3.40%	3.50%
OHIO | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	0.50%	0.50%
NEW YORK | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	3.00%	3.20%
NEW YORK | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	2.20%	1.90%
MISSOURI | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	2.90%	2.80%
MISSOURI | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	0.90%	1.20%
United States, Other | Automobile Loan [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	44.10%	44.00%
United States, Other | Residential Mortgage [Member]
Concentration Risk [Line Items]
Consumer Concentration Risk	41.50%	42.50%

Finance Receivables and Loan100

Finance Receivables and Loans, Net Finance Receivables and Loans, Net (Commercial Concentration Risk) (Details)	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Commercial Concentration Risk	100.00%	100.00%
TEXAS
Concentration Risk [Line Items]
Commercial Concentration Risk	15.70%	16.10%
FLORIDA
Concentration Risk [Line Items]
Commercial Concentration Risk	10.30%	10.20%
CALIFORNIA
Concentration Risk [Line Items]
Commercial Concentration Risk	8.20%	7.90%
MICHIGAN
Concentration Risk [Line Items]
Commercial Concentration Risk	7.70%	7.60%
GEORGIA
Concentration Risk [Line Items]
Commercial Concentration Risk	4.60%	3.60%
NEW JERSEY
Concentration Risk [Line Items]
Commercial Concentration Risk	3.60%	4.20%
NORTH CAROLINA
Concentration Risk [Line Items]
Commercial Concentration Risk	3.60%	3.60%
SOUTH CAROLINA
Concentration Risk [Line Items]
Commercial Concentration Risk	3.50%	2.70%
PENNSYLVANIA
Concentration Risk [Line Items]
Commercial Concentration Risk	3.00%	3.10%
MISSOURI
Concentration Risk [Line Items]
Commercial Concentration Risk	2.40%	2.50%
United States, Other
Concentration Risk [Line Items]
Commercial Concentration Risk	37.40%	38.50%

Finance Receivables and Loan101

Finance Receivables and Loans, Net Finance Receivables and Loans, Net (Commercial Criticized Exposure) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Commercial Criticized Finance Receivables and Loans	$ 1	$ 1
5500 Retail, Auto Dealers and Gasoline Stations [Member]
Concentration Risk [Line Items]
Commercial Criticized Finance Receivables and Loans	0.763	0.812
7380 Services, Miscellaneous Business Services [Member]
Concentration Risk [Line Items]
Commercial Criticized Finance Receivables and Loans	0.067	0.063
8071 Services, Medical Laboratories [Member]
Concentration Risk [Line Items]
Commercial Criticized Finance Receivables and Loans	0.049	0.023
810000 to 819999 Other Services (except Public Administration) [Member]
Concentration Risk [Line Items]
Commercial Criticized Finance Receivables and Loans	$ 0.121	$ 0.102

Investment in Operating Leas102

Investment in Operating Leases, Net (Investments In Operating Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Leases, Operating [Abstract]
Property Subject to or Available for Operating Lease, Gross	$ 10,556	$ 14,584
Property Subject to or Available for Operating Lease, Accumulated Depreciation	(1,815)	(3,114)
Property Subject to or Available for Operating Lease, Net	$ 8,741	$ 11,470

Investment in Operating Leas103

Investment in Operating Leases, Net (Schedule Of Depreciation Expense On Operating Lease Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases, Operating [Abstract]
Depreciation Expense On Operating Lease Assets	$ 1,368	$ 1,982	$ 2,600
Gross Remarketing (Gains) Losses	(124)	(213)	(351)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	$ 1,244	$ 1,769	$ 2,249

Investment in Operating Leas104

Investment in Operating Leases, Net Invest in Operating Leases, Net (Future Nonresidual Rental Payments) (Details) $ in Millions	Dec. 31, 2017USD ($)
Future Lease Nonresidual Rental Payments [Abstract]
Operating Leases, Future Minimum Payments Receivable, Current	$ 1,319
Operating Leases, Future Minimum Payments Receivable, in Two Years	839
Operating Leases, Future Minimum Payments Receivable, in Three Years	364
Operating Leases, Future Minimum Payments Receivable, in Four Years	46
Operating Leases, Future Minimum Payments Receivable, Thereafter	4
Operating Leases, Future Minimum Payments Receivable	$ 2,572

Securitizations and Variable105

Securitizations and Variable Interest Entities (Schedule of Variable Interest Entities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale, Gain (Loss) on Sale	$ 2	$ 0	$ (3)
Assets of nonconsolidated variable interest entities	1,964	2,899
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	2,791	3,574
Carrying value of assets for VIEs for which we have continuing involvement	30,776	37,631
Carrying value of liabilities for VIEs for which we have continuing involvement	10,483	13,490
Commercial Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	592	460
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	248	169
Assets of nonconsolidated variable interest entities	0	0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	790	651
Automobile Loan [Member] | Consumer Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	17,597	20,869
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	7,677	8,557
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	37	24
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0	0
Assets of nonconsolidated variable interest entities	1,964	2,899
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	2,001	2,923
Automobile Loan [Member] | Consumer Portfolio Segment [Member] | Held-to-maturity Securities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	36
Automobile Loan [Member] | Consumer Portfolio Segment [Member] | Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	1
Automobile Loan [Member] | Commercial Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	12,550	16,278
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	2,558	4,764
Unencumbered [Member] | Automobile Loan [Member] | Consumer Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	8,527	9,600
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 29	$ 50

Securitizations and Variable106

Securitizations and Variable Interest Entities Securitizations and Variable Interest Entities (On-balance Sheet Variable Interest Entities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Securitization and Variable Interest Entities On-balance Sheet Variable Interest Entities [Line Items]
Loans and Leases Receivable, Gross	$ 122,893	$ 118,944
Loans and Leases Receivable, Net Amount	121,617	117,800
Property Subject to or Available for Operating Lease, Net	8,741	11,470
Other Assets	5,663	6,854
Assets	167,148	163,728	$ 158,581
Long-term Debt	44,226	54,128
Liabilities	153,654	150,411
Variable Interest Entity, Primary Beneficiary [Member]
Securitization and Variable Interest Entities On-balance Sheet Variable Interest Entities [Line Items]
Loans and Leases Receivable, Allowance	(136)	(173)
Loans and Leases Receivable, Net Amount	20,487	24,457
Property Subject to or Available for Operating Lease, Net	444	1,745
Other Assets	689	1,390
Assets	21,620	27,592
Long-term Debt	10,197	13,259
Accounts Payable and Accrued Liabilities, Noncurrent	9	12
Liabilities	10,206	13,271
Consumer Portfolio Segment [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Securitization and Variable Interest Entities On-balance Sheet Variable Interest Entities [Line Items]
Loans and Leases Receivable, Gross	8,186	8,929
Commercial Portfolio Segment [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Securitization and Variable Interest Entities On-balance Sheet Variable Interest Entities [Line Items]
Loans and Leases Receivable, Gross	$ 12,437	$ 15,701

Securitizations and Variable107

Securitizations and Variable Interest Entities (Schedule of Cash Flow Received from and Paid to Nonconsolidated Securitization Entities) (Details) - Consumer Portfolio Segment [Member] - Automobile Loan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flow Received and Paid to Nonconsolidated Securitization Entities [Line Items]
Cash Flows Between Transferor and Transferee, Proceeds from New Transfers	$ 1,187	$ 1,715	$ 1,551
Cash Flows Between Transferor and Transferee, Purchases of Previously Transferred Financial Assets	(491)	0	0
Cash Flows Between Transferor and Transferee, Servicing Fees	31	35	28
Cash Flows Between Transferor and Transferee, Beneficial Interest	21	0	0
Cash Flows Between Transferor and Transferee, Receipts on Transferor's Interest in Transferred Financial Assets, Other	$ 4	$ 8	$ 0

Securitizations and Variable108

Securitizations and Variable Interest Entities (Schedule of Quantitative Information and Net Credit Losses about Securitized and Other Financial Assets Managed Together) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	$ 3,363	$ 5,556
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	20	19
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	16	11
Off-Balance Sheet Loans [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	1,964	2,392
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	16	13
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	13	8
Off-Balance Sheet Loans [Member] | Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	1,964	2,392
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	16	13
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	13	8
Whole-Loan Transactions [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	1,399	3,164
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	4	6
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	$ 3	$ 3

Servicing Activities (Schedule

Servicing Activities (Schedule of Total Serviced Automobile Loans Outstanding) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Automobile Serviced Assets [Line Items]
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	$ 51	$ 64	$ 45
Total Primary Serviced Assets	116,878	121,480
Consumer Loan [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	67,631	65,646
Commercial Loan [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	37,058	38,853
Operating Leases [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	8,682	11,311
Other Assets [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	121	67
Asset-backed Securities, Securitized Loans and Receivables [Member] | Off-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	1,977	2,412
Whole-Loan Transactions [Member] | Off-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	$ 1,409	$ 3,191

Other Assets (Schedule of Other

Other Assets (Schedule of Other Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Aug. 01, 2016	Jun. 01, 2016
Other Assets [Abstract]
Property, Plant and Equipment, Gross	$ 1,064	$ 901
Accumulated Depreciation, Depletion and Amortization, Property Plant and Equipment	(608)	(525)
Property, Plant and Equipment, Net	456	376
Nonmarketable equity securities	1,233	1,046
Restricted cash collections for securitization trusts	812	1,694
Interest Receivable	550	476
Deferred Tax Assets, Net	461	994
Goodwill	240	240
Accounts and Other Receivables, Net, Current	116	100
Cash reserve deposits held for securitization trusts	111	184
Restricted Cash and Cash Equivalents	94	111
Derivative Asset, Fair Value, Gross Asset	39	95
Cash and securities collateral placed with counterparties	29	167
Other Assets, Miscellaneous	1,522	1,371
Other Assets	5,663	6,854
Federal Home Loan Bank Stock	745	577
Federal Reserve Bank Stock	445	435
Goodwill [Line Items]
Goodwill	240	240
Insurance Operations Member
Other Assets [Abstract]
Goodwill	27	27
Goodwill [Line Items]
Goodwill	27	27
Corporate and Other [Member]
Other Assets [Abstract]
Goodwill	193	193		$ 193
Goodwill [Line Items]
Goodwill	193	193		$ 193
Automotive Finance Operations [Member]
Other Assets [Abstract]
Goodwill	20	20	$ 20
Goodwill [Line Items]
Goodwill	$ 20	$ 20	$ 20

Deposit Liabilities (Schedule o

Deposit Liabilities (Schedule of Deposit Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deposits [Abstract]
Noninterest-bearing deposit liabilities	$ 108	$ 84
Interest-bearing Deposit Liabilities, by Component [Abstract]
Deposits, Savings Deposits	49,267	46,976
Time Deposits	43,869	31,795
Dealer deposits	12	167
Deposits	93,256	79,022
Time Deposits, $100,000 or More	18,900	12,100
Time Deposits, at or Above FDIC Insurance Limit	$ 5,300	$ 3,500

Deposit Liabilities Deposit Lia

Deposit Liabilities Deposit Liabilities (Time Deposit Maturities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Maturities for Total Time Deposits [Line Items]
Time Deposits	$ 43,869	$ 31,795
One year, or less [Member]
Schedule of Maturities for Total Time Deposits [Line Items]
Time Deposits	28,764
Two years, or less [Member]
Schedule of Maturities for Total Time Deposits [Line Items]
Time Deposits	8,613
Three years, or less [Member]
Schedule of Maturities for Total Time Deposits [Line Items]
Time Deposits	3,579
Four years, or less [Member]
Schedule of Maturities for Total Time Deposits [Line Items]
Time Deposits	1,418
Five years, or less [Member]
Schedule of Maturities for Total Time Deposits [Line Items]
Time Deposits	1,495
Total deposits [Member]
Schedule of Maturities for Total Time Deposits [Line Items]
Time Deposits	$ 43,869

