Ally Financial (ALLY) 10-Q 7 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	3 Months Ended
	Mar. 31, 2018	May 03, 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-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		430,028,556
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 9,452,901,086

Condensed Consolidated Statemen

Condensed Consolidated Statement of Comprehensive Income Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Revenue and Other Income [Line Items]
Interest and Fee Income, Loans and Leases	$ 1,543	$ 1,368
Interest and Dividend Income, Securities, Operating, Available-for-sale	176	134
Interest Income, Deposits with Financial Institutions	15	5
Operating Leases, Income Statement, Lease Revenue	382	543
Total financing revenue and other interest income	2,116	2,050
Interest Expense [Abstract]
Interest Expense, Deposits	351	231
Interest Expense, Short-term Borrowings	32	27
Interest Expense, Long-term Debt	411	424
Interest Expense	794	682
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	273	389
Net Financing Revenue	1,049	979
Other revenue [Abstract]
Insurance Services Revenue	256	241
Gain (Loss) on Sales of Loans, Net	1	14
Gain (Loss) on Investments	(12)	27
Noninterest Income, Other Operating Income	109	114
Nonoperating Income (Expense)	354	396
Revenues	1,403	1,375
Provision for Loan Losses Expensed	261	271
Noninterest Expense [Abstract]
Labor and Related Expense	306	285
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	63	88
Other Noninterest Expense	445	405
Noninterest Expense	814	778
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	328	326
Income Tax Expense (Benefit)	76	113
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	252	213
Net Income (Loss) Attributable to Parent	250	214
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(328)	20
Other Comprehensive Income (Loss), Net of Tax	(328)	20
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(78)	234
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ (2)	$ 1
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.58	$ 0.46
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	(0.01)	0
Earnings Per Share, Basic	0.57	0.46
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.57	0.46
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	(0.01)	0
Earnings Per Share, Diluted	0.57	0.46
Common Stock, Dividends, Per Share, Declared	$ 0.13	$ 0.08
Retained Earnings [Member]
Net Income (Loss) Attributable to Parent	$ 250	$ 214

Condensed Consolidated Balance

Condensed Consolidated Balance Sheet & Mini Balance Sheet - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets [Abstract]
Cash and Due from Banks	$ 768	$ 844
Interest-bearing Deposits in Banks and Other Financial Institutions	2,953	3,408
Cash and Cash Equivalents, at Carrying Value	3,721	4,252
Equity Securities	680	518
Available-for-sale securities	22,726	22,303
Held-to-maturity securities	1,967	1,899
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	126	108
Finance receivables and loans, net [Abstract]
Loans and Leases Receivable, Net of Deferred Income	125,327	122,893
Financing Receivable, Allowance for Credit Losses	1,278	1,276
Loans and Leases Receivable, Net Amount	124,049	121,617
Property Subject to or Available for Operating Lease, Net	8,530	8,741
Premiums receivable and other insurance assets	2,197	2,047
Other Assets	6,025	5,663
Assets	170,021	167,148
Liabilities and Equity [Abstract]
Noninterest-bearing deposit liabilities	122	108
Interest-bearing Deposit Liabilities	97,324	93,148
Deposits	97,446	93,256
Short-term Debt	9,564	11,413
Long-term Debt	45,076	44,226
Interest payable	494	375
Unearned Premiums	2,904	2,604
Accounts Payable and Accrued Liabilities	1,455	1,780
Liabilities	156,939	153,654
Equity [Abstract]
Common Stocks, Including Additional Paid in Capital, Net of Discount	21,273	21,245
Retained Earnings (Accumulated Deficit)	(6,318)	(6,406)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(578)	(235)
Treasury stock, Value	(1,295)	(1,110)
Stockholders' Equity Attributable to Parent, Total	13,082	13,494
Liabilities and Equity	170,021	167,148
Variable Interest Entity, Primary Beneficiary [Member]
Finance receivables and loans, net [Abstract]
Loans and Leases Receivable, Net of Deferred Income	19,080	20,623
Financing Receivable, Allowance for Credit Losses	142	136
Loans and Leases Receivable, Net Amount	18,938	20,487
Property Subject to or Available for Operating Lease, Net	337	444
Other Assets	785	689
Assets	20,060	21,620
Liabilities and Equity [Abstract]
Long-term Debt	11,710	10,197
Accounts Payable and Accrued Liabilities	12	9
Liabilities	$ 11,722	$ 10,206

Consolidated Balance Sheet and

Consolidated Balance Sheet and Mini Balance Sheet (Paranthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
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	491,993,371	489,883,553
Common Stock, Shares, Outstanding		437,053,936
Treasury Stock, Shares	59,302,489	52,829,617
Held-to-maturity Securities, Fair Value	$ 1,895	$ 1,865
End of Period [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Common Stock, Shares, Outstanding	432,690,882	437,054,000

Condensed Consolidated Stateme5

Condensed Consolidated Statement of Changes in Equity - USD ($) $ in Millions	Total	Common stock and paid-in capital [Member]	Retained Earnings [Member]	Accumulated other comprehensive (loss) income [Member]	Treasury stock [Member]
Dividends Payable, Amount Per Share	$ 0.08
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent, Total	$ 13,317	$ 21,166	$ (7,151)		$ (357)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(341)			$ (341)
Net Income (Loss) Attributable to Parent	214		214
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	21	21
Other Comprehensive Income (Loss), Net of Tax	20			20
Treasury Stock, Value, Acquired, Cost Method	(169)				(169)
Dividends, Common Stock, Cash	$ (38)		(38)
Dividends Payable, Amount Per Share	$ 0.08
Stockholders' Equity Attributable to Parent, Total	$ 13,365	21,187	(6,975)		(526)
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (321)			(321)
Dividends Payable, Amount Per Share	$ 0.12
Stockholders' Equity Attributable to Parent, Total	$ 13,494	21,245	(6,406)		(1,110)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(235)			(235)
Net Income (Loss) Attributable to Parent	250		250
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	28	28
Other Comprehensive Income (Loss), Net of Tax	(328)			(328)
Treasury Stock, Value, Acquired, Cost Method	(185)				(185)
Dividends, Common Stock, Cash	$ (58)		(58)
Dividends Payable, Amount Per Share	$ 0.13
Stockholders' Equity Attributable to Parent, Total	$ 13,082	$ 21,273	$ (6,318)		$ (1,295)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(578)			$ (578)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2014-09 [Member]	(126)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01 [Member]	(20)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02 [Member]	$ 42

Condensed Consolidated Stateme6

Condensed Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income (Loss) Attributable to Parent	$ 250	$ 214
Depreciation, Amortization and Accretion, Net	434	534
Provision for Loan Losses Expensed Including Discontinued Operations	261	271
Gain Loss on Sales of Loans Net Including Discontinued Operations	(1)	(14)
Availableforsale Securities Gross Realized Gain Loss Excluding Otti Including Disc Ops	12	(27)
Payments for Origination and Purchases of Loans Held-for-sale	(248)	(21)
Proceeds from Sale of Loans Held-for-sale	230	20
Increase (Decrease) in Deferred Income Taxes	83	91
Increase (Decrease) in Interest Payable, Net	120	31
Increase (Decrease) in Other Operating Assets	29	60
Increase (Decrease) in Other Operating Liabilities	(106)	(20)
Increase (Decrease) in Other Operating Assets and Liabilities, Net	33	36
Net Cash Provided by (Used in) Operating Activities	1,097	1,175
Net Cash (Used in) Provided by Investing Activities [Abstract]
Purchases of Equity Securities	(374)	(137)
Proceeds from Sales of Equity Securities	220	314
Payments to Acquire Available-for-sale Securities	(2,360)	(2,696)
Proceeds from Sale of Available-for-sale Securities	328	731
Proceeds from maturities and repayment of available-for-sale securities	795	589
Payments to Acquire Held-to-maturity Securities	(155)	(215)
Proceeds from Sale and Maturity of Held-to-maturity Securities	35	5
Payments for (Proceeds from) Loans and Leases	(1,497)	(405)
Proceeds from Sale of Loans Held-for-investment	0	1,164
Originations and repayments of loans held-for-investment and other	(1,300)	(1,174)
Purchases of operating lease assets	(969)	(893)
Disposals of Operating Lease Assets	976	1,545
Increase (Decrease) in Non marketable equity securities	(19)	213
Payments for (Proceeds from) Other Investing Activities	(82)	(56)
Net cash provided by investing activities	(4,402)	(1,015)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Proceeds from (Repayments of) Short-term Debt	(1,848)	(4,303)
Increase (Decrease) in Deposits	4,173	5,451
Proceeds from Issuance of Long-term Debt	6,665	4,488
Repayments of long-term debt	(5,771)	(7,573)
Payments for Repurchase of Common Stock	(185)	(169)
Payments of Dividends	(58)	(38)
Net cash (used in) provided by financing activities	2,976	(2,144)
Effect of Exchange Rate on Cash and Cash Equivalents	(2)	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(331)	(1,984)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	4,938	5,897
Cash and Cash Equivalents, at Carrying Value	3,721	4,302
Restricted Cash	1,217	1,595
Supplemental Cash Flow Information [Abstract]
Interest Paid	667	648
Income Taxes Paid	5	2
Held-to-maturity securities received in consideration for loans sold	0	56
Transfer of Portfolio Loans and Leases to Held-for-sale	0	1,213
Proceeds from sales and repayments of mortgage loans held-for-investment originally designated as held-for-sale	$ 11	$ 8

Description of Business, Basis

Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
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 Changes in 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. 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. 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. The Condensed Consolidated Financial Statements at March 31, 2018 , and for the three months ended March 31, 2018 , and 2017 , are unaudited but reflect all adjustments that are, in management’s opinion, necessary for the fair presentation of the results for the interim periods presented. All such adjustments are of a normal recurring nature. These unaudited Condensed Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements (and the related Notes) included in our Annual Report on Form 10-K for the year ended December 31, 2017 , as filed on February 21, 2018, with the U.S. Securities and Exchange Commission (SEC). Significant Accounting Policies Investments Our investment portfolio includes various debt and equity securities. Our debt securities include government securities, corporate bonds, asset-backed securities (ABS), and mortgage-backed securities (MBS). Debt 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 securities as trading when the securities are acquired for the purpose of selling or holding them for a short period of time. Debt securities not classified as either held-to-maturity or trading are classified as available-for-sale. Our portfolio includes debt securities classified as available-for-sale and held-to-maturity. Our available-for-sale debt securities are carried at fair value with unrealized gains and losses included in accumulated other comprehensive loss and are subject to impairment. Our held-to-maturity debt securities are carried at amortized cost and are subject to impairment. We assess our debt 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 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 debt 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 Condensed Consolidated Statement of Comprehensive Income, and a new cost basis in the investment is established. The noncredit loss component of an available-for-sale debt security continues to be recorded in other comprehensive (loss) income 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. Subsequent increases and decreases to the fair value of available-for-sale debt securities are included in other comprehensive (loss) income, so long as they are not attributable to another other-than-temporary 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. Our investment in equity securities includes securities that are recognized at fair value with changes in the market value recorded in earnings, and equity securities that are recognized using other measurement principles. Effective January 1, 2018, equity securities that are publicly traded and have a readily determinable fair value, as well as certain investments that do not have a readily determinable fair value and are not eligible to be recognized using other measurement principles, are recorded at fair value with changes in fair value recorded in earnings and reported in other gain (loss) on investments, net in our Condensed Consolidated Statement of Comprehensive Income . These investments, which are primarily attributable to the investment portfolio of our Insurance operations, are included in equity securities on our Condensed Consolidated Balance Sheet . Refer to Note 6 for further information on our equity securities that have a readily determinable market value. Our equity securities recognized using other measurement principles include investments in Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock held to meet regulatory requirements, equity investments related to low income housing tax credits and the Community Reinvestment Act (CRA), which are not publicly traded and do not have a readily determinable fair value, and other equity investments that are not publicly traded and do not have a readily determinable fair value. 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 included in other liabilities. The majority of our CRA investments are accounted for using the equity method of accounting. Our investments in low income housing tax credits and CRA investments are included in other assets on our Condensed Consolidated Balance Sheet. Our investments in FHLB and FRB stock are carried at cost. Our remaining investments in equity securities are recorded at cost, less impairment and adjusted for observable price differences under the measurement alternative provided under GAAP. These investments, along with our investments in FHLB and FRB stock, are included in nonmarketable equity investments in other assets on our Condensed Consolidated Balance Sheet. As conditions warrant, we review these investments for impairment and adjust the carrying value of the investment if it is deemed to be impaired. Investments recorded under the measurement alternative are also reviewed at each reporting period to determine if any adjustments are required for observable price changes in identical or similar securities. Realized gains and losses on the sale of securities are determined using the specific identification method and are reported in other gain (loss) on investments, net in our Condensed Consolidated Statement of Comprehensive Income. Derivative Instruments and Hedging Activities 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 18 . 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 changes in fair value of the derivative financial instruments are recorded in accumulated other comprehensive loss 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 loss as part of the cumulative translation adjustment. 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 loss, 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 loss 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 Taxes In calculating the provision for interim income taxes, in accordance with Accounting Standards Codification (ASC) 740, Income Taxes , we apply an estimated annual effective tax rate to year-to-date ordinary income. At the end of each interim period, we estimate the effective tax rate expected to be applicable for the full fiscal year. This method differs from that described in Note 1 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K, which describes our annual significant income tax accounting policy and related methodology. Refer to Note 1 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K regarding additional significant accounting policies. 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 Condensed Consolidated Statement of Cash Flows and additional disclosures surrounding restricted cash balances, but did not result in a change to our Condensed Consolidated Statement of Comprehensive Income or Condensed Consolidated Balance Sheet. 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. 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 issued several additional ASUs to clarify guidance and provide implementation support for ASU 2014-09. The clarifying guidance elaborates on the key concepts within ASU 2014-09 and clarifies how those concepts interact with other GAAP requirements. On January 1, 2018, we adopted ASU 2014-09 and all subsequent ASUs that modified ASU 2014-09 (collectively, the amendments to the revenue recognition principles), which have been codified in ASC 606, Revenue from Contracts with Customers, and ASC 610-20, Gains and Losses from the Derecognition of Nonfinancial Assets , respectively. We elected to adopt this guidance using the modified retrospective approach applied to all contracts with customers that were not completed as of January 1, 2018. The adoption of the amendments resulted in a reduction to our opening retained earnings of approximately $126 million , net of income taxes. Refer to Note 2 for further details. Financial Instruments — Recognition and Measurement of Financial Assets (ASU 2016-01) As of January 1, 2018, we adopted 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. The FASB subsequently issued ASU 2018-03 to clarify guidance and provide implementation support for ASU 2016-01, which we elected to early-adopt as of January 1, 2018, to align with the adoption of ASU 2016-01. 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 are no longer recognized through other comprehensive (loss) income , which creates additional volatility in our Condensed Consolidated Statement of 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 (loss) income and not as a component of net income. We adopted these amendments, as required, on a modified retrospective basis with a cumulative effect adjustment as of the beginning of the fiscal year of initial adoption. The adoption of the amendments resulted in a reduction to our opening retained earnings of approximately $20 million , net of income taxes. Derivatives and Hedging — Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12) As of January 1, 2018, we elected to early-adopt ASU 2017-12. The amendments in this update enhance the financial reporting of hedging relationships to better align hedge accounting with an entity’s risk management activities. This update also makes certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP and better portrays economic results through changes to both the designation and measurement guidance for qualifying hedging relationships and presentation of hedge results. We adopted the amendments to all cash flow and net investment hedge relationships that existed on the date of adoption using a modified retrospective approach. No cumulative effect adjustment to our opening retained earnings was required as a result of the adoption. The presentation and disclosure requirements included in this update were adopted prospectively. Refer to Note 18 for further details. 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 the impact of income tax effects resulting from the Tax Cuts and Jobs Act of 2017 (the Tax Act) on items included in accumulated other comprehensive income. Our policy is to use the portfolio method with respect to reclassification of stranded income tax effects in accumulated other comprehensive loss. The amendments in ASU 2018-02 provide entities an election to reclassify the income tax effect of the Tax Act from accumulated other comprehensive income to retained earnings. We elected to early-adopt this standard as of January 1, 2018, and reclassified the effect of the change in the federal corporate income tax rate on items included in accumulated other comprehensive loss. This election resulted in a reclassification of $42 million from accumulated other comprehensive loss to retained earnings. Recently Issued Accounting Standards 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. 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). While 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, as well as reviewing our leases where we are the lessor to determine the impact of the changes to capitalizable costs, we do not anticipate the adoption of these amendments will 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. 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.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue from Contracts with Customers On January 1, 2018, we adopted the amendments to the revenue recognition principles using the modified retrospective approach applied to contracts with customers outstanding as of the date of adoption. Results for reporting periods beginning after January 1, 2018, are presented in accordance with the amendments to the revenue recognition principles, while prior period amounts have not been adjusted and continue to be presented in accordance with the accounting standards in effect for those periods. Refer to Note 1 for additional information. Our primary revenue sources, which include financing revenue and other interest income, are addressed by other GAAP and are not in the scope of the amendments to the revenue recognition principles. As part of our Insurance operations, we recognize revenue from insurance contracts, which are addressed by other GAAP and are not included in the scope of the amendments to the revenue recognition principles. Certain noninsurance contracts within our Insurance operations, including vehicle service contracts (VSCs), guaranteed asset protection (GAP) contracts, and vehicle maintenance contracts (VMCs), are included in the scope of the amendments to the revenue recognition principles. Under the previous guidance, a portion of revenue earned on noninsurance contracts was recognized at contract inception, while the remainder was recognized over the contract term on a basis proportionate to the anticipated cost emergence. In addition, dealer and sales commissions incurred to obtain a noninsurance contract were recognized as expense when incurred, and certain direct-response advertising costs were deferred and recognized as expense over the term of the contract. Upon adoption of the amendments to the revenue recognition principles, all revenue associated with noninsurance contracts is recognized over the contract term on a basis proportionate to the anticipated cost emergence. Further, commissions and sales expense incurred to obtain these contracts are capitalized and recognized as expense over the contract term, and all advertising costs are recognized as expense when incurred. The following table presents the impact to our Condensed Consolidated Balance Sheet as of January 1, 2018, as a result of adopting the amendments to the revenue recognition principles. ($ in millions) As reported, December 31, 2017 Adjustment related to adoption As adjusted, January 1, 2018 Assets Premiums receivable and other insurance assets $ 2,047 $ 122 $ 2,169 Other assets 5,663 41 5,704 Total assets $ 167,148 $ 163 $ 167,311 Liabilities Unearned insurance premiums and service revenue $ 2,604 $ 289 $ 2,893 Total liabilities 153,654 289 153,943 Equity Accumulated deficit (6,406 ) (126 ) (6,532 ) Total equity 13,494 (126 ) 13,368 Total liabilities and equity $ 167,148 $ 163 $ 167,311 The following tables present the impact of adopting the amendments to the revenue recognition principles to our Condensed Consolidated Statement of Comprehensive Income and Condensed Consolidated Balance Sheet . Three months ended March 31, 2018 ($ in millions) As reported Effect of adoption Other revenue Insurance premiums and service revenue earned $ 256 $ (6 ) Total other revenue 354 (6 ) Total net revenue 1,403 (6 ) Noninterest expense Compensation and benefits expense 306 (1 ) Other operating expenses 445 (2 ) Total noninterest expense 814 (3 ) Income from continuing operations before income tax expense 328 (3 ) Income tax expense from continuing operations 76 (1 ) Net income from continuing operations 252 (2 ) Net income 250 (2 ) Comprehensive loss $ (78 ) $ (2 ) March 31, 2018 ($ in millions) As reported Effect of adoption Assets Premiums receivable and other insurance assets $ 2,197 $ 125 Other assets 6,025 42 Total assets 170,021 167 Liabilities Unearned insurance premiums and service revenue $ 2,904 $ 295 Total liabilities 156,939 295 Equity Accumulated deficit (6,318 ) (128 ) Total equity 13,082 (128 ) Total liabilities and equity $ 170,021 $ 167 The following is a description of our primary revenue sources that are derived from contracts with customers. As a result of the adoption of the amendments to the revenue recognition principles, our only revenue source for which the recognition pattern was affected was that of noninsurance contracts, as described in this note. Revenue from contracts with customers is recognized when control of the promised goods or services is transferred to our customers, and in an amount that reflects the consideration that we expect to receive in exchange for those goods or services. For information regarding our revenue recognition policies outside the scope of the amendments to the revenue recognition principles of ASC 606, Revenue from Contracts with Customers , refer to Note 1 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K. • Noninsurance contracts — We sell VSCs that offer owners mechanical repair protection and roadside assistance for new and used vehicles beyond the manufacturer’s new vehicle limited warranty. We sell GAP contracts that protect the customer against having to pay certain amounts to a lender above the fair market value of their vehicle if the vehicle is damaged and declared a total loss or stolen. We also sell VMCs that provide coverage for certain agreed-upon services, such as oil changes and tire rotations, over the coverage period. We receive payment in full at the inception of each of these contracts. Our performance obligation for these contracts is satisfied over the term of the contract and we recognize revenue over the contract term on a basis proportionate to the anticipated cost emergence, as we believe this is the most appropriate method to measure progress towards satisfaction of the performance obligation. Upon adoption of the amendments to the revenue recognition principles, unearned revenue of $289 million was recognized as a component of unearned insurance premiums and service revenue on our Condensed Consolidated Balance Sheet associated with outstanding contracts at January 1, 2018, and $22 million of this balance was recognized as insurance premiums and service revenue earned in our Condensed Consolidated Statement of Comprehensive Income during the three months ended March 31, 2018 . At March 31, 2018 , we had unearned revenue of $2.5 billion associated with outstanding contracts, and with respect to this balance we expect to recognize revenue of $568 million during the remainder of 2018 , $643 million in 2019 , $528 million in 2020 , $378 million in 2021 , and $389 million thereafter. The incremental costs to obtain these contracts are initially deferred and recorded as a component of premiums receivable and other insurance assets on our Condensed Consolidated Balance Sheet . These deferred costs are amortized as an expense over the term of the related contract commensurate with how the related revenue is recognized, and are included in compensation and benefits and other operating expenses in our Condensed Consolidated Statement of Comprehensive Income . We had deferred insurance assets of $1.4 billion at March 31, 2018 , and recognized $103 million of expense during the three months ended March 31, 2018 . • Sale of off-lease vehicles — When a customer’s vehicle lease matures, the customer has the option of purchasing or returning the vehicle. If the vehicle is returned to us, we obtain possession with the intent to sell through SmartAuction—our online auction platform, our dealer channel, or through various other physical auctions. Our performance obligation is satisfied and the remarketing gain or loss is recognized when control of the vehicle has passed to the buyer, which coincides with the sale date. Our actual sales proceeds from remarketing the vehicle may be higher or lower than the estimated residual value resulting in a gain or loss on remarketing recorded through depreciation expense on operating lease assets in our Condensed Consolidated Statement of Comprehensive Income . • Remarketing fee income — In addition to using SmartAuction as a remarketing channel for our returned lease vehicles, we maintain the internet auction site and administer the auction process for third-party use. We earn a service fee from dealers for every third-party vehicle sold through SmartAuction. Our performance obligation is to provide the online marketplace for used vehicle transactions to be consummated. This obligation is satisfied and revenue is recognized when control of the vehicle has passed to the buyer, which coincides with the sale date. This revenue is recorded as remarketing fees within other income in our Condensed Consolidated Statement of Comprehensive Income . • Brokerage commissions and other revenues through Ally Invest — We charge fees to customers related to their use of certain services on our Ally Invest digital wealth management and online brokerage platform. These fees include commissions on customer-directed trades, account service fees, account management fees on professional portfolio management services, subscriptions for market data feeds, and other ancillary fees. Commissions on customer-directed trades and account service fees are based on published fee schedules and are generated from a customer option to purchase the services offered under the contract. These options do not represent a material right and are only considered a contract when the customer executes their option to purchase these services. Based on this, the term of the contract does not extend beyond services provided, and as such revenue is recognized upon the completion of our performance obligation, which we view as the successful execution of the trade or service. Revenue on professional portfolio management services is calculated monthly based upon a fixed percentage of the client’s assets under management. Due to the fact that this revenue stream is composed of variable consideration that is based on factors outside of our control, we have deemed this revenue as constrained and we are unable to estimate the initial transaction price at the inception of the contract. We have elected to use the practical expedient under GAAP to recognize revenue monthly based on the amount we are able to invoice the customer. Subscriptions for market data feeds are based on published fee schedules, and our performance obligation for these contracts is satisfied over the term of the contract, which does not exceed 12 months. We receive payment in full at contract inception and recognize revenue over the related contract term on a straight-line basis, as we believe this is the most appropriate method to measure progress towards satisfaction of the performance obligation. We also earn revenue from a fee-sharing agreement with our clearing broker related to the interest income the clearing broker earns on customer cash balances and margin loans made to our customers. Ally concluded the initial transaction price is exclusively variable consideration and, based on the nature of our performance obligation to allow the clearing broker to collect interest income from cash deposits and customer loans from our customers, we are unable to determine the amount of revenue to be recognized until the total customer cash balance or the total interest income recognized on margin loans has been determined, which occurs monthly. These revenue streams are recorded as other income in our Condensed Consolidated Statement of Comprehensive Income . • Brokered/agent commissions through Insurance operations — We have agreements with third parties to offer various vehicle protection products to consumers. We also have agreements with third-party insurers to offer various insurance coverages to dealers. Our performance obligation for these arrangements is satisfied when a customer or dealer has purchased a vehicle protection product or an insurance policy through the third-party provider. In determining the initial transaction price for these agreements, we noted that revenue on brokered/agent commissions is based on the volume of vehicle protection product contracts sold or a percentage of insurance premium written, which is not known to Ally at the inception of the agreements with these third-party providers. As such, we believe the initial transaction price is exclusively variable consideration and, based on the nature of the performance obligation, we are unable to determine the amount of revenue we will record until the customer purchases a vehicle protection product or a dealer purchases an insurance policy from the third-party provider. Once Ally is notified of vehicle protection product sales or insurance policies issued by the third-party providers, we record the commission earned as insurance premiums and service revenues earned in our Condensed Consolidated Statement of Comprehensive Income . • Deposit account and other banking fees — We charge depositors various account service fees including those for outgoing wires, excessive transactions, overdrafts, stop payments, and returned deposits. These fees are generated from a customer option to purchase services offered under the contract. These options do not represent a material right and are only considered a contract in accordance with the amendments to the revenue recognition principles when the customer exercises their option to purchase these account services. Based on this, the term for our contracts with customers is considered day-to-day, and the contract does not extend beyond the services already provided. Revenue derived from deposit account fees is recorded at the point in time we perform the requested service, and is recorded as other income in our Condensed Consolidated Statement of Comprehensive Income . As a debit card issuer, we also generate interchange fee income from merchants during debit card transactions and incur certain corresponding charges from merchant card networks. Our performance obligation is satisfied when we have initiated the payment of funds from a customer’s account to a merchant through our contractual agreements with the merchant card networks. Interchange fees are reported on a net basis as other income in our Condensed Consolidated Statement of Comprehensive Income , and reflect interchange fee income of $3 million and interchange expenses of $3 million for the three months ended March 31, 2018 . • Other revenue — Other revenue primarily includes service revenue related to various account management functions, fee income derived from third-party loans arranged through Clearlane—our online automotive lender exchange, and revenue associated with licensing and marketing from the Ally CashBack Credit Card—our co-branded credit card. These revenue streams are recorded as other income in our Condensed Consolidated Statement of Comprehensive Income . The following table presents a disaggregated view of our revenue from contracts with customers included in other revenue that falls within the scope of the amendments to the revenue recognition principles. Three months ended March 31, 2018 ($ in millions) Automotive Finance operations Insurance operations Mortgage Finance operations Corporate Finance operations Corporate and Other Consolidated Revenue from contracts with customers Noninsurance contracts $ — $ 123 $ — $ — $ — $ 123 Remarketing fee income 23 — — — — 23 Brokerage commissions and other revenue — — — — 16 16 Brokered/agent commissions — 4 — — — 4 Deposit account and other banking fees — — — — 3 3 Other 2 1 — — — 3 Total revenue from contracts with customers 25 128 — — 19 172 All other revenue 41 118 1 8 14 182 Total other revenue (a) $ 66 $ 246 $ 1 $ 8 $ 33 $ 354 (a) Represents a component of total net revenue. Refer to Note 22 for further information on our reportable operating segments. In addition to the components of other revenue presented above, as part of our Automotive Finance operations, we recognized $18 million of gain on the sale of off-lease vehicles through depreciation expense on operating lease assets in our Condensed Consolidated Statement of Comprehensive Income during the three months ended March 31, 2018 .

Other Income, Net of Losses

Other Income, Net of Losses	3 Months Ended
	Mar. 31, 2018
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. Three months ended March 31, ($ in millions) 2018 2017 Late charges and other administrative fees $ 29 $ 27 Remarketing fees 23 29 Servicing fees 8 16 Income from equity-method investments 6 — Other, net 43 42 Total other income, net of losses $ 109 $ 114

Reserves for Insurance Losses a

Reserves for Insurance Losses and Loss Adjustment Expenses	3 Months Ended
	Mar. 31, 2018
Reserves for Insurance Losses and Loss Adjustment Expense [Abstract]
Reserves for Insurance Losses and Loss Adjustment Expenses [Text Block]	Reserves for Insurance Losses and Loss Adjustment Expenses The following table shows a rollforward of our reserves for insurance losses and loss adjustment expenses. ($ in millions) 2018 2017 Total gross reserves for insurance losses and loss adjustment expenses at January 1, $ 140 $ 149 Less: Reinsurance recoverable 108 108 Net reserves for insurance losses and loss adjustment expenses at January 1, 32 41 Net insurance losses and loss adjustment expenses incurred related to: Current year 60 89 Prior years (a) 3 (1 ) Total net insurance losses and loss adjustment expenses incurred 63 88 Net insurance losses and loss adjustment expenses paid or payable related to: Current year (31 ) (45 ) Prior years (19 ) (23 ) Total net insurance losses and loss adjustment expenses paid or payable (50 ) (68 ) Foreign exchange and other — 2 Net reserves for insurance losses and loss adjustment expenses at March 31, 45 63 Plus: Reinsurance recoverable 112 112 Total gross reserves for insurance losses and loss adjustment expenses at March 31, $ 157 $ 175 (a) There have been no material adverse changes to the reserve for prior years.

Other Operating Expenses

Other Operating Expenses	3 Months Ended
	Mar. 31, 2018
Operating Expenses [Abstract]
Other Operating Income and Expense [Text Block]	Other Operating Expenses Details of other operating expenses were as follows. Three months ended March 31, ($ in millions) 2018 2017 Insurance commissions $ 110 $ 99 Technology and communications 71 69 Lease and loan administration 42 36 Advertising and marketing 39 30 Vehicle remarketing and repossession 32 28 Professional services 32 26 Regulatory and licensing fees 30 27 Premises and equipment depreciation 20 22 Occupancy 11 12 Non-income taxes 8 8 Amortization of intangible assets 3 3 Other 47 45 Total other operating expenses $ 445 $ 405

Investment Securities

Investment Securities	3 Months Ended
	Mar. 31, 2018
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 available-for-sale and held-to-maturity investment securities were as follows. March 31, 2018 December 31, 2017 Amortized cost Gross unrealized Fair value Amortized cost Gross unrealized Fair value ($ in millions) gains losses gains losses Available-for-sale securities Debt securities U.S. Treasury $ 1,855 $ — $ (86 ) $ 1,769 $ 1,831 $ — $ (54 ) $ 1,777 U.S. States and political subdivisions 845 5 (19 ) 831 850 11 (7 ) 854 Foreign government 150 1 (2 ) 149 153 2 (1 ) 154 Agency mortgage-backed residential 15,316 4 (437 ) 14,883 14,412 35 (156 ) 14,291 Mortgage-backed residential 2,456 3 (75 ) 2,384 2,517 11 (34 ) 2,494 Mortgage-backed commercial 582 1 (3 ) 580 541 1 (1 ) 541 Asset-backed 901 2 (3 ) 900 933 4 (1 ) 936 Corporate debt 1,263 1 (34 ) 1,230 1,262 5 (11 ) 1,256 Total available-for-sale securities (a) (b) (c) $ 23,368 $ 17 $ (659 ) 22,726 $ 22,499 $ 69 $ (265 ) $ 22,303 Held-to-maturity securities Debt securities Agency mortgage-backed residential (d) $ 1,936 $ — $ (72 ) $ 1,864 $ 1,863 $ 3 $ (37 ) $ 1,829 Asset-backed retained notes 31 — — 31 36 — — 36 Total held-to-maturity securities $ 1,967 $ — $ (72 ) $ 1,895 $ 1,899 $ 3 $ (37 ) $ 1,865 (a) Certain entities related to our Insurance operations are required to deposit securities with state regulatory authorities. These deposited securities totaled $12 million at both March 31, 2018 , and December 31, 2017. (b) Certain available-for-sale securities are included in fair value hedging relationships. Refer to Note 18 for additional information. (c) Investment securities with a fair value of $8.0 billion and $7.8 billion at March 31, 2018 , and December 31, 2017, 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 $839 million and $1.0 billion of the underlying investment securities at March 31, 2018 , and December 31, 2017, respectively. (d) Securities with a fair value of $993 million and $664 million at March 31, 2018 , and December 31, 2017, respectively, were pledged to secure advances from the FHLB. The maturity distribution of debt securities outstanding is summarized in the following tables. Call or prepayment options may cause actual maturities to differ from contractual maturities. Total Due in one year or less Due after one year through five years Due after five years through ten years Due after ten years ($ in millions) Amount Yield Amount Yield Amount Yield Amount Yield Amount Yield March 31, 2018 Fair value of available-for-sale securities (a) U.S. Treasury $ 1,769 1.8 % $ — — % $ 481 1.7 % $ 1,288 1.8 % $ — — % U.S. States and political subdivisions 831 3.0 70 2.3 42 2.3 219 2.6 500 3.3 Foreign government 149 2.5 — — 77 2.6 72 2.4 — — Agency mortgage-backed residential 14,883 3.2 — — — — 3 2.6 14,880 3.2 Mortgage-backed residential 2,384 3.1 — — — — — — 2,384 3.1 Mortgage-backed commercial 580 3.4 — — — — 31 3.3 549 3.4 Asset-backed 900 3.2 — — 655 3.2 121 3.3 124 2.9 Corporate debt 1,230 3.0 123 2.8 496 2.7 573 3.3 38 4.8 Total available-for-sale securities $ 22,726 3.0 $ 193 2.6 $ 1,751 2.6 $ 2,307 2.3 $ 18,475 3.2 Amortized cost of available-for-sale securities $ 23,368 $ 194 $ 1,776 $ 2,403 $ 18,995 Amortized cost of held-to-maturity securities Agency mortgage-backed residential $ 1,936 3.1 % $ — — % $ — — % $ — — % $ 1,936 3.1 % Asset-backed retained notes 31 1.7 — — 30 1.7 1 3.0 — — Total held-to-maturity securities $ 1,967 3.1 $ — — $ 30 1.7 $ 1 3.0 $ 1,936 3.1 December 31, 2017 Fair value of available-for-sale 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 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 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 (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. The balances of cash equivalents were $18 million and $10 million at March 31, 2018 , and December 31, 2017 , respectively, and were composed primarily of money market accounts and short-term securities, including U.S. Treasury bills. The following table presents interest and dividends on investment securities. Three months ended March 31, ($ in millions) 2018 2017 Taxable interest $ 154 $ 119 Taxable dividends 3 2 Interest and dividends exempt from U.S. federal income tax 6 5 Interest and dividends on investment securities $ 163 $ 126 The following table presents gross gains and losses realized upon the sales of available-for-sale securities, and net gains or losses on equity securities held during the period. There were no other-than-temporary impairments of available-for-sale securities for either period. Three months ended March 31, ($ in millions) 2018 2017 Available-for-sale securities Gross realized gains $ 6 $ 27 Gross realized losses — — Net realized gains on available-for-sale securities 6 27 Net realized gain on equity securities 22 Net unrealized loss on equity securities (a) (40 ) Other (loss) gain on investments, net $ (12 ) $ 27 (a) As a result of our adoption of ASU 2016-01, beginning January 1, 2018, changes in the fair value of our portfolio of equity securities are recognized in net income. Prior to adoption, equity securities were included in our available-for-sale portfolio and unrealized changes in fair value were recognized through other comprehensive (loss) income until realized, at which point we recorded a gain or loss on sale. We adopted ASU 2016-01 on January 1, 2018, on a modified retrospective basis with a cumulative effect adjustment as of the beginning of the fiscal year of initial adoption. Refer to the section titled Recently Adopted Accounting Standards in Note 1 for additional information. The table below summarizes available-for-sale and held-to-maturity securities in an unrealized loss position, which we evaluated for other than temporary impairment applying the methodology described in Note 1 . As of March 31, 2018 , we did not have the intent to sell the available-for-sale or held-to-maturity securities with an unrealized loss position and we do not believe it is more likely than not that we will be required to sell these securities before recovery of their amortized cost basis. As a result of this evaluation, we believe that the securities with an unrealized loss position are not considered to be other-than-temporarily impaired at March 31, 2018 . March 31, 2018 December 31, 2017 Less than 12 months 12 months or longer Less than 12 months 12 months or longer ($ 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 $ 488 $ (16 ) $ 1,282 $ (70 ) $ 471 $ (8 ) $ 1,305 $ (46 ) U.S. States and political subdivisions 436 (9 ) 176 (10 ) 242 (2 ) 183 (5 ) Foreign government 82 (2 ) 4 — 80 (1 ) 4 — Agency mortgage-backed residential 8,951 (183 ) 5,395 (254 ) 4,066 (19 ) 5,671 (137 ) Mortgage-backed residential 1,439 (29 ) 734 (46 ) 857 (2 ) 773 (32 ) Mortgage-backed commercial 71 (2 ) 21 (1 ) 76 (1 ) 21 — Asset-backed 426 (2 ) 76 (1 ) 220 (1 ) 91 — Corporate debt 932 (20 ) 191 (14 ) 529 (4 ) 194 (7 ) Total temporarily impaired available-for-sale securities $ 12,825 $ (263 ) $ 7,879 $ (396 ) $ 6,541 $ (38 ) $ 8,242 $ (227 ) Held-to-maturity securities Agency mortgage-backed residential $ 1,147 $ (26 ) $ 672 $ (46 ) $ 773 $ (5 ) $ 687 $ (32 ) Asset-backed retained certificates 31 — — — 35 — — — Total held-to-maturity debt securities $ 1,178 $ (26 ) $ 672 $ (46 ) $ 808 $ (5 ) $ 687 $ (32 )