Debt Debt (Schedule of Short-te

Debt Debt (Schedule of Short-term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Demand Notes	$ 3,171	$ 3,622
Federal Home Loan Bank, Advances, Maturities Summary, Due in Next Twelve Months	7,350	7,875
Securities Sold under Agreements to Repurchase, Gross	892	1,176
Short-term Debt	$ 11,413	$ 12,673
Short-term Debt, Weighted Average Interest Rate, at Point in Time	1.50%	1.00%
Non-derivative Cash Collateral Placed with Counterparties Associated with the Repurchase Agreements	$ 10	$ 45
Non-derivative Cash Collateral received from counterparties associated with Repurchase Agreements	1
Unsecured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	3,171	3,622
Federal Home Loan Bank, Advances, Maturities Summary, Due in Next Twelve Months	0	0
Securities Sold under Agreements to Repurchase, Gross	0	0
Short-term Debt	3,171	3,622
Secured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	0	0
Federal Home Loan Bank, Advances, Maturities Summary, Due in Next Twelve Months	7,350	7,875
Securities Sold under Agreements to Repurchase, Gross	892	1,176
Short-term Debt	8,242	9,051
Maturity less than 90 Days [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Mortgage-backed Residential Securities Sold under Agreements to Repurchase, Maturity Period	892
Maturity Less than 30 Days [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Mortgage-backed Residential Securities Sold under Agreements to Repurchase, Maturity Period	73
Maturity 31 to 60 Days [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Mortgage-backed Residential Securities Sold under Agreements to Repurchase, Maturity Period	521
Maturity 61 to 90 Days [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Mortgage-backed Residential Securities Sold under Agreements to Repurchase, Maturity Period	$ 298
One year, or less [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Asset-backed Automotive Financial Securities Sold under Agreements to Repurchase, Maturity Period		$ 500

Debt Debt (Long-term Debt) (Det

Debt Debt (Long-term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Derivative, Amount of Hedged Item	$ 208	$ 315
Secured Debt	36,837	43,129
Long-term Debt	44,226	54,128
Subordinated Debt	1,400
Variable Interest Entity Debt	10,200	13,300
Long-term Debt, Excluding Current Maturities	33,037	39,260
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Amount	12,820	17,155
Long-term Debt, Percentage Bearing Variable Interest, Amount	1	1
Trust preferred securities	2,570	2,568
Derivative, Amount of Hedged Item	240	326
Unsecured Debt	$ 15,631	$ 20,050
Debt, Weighted Average Interest Rate	5.68%	5.36%
Long-term Debt	$ 15,631	$ 20,050
Long-term Debt, Excluding Current Maturities	11,909	15,450
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Amount	18,845	17,935
Long-term Debt, Percentage Bearing Variable Interest, Amount	9,782	16,154
Derivative, Amount of Hedged Item	$ (32)	$ (11)
Debt, Weighted Average Interest Rate	1.96%	1.53%
Secured Debt	$ 28,595	$ 34,078
Long-term Debt	28,595	34,078
Long-term Debt Without a Stated Interest Rate	8
Long-term Debt, Excluding Current Maturities	21,128	23,810
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	8,100	14,800
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Secured Debt	$ 10,300	$ 6,100

Debt (Schedule of Debt) (Detail

Debt (Schedule of Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	$ 10,981	$ 14,553
Long-term Debt, Excluding Current Maturities	33,037	39,260
Derivative, Amount of Hedged Item	208	315
Long-term debt	44,226	54,128
Derivative Instrument Converting Fixed Rated Debt into Variable Rate Debt	3,800	2,100
Derivative Instrument Converting Variable Rate debt into Fixed Rate	3,400	132
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	3,482	4,274
Long-term Debt, Excluding Current Maturities	11,909	15,450
Derivative, Amount of Hedged Item	240	326
Long-term debt	15,631	20,050
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	7,499	10,279
Long-term Debt, Excluding Current Maturities	21,128	23,810
Derivative, Amount of Hedged Item	(32)	(11)
Long-term debt	$ 28,595	$ 34,078

Debt (Scheduled Remaining Matur

Debt (Scheduled Remaining Maturity of Long-term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 10,981
Long-term Debt, Maturities, Repayments of Principal in Year Two	9,994
Long-term Debt, Maturities, Repayments of Principal in Year Three	9,091
Long-term Debt, Maturities, Repayments of Principal in Year Four	4,306
Long-term Debt, Maturities, Repayments of Principal in Year Five	2,651
Long-term Debt, Maturities, Repayments of Principal after Year Five	6,995
Derivative, Amount of Hedged Item	208	$ 315
Long-term debt	44,226	54,128
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	3,482
Long-term Debt, Maturities, Repayments of Principal in Year Two	1,642
Long-term Debt, Maturities, Repayments of Principal in Year Three	2,212
Long-term Debt, Maturities, Repayments of Principal in Year Four	594
Long-term Debt, Maturities, Repayments of Principal in Year Five	1,020
Long-term Debt, Maturities, Repayments of Principal after Year Five	6,441
Derivative, Amount of Hedged Item	240	326
Long-term debt	15,631	20,050
Secured Debt [Member]
Debt Instrument [Line Items]
Derivative, Amount of Hedged Item	(32)	(11)
Long-term debt	28,595	$ 34,078
Long-term Debt [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	3,582
Long-term Debt, Maturities, Repayments of Principal in Year Two	1,681
Long-term Debt, Maturities, Repayments of Principal in Year Three	2,251
Long-term Debt, Maturities, Repayments of Principal in Year Four	637
Long-term Debt, Maturities, Repayments of Principal in Year Five	1,067
Long-term Debt, Maturities, Repayments of Principal after Year Five	7,408
Derivative, Amount of Hedged Item	240
Long-term debt	16,866
Long-term Debt [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	7,499
Long-term Debt, Maturities, Repayments of Principal in Year Two	8,352
Long-term Debt, Maturities, Repayments of Principal in Year Three	6,879
Long-term Debt, Maturities, Repayments of Principal in Year Four	3,712
Long-term Debt, Maturities, Repayments of Principal in Year Five	1,631
Long-term Debt, Maturities, Repayments of Principal after Year Five	554
Derivative, Amount of Hedged Item	(32)
Long-term debt	28,595
original issue discount [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Derivative, Amount of Hedged Item	0
Debt Instrument, Unamortized Discount	(100)
Debt Instrument, Unamortized Discount	(1,235)
original issue discount [Member] | Unsecured Debt [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount, Noncurrent	(39)
original issue discount [Member] | Unsecured Debt [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount, Noncurrent	(39)
original issue discount [Member] | Unsecured Debt [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount, Noncurrent	(43)
original issue discount [Member] | Unsecured Debt [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount, Noncurrent	(47)
original issue discount [Member] | Unsecured Debt [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount, Noncurrent	$ (967)

Debt (Pledged Assets Related to

Debt (Pledged Assets Related to Secured Borrowings and Repurchase Agreement) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Pledged Assets related to secured borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	$ 8,371	$ 4,895
Pledged Assets, Mortgage assets held for investment	13,579	10,954
Pledged Assets, Investment in operating leases	457	2,040
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	58,761	65,222
Secured Debt	36,837	43,129
Short-term Debt	11,413	12,673
Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	7,443	4,231
Pledged Assets, Mortgage assets held for investment	13,579	10,954
Pledged Assets, Investment in operating leases	0	913
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	43,694	41,129
Secured Debt	23,278	22,149
Pledged assets for Federal Home Loan Bank [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	25,200	19,000
Pledged assets for Federal Reserve Bank [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	2,300	2,400
Secured Debt [Member]
Pledged Assets related to secured borrowings [Line Items]
Short-term Debt	8,242	9,051
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	19,787	27,846
Consumer Portfolio Segment [Member] | Automobile Loan [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	6,200	5,751
Commercial Portfolio Segment [Member] | Automobile Loan [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	16,567	19,487
Commercial Portfolio Segment [Member] | Automobile Loan [Member] | Ally Bank [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	$ 16,472	$ 19,280

Debt Debt (Narrative - Trust Pr

Debt Debt (Narrative - Trust Preferred Securities) (Details) $ / shares in Units, $ in Billions	Dec. 31, 2017USD ($)$ / shares
Narrative - Trust Preferred Securities [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	8.13%
Preferred Stock, Liquidation Preference Per Share | $ / shares	$ 25
From and including February 15, 2016, to but excluding February 15, 2040, distributions will be payable at an annual rate equal to three-month London interbank offer rate plus:	5.79%
Ally has the right to defer payments of interest for a period not exceeding consecutive quarters of:	20
Percent of principle debt, plus accrued and unpaid interest is the redemption price if Ally redeems the Series 2 TRUPS on or after February 15, 2016.	100.00%
Fixed Income Interest Rate [Member]
Narrative - Trust Preferred Securities [Line Items]
Trust preferred securities | $	$ 2.6

Debt (Committed Funding Facilit

Debt (Committed Funding Facilities) (Details) - Committed Funding Facilities Member - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Outstanding Revolving Funding Facilities	$ 11,900
Line of Credit Facility, Maximum Borrowing Capacity	11,925	$ 18,375
Long-term Line of Credit	8,115	14,800
Line of Credit Facility, Remaining Borrowing Capacity	3,810	3,575
Bank Funding Member | Secured Debt [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	2,675	3,600
Long-term Line of Credit	1,785	3,250
Line of Credit Facility, Remaining Borrowing Capacity	890	350
Revolving secured funding facilities 1 year or greater [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	2,600
Nonbank Funding Member | Secured Debt [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	9,250	13,525
Long-term Line of Credit	6,330	11,550
Line of Credit Facility, Remaining Borrowing Capacity	2,920	1,975
Nonbank Funding Member | Unsecured Debt [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	0	1,250
Long-term Line of Credit	0	0
Line of Credit Facility, Remaining Borrowing Capacity	$ 0	$ 1,250

Accrued Expenses and Other L120

Accrued Expenses and Other Liabilities (Schedule of Accrued Expenses and Other Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts Payable and Accrued Liabilities [Abstract]
Accounts Payable	$ 746	$ 649
Accrued Employee Benefits	248	232
Liability for Claims and Claims Adjustment Expense	140	149	$ 169
Derivative Liability, Fair Value, Gross Liability	41	95
Deferred Revenue	32	56
Cash collateral received from counterparties	17	10
Other Accrued Liabilities	556	546
Accounts Payable and Accrued Liabilities	$ 1,780	$ 1,737

Accumulated Other Comprehens121

Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Beginning Balance Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	$ (273)	$ (159)	$ (21)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	100	(114)	(138)
Ending Balance Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(173)	(273)	(159)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Beginning Balance Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	14	9	36
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	2	5	(27)
Ending Balance Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	16	14	9
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Beginning Balance Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	8	8	7
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	3	0	1
Ending Balance Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	11	8	8
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Beginning Balance Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(90)	(89)	(88)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	(1)	1	1
Ending Balance Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(89)	(90)	(89)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax	235	341	231	$ 66
Other Comprehensive Income (Loss), Net of Tax	106	(110)	(165)
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (235)	$ (341)	$ (231)	$ (66)