Finance Receivables and Loans,

Finance Receivables and Loans, Net	3 Months Ended
	Mar. 31, 2018
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. ($ in millions) March 31, 2018 December 31, 2017 Consumer automotive (a) $ 69,318 $ 68,071 Consumer mortgage Mortgage Finance (b) 12,733 11,657 Mortgage — Legacy (c) 1,950 2,093 Total consumer mortgage 14,683 13,750 Total consumer 84,001 81,821 Commercial Commercial and industrial Automotive 32,781 33,025 Other 4,184 3,887 Commercial real estate 4,361 4,160 Total commercial 41,326 41,072 Total finance receivables and loans (d) $ 125,327 $ 122,893 (a) Certain finance receivables and loans are included in fair value hedging relationships. Refer to Note 18 for additional information. (b) Includes loans originated as interest-only mortgage loans of $19 million and $20 million at March 31, 2018 , and December 31, 2017 , respectively, 34% of which are expected to start principal amortization in 2019 , and 46% in 2020 . The remainder of these loans have already exited the interest-only period. (c) Includes loans originated as interest-only mortgage loans of $459 million and $496 million at March 31, 2018 , and December 31, 2017 , respectively, 2% 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 unearned income, unamortized premiums and discounts, and deferred fees and costs of $586 million and $551 million at March 31, 2018 , and December 31, 2017 , respectively. The following tables present an analysis of the activity in the allowance for loan losses on finance receivables and loans. Three months ended March 31, 2018 ($ in millions) Consumer automotive Consumer mortgage Commercial Total Allowance at January 1, 2018 $ 1,066 $ 79 $ 131 $ 1,276 Charge-offs (a) (365 ) (12 ) — (377 ) Recoveries 112 6 — 118 Net charge-offs (253 ) (6 ) — (259 ) Provision for loan losses 253 1 7 261 Allowance at March 31, 2018 $ 1,066 $ 74 $ 138 $ 1,278 Allowance for loan losses at March 31, 2018 Individually evaluated for impairment $ 40 $ 27 $ 21 $ 88 Collectively evaluated for impairment 1,026 47 117 1,190 Finance receivables and loans at gross carrying value Ending balance $ 69,318 $ 14,683 $ 41,326 $ 125,327 Individually evaluated for impairment 463 230 147 840 Collectively evaluated for impairment 68,855 14,453 41,179 124,487 (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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for more information regarding our charge-off policies. Three months ended March 31, 2017 ($ in millions) Consumer automotive Consumer mortgage Commercial Total Allowance at January 1, 2017 $ 932 $ 91 $ 121 $ 1,144 Charge-offs (a) (341 ) (9 ) — (350 ) Recoveries 90 7 — 97 Net charge-offs (251 ) (2 ) — (253 ) Provision for loan losses 267 (3 ) 7 271 Other (b) (7 ) — — (7 ) Allowance at March 31, 2017 $ 941 $ 86 $ 128 $ 1,155 Allowance for loan losses at March 31, 2017 Individually evaluated for impairment $ 32 $ 33 $ 24 $ 89 Collectively evaluated for impairment 909 53 104 1,066 Finance receivables and loans at gross carrying value Ending balance $ 65,663 $ 10,937 $ 42,402 $ 119,002 Individually evaluated for impairment 388 249 120 757 Collectively evaluated for impairment 65,275 10,688 42,282 118,245 (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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K 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 based on net carrying value. Three months ended March 31, ($ in millions) 2018 2017 Consumer automotive $ — $ 1,213 Consumer mortgage 1 3 Total sales and transfers $ 1 $ 1,216 The following table presents information about significant purchases of finance receivables and loans based on unpaid principal balance at the time of purchase. Three months ended March 31, ($ in millions) 2018 2017 Consumer automotive $ 168 $ 68 Consumer mortgage 1,295 327 Total purchases of finance receivables and loans $ 1,463 $ 395 The following table presents an analysis of our past due finance receivables and loans recorded at gross carrying value. ($ 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 March 31, 2018 Consumer automotive $ 1,574 $ 359 $ 253 $ 2,186 $ 67,132 $ 69,318 Consumer mortgage Mortgage Finance 97 8 18 123 12,610 12,733 Mortgage — Legacy 40 19 61 120 1,830 1,950 Total consumer mortgage 137 27 79 243 14,440 14,683 Total consumer 1,711 386 332 2,429 81,572 84,001 Commercial Commercial and industrial Automotive 23 6 4 33 32,748 32,781 Other — 30 — 30 4,154 4,184 Commercial real estate 4 — — 4 4,357 4,361 Total commercial 27 36 4 67 41,259 41,326 Total consumer and commercial $ 1,738 $ 422 $ 336 $ 2,496 $ 122,831 $ 125,327 December 31, 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 The following table presents the gross carrying value of our finance receivables and loans on nonaccrual status. ($ in millions) March 31, 2018 December 31, 2017 Consumer automotive $ 601 $ 603 Consumer mortgage Mortgage Finance 28 25 Mortgage — Legacy 87 92 Total consumer mortgage 115 117 Total consumer 716 720 Commercial Commercial and industrial Automotive 68 27 Other 74 44 Commercial real estate 5 1 Total commercial 147 72 Total consumer and commercial finance receivables and loans $ 863 $ 792 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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for additional information. March 31, 2018 December 31, 2017 ($ in millions) Performing Nonperforming Total Performing Nonperforming Total Consumer automotive $ 68,717 $ 601 $ 69,318 $ 67,468 $ 603 $ 68,071 Consumer mortgage Mortgage Finance 12,705 28 12,733 11,632 25 11,657 Mortgage — Legacy 1,863 87 1,950 2,001 92 2,093 Total consumer mortgage 14,568 115 14,683 13,633 117 13,750 Total consumer $ 83,285 $ 716 $ 84,001 $ 81,101 $ 720 $ 81,821 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. March 31, 2018 December 31, 2017 ($ in millions) Pass Criticized (a) Total Pass Criticized (a) Total Commercial and industrial Automotive $ 30,433 $ 2,348 $ 32,781 $ 30,982 $ 2,043 $ 33,025 Other 3,284 900 4,184 2,986 901 3,887 Commercial real estate 4,151 210 4,361 4,023 137 4,160 Total commercial $ 37,868 $ 3,458 $ 41,326 $ 37,991 $ 3,081 $ 41,072 (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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K. The following table presents information about our impaired finance receivables and loans. ($ in millions) Unpaid principal balance (a) Gross carrying value Impaired with no allowance Impaired with an allowance Allowance for impaired loans March 31, 2018 Consumer automotive $ 473 $ 463 $ 107 $ 356 $ 40 Consumer mortgage Mortgage Finance 9 9 4 5 — Mortgage — Legacy 226 221 61 160 27 Total consumer mortgage 235 230 65 165 27 Total consumer 708 693 172 521 67 Commercial Commercial and industrial Automotive 68 68 15 53 9 Other 85 74 41 33 11 Commercial real estate 5 5 4 1 1 Total commercial 158 147 60 87 21 Total consumer and commercial finance receivables and loans $ 866 $ 840 $ 232 $ 608 $ 88 December 31, 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 (a) Adjusted for charge-offs. The following table presents average balance and interest income for our impaired finance receivables and loans. 2018 2017 Three months ended March 31, ($ in millions) Average balance Interest income Average balance Interest income Consumer automotive $ 444 $ 7 $ 379 $ 5 Consumer mortgage Mortgage Finance 9 — 8 — Mortgage — Legacy 221 2 241 2 Total consumer mortgage 230 2 249 2 Total consumer 674 9 628 7 Commercial Commercial and industrial Automotive 47 1 33 — Other 52 — 83 — Commercial real estate 3 — 5 — Total commercial 102 1 121 — Total consumer and commercial finance receivables and loans $ 776 $ 10 $ 749 $ 7 Troubled Debt Restructurings 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 $742 million and $712 million at March 31, 2018 , and December 31, 2017 , respectively. Total commitments to lend additional funds to borrowers whose terms had been modified in a TDR were $6 million at both March 31, 2018 , and December 31, 2017 . Refer to Note 1 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for additional information. The following table presents information related to finance receivables and loans recorded at gross carrying value modified in connection with a TDR during the period. 2018 2017 Three months ended March 31, ($ 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 7,042 $ 128 $ 110 6,447 $ 115 $ 99 Consumer mortgage Mortgage Finance 1 1 1 1 — — Mortgage — Legacy 62 10 9 53 12 12 Total consumer mortgage 63 11 10 54 12 12 Total consumer 7,105 139 120 6,501 127 111 Commercial Commercial and industrial Other — — — 1 23 23 Total commercial — — — 1 23 23 Total consumer and commercial finance receivables and loans 7,105 $ 139 $ 120 6,502 $ 150 $ 134 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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for additional information) except for commercial finance receivables and loans, where redefault is defined as 90 days past due. 2018 2017 Three months ended March 31, ($ in millions) Number of loans Gross carrying value Charge-off amount Number of loans Gross carrying value Charge-off amount Consumer automotive 2,326 $ 28 $ 18 1,989 $ 24 $ 16 Consumer mortgage Mortgage Finance — — — 1 1 — Total consumer finance receivables and loans 2,326 $ 28 $ 18 1,990 $ 25 $ 16

Investment in Operating Leases,

Investment in Operating Leases, Net	3 Months Ended
	Mar. 31, 2018
Leases, Operating [Abstract]
Lessor, Operating Leases [Text Block]	Investment in Operating Leases, Net Investments in operating leases were as follows. ($ in millions) March 31, 2018 December 31, 2017 Vehicles $ 10,206 $ 10,556 Accumulated depreciation (1,676 ) (1,815 ) Investment in operating leases, net $ 8,530 $ 8,741 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. Three months ended March 31, ($ in millions) 2018 2017 Depreciation expense on operating lease assets (excluding remarketing gains and losses) $ 291 $ 386 Remarketing (gains) losses (18 ) 3 Net depreciation expense on operating lease assets $ 273 $ 389

Securitizations and Variable In

Securitizations and Variable Interest Entities	3 Months Ended
	Mar. 31, 2018
Securitizations And Variable Interest Entities [Abstract]
Variable Interest Entity Disclosure [Text Block]	Securitizations and Variable Interest Entities 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 Condensed 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. 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. We had no pretax gain on sales of financial assets into nonconsolidated VIEs for the three months ended March 31, 2018 , and a pretax gain of $2 million for the three months ended March 31, 2017. We provide long-term guarantee contracts to investors in certain nonconsolidated affordable housing entities and have extended a line of credit to provide liquidity. Since we do not have control over the entities or the power to make decisions, we do not consolidate the entities and our involvement is limited to the guarantee and the line of credit. We have involvement with various other nonconsolidated equity investments, including affordable housing entities and venture capital funds and loan funds. We do not consolidate these entities and our involvement is limited to our outstanding investment, additional capital committed to these funds plus any previously recognized low income housing tax credits that are subject to recapture. Refer to Note 11 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for further description of our securitization activities and our involvement with VIEs. The following table presents our involvement in consolidated and nonconsolidated VIEs in which we hold variable interests. For additional detail related to the assets and liabilities of consolidated variable interest entities refer to the Condensed Consolidated Balance Sheet. ($ 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 March 31, 2018 On-balance sheet variable interest entities Consumer automotive $ 17,993 (b) $ 8,232 (c) Commercial automotive 10,428 3,521 Off-balance sheet variable interest entities Consumer automotive 32 (d) — $ 1,658 $ 1,691 (e) Commercial other 702 (f) 331 (g) — 882 (h) Total $ 29,155 $ 12,084 $ 1,658 $ 2,573 December 31, 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 (a) Asset values represent the current unpaid principal balance of outstanding consumer finance receivables and loans within the VIEs. (b) Includes $8.4 billion and $8.5 billion of assets that are not encumbered by VIE beneficial interests held by third parties at March 31, 2018 , and December 31, 2017 , respectively. Ally or consolidated affiliates hold the interests in these assets. (c) Includes $31 million and $29 million of liabilities that are not obligations to third-party beneficial interest holders at March 31, 2018 , and December 31, 2017 , respectively. (d) Represents retained notes and certificated residual interests, of which $31 million and $36 million is classified as held-to-maturity securities at March 31, 2018 , and December 31, 2017 , respectively. $1 million is classified as other assets at both March 31, 2018 , and 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. (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. 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 three months ended March 31, 2018 , and 2017. Additionally, this table contains information regarding cash flows received from and paid to nonconsolidated securitization entities that existed during each period. Three months ended March 31, ($ in millions) Consumer automotive 2018 Cash disbursements for repurchases during the period $ (1 ) Servicing fees 5 Cash flows received on retained interests in securitization entities 5 2017 Cash proceeds from transfers completed during the period $ 1,138 Servicing fees 9 Other cash flows 2 Delinquencies and Net Credit Losses The following tables present quantitative information about delinquencies and net credit losses for off-balance sheet securitizations and whole-loan sales where we have continuing involvement. Total amount Amount 60 days or more past due ($ in millions) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Off-balance sheet securitization entities Consumer automotive $ 1,658 $ 1,964 $ 12 $ 16 Total off-balance sheet securitization entities 1,658 1,964 12 16 Whole-loan sales (a) 1,167 1,399 3 4 Total $ 2,825 $ 3,363 $ 15 $ 20 (a) Whole-loan sales are not part of a securitization transaction, but represent consumer automotive pools of loans sold to third-party investors. Net credit losses Three months ended March 31, ($ in millions) 2018 2017 Off-balance sheet securitization entities Consumer automotive $ 3 $ 3 Total off-balance sheet securitization entities 3 3 Whole-loan sales (a) 1 1 Total $ 4 $ 4 (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	3 Months Ended
	Mar. 31, 2018
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 $8 million and $16 million during the three months ended March 31, 2018 , and 2017, respectively. Automotive Finance Serviced Assets The current unpaid principal balance and any related unamortized deferred fees and costs of total serviced automotive finance loans and net investment in operating leases outstanding were as follows. ($ in millions) March 31, 2018 December 31, 2017 On-balance sheet automotive finance loans and leases Consumer automotive $ 68,738 $ 67,631 Commercial automotive 36,935 37,058 Operating leases 8,489 8,682 Other 131 121 Off-balance sheet automotive finance loans Securitizations 1,666 1,977 Whole-loan sales 1,175 1,409 Total serviced automotive finance loans and leases $ 117,134 $ 116,878

Other Assets

Other Assets	3 Months Ended
	Mar. 31, 2018
Other Assets [Abstract]
Other Assets Disclosure [Text Block]	Other Assets The components of other assets were as follows. ($ in millions) March 31, 2018 December 31, 2017 Property and equipment at cost $ 1,107 $ 1,064 Accumulated depreciation (627 ) (608 ) Net property and equipment 480 456 Nonmarketable equity investments (a) 1,250 1,233 Restricted cash collections for securitization trusts (b) 986 812 Accrued interest and rent receivables 533 550 Net deferred tax assets 530 461 Goodwill (c) 240 240 Other accounts receivable 142 116 Restricted cash and cash equivalents (d) 119 94 Cash reserve deposits held for securitization trusts (e) 112 111 Fair value of derivative contracts in receivable position (f) 56 39 Cash collateral placed with counterparties 33 29 Other assets 1,544 1,522 Total other assets $ 6,025 $ 5,663 (a) Includes investments in FHLB stock of $764 million and $745 million at March 31, 2018 , and December 31, 2017, respectively; FRB stock of $446 million and $445 million at March 31, 2018 , and December 31, 2017, respectively; and equity securities without a readily determinable fair value of $40 million at March 31, 2018 , measured at cost with adjustments for impairment and observable changes in price. We have not recorded any impairments or adjustments for observable price differences to these investments during the three months ended March 31, 2018 . (b) Represents cash collections from customer payments on securitized receivables. These funds are distributed to investors as payments on the related secured debt. (c) Includes goodwill of $27 million within our Insurance operations at both March 31, 2018 , and December 31, 2017 ; $193 million within Corporate and Other at both March 31, 2018 , and December 31, 2017 ; and $20 million within Automotive Finance operations at both March 31, 2018 , and December 31, 2017 . No changes to the carrying amount of goodwill were recorded during the three months ended March 31, 2018. (d) 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. (e) Represents credit enhancement in the form of cash reserves for various securitization transactions. (f) For additional information on derivative instruments and hedging activities, refer to Note 18 .

Deposit Liabilities

Deposit Liabilities	3 Months Ended
	Mar. 31, 2018
Deposits [Abstract]
Deposit Liabilities Disclosures [Text Block]	Deposit Liabilities Deposit liabilities consisted of the following. ($ in millions) March 31, 2018 December 31, 2017 Noninterest-bearing deposits $ 122 $ 108 Interest-bearing deposits Savings and money market checking accounts 50,293 49,267 Certificates of deposit 47,025 43,869 Dealer deposits 6 12 Total deposit liabilities $ 97,446 $ 93,256 At March 31, 2018 , and December 31, 2017 , certificates of deposit included $20.6 billion and $18.9 billion , respectively, of those in denominations of $100 thousand or more. At March 31, 2018 , and December 31, 2017 , certificates of deposit included $5.4 billion and $5.3 billion , respectively, of those in denominations in excess of $250 thousand federal insurance limits.

Debt

Debt	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Debt Disclosure [Text Block]	Debt Short-term Borrowings The following table presents the composition of our short-term borrowings portfolio. March 31, 2018 December 31, 2017 ($ in millions) Unsecured Secured (a) Total Unsecured Secured (a) Total Demand notes $ 2,957 $ — $ 2,957 $ 3,171 $ — $ 3,171 Federal Home Loan Bank — 5,900 5,900 — 7,350 7,350 Financial instruments sold under agreements to repurchase — 707 707 — 892 892 Total short-term borrowings $ 2,957 $ 6,607 $ 9,564 $ 3,171 $ 8,242 $ 11,413 (a) Refer to the section below titled Long-term Debt for further details on assets restricted as collateral for payment of the related debt. 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 March 31, 2018 , the financial instruments sold under agreements to repurchase consisted of $707 million of agency mortgage-backed residential debt securities set to mature as follows: $432 million w ithin 31 to 60 days, and $275 million within 61 to 90 days. Refer to Note 6 and Note 21 for further details. 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 March 31, 2018 , we placed cash collateral totaling $5 million and received cash collateral totaling $1 million . At December 31, 2017 , we placed cash collateral totaling $10 million and received cash collateral totaling $1 million . Long-term Debt The following table presents the composition of our long-term debt portfolio. March 31, 2018 December 31, 2017 ($ in millions) Unsecured Secured Total Unsecured Secured Total Long-term debt Due within one year $ 3,681 $ 7,639 $ 11,320 $ 3,482 $ 7,499 $ 10,981 Due after one year (a) 11,153 22,476 33,629 11,909 21,128 33,037 Fair value adjustment (b) 190 (63 ) 127 240 (32 ) 208 Total long-term debt (c) $ 15,024 $ 30,052 $ 45,076 $ 15,631 $ 28,595 $ 44,226 (a) Includes $2.6 billion of trust preferred securities at both March 31, 2018, and December 31, 2017. (b) Represents the basis adjustment associated with the application of hedge accounting on certain of our long-term debt positions. Refer to Note 18 for additional information. (c) Includes advances from the FHLB of Pittsburgh of $12.7 billion and $10.3 billion at March 31, 2018, and December 31, 2017, respectively. The following table presents the scheduled remaining maturity of long-term debt at March 31, 2018 , assuming no early redemptions will occur. The actual payment of secured debt may vary based on the payment activity of the related pledged assets. ($ in millions) 2018 2019 2020 2021 2022 2023 and thereafter Fair value adjustment Total Unsecured Long-term debt $ 2,987 $ 1,680 $ 2,251 $ 650 $ 1,066 $ 7,411 $ 190 $ 16,235 Original issue discount (76 ) (39 ) (39 ) (43 ) (47 ) (967 ) — (1,211 ) Total unsecured 2,911 1,641 2,212 607 1,019 6,444 190 15,024 Secured Long-term debt 4,924 7,467 6,845 5,717 4,094 1,068 (63 ) 30,052 Total long-term debt $ 7,835 $ 9,108 $ 9,057 $ 6,324 $ 5,113 $ 7,512 $ 127 $ 45,076 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. March 31, 2018 December 31, 2017 ($ in millions) Total (a) Ally Bank Total (a) Ally Bank Investment securities (b) $ 8,891 $ 8,443 $ 8,371 $ 7,443 Mortgage assets held-for-investment and lending receivables 14,501 14,501 13,579 13,579 Consumer automotive finance receivables 17,472 6,639 19,787 6,200 Commercial automotive finance receivables 14,618 14,558 16,567 16,472 Operating leases 350 — 457 — Total assets restricted as collateral (c) (d) $ 55,832 $ 44,141 $ 58,761 $ 43,694 Secured debt $ 36,659 (e) $ 25,874 $ 36,837 (e) $ 23,278 (a) Ally Bank is a component of the total column. (b) A portion of the restricted investment securities at March 31, 2018 , and December 31, 2017 , 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 $27.0 billion and $25.2 billion at March 31, 2018 , and December 31, 2017 , 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 at both March 31, 2018 , and December 31, 2017 . These assets were composed of consumer automotive finance receivables and loans. 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 Condensed Consolidated Balance Sheet . Refer to Note 11 for additional information. (e) Includes $6.6 billion and $8.2 billion of short-term borrowings at March 31, 2018 , and December 31, 2017 , respectively. Trust Preferred Securities At March 31, 2018 , 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. To but excluding February 15, 2040, distributions are payable at an annual rate equal to three-month London interbank offer rate plus 5.785% payable quarterly in arrears. 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 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. 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 Condensed Consolidated Balance Sheet . As of March 31, 2018 , Ally Bank had exclusive access to $1.5 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 March 31, 2018 , all of our $8.7 billion of committed capacity was revolving. Our revolving facilities generally have an original tenor ranging from 364 days to two years. As of March 31, 2018 , we had $6.6 billion of committed funding capacity from revolving facilities with a remaining tenor greater than 364 days. Committed Funding Facilities Outstanding Unused capacity (a) Total capacity ($ in millions) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Bank funding Secured $ 1,500 $ 1,785 $ — $ 890 $ 1,500 $ 2,675 Parent funding Secured 4,255 6,330 2,970 2,920 7,225 9,250 Total committed facilities $ 5,755 $ 8,115 $ 2,970 $ 3,810 $ 8,725 $ 11,925 (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.

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	3 Months Ended
	Mar. 31, 2018
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. ($ in millions) March 31, 2018 December 31, 2017 Accounts payable $ 390 $ 746 Employee compensation and benefits 161 248 Reserves for insurance losses and loss adjustment expenses 157 140 Fair value of derivative contracts in payable position (a) 56 41 Deferred revenue 34 32 Cash collateral received from counterparties 31 17 Other liabilities 626 556 Total accrued expenses and other liabilities $ 1,455 $ 1,780 (a) For additional information on derivative instruments and hedging activities, refer to Note 18 .

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2018
Other Comprehensive Income (Loss), Net of Tax [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 December 31, 2016 $ (273 ) $ 14 $ 8 $ (90 ) $ (341 ) 2017 net change 21 — — (1 ) 20 Balance at March 31, 2017 $ (252 ) $ 14 $ 8 $ (91 ) $ (321 ) Balance at December 31, 2017, before cumulative effect of adjustments $ (173 ) $ 16 $ 11 $ (89 ) $ (235 ) Cumulative effect of changes in accounting principles, net of tax (c) Adoption of Accounting Standards Update 2016-01 27 — — — 27 Adoption of Accounting Standards Update 2018-02 (40 ) 4 — (6 ) (42 ) Balance at January 1, 2018, after cumulative effect of adjustments (186 ) 20 11 (95 ) (250 ) 2018 net change (338 ) (1 ) 14 (3 ) (328 ) Balance at March 31, 2018 $ (524 ) $ 19 $ 25 $ (98 ) $ (578 ) (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 18 . (c) Refer to the section titled Recently Adopted Accounting Standards in Note 1 for additional information. The following tables present the before- and after-tax changes in each component of accumulated other comprehensive (loss) income. Three months ended March 31, 2018 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized losses arising during the period $ (436 ) $ 103 $ (333 ) Less: Net realized gains reclassified to income from continuing operations 6 (a) (1 ) (b) 5 Net change (442 ) 104 (338 ) Translation adjustments Net unrealized losses arising during the period (5 ) 1 (4 ) Net investment hedges (c) Net unrealized gains arising during the period 4 (1 ) 3 Cash flow hedges (c) Net unrealized gains arising during the period 18 (4 ) 14 Defined benefit pension plans Net unrealized losses arising during the period (3 ) — (3 ) Other comprehensive loss $ (428 ) $ 100 $ (328 ) (a) Includes gains reclassified to other (loss) gain on investments, net in our Condensed Consolidated Statement of Comprehensive Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Condensed Consolidated Statement of Comprehensive Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 18 . Three months ended March 31, 2017 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized gains arising during the period $ 51 $ (5 ) $ 46 Less: Net realized gains reclassified to income from continuing operations 27 (a) (2 ) (b) 25 Net change 24 (3 ) 21 Translation adjustments Net unrealized gains arising during the period 2 (1 ) 1 Net investment hedges (c) Net unrealized losses arising during the period (2 ) 1 (1 ) Defined benefit pension plans Net unrealized losses arising during the period (1 ) — (1 ) Other comprehensive income $ 23 $ (3 ) $ 20 (a) Includes gains reclassified to other gain on investments, net in our Condensed Consolidated Statement of Comprehensive Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Condensed Consolidated Statement of Comprehensive Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 18 .