Accumulated Other Comprehens122

Accumulated Other Comprehensive Loss (Before and After Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	$ 237	$ 13	$ (65)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	105	185	155
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax	132	(172)	(220)
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	(45)	20	26
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(13)	(38)	(56)
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax	(32)	58	82
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	192	33	(39)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	92	147	99
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	100	(114)	(138)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax and reclassification adjustments		5	(39)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax		(1)	42
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax	12	6	(81)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment before reclassification adjustments, Tax		(2)	13
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax		0	(20)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	(4)	(2)	33
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period before reclassification adjustments, Net of Tax	8	3	(26)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0	(1)	22
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	8	4	(48)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period, Before Tax	(10)	1	29
Other Comprehensive Income (Loss), Reclassification Adjustment for Net Investment Hedges Included in Net Income, Discontinued Operation, before Tax			(4)
Other Comprehensive Income (Loss), Net Investment Hedges, before Tax			33
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Effect [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period, Tax	4	0	(11)
Other Comprehensive Income (Loss), Reclassification Adjustment for Net Investment Hedges Included in Net Income, Discontinued Operation, Tax			1
Other Comprehensive Income (Loss), Net Investment Hedges, Tax			(12)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period Net of Tax	(6)	1	18
Other Comprehensive Income (Loss), Reclassification Adjustment for Net Investment Hedges Included in Net Income, Discontinued Operation, Net of Tax	0	0	(3)
Other Comprehensive Income (Loss), Net Investment Hedges, Net of Tax	(6)	1	21
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During the Period, Before Tax	5		2
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During the Period, Tax	(2)		(1)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	3	0	1
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Tax [Abstract]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax	1	(5)	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax		(4)	1
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax		(1)	(1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Tax [Abstract]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	0	2	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		2	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax		0	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	1	(3)	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	0	(2)	1
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax	1	(1)	(1)
Other Comprehensive Income (Loss), before Tax [Abstract]
Other Comprehensive Income (Loss), before Tax	140	(166)	(267)
Other Comprehensive Income (Loss), Tax [Abstract]
Other Comprehensive Income (Loss), Tax	(34)	56	102
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive Income (Loss), Net of Tax	$ 106	$ (110)	$ (165)

Earnings per Common Share (Sche

Earnings per Common Share (Schedule of Basic and Diluted Earnings per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 179	$ 280	$ 254	$ 213	$ 246	$ 261	$ 357	$ 247	$ 926	$ 1,111	$ 897
Dividends, Preferred Stock, Cash									0	(30)	(2,571)
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic									926	1,081	(1,674)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ 2	$ 2	$ (2)	$ 1	$ 2	$ (52)	$ 3	$ 3	3	(44)	392
Net Income (Loss) Available to Common Stockholders, Basic									$ 929	$ 1,037	$ (1,282)
Weighted Average Number of Shares Outstanding, Basic									453,704	481,105	482,873
Weighted Average Number of Shares Outstanding, Diluted									455,350	482,182	482,873
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Diluted									$ 926	$ 1,081	$ (1,674)
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Diluted									3	(44)	392
Net Income (Loss) Available to Common Stockholders, Diluted									$ 929	$ 1,037	$ (1,282)
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.40	$ 0.62	$ 0.55	$ 0.46	$ 0.52	$ 0.54	$ 0.70	$ 0.48	$ 2.04	$ 2.25	$ (3.47)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									0.01	(0.09)	0.81
Earnings Per Share, Basic	0.41	0.63	0.55	0.46	0.53	0.43	0.71	0.49	2.05	2.15	(2.66)
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.40	0.62	0.55	0.46	0.52	0.54	0.70	0.48	2.03	2.24	(3.47)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share									0.01	(0.09)	0.81
Earnings Per Share, Diluted	$ 0.41	$ 0.63	$ 0.55	$ 0.46	$ 0.52	$ 0.43	$ 0.71	$ 0.49	$ 2.04	$ 2.15	$ (2.66)
Stock Redemption and Repurchase Premium											$ 2,364

Regulatory Capital and Other124

Regulatory Capital and Other Regulatory Matters (Schedule of Regulatory Capital Amount and Ratios) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jan. 10, 2018	Aug. 22, 2017	Jun. 28, 2017	Dec. 31, 2016	Jul. 19, 2016	Jun. 29, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets	4.50%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%
Common equity Tier 1 capital conservation buffer	2.50%
Federal Reserve Bank Stock	$ 445					$ 435
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	$ 400	$ 2,900
Minimum Capital Conservation Buffer	1.30%					0.63%
Increase in Minimum Capital Conservation Buffer	3.00%
Assets greater than $50 billion	$ 50,000
Increase (Decrease) in Dividends Payable	50.00%
FRB Approved Capital Action - Dividends					$ 0.12			$ 0.08
Increase (decrease) in share repurchase program	9.00%
Stock Repurchase Program, Authorized Amount					$ 760		$ 700
Increase (Decrease) in Dividends Payable, per share	$ 0.01		$ 0.01
2017 through 2018 [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Stock Repurchase Program, Authorized Amount	$ 760
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets	4.50%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%
Common Equity Tier 1 Capital	$ 13,237					$ 12,978
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets	9.53%					9.37%
Tier One Risk Based Capital	$ 15,628					$ 15,147
Tier One Risk Based Capital to Risk Weighted Assets	11.25%					10.93%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%
Capital	$ 17,974					$ 17,419
Capital to Risk Weighted Assets	12.94%					12.57%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%
Tier One Leverage Capital	$ 15,628					$ 15,147
Tier One Leverage Capital to Average Assets	9.53%					9.54%
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets	4.50%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%			15.00%
Common Equity Tier 1 Capital	$ 17,059					$ 17,888
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets	15.04%					16.70%
Common Equity Tier 1 Capital Required to be Well Capitalized to Risk-weighted Assets	6.50%
Tier One Risk Based Capital	$ 17,059					$ 17,888
Tier One Risk Based Capital to Risk Weighted Assets	15.04%					16.70%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%
Capital	$ 17,886					$ 18,458
Capital to Risk Weighted Assets	15.77%					17.24%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%
Tier One Leverage Capital	$ 17,059					$ 17,888
Tier One Leverage Capital to Average Assets	12.87%					15.21%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%

Regulatory Capital and Other125

Regulatory Capital and Other Regulatory Matters Regulatory Capital and Other Regulatory Matters (Common Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jan. 10, 2018	Dec. 31, 2015
Accelerated Share Repurchases [Line Items]
Treasury Stock, Value	$ 1,110	$ 357
Common Stock, Shares, Outstanding	437,053,936	467,000,306		481,980,111
Dividends Payable, Amount Per Share	$ 0.13		$ 0.13
Increase (Decrease) in Dividends Payable, per share	$ 0.01		$ 0.01
Assets	$ 167,148	$ 163,728		$ 158,581
Cash Dividends Paid to Parent Company	3,300	0
FRB Required Reserve Balance	370	149
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments	87
Common Share Repurchases, Period One [Member]
Accelerated Share Repurchases [Line Items]
Treasury Stock, Value	$ 190
Treasury Stock, Common, Shares	7,033,000
Dividends Payable, Amount Per Share	$ 0.12
Common Share Repurchases, Period Two [Member]
Accelerated Share Repurchases [Line Items]
Treasury Stock, Value	$ 190
Treasury Stock, Common, Shares	8,507,000
Dividends Payable, Amount Per Share	$ 0.12
Common Share Repurchases, Period Three [Member]
Accelerated Share Repurchases [Line Items]
Treasury Stock, Value	$ 204
Treasury Stock, Common, Shares	10,485,000
Dividends Payable, Amount Per Share	$ 0.08
Common Share Repurchases, Period Four [Member]
Accelerated Share Repurchases [Line Items]
Treasury Stock, Value	$ 169
Treasury Stock, Common, Shares	8,097,000
Dividends Payable, Amount Per Share	$ 0.08
Common Share Repurchases, Period Five [Member]
Accelerated Share Repurchases [Line Items]
Treasury Stock, Value		$ 167
Treasury Stock, Common, Shares		8,745,000
Dividends Payable, Amount Per Share		$ 0.08
Common Share Repurchases, Period Six [Member]
Accelerated Share Repurchases [Line Items]
Treasury Stock, Value		$ 159
Treasury Stock, Common, Shares		8,298,000
Dividends Payable, Amount Per Share		$ 0.08
Beginning of Period [Member] | Common Share Repurchases, Period One [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	443,796,000,000
Beginning of Period [Member] | Common Share Repurchases, Period Two [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	452,292,000
Beginning of Period [Member] | Common Share Repurchases, Period Three [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	462,193,000
Beginning of Period [Member] | Common Share Repurchases, Period Four [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	467,000,000
Beginning of Period [Member] | Common Share Repurchases, Period Five [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding		475,470,000
Beginning of Period [Member] | Common Share Repurchases, Period Six [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding		483,753,000
End of Period [Member] | Common Share Repurchases, Period One [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	437,053,936,000
End of Period [Member] | Common Share Repurchases, Period Two [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	443,796,233,000
End of Period [Member] | Common Share Repurchases, Period Three [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	452,292,000
End of Period [Member] | Common Share Repurchases, Period Four [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	462,193,000
End of Period [Member] | Common Share Repurchases, Period Five [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding		467,000,000
End of Period [Member] | Common Share Repurchases, Period Six [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding		475,470,000
Subsidiaries [Member]
Accelerated Share Repurchases [Line Items]
Assets	$ 137,400	$ 123,500

Derivative Instruments and H126

Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash Collateral Placed with Counterparties Excluding Cash Collateral Associated with Repurchase Agreements	$ 20	$ 122
Securities Collateral Placed with Counterparties	97	72
Non-derivative Cash Collateral Placed with Counterparties Associated with the Repurchase Agreements	10	45
Cash Collateral Received from Counterparties, Excluding Collateral Associated with Repurchase Agreements	17	10
Non-derivative Cash Collateral received from counterparties associated with Repurchase Agreements	1
Non-cash collateral received	$ 2	$ 6

Derivative Instruments and H127

Derivative Instruments and Hedging Activities (Fair Value Amounts of Derivative Instruments Reported on our Condensed Consolidated Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 39	$ 95
Derivative Liability, Fair Value, Gross Liability	41	95
Derivative, Notional Amount	23,762	34,166
Interest Receivable	550	476
Derivative assets in net asset position [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	38	87
Interest Receivable	0	7
Derivative assets in net liability positions [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		8
Interest Receivable	0	1
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	20
Derivative Liability, Fair Value, Gross Liability	1	21
Derivative, Notional Amount	7,051	4,902
Not Designated as Hedging Instrument [Member] | Other Trading [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	39	75
Derivative Liability, Fair Value, Gross Liability	40	74
Derivative, Notional Amount	16,711	29,264
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	19
Derivative Liability, Fair Value, Gross Liability	0	21
Derivative, Notional Amount	6,915	4,731
Foreign Exchange Forward [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	1
Derivative Liability, Fair Value, Gross Liability	1	0
Derivative, Notional Amount	136	171
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	39	73
Derivative Liability, Fair Value, Gross Liability	39	73
Derivative, Notional Amount	16,587	29,172
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative, Notional Amount	0	137
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Futures and Forwards [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative, Notional Amount	23	0
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Written Options [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1	0
Derivative Liability, Fair Value, Gross Liability	39	73
Derivative, Notional Amount	8,327	14,518
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Purchased Options [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	38	73
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative, Notional Amount	8,237	14,517
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	1
Derivative Liability, Fair Value, Gross Liability	1	0
Derivative, Notional Amount	124	92
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	1
Derivative Liability, Fair Value, Gross Liability	1	0
Derivative, Notional Amount	124	92
Equity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	1
Derivative Liability, Fair Value, Gross Liability	0	1
Derivative, Notional Amount	0	0
Equity Contract [Member] | Not Designated as Hedging Instrument [Member] | Written Options [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	0	1
Derivative, Notional Amount	0	0
Equity Contract [Member] | Not Designated as Hedging Instrument [Member] | Purchased Options [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	1
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative, Notional Amount	$ 0	$ 0

Derivative Instruments and H128

Derivative Instruments and Hedging Activities (Statement of Gains and Losses on Derivative Instruments Reported in Statement of Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ (6)	$ (8)	$ (121)
Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	3	(7)	35
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments	(2)	0	(19)
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments	(7)	(1)	(127)
Equity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Price Risk Derivative Instruments Not Designated as Hedging Instruments	0	0	(10)
Interest Income [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(3)	0	39
Interest Income [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Hedges of Retail Auto Loans Held for Investment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	1	18	64
Interest Income [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Losses Related to Amortization of Deferred Basis Adjustments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	21	20	8
Interest Income [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Gains Related to Amortization of Deferred Basis Adjustments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	77	84	73
Interest Income [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Losses Related to Amortization of Deferred Basis Adjustments (FHLB) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	2
Interest and Dividends Income [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(1)	0	0
Interest Expense [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	30	(70)	(30)
Interest Expense [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Hedges of Secured Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	3	5	1
Interest Expense [Member] | Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments	0	(2)	(139)
Gains on Mortgage and Automotive Loans [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments	1	0	(2)
Other Income [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments	(3)	0	(17)
Other Income [Member] | Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments	(7)	1	12
Other Income [Member] | Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Revaluation of Foreign-Denominated Debt or Receivable [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments	9	0	132
Employee compensation and benefits [Member] | Equity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Price Risk Derivative Instruments Not Designated as Hedging Instruments	0	0	(10)
Earnings on Derivatives [Member] | Interest Income [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	1	(2)	(9)
Earnings on Derivatives [Member] | Interest and Dividends Income [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	1	0	0
Earnings on Derivatives [Member] | Interest Expense [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(25)	65	35
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Interest Rate Contract [Member] | Hedges of Unsecured Debt Held for Investment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ 24	$ 40	$ 97

Derivative Instruments and H129

Derivative Instruments and Hedging Activities (Derivative Instruments Used in Net Investment Hedge Accounting Relationships) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Cumulative Translation Adjustment, Net of Tax, Period Increase (Decrease)	$ 12	$ 4	$ 59
Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	5	0	2
Foreign Exchange Contract [Member] | Net Investment Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0	(4)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ (10)	$ 1	$ 33

Income Taxes Income Taxes (Sche

Income Taxes Income Taxes (Schedule of Significant Components of Income Tax Expense) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)									$ (17)	$ 0	$ 0
Current Foreign Tax Expense (Benefit)									6	8	6
Current State and Local Tax Expense (Benefit)									53	9	3
Current Income Tax Expense (Benefit)									42	17	9
Deferred Federal Income Tax Expense (Benefit)									566	423	454
Deferred Foreign Income Tax Expense (Benefit)									0	0	1
Deferred State and Local Income Tax Expense (Benefit)									(27)	30	32
Deferred Income Tax Expense (Benefit)									539	453	487
Income Tax Expense (Benefit)	$ 231	$ 115	$ 122	$ 113	$ 134	$ 130	$ 56	$ 150	$ 581	$ 470	$ 496

Income Taxes Income Taxes (S131

Income Taxes Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax Act Impacts [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount									$ 527	$ 553	$ 488
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount									(49)	51	(25)
Effective Income Tax Rate Reconciliation, Tax Credit, Amount									(12)	(15)	(13)
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount									7	35	38
Effective Income Tax Rate Reconciliation, Equity in Earnings (Losses) of Unconsolidated Subsidiary, Amount									4	7	14
Effective Income Tax Rate Reconciliation, Change in Unrecognized Tax Benefits									1	(161)	(5)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount									(16)	0	(1)
Income Tax Expense (Benefit)	$ 231	$ 115	$ 122	$ 113	$ 134	$ 130	$ 56	$ 150	581	470	496
Deferred Tax Assets, Net	461				$ 994				461	994
Income Tax Expense Before Tax Act Adjustments [Member]
Tax Act Impacts [Line Items]
Income Tax Expense (Benefit)									462	470	496
Net impacts as a result of the Tax Act [Member]
Tax Act Impacts [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount									119	$ 0	$ 0
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount									549
Affordable Housing Tax Credits and Other Tax Benefits, Amount									7
Deferred Tax Assets, Net	421								421
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	$ 16								$ 16

Income Taxes Income Taxes (S132

Income Taxes Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	$ 2,002
Deferred Tax Assets, Valuation Allowance	(1,123)
Deferred Tax Assets, Net	461	$ 994
Other Assets	5,663	6,854
Accounts Payable and Accrued Liabilities	1,780	1,737
Deferred Tax Asset [Member]
Tax Credit Carryforward [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	2,002	1,987
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	450	546
Deferred Tax Assets, Tax Loss Carryforward	302	936
Deferred Tax Assets, State and local taxes	200	162
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve	85	141
Deferred Tax Assets, Hedging Transactions	49	123
Deferred Tax Assets, Other	108	208
Deferred Tax Assets, Gross	3,196	4,103
Deferred Tax Assets, Valuation Allowance	(1,123)	(646)
Deferred Tax Assets, Net of Valuation Allowance	2,073	3,457
Other Assets	461	994
Deferred Tax Liability [Member]
Tax Credit Carryforward [Line Items]
Deferred Tax Liabilities, Leasing Arrangements	1,212	1,789
Deferred tax liabilities, deferred expense, deferred acquisition cost	269	424
Deferred Tax Liabilities, Financing Arrangements	95	161
Deferred Tax Liabilities, Other	44	107
Deferred Tax Liabilities, Gross	1,620	2,481
Deferred Tax Assets, Net	453	976
Accounts Payable and Accrued Liabilities	8	$ 18
Net impacts as a result of the Tax Act [Member]
Tax Credit Carryforward [Line Items]
Deferred Tax Assets, Net	421
Deferred Tax Assets, Change	128
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	549
Monetization of Deferred Tax Assets	$ 395

Income Taxes Income Taxes (S133

Income Taxes Income Taxes (Schedule of Deferred tax assets and related valuation allowances recognized for net operating and other loss carryforwards and tax carryforwards) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	$ 2,002
Tax Credit Carryforward, Valuation Allowance	(983)
Net Deferred Tax Assets, Tax Credit Carryforwards	1,019
Deferred Tax Assets, Operating Loss Carryforwards	302
Operating Loss Carryforwards, Valuation Allowance	0
Net Deferred Tax Assets, Operating Loss Carryforwards	302
Deferred Tax Assets, Capital Loss Carryforwards	2
Capital Loss Carryforwards, Valuation Allowance	(2)
Net Deferred Tax Assets, Capital Loss Carryforwards	0
Deferred Tax Assets, State and Local Tax Carryforwards	557
State and Local Tax Carryforwards, Valuation Allowance	(137)
Net Deferred Tax Assets, State and Local Tax Carryforwards	420
Deferred Tax Assets, Other Non-Attribute	(983)
Other Non-Attribute, Valuation Allowance	(3)
Net Deferred Tax Assets, Other Non-Attribute	(986)
Deferred Tax Assets, Gross, Net of Deferred Tax Liabilities	1,576
Deferred Tax Assets, Valuation Allowance	(1,123)
Deferred Tax Assets, Net	461	$ 994
Foreign Tax Credits [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	1,772
Tax Credit Carryforward, Valuation Allowance	(983)
Net Deferred Tax Assets, Tax Credit Carryforwards	789
General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	213
Tax Credit Carryforward, Valuation Allowance	0
Net Deferred Tax Assets, Tax Credit Carryforwards	213
AMT Credits [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	17
Tax Credit Carryforward, Valuation Allowance	0
Net Deferred Tax Assets, Tax Credit Carryforwards	17
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	253
Operating Loss Carryforwards, Valuation Allowance	(135)
Net Deferred Tax Assets, Operating Loss Carryforwards	118
Net impacts as a result of the Tax Act [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Net	421
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	549
Deferred Tax Liability [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Net	$ 453	$ 976

Income Taxes Income Taxes (S134

Income Taxes Income Taxes (Schedule of Unrecognized Tax Benefits Roll Forward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits	$ 14	$ 185	$ 191
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	0	0	0
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	3	12	7
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(1)	0	0
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	0	(182)	(10)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	(1)	(1)	(3)
Unrecognized Tax Benefits	$ 15	$ 14	$ 185

Income Taxes Income Taxes (Narr

Income Taxes Income Taxes (Narrative - Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 177	$ 12	$ 9
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	2	1	$ 1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ 1
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit		$ 15

Fair Value (Fair Value Measurem

Fair Value (Fair Value Measurements - Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 22,821	$ 18,926
Available-for-sale, Equity Investment in Any One Industry Did Not Exceed Percentage	14.00%	14.00%
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 22,821	$ 18,926
Mortgages Held-for-sale, Fair Value Disclosure	13
Retained Interest, Fair Value Disclosure	5	29
Derivative Assets	39	95
Assets, Fair Value Disclosure	22,878	19,050
Derivative Liability	(41)	(95)
Financial and Nonfinancial Liabilities, Fair Value Disclosure	(41)	(95)
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	(39)	(94)
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	(2)
Fair Value, Measurements, Recurring [Member] | Other Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability		(1)
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	22,303	18,331
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,777	1,620
Fair Value, Measurements, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	854	782
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	154	162
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	14,291	10,290
Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,494	2,097
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	541	537
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	936	1,400
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,256	1,443
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	518	595
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	39	92
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets		2
Fair Value, Measurements, Recurring [Member] | Other Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets		1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,303	2,226
Mortgages Held-for-sale, Fair Value Disclosure	0
Retained Interest, Fair Value Disclosure	0	0
Derivative Assets	0	1
Assets, Fair Value Disclosure	2,303	2,227
Derivative Liability	0	(1)
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	(1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability		(1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,785	1,631
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,777	1,620
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	8	11
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	518	595
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets		1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	20,518	16,700
Mortgages Held-for-sale, Fair Value Disclosure	0
Retained Interest, Fair Value Disclosure	0	0
Derivative Assets	38	94
Assets, Fair Value Disclosure	20,556	16,794
Derivative Liability	(41)	(94)
Financial and Nonfinancial Liabilities, Fair Value Disclosure	(41)	(94)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	(39)	(94)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	(2)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	20,518	16,700
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	854	782
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	146	151
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	14,291	10,290
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,494	2,097
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	541	537
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	936	1,400
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,256	1,443
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	38	92
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets		2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Mortgages Held-for-sale, Fair Value Disclosure	13
Retained Interest, Fair Value Disclosure	5	29
Derivative Assets	1	0
Assets, Fair Value Disclosure	19	29
Derivative Liability	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	$ 1	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets		$ 0

Fair Value (Fair Value Measu137

Fair Value (Fair Value Measurements - Reconciliation of Level 3 Assets And Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning balance	$ 29	$ 40
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	4	4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	137	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(118)	9
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(33)	(24)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Assets, Ending balance	19	29
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	1	0
Loans Held-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning balance	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	137
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(126)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Assets, Ending balance	13	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0
Retained Interest [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning balance	29	40
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	1	4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	8	9
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(33)	(24)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Assets, Ending balance	5	29
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning balance	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Assets, Ending balance	1	$ 0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 1