Earnings per Common Share

Earnings per Common Share	3 Months Ended
	Mar. 31, 2018
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. Three months ended March 31, ($ in millions, except per share data; shares in thousands) (a) 2018 2017 Net income from continuing operations attributable to common stockholders $ 252 $ 213 (Loss) income from discontinued operations, net of tax (2 ) 1 Net income attributable to common stockholders $ 250 $ 214 Basic weighted-average common shares outstanding (b) 436,213 465,961 Diluted weighted-average common shares outstanding (b) 438,931 466,829 Basic earnings per common share Net income from continuing operations $ 0.58 $ 0.46 Loss from discontinued operations, net of tax (0.01 ) — Net income $ 0.57 $ 0.46 Diluted earnings per common share Net income from continuing operations $ 0.57 $ 0.46 Loss from discontinued operations, net of tax (0.01 ) — Net income $ 0.57 $ 0.46 (a) Figures in the table may not recalculate exactly due to rounding. Earnings per share is calculated based on unrounded numbers. (b) Includes shares related to share-based compensation that vested but were not yet issued for the three months ended March 31, 2018 , and 2017 .

Regulatory Capital and Other Re

Regulatory Capital and Other Regulatory Matters	3 Months Ended
	Mar. 31, 2018
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 Basel III 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 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 Condensed 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 April 13, 2018, the FRB and other U.S. banking agencies proposed a revision to their regulatory capital rules to address the regulatory capital treatment related to ASU 2016-13, which Ally plans to adopt effective January 1, 2020, as further described in Note 1 . We expect the implementation of ASU 2016-13 will significantly increase our allowance for credit losses upon adoption. If finalized, the proposed changes to the regulatory capital rules would allow Ally to phase in the impact to our regulatory capital as a result of the increase to our allowance for credit losses on a straight-line basis over a three-year period. In addition, the U.S. banking agencies are proposing to make amendments to the stress testing regulations which would exclude the impact of the adoption of ASU 2016-13 until the 2020 stress testing cycle. On April 10, 2018, the FRB issued a proposal that would seek to more closely align forward-looking stress testing results with the FRB’s non-stress capital requirements for banking organizations with $50 billion or more in assets. The proposal would introduce a “stress capital buffer” based on firm-specific stress test performance, which would effectively replace the capital conservation buffer for determining non-stress capital requirements. The proposal would also incorporate several other changes to the CCAR process including eliminating the CCAR quantitative objection, narrowing the set of planned capital actions assumed to occur in the stress scenario and eliminating the thirty percent dividend payout ratio as a criterion for heightened scrutiny of a firm’s capital plan, among other proposed changes. If finalized, the rule would be effective on December 31, 2018, and a firm’s first stress buffer requirements would generally be effective on October 1, 2019. We are currently evaluating the effect this proposal will have on our capital planning and stress testing requirements. 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 $446 million of FRB stock at March 31, 2018 . 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% . 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. March 31, 2018 December 31, 2017 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. $ 13,079 9.26 % $ 13,237 9.53 % 4.50 % (b) Ally Bank 16,535 13.93 17,059 15.04 4.50 6.50 % Tier 1 (to risk-weighted assets) Ally Financial Inc. $ 15,512 10.98 % $ 15,628 11.25 % 6.00 % 6.00 % Ally Bank 16,535 13.93 17,059 15.04 6.00 8.00 Total (to risk-weighted assets) Ally Financial Inc. $ 17,760 12.57 % $ 17,974 12.94 % 8.00 % 10.00 % Ally Bank 17,480 14.72 17,886 15.77 8.00 10.00 Tier 1 leverage (to adjusted quarterly average assets) (c) Ally Financial Inc. $ 15,512 9.26 % $ 15,628 9.53 % 4.00 % (b) Ally Bank 16,535 11.94 17,059 12.87 4.00 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 1.875% and 1.25% at March 31, 2018, and December 31, 2017, 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. At March 31, 2018 , 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 and capital buffers 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 April 10, 2018 , the Board declared a quarterly cash dividend of $0.13 per share on all common stock, payable on May 15, 2018 . The following table presents information related to our common stock for each quarter since the commencement of our common stock repurchase programs and initiation of a quarterly cash dividend on common stock. Common stock repurchased during period (a) Number of common shares outstanding Cash dividends declared per common share (b) ($ in millions, except per share data; shares in thousands) Approximate dollar value Number of shares Beginning of period End of period 2016 Third quarter $ 159 8,298 483,753 475,470 $ 0.08 Fourth quarter 167 8,745 475,470 467,000 0.08 2017 First quarter $ 169 8,097 467,000 462,193 $ 0.08 Second quarter 204 10,485 462,193 452,292 0.08 Third quarter 190 8,507 452,292 443,796 0.12 Fourth quarter 190 7,033 443,796 437,054 0.12 2018 First quarter $ 185 6,473 437,054 432,691 $ 0.13 (a) Includes shares of common stock withheld to cover income taxes owed by participants in our share-based incentive plans. (b) On April 10, 2018 , the Board declared a quarterly cash dividend of $0.13 per share on all common stock, payable on May 15, 2018 . Refer to Note 25 for further information regarding this common stock dividend. Ally submitted its 2018 capital plan on April 5, 2018, with capital actions including distributions to common stockholders through share repurchases and cash dividends. We expect to receive the FRB’s response (either a non-objection or objection) to Ally’s 2018 capital plan by June 30, 2018. 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.

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Derivative Instruments and Hedging Activities We enter into derivative instruments, such as interest rate, foreign-currency, and equity swaps, futures, forwards, and options in connection with our risk management activities. 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. Interest Rate Risk We monitor our mix of fixed- and variable-rate assets and liabilities and 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 these trades 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 securities within our available-for-sale portfolio, and pay-fixed swaps designated as fair value hedges of closed portfolios of fixed-rate held-for-investment retail automotive loan assets in which the hedged item is the last layer expected to be remaining at the end of the hedging relationship. 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 and deposit liabilities. We may also execute economic hedges, which consist of interest rate swaps, interest rate caps, forwards, futures, options, and swaptions to mitigate interest rate risk. 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 any foreign-denominated debt, centralized lending, 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. 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 three months ended March 31, 2018 , or 2017 . We placed cash collateral totaling $28 million and securities collateral totaling $100 million at March 31, 2018 , and $20 million and $97 million at December 31, 2017 , 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. Refer to Note 13 for details on the repurchase agreements. The receivables for cash collateral placed are included on our Condensed Consolidated Balance Sheet in other assets. We received cash collateral from counterparties totaling $30 million and $17 million at March 31, 2018 , and December 31, 2017 , respectively, primarily to support these derivative positions. This amount also excludes cash and securities pledged as collateral under repurchase agreements. The payables for cash collateral received are included on our Condensed 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 Condensed Consolidated Balance Sheet unless certain conditions are met. We received noncash collateral of $2 million at both March 31, 2018 , and December 31, 2017 . Included in these amounts is noncash collateral where we have been granted the right to sell or pledge the underlying assets. We have not sold or pledged any of the noncash collateral received under these agreements. Balance Sheet Presentation The following table summarizes the amounts of derivative instruments reported on our Condensed Consolidated Balance Sheet . The amounts are presented on a gross basis, are segregated by derivatives that are designated and qualifying as hedging instruments or those that are not, and are further segregated by type of contract within those two categories. Derivative contracts in a receivable and payable position exclude open trade equity on derivatives cleared through central clearing counterparties. Any associated collateral exchanged with our central clearing counterparties are treated as settlements of the derivative exposure, rather than collateral. Such payments are recognized as settlements of the derivatives contracts in a receivable and payable position on our Condensed Consolidated Balance Sheet . Notional amounts are reference amounts from which contractual obligations are derived and are not recorded on the balance sheet. In our view, derivative notional is not an accurate measure of our derivative exposure when viewed in isolation from other factors, such as market rate fluctuations and counterparty credit risk. March 31, 2018 December 31, 2017 Derivative contracts in a Notional amount Derivative contracts in a Notional amount ($ in millions) receivable position payable position receivable position payable position Derivatives designated as accounting hedges Interest rate contracts Swaps $ — $ — $ 20,250 $ — $ — $ 6,915 Foreign exchange contracts Forwards — — 145 — 1 136 Total derivatives designated as accounting hedges — — 20,395 — 1 7,051 Derivatives not designated as accounting hedges Interest rate contracts Futures and forwards — — 5 — — 23 Written options 1 55 6,139 1 39 8,327 Purchased options 55 — 6,081 38 — 8,237 Total interest rate risk 56 55 12,225 39 39 16,587 Foreign exchange contracts Futures and forwards — — 297 — 1 124 Total foreign exchange risk — — 297 — 1 124 Equity contracts Written options — 1 — — — — Total equity risk — 1 — — — — Total derivatives not designated as accounting hedges 56 56 12,522 39 40 16,711 Total derivatives $ 56 $ 56 $ 32,917 $ 39 $ 41 $ 23,762 The following table presents amounts recorded on our Condensed Consolidated Balance Sheet related to cumulative basis adjustments for fair value hedges. ($ in millions) Carrying amount of the hedged items Cumulative amount of fair value hedging adjustment included in the carrying amount of the hedged items Total Discontinued (a) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Assets Available-for-sale securities (b) $ 985 $ 173 $ — $ 2 $ 2 $ 2 Finance receivables and loans, net (c) 22,121 2,305 (31 ) 18 14 19 Liabilities Long-term debt $ 14,958 $ 14,640 $ 127 $ 208 $ 163 $ 235 (a) Represents the fair value hedging adjustment on qualifying hedges for which the hedging relationship was discontinued. This represents a subset of the amounts reported in the total hedging adjustment. (b) The carrying amount of hedged available-for-sale securities is presented above using amortized cost. Refer to Note 6 for a reconciliation of the amortized cost and fair value of available-for-sale securities. (c) The hedged item represents the carrying value of the hedged portfolio of assets. The amount that is identified as the last of layer in the hedge relationship is $9.7 billion as of March 31, 2018 . The basis adjustment associated with the last-of-layer relationship is $45 million liability as of March 31, 2018 , which would be allocated across the entire remaining closed pool upon termination or maturity of the hedge relationship. A last-of-layer hedge strategy did not exist at December 31, 2017 . Statement of Comprehensive Income Presentation The following table summarizes the location and amounts of gains and losses on derivative instruments not designated as accounting hedges reported in our Condensed Consolidated Statement of Comprehensive Income . Three months ended March 31, ($ in millions) 2018 2017 Gain (loss) recognized in earnings Interest rate contracts Other income, net of losses $ 2 $ (2 ) Total interest rate contracts 2 (2 ) Foreign exchange contracts (a) Other income, net of losses — (1 ) Total foreign exchange contracts — (1 ) Gain (loss) recognized in earnings $ 2 $ (3 ) (a) Amounts exclude gains and losses related to the revaluation of the related foreign-denominated debt or receivables. Gains of $0 million and $1 million were recognized for the three months ended March 31, 2018 , and 2017 , respectively. The following table summarizes the location and amounts of gains and losses on derivative instruments designated as fair value hedges reported in our Condensed Consolidated Statement of Comprehensive Income . We had no gains or losses on derivative instruments designated as cash flow hedges for the periods shown. Interest and fees on finance receivables and loans Interest and dividends on investment securities and other earning assets Interest on long-term debt Three months ended March 31, ($ in millions) 2018 2017 2018 2017 2018 2017 Gain (loss) on fair value hedging relationships Interest rate contracts Hedged fixed-rate unsecured debt $ — $ — $ — $ — $ 36 $ (2 ) Derivatives designated as hedging instruments on fixed-rate unsecured debt — — — — (35 ) 3 Hedged fixed-rate FHLB advances — — — — 33 (1 ) Derivatives designated as hedging instruments on fixed-rate FHLB advances — — — — (33 ) 1 Hedged available-for-sale securities — — (3 ) — — — Derivatives designated as hedging instruments on available-for-sale securities — — 3 — — — Hedged fixed-rate retail automotive loans (45 ) (4 ) — — — — Derivatives designated as hedging instruments on fixed-rate retail automotive loans 45 2 — — — — Total (loss) gain on fair value hedging relationships $ — $ (2 ) $ — $ — $ 1 $ 1 Total amounts presented in the Condensed Consolidated Statement of Comprehensive Income $ 1,543 $ 1,368 $ 176 $ 134 $ 411 $ 424 The following table summarizes the location and amounts of gains and losses related to interest and amortization on derivative instruments designated as fair value and cash flow hedges reported in our Condensed Consolidated Statement of Comprehensive Income . Interest and fees on finance receivables and loans Interest and dividends on investment securities and other earning assets Interest on long-term debt Three months ended March 31, ($ in millions) 2018 2017 2018 2017 2018 2017 Gain (loss) on fair value hedging relationships Interest rate contracts Amortization of deferred unsecured debt basis adjustments $ — $ — $ — $ — $ 15 $ 20 Interest for qualifying accounting hedges of unsecured debt — — — — 3 5 Amortization of deferred secured debt basis adjustments (FHLB advances) — — — — (1 ) (1 ) Interest for qualifying accounting hedges of secured debt (FHLB advances) — — — — 2 — Interest for qualifying accounting hedges of available-for-sale securities — — (1 ) — — — Amortization of deferred loan basis adjustments (4 ) (5 ) — — — — Interest for qualifying accounting hedges of retail automotive loans held-for-investment (7 ) (1 ) — — — — Total (loss) gain on fair value hedging relationships (11 ) (6 ) (1 ) — 19 24 Gain on cash flow hedging relationships Interest rate contracts (a) Interest for qualifying accounting hedges of variable-rate borrowings — — — — 1 — Total gain on cash flow hedging relationships $ — $ — $ — $ — $ 1 $ — Total amounts presented in the Condensed Consolidated Statement of Comprehensive Income $ 1,543 $ 1,368 $ 176 $ 134 $ 411 $ 424 (a) During the next twelve months, we estimate $13 million will be reclassified into pretax earnings from derivatives designated as cash flow hedges. The following table summarizes the effect of cash flow hedges on accumulated other comprehensive loss. Three months ended March 31, ($ in millions) 2018 2017 Cash flow hedges Interest rate contracts Gain recognized in other comprehensive loss $ 18 $ — The following table summarizes the effect of net investment hedges on accumulated other comprehensive loss and the Condensed Consolidated Statement of Comprehensive Income . Gain (loss) recognized in other comprehensive (loss) income on derivatives Three months ended March 31, ($ in millions) 2018 2017 Foreign exchange contracts (a) (b) $ 4 $ (2 ) (a) There were no amounts excluded from effectiveness testing for the three months ended March 31, 2018 , or 2017 , respectively. (b) Gains and losses reclassified from accumulated other comprehensive loss are reported as other income, net of losses, on the Condensed Consolidated Statement of Comprehensive Income . There were no amounts reclassified for the three months ended March 31, 2018 , or 2017 , respectively.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes We recognized total income tax expense from continuing operations of $76 million for the three months ended March 31, 2018 , compared to income tax expense of $113 million for the same period in 2017 . The decrease in income tax expense for the three months ended March 31, 2018 , compared to the same period in 2017 , was primarily driven by the reduction of the U.S. federal corporate tax rate enacted as a result of the Tax Act, partially offset by tax benefits in 2017 from the release of valuation allowance against our capital-in-nature deferred tax assets and foreign tax credit carryforwards. As further described in Note 1 , we elected to early-adopt ASU 2018-02 effective January 1, 2018. As a result of this adoption, we reclassified $42 million from accumulated other comprehensive loss to retained earnings, which eliminated the stranded federal income tax effects in accumulated other comprehensive loss resulting from the Tax Act. Our policy is to use the portfolio method with respect to reclassification of stranded income tax effects in accumulated other comprehensive loss. 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 credits 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.

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2018
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. There were no transfers between any levels for the three months ended March 31, 2018. The 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. • Equity Securities — Includes various marketable equity securities measured at fair value with changes in fair value recognized in net income. Measurements based on observable market prices are classified as Level 1. • 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, caps, floors, and agency to-be-announced securities. We utilize third-party-developed valuation models that are widely accepted in the market to value these 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 derivative contracts as Level 2 because all significant inputs into these models were market observable. 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 Condensed 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 March 31, 2018 ($ in millions) Level 1 Level 2 Level 3 Total Assets Investment securities Equity securities (a) $ 668 $ — $ 12 $ 680 Available-for-sale securities Debt securities U.S. Treasury 1,769 — — 1,769 U.S. States and political subdivisions — 831 — 831 Foreign government 7 142 — 149 Agency mortgage-backed residential — 14,883 — 14,883 Mortgage-backed residential — 2,384 — 2,384 Mortgage-backed commercial — 580 — 580 Asset-backed — 900 — 900 Corporate debt — 1,230 — 1,230 Total available-for-sale securities 1,776 20,950 — 22,726 Mortgage loans held-for-sale (b) — — 7 7 Interests retained in financial asset sales — — 5 5 Derivative contracts in a receivable position Interest rate — 55 1 56 Total derivative contracts in a receivable position — 55 1 56 Total assets $ 2,444 $ 21,005 $ 25 $ 23,474 Liabilities Accrued expenses and other liabilities Derivative contracts in a payable position Interest rate $ — $ 55 $ — $ 55 Other 1 — — 1 Total derivative contracts in a payable position 1 55 — 56 Total liabilities $ 1 $ 55 $ — $ 56 (a) Our investment in any one industry did not exceed 13% . (b) Carried at fair value due to fair value option elections. Recurring fair value measurements December 31, 2017 ($ in millions) Level 1 Level 2 Level 3 Total Assets Investment securities Equity securities (a) $ 518 $ — $ — $ 518 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 available-for-sale securities 1,785 20,518 — 22,303 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. 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 (losses) gains Fair value at March 31, 2018 Net unrealized losses included in earnings still held at March 31, 2018 ($ in millions) Fair value at Jan. 1, 2018 included in earnings included in OCI Purchases Sales Issuances Settlements Assets Equity securities (a) $ 19 $ (4 ) (b) $ — $ — $ — $ — $ (3 ) $ 12 $ (5 ) Mortgage loans held-for-sale (c) 13 1 (d) — 59 (66 ) — — 7 — Other assets Interests retained in financial asset sales 5 — — — — — — 5 — Derivative assets 1 — — — — — — 1 — Total assets $ 38 $ (3 ) $ — $ 59 $ (66 ) $ — $ (3 ) $ 25 $ (5 ) (a) In connection with our adoption of ASU 2016-01 on January 1, 2018, certain of our equity securities previously measured using the cost method of accounting are now measured at fair value on a recurring basis, and have been categorized as Level 3 within the fair value hierarchy. Accordingly, the fair value of such investments has been included in the opening balance of the reconciliation above. (b) Reported as other loss on investments, net, in the Condensed Consolidated Statement of Comprehensive Income . (c) Carried at fair value due to fair value option elections. (d) Reported as gain on mortgage and automotive loans, net, in the Condensed Consolidated Statement of Comprehensive Income . Level 3 recurring fair value measurements Fair value at Jan. 1, 2017 Net realized/unrealized gains Purchases Sales Issuances Settlements Fair value at March 31, 2017 Net unrealized gains included in earnings still held at March 31, 2017 ($ in millions) included in earnings included in OCI Assets Mortgage loans held-for-sale (a) $ — $ — $ — $ 3 $ (2 ) $ — $ — $ 1 $ — Other assets Interests retained in financial asset sales 29 — — — 4 — (2 ) 31 — Total assets $ 29 $ — $ — $ 3 $ 2 $ — $ (2 ) $ 32 $ — (a) Carried at fair value due to fair value option elections. 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 three months ended March 31, 2018 ($ in millions) Level 1 Level 2 Level 3 Total Assets Loans held-for-sale, net $ — $ — $ 119 $ 119 $ — n/m (a) Commercial finance receivables and loans, net (b) Automotive — — 51 51 (10 ) n/m (a) Other — — 22 22 (11 ) n/m (a) Total commercial finance receivables and loans, net — — 73 73 (21 ) n/m (a) Other assets Repossessed and foreclosed assets (c) — — 13 13 (1 ) n/m (a) Total assets $ — $ — $ 205 $ 205 $ (22 ) 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 2018 . 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 (loss) included in earnings for the three months 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. 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 derivatives. Our intent in electing fair value measurement was to mitigate a divergence between accounting gains or 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 March 31, 2018 , and December 31, 2017 . Estimated fair value ($ in millions) Carrying value Level 1 Level 2 Level 3 Total March 31, 2018 Financial assets Held-to-maturity securities $ 1,967 $ — $ 1,895 $ — $ 1,895 Loans held-for-sale, net 119 — — 119 119 Finance receivables and loans, net 124,049 — — 125,530 125,530 Nonmarketable equity investments 1,210 — 1,210 — 1,210 Financial liabilities Deposit liabilities (a) $ 49,025 $ — $ — $ 48,845 $ 48,845 Short-term borrowings 9,564 — — 9,567 9,567 Long-term debt 45,076 — 28,384 18,589 46,973 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 (a) $ 45,869 $ — $ — $ 45,827 $ 45,827 Short-term borrowings 11,413 — — 11,417 11,417 Long-term debt 44,226 — 27,807 18,817 46,624 (a) In connection with our adoption of ASU 2016-01 on January 1, 2018, deposit liabilities with no defined or contractual maturities are no longer included in the table above. Amounts for December 31, 2017, have been adjusted to conform to the current presentation and exclude $47.4 billion and $45.2 billion of deposit liabilities with no defined or contractual maturities from the carrying value and Level 3 fair value, respectively. Refer to Note 12 for information regarding the composition of our deposits portfolio, and Note 1 for further information regarding recently adopted accounting standards.