Fair Value (Fair Value Measu138

Fair Value (Fair Value Measurements - Nonrecurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	$ 108	$ 0
Fair Value, Measurements, Nonrecurring [Member] | Loans held-for-sale, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	77
Lower of cost or fair value or valuation reserve allowance	0
Fair Value, Measurements, Nonrecurring [Member] | Commercial Finance Receivables And Loans, Automotive [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	20	27
Lower of cost or fair value or valuation reserve allowance	(3)	(4)
Fair Value, Measurements, Nonrecurring [Member] | Commercial Finance Receivables And Loans, Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	22	65
Lower of cost or fair value or valuation reserve allowance	(12)	(19)
Fair Value, Measurements, Nonrecurring [Member] | Commercial Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	42	92
Lower of cost or fair value or valuation reserve allowance	(15)	(23)
Fair Value, Measurements, Nonrecurring [Member] | Repossessed And Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	14	12
Lower of cost or fair value or valuation reserve allowance	(1)	(4)
Fair Value, Measurements, Nonrecurring [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	3	4
Lower of cost or fair value or valuation reserve allowance	0	0
Fair Value, Measurements, Nonrecurring [Member] | Assets, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	136	108
Lower of cost or fair value or valuation reserve allowance	(16)	(27)
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Loans held-for-sale, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Finance Receivables And Loans, Automotive [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Finance Receivables And Loans, Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Repossessed And Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Assets, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Loans held-for-sale, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Finance Receivables And Loans, Automotive [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Finance Receivables And Loans, Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Repossessed And Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Assets, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Loans held-for-sale, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	77
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Finance Receivables And Loans, Automotive [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	20	27
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Finance Receivables And Loans, Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	22	65
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	42	92
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Repossessed And Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	14	12
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	3	4
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Assets, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	$ 136	$ 108

Fair Value (Fair Value of Finan

Fair Value (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 1,899	$ 839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	108	0
Loans and Leases Receivable, Net Amount	121,617	117,800
Nonmarketable equity securities	1,233	1,046
Deposits	93,256	79,022
Short-term Debt	11,413	12,673
Long-term Debt	44,226	54,128
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,899	839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	95
Loans and Leases Receivable, Net Amount	121,617	117,800
Nonmarketable equity securities	1,233	1,046
Deposits	93,256	79,022
Short-term Debt	11,413	12,673
Long-term Debt	44,226	54,128
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,865	789
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	95
Loans and Leases Receivable, Net Amount	123,302	118,750
Nonmarketable equity securities	1,239	1,067
Deposits	91,029	78,469
Short-term Debt	11,417	12,675
Long-term Debt	46,624	56,120
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	0	0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Net Amount	0	0
Nonmarketable equity securities	0	0
Deposits	0	0
Short-term Debt	0	0
Long-term Debt	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,865	789
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Net Amount	0	0
Nonmarketable equity securities	1,190	1,012
Deposits	0	0
Short-term Debt	0	0
Long-term Debt	27,807	22,036
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	0	0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	95
Loans and Leases Receivable, Net Amount	123,302	118,750
Nonmarketable equity securities	49	55
Deposits	91,029	78,469
Short-term Debt	11,417	12,675
Long-term Debt	$ 18,817	$ 34,084

Offsetting Assets and Liabil140

Offsetting Assets and Liabilities Offsetting Assets and Liabilities (Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 39	$ 95
Derivative Liability, Fair Value, Gross Liability	41	95
Customer Securities for which Entity has Right to Sell or Repledge, Fair Value	2	6
Derivative assets in net asset position [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	38	87
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	38	87
Derivative Asset, Not Subject to Master Netting Arrangement	0	4
Derivative, Collateral, Obligation to Return Cash	0	(9)
Derivative Asset	38	74
Derivative assets in net liability positions [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset		8
Gross Amounts Offset in the Condensed Consolidated Balance Sheet		0
Derivative Asset, Fair Value, Amount Offset Against Collateral		8
Derivative Asset, Not Subject to Master Netting Arrangement		8
Derivative, Collateral, Obligation to Return Cash		0
Derivative Asset		0
Derivative assets with no offsetting arrangements [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	1
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1
Derivative Asset, Not Subject to Master Netting Arrangement	0
Derivative, Collateral, Obligation to Return Cash	0
Derivative Asset	1
Total Derivative Assets [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	39	95
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	39	95
Derivative Asset, Not Subject to Master Netting Arrangement	0	12
Derivative, Collateral, Obligation to Return Cash	0	(9)
Derivative Asset	39	74
Derivative Liabilities in Net Liability Positions [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Gross Liability	41	91
Derivative Liability, Fair Value, Amount Offset Against Collateral	41	91
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	8
Derivative, Collateral, Right to Reclaim Cash	1	13
Derivative Liability	40	70
Derivative liabilities in net asset positions [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet		0
Derivative Liability, Fair Value, Gross Liability		4
Derivative Liability, Fair Value, Amount Offset Against Collateral		4
Derivative Liability, Not Subject to Master Netting Arrangement Deduction		4
Derivative, Collateral, Right to Reclaim Cash		0
Derivative Liability		0
Total derivative liabilities excluding repurchase agreements [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet		0
Derivative Liability, Fair Value, Gross Liability		95
Derivative Liability, Fair Value, Amount Offset Against Collateral		95
Derivative Liability, Not Subject to Master Netting Arrangement Deduction		12
Derivative, Collateral, Right to Reclaim Cash		13
Derivative Liability		70
Securities sold under agreement to repurchase [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Gross Liability	892	676
Derivative Liability, Fair Value, Amount Offset Against Collateral	892	676
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Derivative, Collateral, Right to Reclaim Cash	892	676
Derivative Liability	0	0
Total Derivative Liabilities [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Gross Liability	933	771
Derivative Liability, Fair Value, Amount Offset Against Collateral	933	771
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	12
Derivative, Collateral, Right to Reclaim Cash	893	689
Derivative Liability	$ 40	$ 70

Segment and Geographic Infor141

Segment and Geographic Information (Financial Information Operating Segments) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net Financing Revenue	$ 1,094	$ 1,081	$ 1,067	$ 979	$ 976	$ 996	$ 984	$ 951	$ 4,221	$ 3,907	$ 3,719
Nonoperating Income (Expense)	379	381	388	396	392	388	374	376	1,544	1,530	1,142
Revenue, Net	1,473	1,462	1,455	1,375	1,368	1,384	1,358	1,327	5,765	5,437	4,861
Provision for Loan Losses Expensed	294	314	269	271	267	258	172	220	1,148	917	707
Noninterest Expense	769	753	810	778	721	735	773	710	3,110	2,939	2,761
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	410	$ 395	$ 376	$ 326	380	$ 391	$ 413	$ 397	1,507	1,581	1,393
Assets	167,148				163,728				167,148	163,728	158,581
Interest Income (Expense), after Provision for Loan Loss									3,073	2,990	3,000
Automotive Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue									3,713	3,665	3,429
Nonoperating Income (Expense)									355	306	235
Revenue, Net									4,068	3,971	3,664
Provision for Loan Losses Expensed									1,134	924	696
Noninterest Expense									1,714	1,667	1,633
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									1,220	1,380	1,335
Assets	114,089				116,347				114,089	116,347	115,636
Insurance Operations Member
Segment Reporting Information [Line Items]
Net Financing Revenue									59	61	57
Nonoperating Income (Expense)									1,059	1,036	1,033
Revenue, Net									1,118	1,097	1,090
Provision for Loan Losses Expensed									0	0	0
Noninterest Expense									950	940	879
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									168	157	211
Assets	7,464				7,172				7,464	7,172	7,053
Mortgage Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue									132	97	57
Nonoperating Income (Expense)									4	0	0
Revenue, Net									136	97	57
Provision for Loan Losses Expensed									8	(4)	7
Noninterest Expense									108	67	39
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									20	34	11
Assets	11,708				8,307				11,708	8,307	6,461
Corporate Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue									167	121	89
Nonoperating Income (Expense)									45	26	25
Revenue, Net									212	147	114
Provision for Loan Losses Expensed									22	10	9
Noninterest Expense									76	66	55
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									114	71	50
Assets	3,979				3,183				3,979	3,183	2,677
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue									150	(37)	87
Nonoperating Income (Expense)									81	162	(151)
Revenue, Net									231	125	(64)
Provision for Loan Losses Expensed									(16)	(13)	(5)
Noninterest Expense									262	199	155
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									(15)	(61)	(214)
Assets	$ 29,908				$ 28,719				$ 29,908	$ 28,719	$ 26,754

Segment and Geographic Infor142

Segment and Geographic Information Segment and Geographic Information (Information Concerning Principal Geographic Areas) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net	$ 1,473	$ 1,462	$ 1,455	$ 1,375	$ 1,368	$ 1,384	$ 1,358	$ 1,327	$ 5,765	$ 5,437	$ 4,861
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	410	395	376	326	380	391	413	397	1,507	1,581	1,393
Net Income (Loss) Attributable to Parent	181	$ 282	$ 252	$ 214	248	$ 209	$ 360	$ 250	929	1,067	1,289
Identifiable Assets	166,908				163,488				166,908	163,488	158,554
Long-Lived Assets	9,197				11,846				9,197	11,846	16,506
CANADA
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									89	90	98
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									42	44	47
Net Income (Loss) Attributable to Parent									37	32	35
Identifiable Assets	406				499				406	499	514
Long-Lived Assets	0				0				0	0	0
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									0	0	1
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									(1)	0	4
Net Income (Loss) Attributable to Parent									(6)	(1)	27
Identifiable Assets	315				276				315	276	325
Long-Lived Assets	0				0				0	0	0
Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									0	0	0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									0	0	0
Net Income (Loss) Attributable to Parent									0	(1)	(2)
Identifiable Assets	23				23				23	23	28
Long-Lived Assets	0				0				0	0	0
Asia Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									0	0	0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									0	0	0
Net Income (Loss) Attributable to Parent									0	0	452
Identifiable Assets	2				2				2	2	2
Long-Lived Assets	0				0				0	0	0
Foreign [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									89	90	99
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									41	44	51
Net Income (Loss) Attributable to Parent									31	30	512
Identifiable Assets	746				800				746	800	869
Long-Lived Assets	0				0				0	0	0
Domestic [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									5,676	5,347	4,762
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									1,466	1,537	1,342
Net Income (Loss) Attributable to Parent									898	1,037	777
Identifiable Assets	166,162				162,688				166,162	162,688	157,685
Long-Lived Assets	$ 9,197				$ 11,846				$ 9,197	$ 11,846	$ 16,506

Parent and Guarantor Consoli143

Parent and Guarantor Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									$ 5,819	$ 5,162	$ 4,570
Interest and Fee Income, Loans and Leases Held-for-sale									0	0	40
Interest and Dividend Income, Securities, Operating									599	418	381
Interest Income, Deposits with Financial Institutions									37	14	8
Operating Leases, Income Statement, Lease Revenue									1,867	2,711	3,398
Total financing revenue and other interest income									8,322	8,305	8,397
Interest Expense, Deposits									1,077	830	718
Interest Expense, Short-term Borrowings									127	57	49
Interest Expense, Long-term Debt									1,653	1,742	1,662
Interest Expense, Related Party									0	0	0
Interest Expense									2,857	2,629	2,429
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease									1,244	1,769	2,249
Net Financing Revenue	$ 1,094	$ 1,081	$ 1,067	$ 979	$ 976	$ 996	$ 984	$ 951	4,221	3,907	3,719
Dividends from Bank Subsidiary									0		0
Dividends From Non Bank Subsidiary									0	0	0
Insurance Services Revenue									973	945	940
Gain (Loss) on Sales of Loans, Net									68	11	45
Gain (Loss) on Extinguishment of Debt									(7)	(5)	(357)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments									102	185	155
Noninterest Income, Other Operating Income									408	394	359
Nonoperating Income (Expense)	379	381	388	396	392	388	374	376	1,544	1,530	1,142
Revenues									5,765	5,437	4,861
Provision for Loan Losses Expensed	294	314	269	271	267	258	172	220	1,148	917	707
Labor and Related Expense									1,095	992	963
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									332	342	293
Other Noninterest Expense									1,683	1,605	1,505
Noninterest Expense	769	753	810	778	721	735	773	710	3,110	2,939	2,761
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	410	395	376	326	380	391	413	397	1,507	1,581	1,393
Income Tax Expense (Benefit)	231	115	122	113	134	130	56	150	581	470	496
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	179	280	254	213	246	261	357	247	926	1,111	897
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	2	2	(2)	1	2	(52)	3	3	3	(44)	392
Undistributed income of bank subsidiaries									0	0	0
Undistributed income of nonbank subsidiaries									0	0	0
Net Income (Loss) Attributable to Parent	$ 181	$ 282	$ 252	$ 214	$ 248	$ 209	$ 360	$ 250	929	1,067	1,289
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									106	(110)	(165)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									1,035	957	1,124
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									(27)	(104)	(83)
Interest and Fee Income, Loans and Leases Held-for-sale											0
Interest and Dividend Income, Securities, Operating									0	0	0
Interest Income, Deposits with Financial Institutions									7	5	1
Operating Leases, Income Statement, Lease Revenue									11	17	9
Total financing revenue and other interest income									7	(71)	(56)
Interest Expense, Deposits									3	8	10
Interest Expense, Short-term Borrowings									60	40	40
Interest Expense, Long-term Debt									1,101	1,161	1,121
Interest Expense, Related Party									15	20	32
Interest Expense									1,179	1,229	1,203
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease									11	14	7
Net Financing Revenue									(1,183)	(1,314)	(1,266)
Dividends from Bank Subsidiary									3,300		525
Dividends From Non Bank Subsidiary									752	965	1,123
Insurance Services Revenue									0	0	0
Gain (Loss) on Sales of Loans, Net									40	(11)	(9)
Gain (Loss) on Extinguishment of Debt									(1)	(3)	(355)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments									0	0	0
Noninterest Income, Other Operating Income									676	1,253	1,373
Nonoperating Income (Expense)									715	1,239	1,009
Revenues									3,584	890	1,391
Provision for Loan Losses Expensed									465	408	157
Labor and Related Expense									180	573	571
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									0	0	0
Other Noninterest Expense									899	1,261	1,247
Noninterest Expense									1,079	1,834	1,818
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									2,040	(1,352)	(584)
Income Tax Expense (Benefit)									337	(279)	(267)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									1,703	(1,073)	(317)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									7	(39)	356
Undistributed income of bank subsidiaries									(1,168)	1,273	581
Undistributed income of nonbank subsidiaries									387	906	669
Net Income (Loss) Attributable to Parent									929	1,067	1,289
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									106	(110)	(165)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									1,035	957	1,124
Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									0	0	0
Interest and Fee Income, Loans and Leases Held-for-sale											0
Interest and Dividend Income, Securities, Operating									0	0	0
Interest Income, Deposits with Financial Institutions									0	0	0
Operating Leases, Income Statement, Lease Revenue									0	0	0
Total financing revenue and other interest income									0	0	0
Interest Expense, Deposits									0	0	0
Interest Expense, Short-term Borrowings									0	0	0
Interest Expense, Long-term Debt									0	0	0
Interest Expense, Related Party									0	0	0
Interest Expense									0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease									0	0	0
Net Financing Revenue									0	0	0
Dividends from Bank Subsidiary									3,300		525
Dividends From Non Bank Subsidiary									0	0	0
Insurance Services Revenue									0	0	0
Gain (Loss) on Sales of Loans, Net									0	0	0
Gain (Loss) on Extinguishment of Debt									0	0	0
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments									0	0	0
Noninterest Income, Other Operating Income									0	0	0
Nonoperating Income (Expense)									0	0	0
Revenues									3,300	0	525
Provision for Loan Losses Expensed									0	0	0
Labor and Related Expense									0	0	0
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									0	0	0
Other Noninterest Expense									0	0	0
Noninterest Expense									0	0	0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									3,300	0	525
Income Tax Expense (Benefit)									0	(82)	0
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									3,300	82	525
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									0	0	0
Undistributed income of bank subsidiaries									(1,168)	1,273	581
Undistributed income of nonbank subsidiaries									0	(2)	(1)
Net Income (Loss) Attributable to Parent									2,132	1,353	1,105
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									65	(63)	(43)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									2,197	1,290	1,062
Non-Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									5,846	5,266	4,653
Interest and Fee Income, Loans and Leases Held-for-sale											40
Interest and Dividend Income, Securities, Operating									601	421	381
Interest Income, Deposits with Financial Institutions									30	9	7
Operating Leases, Income Statement, Lease Revenue									1,856	2,694	3,389
Total financing revenue and other interest income									8,346	8,407	8,502
Interest Expense, Deposits									1,078	822	708
Interest Expense, Short-term Borrowings									67	17	9
Interest Expense, Long-term Debt									552	581	541
Interest Expense, Related Party									12	11	17
Interest Expense									1,709	1,431	1,275
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease									1,233	1,755	2,242
Net Financing Revenue									5,404	5,221	4,985
Dividends from Bank Subsidiary									0		0
Dividends From Non Bank Subsidiary									0	0	0
Insurance Services Revenue									973	945	940
Gain (Loss) on Sales of Loans, Net									28	22	54
Gain (Loss) on Extinguishment of Debt									(6)	(2)	(2)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments									102	176	155
Noninterest Income, Other Operating Income									840	937	1,373
Nonoperating Income (Expense)									1,937	2,078	2,520
Revenues									7,341	7,299	7,505
Provision for Loan Losses Expensed									683	509	550
Labor and Related Expense									915	419	842
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									332	342	293
Other Noninterest Expense									1,892	2,130	2,195
Noninterest Expense									3,139	2,891	3,330
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									3,519	3,899	3,625
Income Tax Expense (Benefit)									244	831	763
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									3,275	3,068	2,862
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									(4)	(5)	36
Undistributed income of bank subsidiaries									0	0	0
Undistributed income of nonbank subsidiaries									0	0	0
Net Income (Loss) Attributable to Parent									3,271	3,063	2,898
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									104	(106)	(172)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									3,375	2,957	2,726
Affiliated Entity [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									0	0	0
Interest Income, Deposits with Financial Institutions									0	0	0
Affiliated Entity [Member] | Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									12	11	17
Interest Income, Deposits with Financial Institutions									4	0	0
Affiliated Entity [Member] | Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									0	0	0
Interest Income, Deposits with Financial Institutions									0	0	0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									6	8	24
Interest Income, Deposits with Financial Institutions									7	9	8
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									0	0	0
Interest and Fee Income, Loans and Leases Held-for-sale											0
Interest and Dividend Income, Securities, Operating									(2)	(3)	0
Interest Income, Deposits with Financial Institutions									0	0	0
Operating Leases, Income Statement, Lease Revenue									0	0	0
Total financing revenue and other interest income									(31)	(31)	(49)
Interest Expense, Deposits									(4)	0	0
Interest Expense, Short-term Borrowings									0	0	0
Interest Expense, Long-term Debt									0	0	0
Interest Expense, Related Party									(27)	(31)	(49)
Interest Expense									(31)	(31)	(49)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease									0	0	0
Net Financing Revenue									0	0	0
Dividends from Bank Subsidiary									(6,600)		(1,050)
Dividends From Non Bank Subsidiary									(752)	(965)	(1,123)
Insurance Services Revenue									0	0	0
Gain (Loss) on Sales of Loans, Net									0	0	0
Gain (Loss) on Extinguishment of Debt									0	0	0
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments									0	9	0
Noninterest Income, Other Operating Income									(1,108)	(1,796)	(2,387)
Nonoperating Income (Expense)									(1,108)	(1,787)	(2,387)
Revenues									(8,460)	(2,752)	(4,560)
Provision for Loan Losses Expensed									0	0	0
Labor and Related Expense									0	0	(450)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									0	0	0
Other Noninterest Expense									(1,108)	(1,786)	(1,937)
Noninterest Expense									(1,108)	(1,786)	(2,387)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									(7,352)	(966)	(2,173)
Income Tax Expense (Benefit)									0	0	0
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									(7,352)	(966)	(2,173)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									0	0	0
Undistributed income of bank subsidiaries									2,336	(2,546)	(1,162)
Undistributed income of nonbank subsidiaries									(387)	(904)	(668)
Net Income (Loss) Attributable to Parent									(5,403)	(4,416)	(4,003)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(169)	169	215
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(5,572)	(4,247)	(3,788)
Consolidation, Eliminations [Member] | Affiliated Entity [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases									(18)	(19)	(41)
Interest Income, Deposits with Financial Institutions									$ (11)	$ (9)	$ (8)