Offsetting Assets and Liabiliti

Offsetting Assets and Liabilities	3 Months Ended
	Mar. 31, 2018
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 March 31, 2018 , these instruments are reported as gross assets and gross liabilities on the Condensed 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 Condensed Consolidated Balance Sheet Net amounts of assets/liabilities presented on the Condensed Consolidated Balance Sheet Gross amounts not offset on the Condensed Consolidated Balance Sheet March 31, 2018 ($ in millions) Financial instruments Collateral (a) (b) (c) Net amount Assets Derivative assets in net asset positions $ 55 $ — $ 55 $ — $ — $ 55 Derivative assets with no offsetting arrangements 1 — 1 — — 1 Total assets (d) $ 56 $ — $ 56 $ — $ — $ 56 Liabilities Derivative liabilities in net liability positions (d) $ 56 $ — $ 56 $ — $ (1 ) $ 55 Securities sold under agreements to repurchase (e) 707 — 707 — (707 ) — Total liabilities $ 763 $ — $ 763 $ — $ (708 ) $ 55 (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 March 31, 2018 . We do not record such collateral received on our Condensed 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 $2 million at March 31, 2018 . We have not sold or pledged any of the noncash collateral received under these agreements as of March 31, 2018 . (d) For additional information on derivative instruments and hedging activities, refer to Note 18 . (e) For additional information on securities sold under agreements to repurchase, refer to Note 13 . Gross amounts of recognized assets/liabilities Gross amounts offset on the Condensed Consolidated Balance Sheet Net amounts of assets/liabilities presented on the Condensed Consolidated Balance Sheet Gross amounts not offset on the Condensed Consolidated Balance Sheet December 31, 2017 ($ 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 Condensed 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 18 . (e) For additional information on securities sold under agreements to repurchase, refer to Note 13 .

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment Reporting Disclosure [Text Block]	Segment 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 low-to-moderate income (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 , and we retain no mortgage servicing rights associated with those loans that are sold. 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 is based in part on internal allocations, which involve management judgment. Financial information for our reportable operating segments is summarized as follows. Three months ended March 31, ($ in millions) Automotive Finance operations Insurance operations Mortgage Finance operations Corporate Finance operations Corporate and Other Consolidated (a) 2018 Net financing revenue and other interest income $ 909 $ 12 $ 43 $ 46 $ 39 $ 1,049 Other revenue 66 246 1 8 33 354 Total net revenue 975 258 44 54 72 1,403 Provision for loan losses 259 — 2 — — 261 Total noninterest expense 448 231 34 25 76 814 Income (loss) from continuing operations before income tax expense $ 268 $ 27 $ 8 $ 29 $ (4 ) $ 328 Total assets $ 114,934 $ 7,557 $ 12,780 $ 4,375 $ 30,375 $ 170,021 2017 Net financing revenue and other interest income $ 892 $ 15 $ 34 $ 34 $ 4 $ 979 Other revenue 101 264 — 18 13 396 Total net revenue 993 279 34 52 17 1,375 Provision for loan losses 268 — 1 6 (4 ) 271 Total noninterest expense 437 239 24 21 57 778 Income (loss) from continuing operations before income tax expense $ 288 $ 40 $ 9 $ 25 $ (36 ) $ 326 Total assets $ 115,154 $ 7,230 $ 8,362 $ 3,438 $ 27,917 $ 162,101 (a) Net financing revenue and other interest income after the provision for loan losses totaled $788 million and $708 million for the three months ended March 31, 2018 , and March 31, 2017 , respectively.

Parent and Guarantor Condensed

Parent and Guarantor Condensed Consolidating Financial Statements	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Condensed Financial Statements [Text Block]	Parent and Guarantor Condensed 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 March 31, 2018 , 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 Three months ended March 31, 2018 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Financing revenue and other interest income Interest and fees on finance receivables and loans $ 11 $ — $ 1,532 $ — $ 1,543 Interest and fees on finance receivables and loans — intercompany 2 — 1 (3 ) — Interest and dividends on investment securities and other earning assets — — 176 — 176 Interest on cash and cash equivalents 2 — 14 (1 ) 15 Interest-bearing cash — intercompany 2 — 2 (4 ) — Operating leases 2 — 380 — 382 Total financing revenue and other interest income 19 — 2,105 (8 ) 2,116 Interest expense Interest on deposits — — 354 (3 ) 351 Interest on short-term borrowings 10 — 22 — 32 Interest on long-term debt 258 — 153 — 411 Interest on intercompany debt 3 — 2 (5 ) — Total interest expense 271 — 531 (8 ) 794 Net depreciation expense on operating lease assets 4 — 269 — 273 Net financing revenue (256 ) — 1,305 — 1,049 Cash dividends from subsidiaries Bank subsidiary 1,000 1,000 — (2,000 ) — Nonbank subsidiaries 169 — — (169 ) — Other revenue Insurance premiums and service revenue earned — — 256 — 256 Gain on mortgage and automotive loans, net 28 — 1 (28 ) 1 Other loss on investments, net — — (12 ) — (12 ) Other income, net of losses 96 — 221 (208 ) 109 Total other revenue 124 — 466 (236 ) 354 Total net revenue 1,037 1,000 1,771 (2,405 ) 1,403 Provision for loan losses 81 — 208 (28 ) 261 Noninterest expense Compensation and benefits expense 23 — 283 — 306 Insurance losses and loss adjustment expenses — — 63 — 63 Other operating expenses 182 — 471 (208 ) 445 Total noninterest expense 205 — 817 (208 ) 814 Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries 751 1,000 746 (2,169 ) 328 Income tax (benefit) expense from continuing operations (56 ) — 132 — 76 Net income from continuing operations 807 1,000 614 (2,169 ) 252 Loss from discontinued operations, net of tax (1 ) — (1 ) — (2 ) Undistributed (loss) income of subsidiaries Bank subsidiary (597 ) (597 ) — 1,194 — Nonbank subsidiaries 41 — — (41 ) — Net income 250 403 613 (1,016 ) 250 Other comprehensive loss, net of tax (328 ) (276 ) (339 ) 615 (328 ) Comprehensive (loss) income $ (78 ) $ 127 $ 274 $ (401 ) $ (78 ) Three months ended March 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 $ (35 ) $ — $ 1,403 $ — $ 1,368 Interest and fees on finance receivables and loans — intercompany 4 — 3 (7 ) — Interest and dividends on investment securities and other earning assets — — 135 (1 ) 134 Interest on cash and cash equivalents 2 — 3 — 5 Interest-bearing cash — intercompany — — 1 (1 ) — Operating leases 3 — 540 — 543 Total financing (loss) revenue and other interest income (26 ) — 2,085 (9 ) 2,050 Interest expense Interest on deposits 1 — 230 — 231 Interest on short-term borrowings 17 — 10 — 27 Interest on long-term debt 281 — 143 — 424 Interest on intercompany debt 4 — 4 (8 ) — Total interest expense 303 — 387 (8 ) 682 Net depreciation expense on operating lease assets 2 — 387 — 389 Net financing revenue (331 ) — 1,311 (1 ) 979 Cash dividends from subsidiaries Nonbank subsidiaries 41 — — (41 ) — Other revenue Insurance premiums and service revenue earned — — 241 — 241 (Loss) gain on mortgage and automotive loans, net (2 ) — 16 — 14 Other gain on investments, net — — 27 — 27 Other income, net of losses 268 — 223 (377 ) 114 Total other revenue 266 — 507 (377 ) 396 Total net revenue (24 ) — 1,818 (419 ) 1,375 Provision for loan losses 107 — 164 — 271 Noninterest expense Compensation and benefits expense 122 — 163 — 285 Insurance losses and loss adjustment expenses — — 88 — 88 Other operating expenses 288 — 494 (377 ) 405 Total noninterest expense 410 — 745 (377 ) 778 (Loss) income from continuing operations before income tax (benefit) expense and undistributed income of subsidiaries (541 ) — 909 (42 ) 326 Income tax (benefit) expense from continuing operations (134 ) — 247 — 113 Net (loss) income from continuing operations (407 ) — 662 (42 ) 213 Income (loss) from discontinued operations, net of tax 2 — (1 ) — 1 Undistributed income of subsidiaries Bank subsidiary 389 389 — (778 ) — Nonbank subsidiaries 230 — — (230 ) — Net income 214 389 661 (1,050 ) 214 Other comprehensive income, net of tax 20 5 19 (24 ) 20 Comprehensive income $ 234 $ 394 $ 680 $ (1,074 ) $ 234 Condensed Consolidating Balance Sheet March 31, 2018 ($ in millions) Parent (a) Guarantors Nonguarantors (a) Consolidating adjustments Ally consolidated Assets Cash and cash equivalents Noninterest-bearing $ 56 $ — $ 712 $ — $ 768 Interest-bearing 5 — 2,948 — 2,953 Interest-bearing — intercompany 735 — 577 (1,312 ) — Total cash and cash equivalents 796 — 4,237 (1,312 ) 3,721 Equity securities — — 680 — 680 Available-for-sale securities — — 22,726 — 22,726 Held-to-maturity securities — — 2,033 (66 ) 1,967 Loans held-for-sale, net — — 126 — 126 Finance receivables and loans, net Finance receivables and loans, net 6,443 — 118,884 — 125,327 Intercompany loans to Nonbank subsidiaries 1,311 — 415 (1,726 ) — Allowance for loan losses (145 ) — (1,133 ) — (1,278 ) Total finance receivables and loans, net 7,609 — 118,166 (1,726 ) 124,049 Investment in operating leases, net 14 — 8,516 — 8,530 Intercompany receivables from Bank subsidiary 86 — — (86 ) — Nonbank subsidiaries 41 — 61 (102 ) — Investment in subsidiaries Bank subsidiary 16,163 16,163 — (32,326 ) — Nonbank subsidiaries 7,520 — — (7,520 ) — Premiums receivable and other insurance assets — — 2,197 — 2,197 Other assets 2,221 — 5,072 (1,268 ) 6,025 Total assets $ 34,450 $ 16,163 $ 163,814 $ (44,406 ) $ 170,021 Liabilities Deposit liabilities Noninterest-bearing $ — $ — $ 122 $ — $ 122 Interest-bearing 6 — 97,318 — 97,324 Interest-bearing — intercompany — — 735 (735 ) — Total deposit liabilities 6 — 98,175 (735 ) 97,446 Short-term borrowings 2,957 — 6,607 — 9,564 Long-term debt 16,808 — 28,268 — 45,076 Intercompany debt to Bank subsidiary 65 — — (65 ) — Nonbank subsidiaries 992 — 1,311 (2,303 ) — Intercompany payables to Nonbank subsidiaries 115 — 106 (221 ) — Interest payable 209 — 285 — 494 Unearned insurance premiums and service revenue — — 2,904 — 2,904 Accrued expenses and other liabilities 216 — 2,473 (1,234 ) 1,455 Total liabilities 21,368 — 140,129 (4,558 ) 156,939 Total equity 13,082 16,163 23,685 (39,848 ) 13,082 Total liabilities and equity $ 34,450 $ 16,163 $ 163,814 $ (44,406 ) $ 170,021 (a) Amounts presented are based upon the legal transfer of the underlying assets to VIEs in order to reflect legal ownership. 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 Equity securities — — 518 — 518 Available-for-sale securities — — 22,303 — 22,303 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. Condensed Consolidating Statement of Cash Flows Three months ended March 31, 2018 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash provided by operating activities $ 456 $ 1,000 $ 1,812 $ (2,171 ) $ 1,097 Investing activities Purchases of equity securities — — (374 ) — (374 ) Proceeds from sales of equity securities — — 220 — 220 Purchases of available-for-sale securities — — (2,360 ) — (2,360 ) Proceeds from sales of available-for-sale securities — — 328 — 328 Proceeds from repayments of available-for-sale securities — — 795 — 795 Purchases of held-to-maturity securities — — (155 ) — (155 ) Proceeds from repayments of held-to-maturity securities — — 35 — 35 Net change in investment securities — intercompany — — 9 (9 ) — Purchases of finance receivables and loans held-for-investment — — (2,317 ) 820 (1,497 ) Proceeds from sales of finance receivables and loans initially held-for-investment 820 — — (820 ) — Originations and repayments of finance receivables and loans held-for-investment and other, net 432 — (1,732 ) — (1,300 ) Net change in loans — intercompany (423 ) — 1 422 — Purchases of operating lease assets — — (969 ) — (969 ) Disposals of operating lease assets 4 — 972 — 976 Capital contributions to subsidiaries (49 ) (6 ) — 55 — Returns of contributed capital 38 — — (38 ) — Net change in nonmarketable equity investments — — (19 ) — (19 ) Other, net (3 ) — (80 ) 1 (82 ) Net cash provided by (used in) investing activities 819 (6 ) (5,646 ) 431 (4,402 ) Financing activities Net change in short-term borrowings — third party (214 ) — (1,634 ) — (1,848 ) Net (decrease) increase in deposits (6 ) — 3,776 403 4,173 Proceeds from issuance of long-term debt — third party 15 — 6,650 — 6,665 Repayments of long-term debt — third party (1,152 ) — (4,619 ) — (5,771 ) Net change in debt — intercompany (127 ) — 422 (295 ) — Repurchase of common stock (185 ) — — — (185 ) Dividends paid — third party (58 ) — — — (58 ) Dividends paid and returns of contributed capital — intercompany — (1,000 ) (1,208 ) 2,208 — Capital contributions from parent — 6 49 (55 ) — Net cash (used in) provided by financing activities (1,727 ) (994 ) 3,436 2,261 2,976 Effect of exchange-rate changes on cash and cash equivalents — — (2 ) — (2 ) Net decrease in cash and cash equivalents and restricted cash (452 ) — (400 ) 521 (331 ) Cash and cash equivalents and restricted cash at beginning of year 1,395 — 5,707 (1,833 ) 5,269 Cash and cash equivalents and restricted cash at March 31, $ 943 $ — $ 5,307 $ (1,312 ) $ 4,938 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. March 31, 2018 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Cash and cash equivalents as disclosed on the Condensed Consolidated Balance Sheet $ 796 $ — $ 4,237 $ (1,312 ) $ 3,721 Restricted cash included in other assets on the Condensed Consolidated Balance Sheet (a) 147 — 1,070 — 1,217 Total cash and cash equivalents and restricted cash as disclosed in the Condensed Consolidated Statement of Cash Flows $ 943 $ — $ 5,307 $ (1,312 ) $ 4,938 (a) Restricted cash balances relate primarily to Ally securitization arrangements. Refer to Note 11 for additional details describing the nature of restricted cash balances. Three months ended March 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash (used in) provided by operating activities $ (149 ) $ — $ 1,284 $ 40 $ 1,175 Investing activities Purchases of equity securities — — (137 ) — (137 ) Proceeds from sales of equity securities — — 314 — 314 Purchases of available-for-sale securities — — (2,696 ) — (2,696 ) Proceeds from sales of available-for-sale securities — — 731 — 731 Proceeds from repayments of available-for-sale securities — — 589 — 589 Purchases of held-to-maturity securities — — (215 ) — (215 ) Proceeds from repayments of held-to-maturity securities — — 5 — 5 Net change in investment securities — intercompany 1 — 261 (262 ) — Purchases of finance receivables and loans held-for-investment (15 ) — (390 ) — (405 ) Proceeds from sales of finance receivables and loans initially held-for-investment — — 1,164 — 1,164 Originations and repayments of finance receivables and loans held-for-investment and other, net 931 — (1,145 ) (960 ) (1,174 ) Net change in loans — intercompany 1,146 — 170 (1,316 ) — Purchases of operating lease assets — — (893 ) — (893 ) Disposals of operating lease assets 1 — 1,544 — 1,545 Capital contributions to subsidiaries (83 ) — — 83 — Returns of contributed capital 645 — — (645 ) — Net change in nonmarketable equity investments — — 213 — 213 Other, net (26 ) — 64 (94 ) (56 ) Net cash provided by (used in) investing activities 2,600 — (421 ) (3,194 ) (1,015 ) Financing activities Net change in short-term borrowings — third party 1,278 — (5,581 ) — (4,303 ) Net (decrease) increase in deposits (82 ) — 5,533 — 5,451 Proceeds from issuance of long-term debt — third party 330 — 3,196 962 4,488 Repayments of long-term debt — third party (2,870 ) — (4,703 ) — (7,573 ) Net change in debt — intercompany (203 ) — (1,146 ) 1,349 — Repurchase of common stock (169 ) — — — (169 ) Dividends paid — third party (38 ) — — — (38 ) Dividends paid and returns of contributed capital — intercompany — — (686 ) 686 — Capital contributions from parent — — 83 (83 ) — Net cash used in financing activities (1,754 ) — (3,304 ) 2,914 (2,144 ) Effect of exchange-rate changes on cash and cash equivalents — — — — — Net increase (decrease) in cash and cash equivalents and restricted cash 697 — (2,441 ) (240 ) (1,984 ) 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 March 31, $ 1,686 $ — $ 4,852 $ (641 ) $ 5,897 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. March 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Cash and cash equivalents as disclosed on the Condensed Consolidated Balance Sheet $ 1,490 $ — $ 3,453 $ (641 ) $ 4,302 Restricted cash included in other assets on the Condensed Consolidated Balance Sheet (a) 196 — 1,399 — 1,595 Total cash and cash equivalents and restricted cash as disclosed in the Condensed Consolidated Statement of Cash Flows $ 1,686 $ — $ 4,852 $ (641 ) $ 5,897 (a) Restricted cash balances relate primarily to Ally securitization arrangements. Refer to Note 11 for additional details describing the nature of restricted cash balances.

Contingencies and Other Risks

Contingencies and Other Risks	3 Months Ended
	Mar. 31, 2018
Loss Contingency [Abstract]
Contingencies Disclosure [Text Block]	Contingencies and Other Risks 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. In April 2018, the court entered a scheduling order setting deadlines for briefing of defendants’ joint motion for summary disposition. 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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for additional information related to our policy for establishing reserves for legal and regulatory matters.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events Declaration of Quarterly Dividend On April 10, 2018 , the Board declared a quarterly cash dividend of $0.13 per share on all common stock. The dividend is payable on May 15, 2018 , to stockholders of record at the close of business on May 1, 2018.

Description of Business, Basi32

Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
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. 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.
Investment, Policy [Policy Text Block]	Our investment portfolio includes various debt and equity securities. Our debt securities include government securities, corporate bonds, asset-backed securities (ABS), and mortgage-backed securities (MBS). Debt 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 securities as trading when the securities are acquired for the purpose of selling or holding them for a short period of time. Debt securities not classified as either held-to-maturity or trading are classified as available-for-sale. Our portfolio includes debt securities classified as available-for-sale and held-to-maturity. Our available-for-sale debt securities are carried at fair value with unrealized gains and losses included in accumulated other comprehensive loss and are subject to impairment. Our held-to-maturity debt securities are carried at amortized cost and are subject to impairment. We assess our debt 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 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 debt 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 Condensed Consolidated Statement of Comprehensive Income, and a new cost basis in the investment is established. The noncredit loss component of an available-for-sale debt security continues to be recorded in other comprehensive (loss) income 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. Subsequent increases and decreases to the fair value of available-for-sale debt securities are included in other comprehensive (loss) income, so long as they are not attributable to another other-than-temporary 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. Our investment in equity securities includes securities that are recognized at fair value with changes in the market value recorded in earnings, and equity securities that are recognized using other measurement principles. Effective January 1, 2018, equity securities that are publicly traded and have a readily determinable fair value, as well as certain investments that do not have a readily determinable fair value and are not eligible to be recognized using other measurement principles, are recorded at fair value with changes in fair value recorded in earnings and reported in other gain (loss) on investments, net in our Condensed Consolidated Statement of Comprehensive Income . These investments, which are primarily attributable to the investment portfolio of our Insurance operations, are included in equity securities on our Condensed Consolidated Balance Sheet . Refer to Note 6 for further information on our equity securities that have a readily determinable market value. Our equity securities recognized using other measurement principles include investments in Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock held to meet regulatory requirements, equity investments related to low income housing tax credits and the Community Reinvestment Act (CRA), which are not publicly traded and do not have a readily determinable fair value, and other equity investments that are not publicly traded and do not have a readily determinable fair value. 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 included in other liabilities. The majority of our CRA investments are accounted for using the equity method of accounting. Our investments in low income housing tax credits and CRA investments are included in other assets on our Condensed Consolidated Balance Sheet. Our investments in FHLB and FRB stock are carried at cost. Our remaining investments in equity securities are recorded at cost, less impairment and adjusted for observable price differences under the measurement alternative provided under GAAP. These investments, along with our investments in FHLB and FRB stock, are included in nonmarketable equity investments in other assets on our Condensed Consolidated Balance Sheet. As conditions warrant, we review these investments for impairment and adjust the carrying value of the investment if it is deemed to be impaired. Investments recorded under the measurement alternative are also reviewed at each reporting period to determine if any adjustments are required for observable price changes in identical or similar securities. Realized gains and losses on the sale of securities are determined using the specific identification method and are reported in other gain (loss) on investments, net in our Condensed Consolidated Statement of Comprehensive Income.
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 18 . 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 changes in fair value of the derivative financial instruments are recorded in accumulated other comprehensive loss 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 loss as part of the cumulative translation adjustment. 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 loss, 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 loss 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]	In calculating the provision for interim income taxes, in accordance with Accounting Standards Codification (ASC) 740, Income Taxes , we apply an estimated annual effective tax rate to year-to-date ordinary income. At the end of each interim period, we estimate the effective tax rate expected to be applicable for the full fiscal year. This method differs from that described in Note 1 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K, which describes our annual significant income tax accounting policy and related methodology. Refer to Note 1 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K regarding additional significant accounting policies.
New Accounting Pronouncements or Change in Accounting Principle [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 Condensed Consolidated Statement of Cash Flows and additional disclosures surrounding restricted cash balances, but did not result in a change to our Condensed Consolidated Statement of Comprehensive Income or Condensed Consolidated Balance Sheet. 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. 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 issued several additional ASUs to clarify guidance and provide implementation support for ASU 2014-09. The clarifying guidance elaborates on the key concepts within ASU 2014-09 and clarifies how those concepts interact with other GAAP requirements. On January 1, 2018, we adopted ASU 2014-09 and all subsequent ASUs that modified ASU 2014-09 (collectively, the amendments to the revenue recognition principles), which have been codified in ASC 606, Revenue from Contracts with Customers, and ASC 610-20, Gains and Losses from the Derecognition of Nonfinancial Assets , respectively. We elected to adopt this guidance using the modified retrospective approach applied to all contracts with customers that were not completed as of January 1, 2018. The adoption of the amendments resulted in a reduction to our opening retained earnings of approximately $126 million , net of income taxes. Refer to Note 2 for further details. Financial Instruments — Recognition and Measurement of Financial Assets (ASU 2016-01) As of January 1, 2018, we adopted 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. The FASB subsequently issued ASU 2018-03 to clarify guidance and provide implementation support for ASU 2016-01, which we elected to early-adopt as of January 1, 2018, to align with the adoption of ASU 2016-01. 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 are no longer recognized through other comprehensive (loss) income , which creates additional volatility in our Condensed Consolidated Statement of 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 (loss) income and not as a component of net income. We adopted these amendments, as required, on a modified retrospective basis with a cumulative effect adjustment as of the beginning of the fiscal year of initial adoption. The adoption of the amendments resulted in a reduction to our opening retained earnings of approximately $20 million , net of income taxes. Derivatives and Hedging — Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12) As of January 1, 2018, we elected to early-adopt ASU 2017-12. The amendments in this update enhance the financial reporting of hedging relationships to better align hedge accounting with an entity’s risk management activities. This update also makes certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP and better portrays economic results through changes to both the designation and measurement guidance for qualifying hedging relationships and presentation of hedge results. We adopted the amendments to all cash flow and net investment hedge relationships that existed on the date of adoption using a modified retrospective approach. No cumulative effect adjustment to our opening retained earnings was required as a result of the adoption. The presentation and disclosure requirements included in this update were adopted prospectively. Refer to Note 18 for further details. 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 the impact of income tax effects resulting from the Tax Cuts and Jobs Act of 2017 (the Tax Act) on items included in accumulated other comprehensive income. Our policy is to use the portfolio method with respect to reclassification of stranded income tax effects in accumulated other comprehensive loss. The amendments in ASU 2018-02 provide entities an election to reclassify the income tax effect of the Tax Act from accumulated other comprehensive income to retained earnings. We elected to early-adopt this standard as of January 1, 2018, and reclassified the effect of the change in the federal corporate income tax rate on items included in accumulated other comprehensive loss. This election resulted in a reclassification of $42 million from accumulated other comprehensive loss to retained earnings. Recently Issued Accounting Standards 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. 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). While 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, as well as reviewing our leases where we are the lessor to determine the impact of the changes to capitalizable costs, we do not anticipate the adoption of these amendments will 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. 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.
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [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 Condensed Consolidated Statement of Cash Flows and additional disclosures surrounding restricted cash balances, but did not result in a change to our Condensed Consolidated Statement of Comprehensive Income or Condensed Consolidated Balance Sheet.
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [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. 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 issued several additional ASUs to clarify guidance and provide implementation support for ASU 2014-09. The clarifying guidance elaborates on the key concepts within ASU 2014-09 and clarifies how those concepts interact with other GAAP requirements. On January 1, 2018, we adopted ASU 2014-09 and all subsequent ASUs that modified ASU 2014-09 (collectively, the amendments to the revenue recognition principles), which have been codified in ASC 606, Revenue from Contracts with Customers, and ASC 610-20, Gains and Losses from the Derecognition of Nonfinancial Assets , respectively. We elected to adopt this guidance using the modified retrospective approach applied to all contracts with customers that were not completed as of January 1, 2018. The adoption of the amendments resulted in a reduction to our opening retained earnings of approximately $126 million , net of income taxes. Refer to Note 2 for further details.
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	As of January 1, 2018, we adopted 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. The FASB subsequently issued ASU 2018-03 to clarify guidance and provide implementation support for ASU 2016-01, which we elected to early-adopt as of January 1, 2018, to align with the adoption of ASU 2016-01. 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 are no longer recognized through other comprehensive (loss) income , which creates additional volatility in our Condensed Consolidated Statement of 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 (loss) income and not as a component of net income. We adopted these amendments, as required, on a modified retrospective basis with a cumulative effect adjustment as of the beginning of the fiscal year of initial adoption. The adoption of the amendments resulted in a reduction to our opening retained earnings of approximately $20 million , net of income taxes
Accounting Standards Update 2017-12 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncements, Policy [Policy Text Block]	As of January 1, 2018, we elected to early-adopt ASU 2017-12. The amendments in this update enhance the financial reporting of hedging relationships to better align hedge accounting with an entity’s risk management activities. This update also makes certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP and better portrays economic results through changes to both the designation and measurement guidance for qualifying hedging relationships and presentation of hedge results. We adopted the amendments to all cash flow and net investment hedge relationships that existed on the date of adoption using a modified retrospective approach. No cumulative effect adjustment to our opening retained earnings was required as a result of the adoption. The presentation and disclosure requirements included in this update were adopted prospectively. Refer to Note 18 for further details.
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [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 the impact of income tax effects resulting from the Tax Cuts and Jobs Act of 2017 (the Tax Act) on items included in accumulated other comprehensive income. Our policy is to use the portfolio method with respect to reclassification of stranded income tax effects in accumulated other comprehensive loss. The amendments in ASU 2018-02 provide entities an election to reclassify the income tax effect of the Tax Act from accumulated other comprehensive income to retained earnings. We elected to early-adopt this standard as of January 1, 2018, and reclassified the effect of the change in the federal corporate income tax rate on items included in accumulated other comprehensive loss. This election resulted in a reclassification of $42 million from accumulated other comprehensive loss to retained earnings.
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [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. 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). While 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, as well as reviewing our leases where we are the lessor to determine the impact of the changes to capitalizable costs, we do not anticipate the adoption of these amendments will 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 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [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]
New Accounting Pronouncements or Change in Accounting Principle [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.

Fair Value Fair Value (Policies

Fair Value Fair Value (Policies)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurement, Policy [Policy Text Block]	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.

Revenue from Contracts with C34

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	The following table presents the impact to our Condensed Consolidated Balance Sheet as of January 1, 2018, as a result of adopting the amendments to the revenue recognition principles. ($ in millions) As reported, December 31, 2017 Adjustment related to adoption As adjusted, January 1, 2018 Assets Premiums receivable and other insurance assets $ 2,047 $ 122 $ 2,169 Other assets 5,663 41 5,704 Total assets $ 167,148 $ 163 $ 167,311 Liabilities Unearned insurance premiums and service revenue $ 2,604 $ 289 $ 2,893 Total liabilities 153,654 289 153,943 Equity Accumulated deficit (6,406 ) (126 ) (6,532 ) Total equity 13,494 (126 ) 13,368 Total liabilities and equity $ 167,148 $ 163 $ 167,311
Impact of ASU 2014-09 on Balance Sheet and Income Statement [Table Text Block]	The following tables present the impact of adopting the amendments to the revenue recognition principles to our Condensed Consolidated Statement of Comprehensive Income and Condensed Consolidated Balance Sheet . Three months ended March 31, 2018 ($ in millions) As reported Effect of adoption Other revenue Insurance premiums and service revenue earned $ 256 $ (6 ) Total other revenue 354 (6 ) Total net revenue 1,403 (6 ) Noninterest expense Compensation and benefits expense 306 (1 ) Other operating expenses 445 (2 ) Total noninterest expense 814 (3 ) Income from continuing operations before income tax expense 328 (3 ) Income tax expense from continuing operations 76 (1 ) Net income from continuing operations 252 (2 ) Net income 250 (2 ) Comprehensive loss $ (78 ) $ (2 ) March 31, 2018 ($ in millions) As reported Effect of adoption Assets Premiums receivable and other insurance assets $ 2,197 $ 125 Other assets 6,025 42 Total assets 170,021 167 Liabilities Unearned insurance premiums and service revenue $ 2,904 $ 295 Total liabilities 156,939 295 Equity Accumulated deficit (6,318 ) (128 ) Total equity 13,082 (128 ) Total liabilities and equity $ 170,021 $ 167
Disaggregation of Revenue [Table Text Block]	The following table presents a disaggregated view of our revenue from contracts with customers included in other revenue that falls within the scope of the amendments to the revenue recognition principles. Three months ended March 31, 2018 ($ in millions) Automotive Finance operations Insurance operations Mortgage Finance operations Corporate Finance operations Corporate and Other Consolidated Revenue from contracts with customers Noninsurance contracts $ — $ 123 $ — $ — $ — $ 123 Remarketing fee income 23 — — — — 23 Brokerage commissions and other revenue — — — — 16 16 Brokered/agent commissions — 4 — — — 4 Deposit account and other banking fees — — — — 3 3 Other 2 1 — — — 3 Total revenue from contracts with customers 25 128 — — 19 172 All other revenue 41 118 1 8 14 182 Total other revenue (a) $ 66 $ 246 $ 1 $ 8 $ 33 $ 354 (a) Represents a component of total net revenue. Refer to Note 22 for further information on our reportable operating segments. In addition to the components of other revenue presented above, as part of our Automotive Finance operations, we recognized $18 million of gain on the sale of off-lease vehicles through depreciation expense on operating lease assets in our Condensed Consolidated Statement of Comprehensive Income during the three months ended March 31, 2018 .

Other Income, Net of Losses (Ta

Other Income, Net of Losses (Tables)	3 Months Ended
	Mar. 31, 2018
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. Three months ended March 31, ($ in millions) 2018 2017 Late charges and other administrative fees $ 29 $ 27 Remarketing fees 23 29 Servicing fees 8 16 Income from equity-method investments 6 — Other, net 43 42 Total other income, net of losses $ 109 $ 114

Reserves for Insurance Losses36

Reserves for Insurance Losses and Loss Adjustment Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Reserves for Insurance Losses and Loss Adjustment Expense [Abstract]
Short-Duration Insurance and Deposit Contracts [Text Block]	The following table shows a rollforward of our reserves for insurance losses and loss adjustment expenses. ($ in millions) 2018 2017 Total gross reserves for insurance losses and loss adjustment expenses at January 1, $ 140 $ 149 Less: Reinsurance recoverable 108 108 Net reserves for insurance losses and loss adjustment expenses at January 1, 32 41 Net insurance losses and loss adjustment expenses incurred related to: Current year 60 89 Prior years (a) 3 (1 ) Total net insurance losses and loss adjustment expenses incurred 63 88 Net insurance losses and loss adjustment expenses paid or payable related to: Current year (31 ) (45 ) Prior years (19 ) (23 ) Total net insurance losses and loss adjustment expenses paid or payable (50 ) (68 ) Foreign exchange and other — 2 Net reserves for insurance losses and loss adjustment expenses at March 31, 45 63 Plus: Reinsurance recoverable 112 112 Total gross reserves for insurance losses and loss adjustment expenses at March 31, $ 157 $ 175 (a) There have been no material adverse changes to the reserve for prior years.

Other Operating Expenses (Table

Other Operating Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Operating Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Details of other operating expenses were as follows. Three months ended March 31, ($ in millions) 2018 2017 Insurance commissions $ 110 $ 99 Technology and communications 71 69 Lease and loan administration 42 36 Advertising and marketing 39 30 Vehicle remarketing and repossession 32 28 Professional services 32 26 Regulatory and licensing fees 30 27 Premises and equipment depreciation 20 22 Occupancy 11 12 Non-income taxes 8 8 Amortization of intangible assets 3 3 Other 47 45 Total other operating expenses $ 445 $ 405

Investment Securities (Tables)

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Marketable Securities [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 available-for-sale and held-to-maturity investment securities were as follows. March 31, 2018 December 31, 2017 Amortized cost Gross unrealized Fair value Amortized cost Gross unrealized Fair value ($ in millions) gains losses gains losses Available-for-sale securities Debt securities U.S. Treasury $ 1,855 $ — $ (86 ) $ 1,769 $ 1,831 $ — $ (54 ) $ 1,777 U.S. States and political subdivisions 845 5 (19 ) 831 850 11 (7 ) 854 Foreign government 150 1 (2 ) 149 153 2 (1 ) 154 Agency mortgage-backed residential 15,316 4 (437 ) 14,883 14,412 35 (156 ) 14,291 Mortgage-backed residential 2,456 3 (75 ) 2,384 2,517 11 (34 ) 2,494 Mortgage-backed commercial 582 1 (3 ) 580 541 1 (1 ) 541 Asset-backed 901 2 (3 ) 900 933 4 (1 ) 936 Corporate debt 1,263 1 (34 ) 1,230 1,262 5 (11 ) 1,256 Total available-for-sale securities (a) (b) (c) $ 23,368 $ 17 $ (659 ) 22,726 $ 22,499 $ 69 $ (265 ) $ 22,303 Held-to-maturity securities Debt securities Agency mortgage-backed residential (d) $ 1,936 $ — $ (72 ) $ 1,864 $ 1,863 $ 3 $ (37 ) $ 1,829 Asset-backed retained notes 31 — — 31 36 — — 36 Total held-to-maturity securities $ 1,967 $ — $ (72 ) $ 1,895 $ 1,899 $ 3 $ (37 ) $ 1,865 (a) Certain entities related to our Insurance operations are required to deposit securities with state regulatory authorities. These deposited securities totaled $12 million at both March 31, 2018 , and December 31, 2017. (b) Certain available-for-sale securities are included in fair value hedging relationships. Refer to Note 18 for additional information. (c) Investment securities with a fair value of $8.0 billion and $7.8 billion at March 31, 2018 , and December 31, 2017, 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 $839 million and $1.0 billion of the underlying investment securities at March 31, 2018 , and December 31, 2017, respectively. (d) Securities with a fair value of $993 million and $664 million at March 31, 2018 , and December 31, 2017, respectively, were pledged to secure advances from the FHLB.
Investments Classified by Contractual Maturity Date [Table Text Block]	The maturity distribution of debt securities outstanding is summarized in the following tables. Call or prepayment options may cause actual maturities to differ from contractual maturities. Total Due in one year or less Due after one year through five years Due after five years through ten years Due after ten years ($ in millions) Amount Yield Amount Yield Amount Yield Amount Yield Amount Yield March 31, 2018 Fair value of available-for-sale securities (a) U.S. Treasury $ 1,769 1.8 % $ — — % $ 481 1.7 % $ 1,288 1.8 % $ — — % U.S. States and political subdivisions 831 3.0 70 2.3 42 2.3 219 2.6 500 3.3 Foreign government 149 2.5 — — 77 2.6 72 2.4 — — Agency mortgage-backed residential 14,883 3.2 — — — — 3 2.6 14,880 3.2 Mortgage-backed residential 2,384 3.1 — — — — — — 2,384 3.1 Mortgage-backed commercial 580 3.4 — — — — 31 3.3 549 3.4 Asset-backed 900 3.2 — — 655 3.2 121 3.3 124 2.9 Corporate debt 1,230 3.0 123 2.8 496 2.7 573 3.3 38 4.8 Total available-for-sale securities $ 22,726 3.0 $ 193 2.6 $ 1,751 2.6 $ 2,307 2.3 $ 18,475 3.2 Amortized cost of available-for-sale securities $ 23,368 $ 194 $ 1,776 $ 2,403 $ 18,995 Amortized cost of held-to-maturity securities Agency mortgage-backed residential $ 1,936 3.1 % $ — — % $ — — % $ — — % $ 1,936 3.1 % Asset-backed retained notes 31 1.7 — — 30 1.7 1 3.0 — — Total held-to-maturity securities $ 1,967 3.1 $ — — $ 30 1.7 $ 1 3.0 $ 1,936 3.1 December 31, 2017 Fair value of available-for-sale 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 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 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 (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.
Investment Income [Table Text Block]	The following table presents interest and dividends on investment securities. Three months ended March 31, ($ in millions) 2018 2017 Taxable interest $ 154 $ 119 Taxable dividends 3 2 Interest and dividends exempt from U.S. federal income tax 6 5 Interest and dividends on investment securities $ 163 $ 126
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 net gains or losses on equity securities held during the period. There were no other-than-temporary impairments of available-for-sale securities for either period. Three months ended March 31, ($ in millions) 2018 2017 Available-for-sale securities Gross realized gains $ 6 $ 27 Gross realized losses — — Net realized gains on available-for-sale securities 6 27 Net realized gain on equity securities 22 Net unrealized loss on equity securities (a) (40 ) Other (loss) gain on investments, net $ (12 ) $ 27 (a) As a result of our adoption of ASU 2016-01, beginning January 1, 2018, changes in the fair value of our portfolio of equity securities are recognized in net income. Prior to adoption, equity securities were included in our available-for-sale portfolio and unrealized changes in fair value were recognized through other comprehensive (loss) income until realized, at which point we recorded a gain or loss on sale. We adopted ASU 2016-01 on January 1, 2018, on a modified retrospective basis with a cumulative effect adjustment as of the beginning of the fiscal year of initial adoption. Refer to the section titled Recently Adopted Accounting Standards in Note 1 for additional information.
Schedule of Unrealized Loss on Investments [Table Text Block]	The table below summarizes available-for-sale and held-to-maturity securities in an unrealized loss position, which we evaluated for other than temporary impairment applying the methodology described in Note 1 . As of March 31, 2018 , we did not have the intent to sell the available-for-sale or held-to-maturity securities with an unrealized loss position and we do not believe it is more likely than not that we will be required to sell these securities before recovery of their amortized cost basis. As a result of this evaluation, we believe that the securities with an unrealized loss position are not considered to be other-than-temporarily impaired at March 31, 2018 . March 31, 2018 December 31, 2017 Less than 12 months 12 months or longer Less than 12 months 12 months or longer ($ 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 $ 488 $ (16 ) $ 1,282 $ (70 ) $ 471 $ (8 ) $ 1,305 $ (46 ) U.S. States and political subdivisions 436 (9 ) 176 (10 ) 242 (2 ) 183 (5 ) Foreign government 82 (2 ) 4 — 80 (1 ) 4 — Agency mortgage-backed residential 8,951 (183 ) 5,395 (254 ) 4,066 (19 ) 5,671 (137 ) Mortgage-backed residential 1,439 (29 ) 734 (46 ) 857 (2 ) 773 (32 ) Mortgage-backed commercial 71 (2 ) 21 (1 ) 76 (1 ) 21 — Asset-backed 426 (2 ) 76 (1 ) 220 (1 ) 91 — Corporate debt 932 (20 ) 191 (14 ) 529 (4 ) 194 (7 ) Total temporarily impaired available-for-sale securities $ 12,825 $ (263 ) $ 7,879 $ (396 ) $ 6,541 $ (38 ) $ 8,242 $ (227 ) Held-to-maturity securities Agency mortgage-backed residential $ 1,147 $ (26 ) $ 672 $ (46 ) $ 773 $ (5 ) $ 687 $ (32 ) Asset-backed retained certificates 31 — — — 35 — — — Total held-to-maturity debt securities $ 1,178 $ (26 ) $ 672 $ (46 ) $ 808 $ (5 ) $ 687 $ (32 )