Parent and Guarantor Consoli144

Parent and Guarantor Consolidating Financial Statements (Schedule of Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	$ 844		$ 1,547
Interest-bearing Deposits in Banks and Other Financial Institutions	3,408		4,387
Cash and Cash Equivalents, at Carrying Value	4,252		5,934
Trading Securities			0
Available-for-sale securities	22,821		18,926
Held-to-maturity securities	1,899		839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	108		0
Loans and Leases Receivable, Gross	122,893		118,944
Loans to bank subsidiary			0
Loans to nonbank subsidiary	0		0
Financing Receivable, Allowance for Credit Losses	1,276		1,144	$ 1,054
Loans and Leases Receivable, Net Amount	121,617		117,800
Property Subject to or Available for Operating Lease, Net	8,741		11,470
Receivables from bank subsidiary	0		0
Receivables from nonbank subsidiary	0		0
Investment in bank subsidiaries	0		0
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	2,047		1,905
Other Assets	5,663		6,854
Assets	167,148		163,728	158,581
Noninterest-bearing deposit liabilities	108		84
Interest-bearing Deposit Liabilities	93,148		78,938
Deposits	93,256		79,022
Short-term Debt	11,413		12,673
Long-term Debt	44,226		54,128
Debt Payable To Bank Subsidiaries	0		0
Debt Payable To Nonbank Subsidiaries	0		0
Payables to Bank Subsidiaries		$ 0
Payables to Nonbank Subsidiaries	0		0
Interest payable	375		351
Unearned Premiums	2,604		2,500
Accounts Payable and Accrued Liabilities	1,780		1,737
Liabilities	153,654		150,411
Stockholders' Equity Attributable to Parent	13,494		13,317	$ 13,439	$ 15,399
Liabilities and Equity	167,148		163,728
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	74		720
Interest-bearing Deposits in Banks and Other Financial Institutions	5		100
Cash and Cash Equivalents, at Carrying Value	1,217		820
Trading Securities			0
Available-for-sale securities	0		0
Held-to-maturity securities	0		0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Gross	7,434		4,705
Loans to bank subsidiary			1,125
Loans to nonbank subsidiary	879		1,779
Financing Receivable, Allowance for Credit Losses	185		115
Loans and Leases Receivable, Net Amount	8,128		7,494
Property Subject to or Available for Operating Lease, Net	19		42
Receivables from bank subsidiary	80		299
Receivables from nonbank subsidiary	71		107
Investment in bank subsidiaries	16,962		17,727
Investment in nonbank subsidiaries	8,111		10,318
Premiums receivable and other insurance assets	0		0
Other Assets	2,207		4,347
Assets	36,795		41,154
Noninterest-bearing deposit liabilities	0		0
Interest-bearing Deposit Liabilities	12		167
Deposits	12		167
Short-term Debt	3,171		3,622
Long-term Debt	17,966		21,798
Debt Payable To Bank Subsidiaries	74		330
Debt Payable To Nonbank Subsidiaries	1,103		1,027
Payables to Bank Subsidiaries		4
Payables to Nonbank Subsidiaries	132		153
Interest payable	200		253
Unearned Premiums	0		0
Accounts Payable and Accrued Liabilities	639		487
Liabilities	23,301		27,837
Stockholders' Equity Attributable to Parent	13,494		13,317
Liabilities and Equity	36,795		41,154
Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	0		0
Interest-bearing Deposits in Banks and Other Financial Institutions	0		0
Cash and Cash Equivalents, at Carrying Value	0		0
Trading Securities			0
Available-for-sale securities	0		0
Held-to-maturity securities	0		0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Gross	0		0
Loans to bank subsidiary			0
Loans to nonbank subsidiary	0		0
Financing Receivable, Allowance for Credit Losses	0		0
Loans and Leases Receivable, Net Amount	0		0
Property Subject to or Available for Operating Lease, Net	0		0
Receivables from bank subsidiary	0		0
Receivables from nonbank subsidiary	0		0
Investment in bank subsidiaries	16,962		17,727
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	0		0
Other Assets	0		0
Assets	16,962		17,727
Noninterest-bearing deposit liabilities	0		0
Interest-bearing Deposit Liabilities	0		0
Deposits	0		0
Short-term Debt	0		0
Long-term Debt	0		0
Debt Payable To Bank Subsidiaries	0		0
Debt Payable To Nonbank Subsidiaries	0		0
Payables to Bank Subsidiaries		0
Payables to Nonbank Subsidiaries	0		0
Interest payable	0		0
Unearned Premiums	0		0
Accounts Payable and Accrued Liabilities	0		0
Liabilities	0		0
Stockholders' Equity Attributable to Parent	16,962		17,727
Liabilities and Equity	16,962		17,727
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	770		827
Interest-bearing Deposits in Banks and Other Financial Institutions	3,403		4,287
Cash and Cash Equivalents, at Carrying Value	4,868		5,515
Trading Securities			82
Available-for-sale securities	22,821		19,253
Held-to-maturity securities	1,973		839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	108
Loans and Leases Receivable, Gross	115,459		114,239
Loans to bank subsidiary			0
Loans to nonbank subsidiary	408		626
Financing Receivable, Allowance for Credit Losses	1,091		1,029
Loans and Leases Receivable, Net Amount	114,776		113,836
Property Subject to or Available for Operating Lease, Net	8,722		11,428
Receivables from bank subsidiary	0		0
Receivables from nonbank subsidiary	77		67
Investment in bank subsidiaries	0		0
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	2,082		1,936
Other Assets	5,105		5,085
Assets	160,532		158,041
Noninterest-bearing deposit liabilities	108		84
Interest-bearing Deposit Liabilities	93,136		78,771
Deposits	94,383		78,855
Short-term Debt	8,242		9,051
Long-term Debt	26,260		32,330
Debt Payable To Bank Subsidiaries	0		0
Debt Payable To Nonbank Subsidiaries	879		2,903
Payables to Bank Subsidiaries		0
Payables to Nonbank Subsidiaries	127		351
Interest payable	175		98
Unearned Premiums	2,604		2,500
Accounts Payable and Accrued Liabilities	2,790		3,911
Liabilities	135,460		129,999
Stockholders' Equity Attributable to Parent	25,072		28,042
Liabilities and Equity	160,532		158,041
Affiliated Entity [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	0		0
Interest-bearing Deposit Liabilities	0
Affiliated Entity [Member] | Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	1,138		0
Interest-bearing Deposit Liabilities	0
Affiliated Entity [Member] | Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	0		0
Interest-bearing Deposit Liabilities	0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	695		401
Interest-bearing Deposit Liabilities	1,139
Consolidation, Eliminations [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	0		0
Interest-bearing Deposits in Banks and Other Financial Institutions	0		0
Cash and Cash Equivalents, at Carrying Value	(1,833)		(401)
Trading Securities			(82)
Available-for-sale securities	0		(327)
Held-to-maturity securities	(74)		0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Gross	0		0
Loans to bank subsidiary			(1,125)
Loans to nonbank subsidiary	(1,287)		(2,405)
Financing Receivable, Allowance for Credit Losses	0		0
Loans and Leases Receivable, Net Amount	(1,287)		(3,530)
Property Subject to or Available for Operating Lease, Net	0		0
Receivables from bank subsidiary	(80)		(299)
Receivables from nonbank subsidiary	(148)		(174)
Investment in bank subsidiaries	(33,924)		(35,454)
Investment in nonbank subsidiaries	(8,111)		(10,318)
Premiums receivable and other insurance assets	(35)		(31)
Other Assets	(1,649)		(2,578)
Assets	(47,141)		(53,194)
Noninterest-bearing deposit liabilities	0		0
Interest-bearing Deposit Liabilities	0		0
Deposits	(1,139)		0
Short-term Debt	0		0
Long-term Debt	0		0
Debt Payable To Bank Subsidiaries	(74)		(330)
Debt Payable To Nonbank Subsidiaries	(1,982)		(3,930)
Payables to Bank Subsidiaries		$ (4)
Payables to Nonbank Subsidiaries	(259)		(504)
Interest payable	0		0
Unearned Premiums	0		0
Accounts Payable and Accrued Liabilities	(1,649)		(2,661)
Liabilities	(5,107)		(7,425)
Stockholders' Equity Attributable to Parent	(42,034)		(45,769)
Liabilities and Equity	(47,141)		(53,194)
Consolidation, Eliminations [Member] | Affiliated Entity [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	(1,833)		$ (401)
Interest-bearing Deposit Liabilities	$ (1,139)

Parent and Guarantor Consoli145

Parent and Guarantor Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 4,079	$ 4,567	$ 5,111
Payments to Acquire Available-for-sale Securities	(11,234)	(16,031)	(12,250)
Proceeds from sales of available-for-sale securities	4,633	11,036	6,874
Proceeds from maturities and repayment of available-for-sale securities	2,899	3,379	4,255
Payments to Acquire Held-to-maturity Securities	(1,026)	(841)	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	68	0	0
Payments to Acquire Loans Held-for-investment	(5,452)	(3,859)	(4,501)
Proceeds from Sale of Loans and Leases Held-for-investment	1,339	4,285	3,197
Originations and repayments of loans held-for-investment and other	(1,063)	(8,826)	(9,344)
Purchases of operating lease assets	(4,052)	(3,274)	(4,685)
Disposals of operating lease assets	5,567	6,304	5,546
Payments to Acquire Interest in Subsidiaries and Affiliates	0	309	0
Proceeds from Contributions from Parent	0	0	0
Returns of contributed capital	0	0	0
Proceeds from Divestiture of Businesses	0	0	1,049
Increase (Decrease) in Non marketable equity securities	(187)	(628)	(147)
Payments for (Proceeds from) Other Investing Activities	(219)	(306)	3
Net cash provided by investing activities	(8,727)	(9,070)	(10,003)
Proceeds from (Repayments of) Short-term Debt	(1,263)	4,564	1,028
Increase (Decrease) in Deposits	14,172	12,508	8,247
Proceeds from issuance of long-term debt	17,969	14,155	30,665
Repayments of long-term debt	(27,908)	(26,412)	(31,350)
Net Change in Debt, Intercompany	0	0	0
Payments for Repurchase of Redeemable Preferred Stock	0	(696)	(559)
Payments for Repurchase of Common Stock	(753)	(341)	(16)
Payments of Dividends	(184)	(108)	(2,571)
Dividends paid and returns of contributed capital, Intercompany	0	0	0
Capital contributions from parent	0	0	0
Net cash (used in) provided by financing activities	2,033	3,670	5,444
Effect of exchange-rate changes on cash and cash equivalents	3	1	(4)
Cash and Cash Equivalents, Period Increase (Decrease)	(2,612)	(832)	548
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	5,269	7,881	8,713	$ 8,165
Restricted Cash	1,017	1,947
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	4,591	241	370
Payments to Acquire Available-for-sale Securities	0	0	0
Proceeds from sales of available-for-sale securities	0	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0
Payments to Acquire Loans Held-for-investment	(35)	(4)	(169)
Proceeds from Sale of Loans and Leases Held-for-investment	106	0	0
Originations and repayments of loans held-for-investment and other	860	2,013	1,954
Purchases of operating lease assets	0	0	(94)
Disposals of operating lease assets	13	25	7
Payments to Acquire Interest in Subsidiaries and Affiliates		309
Proceeds from Contributions from Parent	(1,212)	(3,908)	(796)
Returns of contributed capital	1,567	3,678	1,444
Proceeds from Divestiture of Businesses			1,049
Increase (Decrease) in Non marketable equity securities	0	0	0
Payments for (Proceeds from) Other Investing Activities	(31)	(206)	(47)
Net cash provided by investing activities	3,343	2,166	3,588
Proceeds from (Repayments of) Short-term Debt	(453)	169	115
Increase (Decrease) in Deposits	(156)	(61)	(91)
Proceeds from issuance of long-term debt	354	979	5,428
Repayments of long-term debt	(6,111)	(2,662)	(5,931)
Net Change in Debt, Intercompany	(225)	(382)	(977)
Payments for Repurchase of Redeemable Preferred Stock		(696)	(559)
Payments for Repurchase of Common Stock	(753)	(341)	(16)
Payments of Dividends	(184)	(108)	(2,571)
Dividends paid and returns of contributed capital, Intercompany	0	0	0
Capital contributions from parent	0	0	0
Net cash (used in) provided by financing activities	(7,528)	(3,102)	(4,602)
Effect of exchange-rate changes on cash and cash equivalents	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	406	(695)	(644)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1,395	989	1,684	2,328
Restricted Cash	178	169
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	3,300	6	525
Payments to Acquire Available-for-sale Securities	0	0	0
Proceeds from sales of available-for-sale securities	0	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0
Payments to Acquire Loans Held-for-investment	0	0	0
Proceeds from Sale of Loans and Leases Held-for-investment	0	0	0
Originations and repayments of loans held-for-investment and other	0	0	0
Purchases of operating lease assets	0	0	0
Disposals of operating lease assets	0	0	0
Payments to Acquire Interest in Subsidiaries and Affiliates		0
Proceeds from Contributions from Parent	(5)	0	(1)
Returns of contributed capital	0	8	0
Proceeds from Divestiture of Businesses			0
Increase (Decrease) in Non marketable equity securities	0	0	0
Payments for (Proceeds from) Other Investing Activities	0	0	0
Net cash provided by investing activities	(5)	8	(1)
Proceeds from (Repayments of) Short-term Debt	0	0	0
Increase (Decrease) in Deposits	0	0	0
Proceeds from issuance of long-term debt	0	0	0
Repayments of long-term debt	0	0	0
Net Change in Debt, Intercompany	0	0	0
Payments for Repurchase of Redeemable Preferred Stock		0	0
Payments for Repurchase of Common Stock	0	0	0
Payments of Dividends	0	0	0
Dividends paid and returns of contributed capital, Intercompany	(3,300)	(14)	(525)
Capital contributions from parent	5	0	1
Net cash (used in) provided by financing activities	(3,295)	(14)	(524)
Effect of exchange-rate changes on cash and cash equivalents	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	0	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0	0
Restricted Cash	0	0
Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	3,466	5,383	6,390
Payments to Acquire Available-for-sale Securities	(11,234)	(16,031)	(12,250)
Proceeds from sales of available-for-sale securities	4,633	11,036	6,874
Proceeds from maturities and repayment of available-for-sale securities	2,899	3,379	4,255
Payments to Acquire Held-to-maturity Securities	(1,026)	(841)
Proceeds from Sale and Maturity of Held-to-maturity Securities	68
Payments to Acquire Loans Held-for-investment	(5,417)	(3,855)	(4,332)
Proceeds from Sale of Loans and Leases Held-for-investment	1,233	4,285	3,197
Originations and repayments of loans held-for-investment and other	33	(10,839)	(11,298)
Purchases of operating lease assets	(4,052)	(3,274)	(4,591)
Disposals of operating lease assets	5,554	6,279	5,539
Payments to Acquire Interest in Subsidiaries and Affiliates		0
Proceeds from Contributions from Parent	0	0	0
Returns of contributed capital	0	0	0
Proceeds from Divestiture of Businesses			0
Increase (Decrease) in Non marketable equity securities	(187)	(628)	(147)
Payments for (Proceeds from) Other Investing Activities	(99)	(191)	50
Net cash provided by investing activities	(7,087)	(10,747)	(11,492)
Proceeds from (Repayments of) Short-term Debt	(810)	4,395	913
Increase (Decrease) in Deposits	15,466	12,569	8,338
Proceeds from issuance of long-term debt	15,654	13,176	25,237
Repayments of long-term debt	(21,797)	(23,750)	(25,419)
Net Change in Debt, Intercompany	(2,074)	(877)	(240)
Payments for Repurchase of Redeemable Preferred Stock		0	0
Payments for Repurchase of Common Stock	0	0	0
Payments of Dividends	0	0	0
Dividends paid and returns of contributed capital, Intercompany	(5,619)	(4,644)	(3,092)
Capital contributions from parent	1,212	3,908	796
Net cash (used in) provided by financing activities	2,032	4,777	6,533
Effect of exchange-rate changes on cash and cash equivalents	3	1	(4)
Cash and Cash Equivalents, Period Increase (Decrease)	(1,586)	(586)	1,427
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	5,707	7,293	7,879	6,452
Restricted Cash	839	1,778
Affiliated Entity [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	0
Payments for (Proceeds from) Loans and Leases	0	0	0
Affiliated Entity [Member] | Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	(7)
Payments for (Proceeds from) Loans and Leases	2,068	877	240
Affiliated Entity [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	0
Payments for (Proceeds from) Loans and Leases	0	0	0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	(291)
Payments for (Proceeds from) Loans and Leases	217	(67)	1,211
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(7,278)	(1,063)	(2,174)
Payments to Acquire Available-for-sale Securities	0	0	0
Proceeds from sales of available-for-sale securities	0	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0
Payments to Acquire Loans Held-for-investment	0	0	0
Proceeds from Sale of Loans and Leases Held-for-investment	0	0	0
Originations and repayments of loans held-for-investment and other	(1,956)	0	0
Purchases of operating lease assets	0	0	0
Disposals of operating lease assets	0	0	0
Payments to Acquire Interest in Subsidiaries and Affiliates		0
Proceeds from Contributions from Parent	1,217	3,908	797
Returns of contributed capital	(1,567)	(3,686)	(1,444)
Proceeds from Divestiture of Businesses			0
Increase (Decrease) in Non marketable equity securities	0	0	0
Payments for (Proceeds from) Other Investing Activities	(89)	91	0
Net cash provided by investing activities	(4,978)	(497)	(2,098)
Proceeds from (Repayments of) Short-term Debt	0	0	0
Increase (Decrease) in Deposits	(1,138)	0	0
Proceeds from issuance of long-term debt	1,961	0	0
Repayments of long-term debt	0	0	0
Net Change in Debt, Intercompany	2,299	1,259	1,217
Payments for Repurchase of Redeemable Preferred Stock		0	0
Payments for Repurchase of Common Stock	0	0	0
Payments of Dividends	0	0	0
Dividends paid and returns of contributed capital, Intercompany	8,919	4,658	3,617
Capital contributions from parent	(1,217)	(3,908)	(797)
Net cash (used in) provided by financing activities	10,824	2,009	4,037
Effect of exchange-rate changes on cash and cash equivalents	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	(1,432)	449	(235)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(1,833)	(401)	(850)	$ (615)
Restricted Cash	0	0
Consolidation, Eliminations [Member] | Affiliated Entity [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	298
Payments for (Proceeds from) Loans and Leases	$ (2,285)	$ (810)	$ (1,451)