Finance Receivables and Loans39

Finance Receivables and Loans, Net (Tables)	3 Months Ended
	Mar. 31, 2018
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. ($ in millions) March 31, 2018 December 31, 2017 Consumer automotive (a) $ 69,318 $ 68,071 Consumer mortgage Mortgage Finance (b) 12,733 11,657 Mortgage — Legacy (c) 1,950 2,093 Total consumer mortgage 14,683 13,750 Total consumer 84,001 81,821 Commercial Commercial and industrial Automotive 32,781 33,025 Other 4,184 3,887 Commercial real estate 4,361 4,160 Total commercial 41,326 41,072 Total finance receivables and loans (d) $ 125,327 $ 122,893 (a) Certain finance receivables and loans are included in fair value hedging relationships. Refer to Note 18 for additional information. (b) Includes loans originated as interest-only mortgage loans of $19 million and $20 million at March 31, 2018 , and December 31, 2017 , respectively, 34% of which are expected to start principal amortization in 2019 , and 46% in 2020 . The remainder of these loans have already exited the interest-only period. (c) Includes loans originated as interest-only mortgage loans of $459 million and $496 million at March 31, 2018 , and December 31, 2017 , respectively, 2% 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 unearned income, unamortized premiums and discounts, and deferred fees and costs of $586 million and $551 million at March 31, 2018 , and December 31, 2017 , respectively
Allowance for Credit Losses on Financing Receivables [Table Text Block]	The following tables present an analysis of the activity in the allowance for loan losses on finance receivables and loans. Three months ended March 31, 2018 ($ in millions) Consumer automotive Consumer mortgage Commercial Total Allowance at January 1, 2018 $ 1,066 $ 79 $ 131 $ 1,276 Charge-offs (a) (365 ) (12 ) — (377 ) Recoveries 112 6 — 118 Net charge-offs (253 ) (6 ) — (259 ) Provision for loan losses 253 1 7 261 Allowance at March 31, 2018 $ 1,066 $ 74 $ 138 $ 1,278 Allowance for loan losses at March 31, 2018 Individually evaluated for impairment $ 40 $ 27 $ 21 $ 88 Collectively evaluated for impairment 1,026 47 117 1,190 Finance receivables and loans at gross carrying value Ending balance $ 69,318 $ 14,683 $ 41,326 $ 125,327 Individually evaluated for impairment 463 230 147 840 Collectively evaluated for impairment 68,855 14,453 41,179 124,487 (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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for more information regarding our charge-off policies. Three months ended March 31, 2017 ($ in millions) Consumer automotive Consumer mortgage Commercial Total Allowance at January 1, 2017 $ 932 $ 91 $ 121 $ 1,144 Charge-offs (a) (341 ) (9 ) — (350 ) Recoveries 90 7 — 97 Net charge-offs (251 ) (2 ) — (253 ) Provision for loan losses 267 (3 ) 7 271 Other (b) (7 ) — — (7 ) Allowance at March 31, 2017 $ 941 $ 86 $ 128 $ 1,155 Allowance for loan losses at March 31, 2017 Individually evaluated for impairment $ 32 $ 33 $ 24 $ 89 Collectively evaluated for impairment 909 53 104 1,066 Finance receivables and loans at gross carrying value Ending balance $ 65,663 $ 10,937 $ 42,402 $ 119,002 Individually evaluated for impairment 388 249 120 757 Collectively evaluated for impairment 65,275 10,688 42,282 118,245 (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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K 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 based on net carrying value. Three months ended March 31, ($ in millions) 2018 2017 Consumer automotive $ — $ 1,213 Consumer mortgage 1 3 Total sales and transfers $ 1 $ 1,216
Schedule of Purchases of Financing Receivables and Loans [Table Text Block]	The following table presents information about significant purchases of finance receivables and loans based on unpaid principal balance at the time of purchase. Three months ended March 31, ($ in millions) 2018 2017 Consumer automotive $ 168 $ 68 Consumer mortgage 1,295 327 Total purchases of finance receivables and loans $ 1,463 $ 395
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. ($ 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 March 31, 2018 Consumer automotive $ 1,574 $ 359 $ 253 $ 2,186 $ 67,132 $ 69,318 Consumer mortgage Mortgage Finance 97 8 18 123 12,610 12,733 Mortgage — Legacy 40 19 61 120 1,830 1,950 Total consumer mortgage 137 27 79 243 14,440 14,683 Total consumer 1,711 386 332 2,429 81,572 84,001 Commercial Commercial and industrial Automotive 23 6 4 33 32,748 32,781 Other — 30 — 30 4,154 4,184 Commercial real estate 4 — — 4 4,357 4,361 Total commercial 27 36 4 67 41,259 41,326 Total consumer and commercial $ 1,738 $ 422 $ 336 $ 2,496 $ 122,831 $ 125,327 December 31, 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
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. ($ in millions) March 31, 2018 December 31, 2017 Consumer automotive $ 601 $ 603 Consumer mortgage Mortgage Finance 28 25 Mortgage — Legacy 87 92 Total consumer mortgage 115 117 Total consumer 716 720 Commercial Commercial and industrial Automotive 68 27 Other 74 44 Commercial real estate 5 1 Total commercial 147 72 Total consumer and commercial finance receivables and loans $ 863 $ 792
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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for additional information. March 31, 2018 December 31, 2017 ($ in millions) Performing Nonperforming Total Performing Nonperforming Total Consumer automotive $ 68,717 $ 601 $ 69,318 $ 67,468 $ 603 $ 68,071 Consumer mortgage Mortgage Finance 12,705 28 12,733 11,632 25 11,657 Mortgage — Legacy 1,863 87 1,950 2,001 92 2,093 Total consumer mortgage 14,568 115 14,683 13,633 117 13,750 Total consumer $ 83,285 $ 716 $ 84,001 $ 81,101 $ 720 $ 81,821
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. March 31, 2018 December 31, 2017 ($ in millions) Pass Criticized (a) Total Pass Criticized (a) Total Commercial and industrial Automotive $ 30,433 $ 2,348 $ 32,781 $ 30,982 $ 2,043 $ 33,025 Other 3,284 900 4,184 2,986 901 3,887 Commercial real estate 4,151 210 4,361 4,023 137 4,160 Total commercial $ 37,868 $ 3,458 $ 41,326 $ 37,991 $ 3,081 $ 41,072 (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. ($ in millions) Unpaid principal balance (a) Gross carrying value Impaired with no allowance Impaired with an allowance Allowance for impaired loans March 31, 2018 Consumer automotive $ 473 $ 463 $ 107 $ 356 $ 40 Consumer mortgage Mortgage Finance 9 9 4 5 — Mortgage — Legacy 226 221 61 160 27 Total consumer mortgage 235 230 65 165 27 Total consumer 708 693 172 521 67 Commercial Commercial and industrial Automotive 68 68 15 53 9 Other 85 74 41 33 11 Commercial real estate 5 5 4 1 1 Total commercial 158 147 60 87 21 Total consumer and commercial finance receivables and loans $ 866 $ 840 $ 232 $ 608 $ 88 December 31, 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 (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. 2018 2017 Three months ended March 31, ($ in millions) Average balance Interest income Average balance Interest income Consumer automotive $ 444 $ 7 $ 379 $ 5 Consumer mortgage Mortgage Finance 9 — 8 — Mortgage — Legacy 221 2 241 2 Total consumer mortgage 230 2 249 2 Total consumer 674 9 628 7 Commercial Commercial and industrial Automotive 47 1 33 — Other 52 — 83 — Commercial real estate 3 — 5 — Total commercial 102 1 121 — Total consumer and commercial finance receivables and loans $ 776 $ 10 $ 749 $ 7
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. 2018 2017 Three months ended March 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 7,042 $ 128 $ 110 6,447 $ 115 $ 99 Consumer mortgage Mortgage Finance 1 1 1 1 — — Mortgage — Legacy 62 10 9 53 12 12 Total consumer mortgage 63 11 10 54 12 12 Total consumer 7,105 139 120 6,501 127 111 Commercial Commercial and industrial Other — — — 1 23 23 Total commercial — — — 1 23 23 Total consumer and commercial finance receivables and loans 7,105 $ 139 $ 120 6,502 $ 150 $ 134
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 to the Consolidated Financial Statements in our 2017 Annual Report on Form 10-K for additional information) except for commercial finance receivables and loans, where redefault is defined as 90 days past due. 2018 2017 Three months ended March 31, ($ in millions) Number of loans Gross carrying value Charge-off amount Number of loans Gross carrying value Charge-off amount Consumer automotive 2,326 $ 28 $ 18 1,989 $ 24 $ 16 Consumer mortgage Mortgage Finance — — — 1 1 — Total consumer finance receivables and loans 2,326 $ 28 $ 18 1,990 $ 25 $ 16

Investment in Operating Lease40

Investment in Operating Leases, Net (Tables)	3 Months Ended
	Mar. 31, 2018
Leases, Operating [Abstract]
Schedule of Property Subject to or Available for Operating Lease [Table Text Block]	Investments in operating leases were as follows. ($ in millions) March 31, 2018 December 31, 2017 Vehicles $ 10,206 $ 10,556 Accumulated depreciation (1,676 ) (1,815 ) Investment in operating leases, net $ 8,530 $ 8,741
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. Three months ended March 31, ($ in millions) 2018 2017 Depreciation expense on operating lease assets (excluding remarketing gains and losses) $ 291 $ 386 Remarketing (gains) losses (18 ) 3 Net depreciation expense on operating lease assets $ 273 $ 389

Securitizations and Variable 41

Securitizations and Variable Interest Entities (Tables)	3 Months Ended
	Mar. 31, 2018
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 Condensed Consolidated Balance Sheet. ($ 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 March 31, 2018 On-balance sheet variable interest entities Consumer automotive $ 17,993 (b) $ 8,232 (c) Commercial automotive 10,428 3,521 Off-balance sheet variable interest entities Consumer automotive 32 (d) — $ 1,658 $ 1,691 (e) Commercial other 702 (f) 331 (g) — 882 (h) Total $ 29,155 $ 12,084 $ 1,658 $ 2,573 December 31, 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 (a) Asset values represent the current unpaid principal balance of outstanding consumer finance receivables and loans within the VIEs. (b) Includes $8.4 billion and $8.5 billion of assets that are not encumbered by VIE beneficial interests held by third parties at March 31, 2018 , and December 31, 2017 , respectively. Ally or consolidated affiliates hold the interests in these assets. (c) Includes $31 million and $29 million of liabilities that are not obligations to third-party beneficial interest holders at March 31, 2018 , and December 31, 2017 , respectively. (d) Represents retained notes and certificated residual interests, of which $31 million and $36 million is classified as held-to-maturity securities at March 31, 2018 , and December 31, 2017 , respectively. $1 million is classified as other assets at both March 31, 2018 , and 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. (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.
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 three months ended March 31, 2018 , and 2017. Additionally, this table contains information regarding cash flows received from and paid to nonconsolidated securitization entities that existed during each period. Three months ended March 31, ($ in millions) Consumer automotive 2018 Cash disbursements for repurchases during the period $ (1 ) Servicing fees 5 Cash flows received on retained interests in securitization entities 5 2017 Cash proceeds from transfers completed during the period $ 1,138 Servicing fees 9 Other cash flows 2
Schedule of Quantitative Information and Net Credit Losses about Securitized and Other Financial Assets Managed Together [Table Text Block]	The following tables present quantitative information about delinquencies and net credit losses for off-balance sheet securitizations and whole-loan sales where we have continuing involvement. Total amount Amount 60 days or more past due ($ in millions) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Off-balance sheet securitization entities Consumer automotive $ 1,658 $ 1,964 $ 12 $ 16 Total off-balance sheet securitization entities 1,658 1,964 12 16 Whole-loan sales (a) 1,167 1,399 3 4 Total $ 2,825 $ 3,363 $ 15 $ 20 (a) Whole-loan sales are not part of a securitization transaction, but represent consumer automotive pools of loans sold to third-party investors. Net credit losses Three months ended March 31, ($ in millions) 2018 2017 Off-balance sheet securitization entities Consumer automotive $ 3 $ 3 Total off-balance sheet securitization entities 3 3 Whole-loan sales (a) 1 1 Total $ 4 $ 4 (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)	3 Months Ended
	Mar. 31, 2018
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. ($ in millions) March 31, 2018 December 31, 2017 On-balance sheet automotive finance loans and leases Consumer automotive $ 68,738 $ 67,631 Commercial automotive 36,935 37,058 Operating leases 8,489 8,682 Other 131 121 Off-balance sheet automotive finance loans Securitizations 1,666 1,977 Whole-loan sales 1,175 1,409 Total serviced automotive finance loans and leases $ 117,134 $ 116,878

Other Assets (Tables)

Other Assets (Tables)	3 Months Ended
	Mar. 31, 2018
Other Assets [Abstract]
Schedule of Other Assets [Table Text Block]	The components of other assets were as follows. ($ in millions) March 31, 2018 December 31, 2017 Property and equipment at cost $ 1,107 $ 1,064 Accumulated depreciation (627 ) (608 ) Net property and equipment 480 456 Nonmarketable equity investments (a) 1,250 1,233 Restricted cash collections for securitization trusts (b) 986 812 Accrued interest and rent receivables 533 550 Net deferred tax assets 530 461 Goodwill (c) 240 240 Other accounts receivable 142 116 Restricted cash and cash equivalents (d) 119 94 Cash reserve deposits held for securitization trusts (e) 112 111 Fair value of derivative contracts in receivable position (f) 56 39 Cash collateral placed with counterparties 33 29 Other assets 1,544 1,522 Total other assets $ 6,025 $ 5,663 (a) Includes investments in FHLB stock of $764 million and $745 million at March 31, 2018 , and December 31, 2017, respectively; FRB stock of $446 million and $445 million at March 31, 2018 , and December 31, 2017, respectively; and equity securities without a readily determinable fair value of $40 million at March 31, 2018 , measured at cost with adjustments for impairment and observable changes in price. We have not recorded any impairments or adjustments for observable price differences to these investments during the three months ended March 31, 2018 . (b) Represents cash collections from customer payments on securitized receivables. These funds are distributed to investors as payments on the related secured debt. (c) Includes goodwill of $27 million within our Insurance operations at both March 31, 2018 , and December 31, 2017 ; $193 million within Corporate and Other at both March 31, 2018 , and December 31, 2017 ; and $20 million within Automotive Finance operations at both March 31, 2018 , and December 31, 2017 . No changes to the carrying amount of goodwill were recorded during the three months ended March 31, 2018. (d) 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. (e) Represents credit enhancement in the form of cash reserves for various securitization transactions. (f) For additional information on derivative instruments and hedging activities, refer to Note 18 .

Deposit Liabilities (Tables)

Deposit Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Deposits [Abstract]
Deposit Liabilities, Type [Table Text Block]	Deposit liabilities consisted of the following. ($ in millions) March 31, 2018 December 31, 2017 Noninterest-bearing deposits $ 122 $ 108 Interest-bearing deposits Savings and money market checking accounts 50,293 49,267 Certificates of deposit 47,025 43,869 Dealer deposits 6 12 Total deposit liabilities $ 97,446 $ 93,256

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Schedule of Short-term Debt [Table Text Block]	The following table presents the composition of our short-term borrowings portfolio. March 31, 2018 December 31, 2017 ($ in millions) Unsecured Secured (a) Total Unsecured Secured (a) Total Demand notes $ 2,957 $ — $ 2,957 $ 3,171 $ — $ 3,171 Federal Home Loan Bank — 5,900 5,900 — 7,350 7,350 Financial instruments sold under agreements to repurchase — 707 707 — 892 892 Total short-term borrowings $ 2,957 $ 6,607 $ 9,564 $ 3,171 $ 8,242 $ 11,413 (a) Refer to the section below titled Long-term Debt for further details on assets restricted as collateral for payment of the related debt.
Long-term Debt [Text Block]	The following table presents the composition of our long-term debt portfolio. March 31, 2018 December 31, 2017 ($ in millions) Unsecured Secured Total Unsecured Secured Total Long-term debt Due within one year $ 3,681 $ 7,639 $ 11,320 $ 3,482 $ 7,499 $ 10,981 Due after one year (a) 11,153 22,476 33,629 11,909 21,128 33,037 Fair value adjustment (b) 190 (63 ) 127 240 (32 ) 208 Total long-term debt (c) $ 15,024 $ 30,052 $ 45,076 $ 15,631 $ 28,595 $ 44,226 (a) Includes $2.6 billion of trust preferred securities at both March 31, 2018, and December 31, 2017. (b) Represents the basis adjustment associated with the application of hedge accounting on certain of our long-term debt positions. Refer to Note 18 for additional information. (c) Includes advances from the FHLB of Pittsburgh of $12.7 billion and $10.3 billion at March 31, 2018, and December 31, 2017, respectively.
Scheduled of Maturities of Long-term Debt [Table Text Block]	The following table presents the scheduled remaining maturity of long-term debt at March 31, 2018 , assuming no early redemptions will occur. The actual payment of secured debt may vary based on the payment activity of the related pledged assets. ($ in millions) 2018 2019 2020 2021 2022 2023 and thereafter Fair value adjustment Total Unsecured Long-term debt $ 2,987 $ 1,680 $ 2,251 $ 650 $ 1,066 $ 7,411 $ 190 $ 16,235 Original issue discount (76 ) (39 ) (39 ) (43 ) (47 ) (967 ) — (1,211 ) Total unsecured 2,911 1,641 2,212 607 1,019 6,444 190 15,024 Secured Long-term debt 4,924 7,467 6,845 5,717 4,094 1,068 (63 ) 30,052 Total long-term debt $ 7,835 $ 9,108 $ 9,057 $ 6,324 $ 5,113 $ 7,512 $ 127 $ 45,076
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. March 31, 2018 December 31, 2017 ($ in millions) Total (a) Ally Bank Total (a) Ally Bank Investment securities (b) $ 8,891 $ 8,443 $ 8,371 $ 7,443 Mortgage assets held-for-investment and lending receivables 14,501 14,501 13,579 13,579 Consumer automotive finance receivables 17,472 6,639 19,787 6,200 Commercial automotive finance receivables 14,618 14,558 16,567 16,472 Operating leases 350 — 457 — Total assets restricted as collateral (c) (d) $ 55,832 $ 44,141 $ 58,761 $ 43,694 Secured debt $ 36,659 (e) $ 25,874 $ 36,837 (e) $ 23,278 (a) Ally Bank is a component of the total column. (b) A portion of the restricted investment securities at March 31, 2018 , and December 31, 2017 , 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 $27.0 billion and $25.2 billion at March 31, 2018 , and December 31, 2017 , 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 at both March 31, 2018 , and December 31, 2017 . These assets were composed of consumer automotive finance receivables and loans. 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 Condensed Consolidated Balance Sheet . Refer to Note 11 for additional information. (e) Includes $6.6 billion and $8.2 billion of short-term borrowings at March 31, 2018 , and December 31, 2017 , respectively
Schedule Of Committed Funding Facilities [Table Text Block]	Outstanding Unused capacity (a) Total capacity ($ in millions) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Bank funding Secured $ 1,500 $ 1,785 $ — $ 890 $ 1,500 $ 2,675 Parent funding Secured 4,255 6,330 2,970 2,920 7,225 9,250 Total committed facilities $ 5,755 $ 8,115 $ 2,970 $ 3,810 $ 8,725 $ 11,925 (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.

Accrued Expenses and Other Li46

Accrued Expenses and Other Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Accounts Payable and Accrued Liabilities [Abstract]
Schedule of Accrued Liabilities [Table Text Block]	The components of accrued expenses and other liabilities were as follows. ($ in millions) March 31, 2018 December 31, 2017 Accounts payable $ 390 $ 746 Employee compensation and benefits 161 248 Reserves for insurance losses and loss adjustment expenses 157 140 Fair value of derivative contracts in payable position (a) 56 41 Deferred revenue 34 32 Cash collateral received from counterparties 31 17 Other liabilities 626 556 Total accrued expenses and other liabilities $ 1,455 $ 1,780 (a) For additional information on derivative instruments and hedging activities, refer to Note 18 .

Accumulated Other Comprehensi47

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2018
Other Comprehensive Income (Loss), Net of Tax [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 December 31, 2016 $ (273 ) $ 14 $ 8 $ (90 ) $ (341 ) 2017 net change 21 — — (1 ) 20 Balance at March 31, 2017 $ (252 ) $ 14 $ 8 $ (91 ) $ (321 ) Balance at December 31, 2017, before cumulative effect of adjustments $ (173 ) $ 16 $ 11 $ (89 ) $ (235 ) Cumulative effect of changes in accounting principles, net of tax (c) Adoption of Accounting Standards Update 2016-01 27 — — — 27 Adoption of Accounting Standards Update 2018-02 (40 ) 4 — (6 ) (42 ) Balance at January 1, 2018, after cumulative effect of adjustments (186 ) 20 11 (95 ) (250 ) 2018 net change (338 ) (1 ) 14 (3 ) (328 ) Balance at March 31, 2018 $ (524 ) $ 19 $ 25 $ (98 ) $ (578 ) (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 18 . (c) Refer to the section titled Recently Adopted Accounting Standards in Note 1 for additional information.
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. Three months ended March 31, 2018 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized losses arising during the period $ (436 ) $ 103 $ (333 ) Less: Net realized gains reclassified to income from continuing operations 6 (a) (1 ) (b) 5 Net change (442 ) 104 (338 ) Translation adjustments Net unrealized losses arising during the period (5 ) 1 (4 ) Net investment hedges (c) Net unrealized gains arising during the period 4 (1 ) 3 Cash flow hedges (c) Net unrealized gains arising during the period 18 (4 ) 14 Defined benefit pension plans Net unrealized losses arising during the period (3 ) — (3 ) Other comprehensive loss $ (428 ) $ 100 $ (328 ) (a) Includes gains reclassified to other (loss) gain on investments, net in our Condensed Consolidated Statement of Comprehensive Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Condensed Consolidated Statement of Comprehensive Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 18 . Three months ended March 31, 2017 ($ in millions) Before tax Tax effect After tax Investment securities Net unrealized gains arising during the period $ 51 $ (5 ) $ 46 Less: Net realized gains reclassified to income from continuing operations 27 (a) (2 ) (b) 25 Net change 24 (3 ) 21 Translation adjustments Net unrealized gains arising during the period 2 (1 ) 1 Net investment hedges (c) Net unrealized losses arising during the period (2 ) 1 (1 ) Defined benefit pension plans Net unrealized losses arising during the period (1 ) — (1 ) Other comprehensive income $ 23 $ (3 ) $ 20 (a) Includes gains reclassified to other gain on investments, net in our Condensed Consolidated Statement of Comprehensive Income . (b) Includes amounts reclassified to income tax expense from continuing operations in our Condensed Consolidated Statement of Comprehensive Income . (c) For additional information on derivative instruments and hedging activities, refer to Note 18 .

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	3 Months Ended
	Mar. 31, 2018
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. Three months ended March 31, ($ in millions, except per share data; shares in thousands) (a) 2018 2017 Net income from continuing operations attributable to common stockholders $ 252 $ 213 (Loss) income from discontinued operations, net of tax (2 ) 1 Net income attributable to common stockholders $ 250 $ 214 Basic weighted-average common shares outstanding (b) 436,213 465,961 Diluted weighted-average common shares outstanding (b) 438,931 466,829 Basic earnings per common share Net income from continuing operations $ 0.58 $ 0.46 Loss from discontinued operations, net of tax (0.01 ) — Net income $ 0.57 $ 0.46 Diluted earnings per common share Net income from continuing operations $ 0.57 $ 0.46 Loss from discontinued operations, net of tax (0.01 ) — Net income $ 0.57 $ 0.46 (a) Figures in the table may not recalculate exactly due to rounding. Earnings per share is calculated based on unrounded numbers. (b) Includes shares related to share-based compensation that vested but were not yet issued for the three months ended March 31, 2018 , and 2017 .