Subsequent Events (Details)

Subsequent Events (Details) - $ / shares	Jan. 10, 2018	Dec. 31, 2017
Subsequent Events [Abstract]
Dividends Payable, Amount Per Share	$ 0.13	$ 0.13
Increase (Decrease) in Dividends Payable, per share	$ 0.01	$ 0.01

Premiums Receivable and Othe147

Premiums Receivable and Other Insurance Assets Premiums Receivable and Other Insurance Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Premiums Receivable and Other Insurance Assets [Abstract]
Prepaid Reinsurance Premiums	$ 507	$ 439
Reinsurance Recoverables, Incurred but Not Reported Claims	108	108
Reinsurance Recoverables on Paid Losses, Gross	19	20
Premiums Receivable, Net	84	80
Deferred Policy Acquisition Costs	1,329	1,258
Premiums receivable and other insurance assets	$ 2,047	$ 1,905

Equity Equity (Common Stock) (D

Equity Equity (Common Stock) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Jun. 28, 2017	Dec. 31, 2016	Jul. 19, 2016	Dec. 31, 2015
Equity [Abstract]
Common Stock, Shares, Issued	485,707,644	482,790,696	480,136,039
Stock Issued During Period, Value, New Issues	4,175,909	2,916,948	2,654,657
Common Stock, Shares, Issued	485,707,644	482,790,696	480,136,039	489,883,553		485,707,644		482,790,696
Treasury Stock, Shares	(18,707,338)	(810,585)	(41,148)
Treasury Stock, Shares, Acquired	(34,122,279)	(17,896,753)	(769,437)
Treasury Stock, Shares	(52,829,617)	(18,707,338)	(810,585)
Common Stock, Shares, Issued	489,883,553	485,707,644	482,790,696
Stock Repurchase Program, Authorized Amount					$ 760		$ 700
Common Stock, Shares, Outstanding				437,053,936		467,000,306		481,980,111

Insurance Premiums and Servi149

Insurance Premiums and Service Revenue Earned Insurance Premiums and Service Revenue Earned (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance Premiums and Service Revenue [Line Items]
Insurance Services Revenue	$ 973	$ 945	$ 940
Insurance Premiums Written [Member]
Insurance Premiums and Service Revenue [Line Items]
Direct Premiums Written	384	317	313
Assumed Premiums Written	2	3	2
Proceeds from Insurance Premiums Collected	386	320	315
Ceded Premiums Written	(254)	(198)	(184)
Premiums Written, Net	132	122	131
Insurance Services Revenue	864	826	846
Insurance Premiums and Service Revenue	996	948	977
Insurance Premiums Earned [Member]
Insurance Premiums and Service Revenue [Line Items]
Direct Premiums Earned	364	318	296
Assumed Premiums Earned	5	5	16
Proceeds from Insurance Premiums Collected	369	323	312
Ceded Premiums Earned	(188)	(141)	(125)
Premiums Earned, Net	181	182	187
Insurance Services Revenue	792	763	753
Insurance Premiums and Service Revenue	$ 973	$ 945	$ 940

Quarterly Financial Statemen150

Quarterly Financial Statements (unaudited) Quarterly Financial Statements (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Statements (unaudited) [Abstract]
Net Financing Revenue	$ 1,094	$ 1,081	$ 1,067	$ 979	$ 976	$ 996	$ 984	$ 951	$ 4,221	$ 3,907	$ 3,719
Nonoperating Income (Expense)	379	381	388	396	392	388	374	376	1,544	1,530	1,142
Revenue, Net	1,473	1,462	1,455	1,375	1,368	1,384	1,358	1,327	5,765	5,437	4,861
Provision for Loan Losses Expensed	294	314	269	271	267	258	172	220	1,148	917	707
Noninterest Expense	769	753	810	778	721	735	773	710	3,110	2,939	2,761
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	410	395	376	326	380	391	413	397	1,507	1,581	1,393
Income Tax Expense (Benefit)	231	115	122	113	134	130	56	150	581	470	496
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	179	280	254	213	246	261	357	247	926	1,111	897
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	2	2	(2)	1	2	(52)	3	3	3	(44)	392
Net Income (Loss) Attributable to Parent	$ 181	$ 282	$ 252	$ 214	$ 248	$ 209	$ 360	$ 250	$ 929	$ 1,067	$ 1,289
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.40	$ 0.62	$ 0.55	$ 0.46	$ 0.52	$ 0.54	$ 0.70	$ 0.48	$ 2.04	$ 2.25	$ (3.47)
Earnings Per Share, Basic	0.41	0.63	0.55	0.46	0.53	0.43	0.71	0.49	2.05	2.15	(2.66)
Income (Loss) from Continuing Operations, Per Diluted Share	0.40	0.62	0.55	0.46	0.52	0.54	0.70	0.48	2.03	2.24	(3.47)
Earnings Per Share, Diluted	0.41	0.63	0.55	0.46	0.52	0.43	0.71	0.49	2.04	2.15	(2.66)
Common Stock, Dividends, Per Share, Declared	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0	$ 0	$ 0.40	$ 0.16	$ 0
Net impacts as a result of the Tax Act [Member]
Tax Act Impacts [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount									$ 119	$ 0	$ 0

Share-based Compensation Pla151

Share-based Compensation Plans Share-based Compensation Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
RSUs and PSUs [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	37,778,224
Minimum Range for PSU Awards Payable Upon Vest	0.00%
Maximum range for PSU awards payable upon vest	150.00%
Restricted Stock Units and Performance Share Units	$ 60	$ 54	$ 49
Number of RSU and PSU shares [Member]
RSUs and PSUs [Line Items]
Outstanding RSUs and PSUs	5,443,000
Granted RSUs and PSUs	3,280,000
Vested RSUs and PSUs	(3,043,000)
Forfeited RSUs and PSUs	(88,000)
Outstanding RSUs and PSUs	5,592,000	5,443,000
Weighted-average grant date fair value per share [Member]
RSUs and PSUs [Line Items]
Outstanding RSUs and PSUs	19
Granted RSUs and PSUs	21.30
Vested RSUs and PSUs	19.84
Forfeited RSUs and PSUs	19.39
Outstanding RSUs and PSUs	19.89	19

Guarantees and Commitments G152

Guarantees and Commitments Guarantees and Commitments (Guarantees to third parties) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Standby letters of credit and other guarantees	$ 8	$ 8
Maximum [Member]
Guarantor Obligations [Line Items]
Standby letters of credit and other guarantees	$ 227	$ 175

Guarantees and Commitments G153

Guarantees and Commitments Guarantees and Commitments (Contractual Financing Commitments) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Guarantees and Commitments [Abstract]
Unused revolving credit line commitments and other	$ 2,341	$ 1,995
Commitment to fund remaining unused balances on home equity lines of credit	318	356
Commitments to provide capital to investees	283	206
Warehouse and construction lending commitments	144	164
Mortgage loan origination commitments	$ 95	$ 0

Guarantees and Commitments G154

Guarantees and Commitments Guarantees and Commitments (Schedule of Lease Commitments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Guarantees and Commitments [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 35
Operating Leases, Future Minimum Payments, Due in Two Years	35
Operating Leases, Future Minimum Payments, Due in Three Years	34
Operating Leases, Future Minimum Payments, Due in Four Years	36
Operating Leases, Future Minimum Payments, Due in Five Years	33
Operating Leases, Future Minimum Payments, Due Thereafter	316
Operating Leases, Future Minimum Payments Due	489
Operating Leases, Rent Expense	$ 46	$ 51	$ 51

Guarantees and Commitments G155

Guarantees and Commitments Guarantees and Commitments (Other Purchase Commitments) (Details) $ in Millions	Dec. 31, 2017USD ($)
Guarantees and Commitments [Abstract]
Other Commitment, Due in Next Twelve Months	$ 85
Other Commitment, Due in Second and Third Year	36
Other Commitment, Due in Fourth Year	2
Other Commitment	$ 123