Regulatory Capital and Other 49

Regulatory Capital and Other Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2018
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. March 31, 2018 December 31, 2017 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. $ 13,079 9.26 % $ 13,237 9.53 % 4.50 % (b) Ally Bank 16,535 13.93 17,059 15.04 4.50 6.50 % Tier 1 (to risk-weighted assets) Ally Financial Inc. $ 15,512 10.98 % $ 15,628 11.25 % 6.00 % 6.00 % Ally Bank 16,535 13.93 17,059 15.04 6.00 8.00 Total (to risk-weighted assets) Ally Financial Inc. $ 17,760 12.57 % $ 17,974 12.94 % 8.00 % 10.00 % Ally Bank 17,480 14.72 17,886 15.77 8.00 10.00 Tier 1 leverage (to adjusted quarterly average assets) (c) Ally Financial Inc. $ 15,512 9.26 % $ 15,628 9.53 % 4.00 % (b) Ally Bank 16,535 11.94 17,059 12.87 4.00 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 1.875% and 1.25% at March 31, 2018, and December 31, 2017, 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.
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. Common stock repurchased during period (a) Number of common shares outstanding Cash dividends declared per common share (b) ($ in millions, except per share data; shares in thousands) Approximate dollar value Number of shares Beginning of period End of period 2016 Third quarter $ 159 8,298 483,753 475,470 $ 0.08 Fourth quarter 167 8,745 475,470 467,000 0.08 2017 First quarter $ 169 8,097 467,000 462,193 $ 0.08 Second quarter 204 10,485 462,193 452,292 0.08 Third quarter 190 8,507 452,292 443,796 0.12 Fourth quarter 190 7,033 443,796 437,054 0.12 2018 First quarter $ 185 6,473 437,054 432,691 $ 0.13 (a) Includes shares of common stock withheld to cover income taxes owed by participants in our share-based incentive plans. (b) On April 10, 2018 , the Board declared a quarterly cash dividend of $0.13 per share on all common stock, payable on May 15, 2018 . Refer to Note 25 for further information regarding this common stock dividend.

Derivative Instruments and He50

Derivative Instruments and Hedging Activities (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position [Table Text Block]	The following table summarizes the amounts of derivative instruments reported on our Condensed Consolidated Balance Sheet . The 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 Condensed 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. March 31, 2018 December 31, 2017 Derivative contracts in a Notional amount Derivative contracts in a Notional amount ($ in millions) receivable position payable position receivable position payable position Derivatives designated as accounting hedges Interest rate contracts Swaps $ — $ — $ 20,250 $ — $ — $ 6,915 Foreign exchange contracts Forwards — — 145 — 1 136 Total derivatives designated as accounting hedges — — 20,395 — 1 7,051 Derivatives not designated as accounting hedges Interest rate contracts Futures and forwards — — 5 — — 23 Written options 1 55 6,139 1 39 8,327 Purchased options 55 — 6,081 38 — 8,237 Total interest rate risk 56 55 12,225 39 39 16,587 Foreign exchange contracts Futures and forwards — — 297 — 1 124 Total foreign exchange risk — — 297 — 1 124 Equity contracts Written options — 1 — — — — Total equity risk — 1 — — — — Total derivatives not designated as accounting hedges 56 56 12,522 39 40 16,711 Total derivatives $ 56 $ 56 $ 32,917 $ 39 $ 41 $ 23,762
Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block]	The following table presents amounts recorded on our Condensed Consolidated Balance Sheet related to cumulative basis adjustments for fair value hedges. ($ in millions) Carrying amount of the hedged items Cumulative amount of fair value hedging adjustment included in the carrying amount of the hedged items Total Discontinued (a) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Assets Available-for-sale securities (b) $ 985 $ 173 $ — $ 2 $ 2 $ 2 Finance receivables and loans, net (c) 22,121 2,305 (31 ) 18 14 19 Liabilities Long-term debt $ 14,958 $ 14,640 $ 127 $ 208 $ 163 $ 235 (a) Represents the fair value hedging adjustment on qualifying hedges for which the hedging relationship was discontinued. This represents a subset of the amounts reported in the total hedging adjustment. (b) The carrying amount of hedged available-for-sale securities is presented above using amortized cost. Refer to Note 6 for a reconciliation of the amortized cost and fair value of available-for-sale securities. (c) The hedged item represents the carrying value of the hedged portfolio of assets. The amount that is identified as the last of layer in the hedge relationship is $9.7 billion as of March 31, 2018 . The basis adjustment associated with the last-of-layer relationship is $45 million liability as of March 31, 2018 , which would be allocated across the entire remaining closed pool upon termination or maturity of the hedge relationship. A last-of-layer hedge strategy did not exist at December 31, 2017 .
Derivative Instruments, Gain (Loss) [Table Text Block]	The following table summarizes the location and amounts of gains and losses on derivative instruments not designated as accounting hedges reported in our Condensed Consolidated Statement of Comprehensive Income . Three months ended March 31, ($ in millions) 2018 2017 Gain (loss) recognized in earnings Interest rate contracts Other income, net of losses $ 2 $ (2 ) Total interest rate contracts 2 (2 ) Foreign exchange contracts (a) Other income, net of losses — (1 ) Total foreign exchange contracts — (1 ) Gain (loss) recognized in earnings $ 2 $ (3 ) (a) Amounts exclude gains and losses related to the revaluation of the related foreign-denominated debt or receivables. Gains of $0 million and $1 million were recognized for the three months ended March 31, 2018 , and 2017 , respectively.
Derivative Instruments Designated as FV Hedges, Gain (Loss) [Table Text Block]	The following table summarizes the location and amounts of gains and losses on derivative instruments designated as fair value hedges reported in our Condensed Consolidated Statement of Comprehensive Income . We had no gains or losses on derivative instruments designated as cash flow hedges for the periods shown. Interest and fees on finance receivables and loans Interest and dividends on investment securities and other earning assets Interest on long-term debt Three months ended March 31, ($ in millions) 2018 2017 2018 2017 2018 2017 Gain (loss) on fair value hedging relationships Interest rate contracts Hedged fixed-rate unsecured debt $ — $ — $ — $ — $ 36 $ (2 ) Derivatives designated as hedging instruments on fixed-rate unsecured debt — — — — (35 ) 3 Hedged fixed-rate FHLB advances — — — — 33 (1 ) Derivatives designated as hedging instruments on fixed-rate FHLB advances — — — — (33 ) 1 Hedged available-for-sale securities — — (3 ) — — — Derivatives designated as hedging instruments on available-for-sale securities — — 3 — — — Hedged fixed-rate retail automotive loans (45 ) (4 ) — — — — Derivatives designated as hedging instruments on fixed-rate retail automotive loans 45 2 — — — — Total (loss) gain on fair value hedging relationships $ — $ (2 ) $ — $ — $ 1 $ 1 Total amounts presented in the Condensed Consolidated Statement of Comprehensive Income $ 1,543 $ 1,368 $ 176 $ 134 $ 411 $ 424
Schedule of Derivative Instruments [Table Text Block]	The following table summarizes the location and amounts of gains and losses related to interest and amortization on derivative instruments designated as fair value and cash flow hedges reported in our Condensed Consolidated Statement of Comprehensive Income . Interest and fees on finance receivables and loans Interest and dividends on investment securities and other earning assets Interest on long-term debt Three months ended March 31, ($ in millions) 2018 2017 2018 2017 2018 2017 Gain (loss) on fair value hedging relationships Interest rate contracts Amortization of deferred unsecured debt basis adjustments $ — $ — $ — $ — $ 15 $ 20 Interest for qualifying accounting hedges of unsecured debt — — — — 3 5 Amortization of deferred secured debt basis adjustments (FHLB advances) — — — — (1 ) (1 ) Interest for qualifying accounting hedges of secured debt (FHLB advances) — — — — 2 — Interest for qualifying accounting hedges of available-for-sale securities — — (1 ) — — — Amortization of deferred loan basis adjustments (4 ) (5 ) — — — — Interest for qualifying accounting hedges of retail automotive loans held-for-investment (7 ) (1 ) — — — — Total (loss) gain on fair value hedging relationships (11 ) (6 ) (1 ) — 19 24 Gain on cash flow hedging relationships Interest rate contracts (a) Interest for qualifying accounting hedges of variable-rate borrowings — — — — 1 — Total gain on cash flow hedging relationships $ — $ — $ — $ — $ 1 $ — Total amounts presented in the Condensed Consolidated Statement of Comprehensive Income $ 1,543 $ 1,368 $ 176 $ 134 $ 411 $ 424 (a) During the next twelve months, we estimate $13 million will be reclassified into pretax earnings from derivatives designated as cash flow hedges.
Schedule of Derivative Instruments, Effect on Other Comprehensive Income [Table Text Block]	The following table summarizes the effect of cash flow hedges on accumulated other comprehensive loss. Three months ended March 31, ($ in millions) 2018 2017 Cash flow hedges Interest rate contracts Gain recognized in other comprehensive loss $ 18 $ — The following table summarizes the effect of net investment hedges on accumulated other comprehensive loss and the Condensed Consolidated Statement of Comprehensive Income . Gain (loss) recognized in other comprehensive (loss) income on derivatives Three months ended March 31, ($ in millions) 2018 2017 Foreign exchange contracts (a) (b) $ 4 $ (2 ) (a) There were no amounts excluded from effectiveness testing for the three months ended March 31, 2018 , or 2017 , respectively. (b) Gains and losses reclassified from accumulated other comprehensive loss are reported as other income, net of losses, on the Condensed Consolidated Statement of Comprehensive Income . There were no amounts reclassified for the three months ended March 31, 2018 , or 2017 , respectively.

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2018
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 March 31, 2018 ($ in millions) Level 1 Level 2 Level 3 Total Assets Investment securities Equity securities (a) $ 668 $ — $ 12 $ 680 Available-for-sale securities Debt securities U.S. Treasury 1,769 — — 1,769 U.S. States and political subdivisions — 831 — 831 Foreign government 7 142 — 149 Agency mortgage-backed residential — 14,883 — 14,883 Mortgage-backed residential — 2,384 — 2,384 Mortgage-backed commercial — 580 — 580 Asset-backed — 900 — 900 Corporate debt — 1,230 — 1,230 Total available-for-sale securities 1,776 20,950 — 22,726 Mortgage loans held-for-sale (b) — — 7 7 Interests retained in financial asset sales — — 5 5 Derivative contracts in a receivable position Interest rate — 55 1 56 Total derivative contracts in a receivable position — 55 1 56 Total assets $ 2,444 $ 21,005 $ 25 $ 23,474 Liabilities Accrued expenses and other liabilities Derivative contracts in a payable position Interest rate $ — $ 55 $ — $ 55 Other 1 — — 1 Total derivative contracts in a payable position 1 55 — 56 Total liabilities $ 1 $ 55 $ — $ 56 (a) Our investment in any one industry did not exceed 13% . (b) Carried at fair value due to fair value option elections. Recurring fair value measurements December 31, 2017 ($ in millions) Level 1 Level 2 Level 3 Total Assets Investment securities Equity securities (a) $ 518 $ — $ — $ 518 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 available-for-sale securities 1,785 20,518 — 22,303 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.
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 (losses) gains Fair value at March 31, 2018 Net unrealized losses included in earnings still held at March 31, 2018 ($ in millions) Fair value at Jan. 1, 2018 included in earnings included in OCI Purchases Sales Issuances Settlements Assets Equity securities (a) $ 19 $ (4 ) (b) $ — $ — $ — $ — $ (3 ) $ 12 $ (5 ) Mortgage loans held-for-sale (c) 13 1 (d) — 59 (66 ) — — 7 — Other assets Interests retained in financial asset sales 5 — — — — — — 5 — Derivative assets 1 — — — — — — 1 — Total assets $ 38 $ (3 ) $ — $ 59 $ (66 ) $ — $ (3 ) $ 25 $ (5 ) (a) In connection with our adoption of ASU 2016-01 on January 1, 2018, certain of our equity securities previously measured using the cost method of accounting are now measured at fair value on a recurring basis, and have been categorized as Level 3 within the fair value hierarchy. Accordingly, the fair value of such investments has been included in the opening balance of the reconciliation above. (b) Reported as other loss on investments, net, in the Condensed Consolidated Statement of Comprehensive Income . (c) Carried at fair value due to fair value option elections. (d) Reported as gain on mortgage and automotive loans, net, in the Condensed Consolidated Statement of Comprehensive Income . Level 3 recurring fair value measurements Fair value at Jan. 1, 2017 Net realized/unrealized gains Purchases Sales Issuances Settlements Fair value at March 31, 2017 Net unrealized gains included in earnings still held at March 31, 2017 ($ in millions) included in earnings included in OCI Assets Mortgage loans held-for-sale (a) $ — $ — $ — $ 3 $ (2 ) $ — $ — $ 1 $ — Other assets Interests retained in financial asset sales 29 — — — 4 — (2 ) 31 — Total assets $ 29 $ — $ — $ 3 $ 2 $ — $ (2 ) $ 32 $ — (a) Carried at fair value due to fair value option elections.
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 three months ended March 31, 2018 ($ in millions) Level 1 Level 2 Level 3 Total Assets Loans held-for-sale, net $ — $ — $ 119 $ 119 $ — n/m (a) Commercial finance receivables and loans, net (b) Automotive — — 51 51 (10 ) n/m (a) Other — — 22 22 (11 ) n/m (a) Total commercial finance receivables and loans, net — — 73 73 (21 ) n/m (a) Other assets Repossessed and foreclosed assets (c) — — 13 13 (1 ) n/m (a) Total assets $ — $ — $ 205 $ 205 $ (22 ) 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 2018 . 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 (loss) included in earnings for the three months 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.
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 March 31, 2018 , and December 31, 2017 . Estimated fair value ($ in millions) Carrying value Level 1 Level 2 Level 3 Total March 31, 2018 Financial assets Held-to-maturity securities $ 1,967 $ — $ 1,895 $ — $ 1,895 Loans held-for-sale, net 119 — — 119 119 Finance receivables and loans, net 124,049 — — 125,530 125,530 Nonmarketable equity investments 1,210 — 1,210 — 1,210 Financial liabilities Deposit liabilities (a) $ 49,025 $ — $ — $ 48,845 $ 48,845 Short-term borrowings 9,564 — — 9,567 9,567 Long-term debt 45,076 — 28,384 18,589 46,973 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 (a) $ 45,869 $ — $ — $ 45,827 $ 45,827 Short-term borrowings 11,413 — — 11,417 11,417 Long-term debt 44,226 — 27,807 18,817 46,624 (a) In connection with our adoption of ASU 2016-01 on January 1, 2018, deposit liabilities with no defined or contractual maturities are no longer included in the table above. Amounts for December 31, 2017, have been adjusted to conform to the current presentation and exclude $47.4 billion and $45.2 billion of deposit liabilities with no defined or contractual maturities from the carrying value and Level 3 fair value, respectively. Refer to Note 12 for information regarding the composition of our deposits portfolio, and Note 1 for further information regarding recently adopted accounting standards.

Offsetting Assets and Liabili52

Offsetting Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
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 Condensed Consolidated Balance Sheet Net amounts of assets/liabilities presented on the Condensed Consolidated Balance Sheet Gross amounts not offset on the Condensed Consolidated Balance Sheet March 31, 2018 ($ in millions) Financial instruments Collateral (a) (b) (c) Net amount Assets Derivative assets in net asset positions $ 55 $ — $ 55 $ — $ — $ 55 Derivative assets with no offsetting arrangements 1 — 1 — — 1 Total assets (d) $ 56 $ — $ 56 $ — $ — $ 56 Liabilities Derivative liabilities in net liability positions (d) $ 56 $ — $ 56 $ — $ (1 ) $ 55 Securities sold under agreements to repurchase (e) 707 — 707 — (707 ) — Total liabilities $ 763 $ — $ 763 $ — $ (708 ) $ 55 (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 March 31, 2018 . We do not record such collateral received on our Condensed 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 $2 million at March 31, 2018 . We have not sold or pledged any of the noncash collateral received under these agreements as of March 31, 2018 . (d) For additional information on derivative instruments and hedging activities, refer to Note 18 . (e) For additional information on securities sold under agreements to repurchase, refer to Note 13 . Gross amounts of recognized assets/liabilities Gross amounts offset on the Condensed Consolidated Balance Sheet Net amounts of assets/liabilities presented on the Condensed Consolidated Balance Sheet Gross amounts not offset on the Condensed Consolidated Balance Sheet December 31, 2017 ($ 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 Condensed 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 18 . (e) For additional information on securities sold under agreements to repurchase, refer to Note 13 .

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Financial information for our reportable operating segments is summarized as follows. Three months ended March 31, ($ in millions) Automotive Finance operations Insurance operations Mortgage Finance operations Corporate Finance operations Corporate and Other Consolidated (a) 2018 Net financing revenue and other interest income $ 909 $ 12 $ 43 $ 46 $ 39 $ 1,049 Other revenue 66 246 1 8 33 354 Total net revenue 975 258 44 54 72 1,403 Provision for loan losses 259 — 2 — — 261 Total noninterest expense 448 231 34 25 76 814 Income (loss) from continuing operations before income tax expense $ 268 $ 27 $ 8 $ 29 $ (4 ) $ 328 Total assets $ 114,934 $ 7,557 $ 12,780 $ 4,375 $ 30,375 $ 170,021 2017 Net financing revenue and other interest income $ 892 $ 15 $ 34 $ 34 $ 4 $ 979 Other revenue 101 264 — 18 13 396 Total net revenue 993 279 34 52 17 1,375 Provision for loan losses 268 — 1 6 (4 ) 271 Total noninterest expense 437 239 24 21 57 778 Income (loss) from continuing operations before income tax expense $ 288 $ 40 $ 9 $ 25 $ (36 ) $ 326 Total assets $ 115,154 $ 7,230 $ 8,362 $ 3,438 $ 27,917 $ 162,101 (a) Net financing revenue and other interest income after the provision for loan losses totaled $788 million and $708 million for the three months ended March 31, 2018 , and March 31, 2017 , respectively

Parent and Guarantor Condense54

Parent and Guarantor Condensed Consolidating Financial Statements (Tables)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Condensed Income Statement [Table Text Block]	Condensed Consolidating Statements of Comprehensive Income Three months ended March 31, 2018 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Financing revenue and other interest income Interest and fees on finance receivables and loans $ 11 $ — $ 1,532 $ — $ 1,543 Interest and fees on finance receivables and loans — intercompany 2 — 1 (3 ) — Interest and dividends on investment securities and other earning assets — — 176 — 176 Interest on cash and cash equivalents 2 — 14 (1 ) 15 Interest-bearing cash — intercompany 2 — 2 (4 ) — Operating leases 2 — 380 — 382 Total financing revenue and other interest income 19 — 2,105 (8 ) 2,116 Interest expense Interest on deposits — — 354 (3 ) 351 Interest on short-term borrowings 10 — 22 — 32 Interest on long-term debt 258 — 153 — 411 Interest on intercompany debt 3 — 2 (5 ) — Total interest expense 271 — 531 (8 ) 794 Net depreciation expense on operating lease assets 4 — 269 — 273 Net financing revenue (256 ) — 1,305 — 1,049 Cash dividends from subsidiaries Bank subsidiary 1,000 1,000 — (2,000 ) — Nonbank subsidiaries 169 — — (169 ) — Other revenue Insurance premiums and service revenue earned — — 256 — 256 Gain on mortgage and automotive loans, net 28 — 1 (28 ) 1 Other loss on investments, net — — (12 ) — (12 ) Other income, net of losses 96 — 221 (208 ) 109 Total other revenue 124 — 466 (236 ) 354 Total net revenue 1,037 1,000 1,771 (2,405 ) 1,403 Provision for loan losses 81 — 208 (28 ) 261 Noninterest expense Compensation and benefits expense 23 — 283 — 306 Insurance losses and loss adjustment expenses — — 63 — 63 Other operating expenses 182 — 471 (208 ) 445 Total noninterest expense 205 — 817 (208 ) 814 Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries 751 1,000 746 (2,169 ) 328 Income tax (benefit) expense from continuing operations (56 ) — 132 — 76 Net income from continuing operations 807 1,000 614 (2,169 ) 252 Loss from discontinued operations, net of tax (1 ) — (1 ) — (2 ) Undistributed (loss) income of subsidiaries Bank subsidiary (597 ) (597 ) — 1,194 — Nonbank subsidiaries 41 — — (41 ) — Net income 250 403 613 (1,016 ) 250 Other comprehensive loss, net of tax (328 ) (276 ) (339 ) 615 (328 ) Comprehensive (loss) income $ (78 ) $ 127 $ 274 $ (401 ) $ (78 ) Three months ended March 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 $ (35 ) $ — $ 1,403 $ — $ 1,368 Interest and fees on finance receivables and loans — intercompany 4 — 3 (7 ) — Interest and dividends on investment securities and other earning assets — — 135 (1 ) 134 Interest on cash and cash equivalents 2 — 3 — 5 Interest-bearing cash — intercompany — — 1 (1 ) — Operating leases 3 — 540 — 543 Total financing (loss) revenue and other interest income (26 ) — 2,085 (9 ) 2,050 Interest expense Interest on deposits 1 — 230 — 231 Interest on short-term borrowings 17 — 10 — 27 Interest on long-term debt 281 — 143 — 424 Interest on intercompany debt 4 — 4 (8 ) — Total interest expense 303 — 387 (8 ) 682 Net depreciation expense on operating lease assets 2 — 387 — 389 Net financing revenue (331 ) — 1,311 (1 ) 979 Cash dividends from subsidiaries Nonbank subsidiaries 41 — — (41 ) — Other revenue Insurance premiums and service revenue earned — — 241 — 241 (Loss) gain on mortgage and automotive loans, net (2 ) — 16 — 14 Other gain on investments, net — — 27 — 27 Other income, net of losses 268 — 223 (377 ) 114 Total other revenue 266 — 507 (377 ) 396 Total net revenue (24 ) — 1,818 (419 ) 1,375 Provision for loan losses 107 — 164 — 271 Noninterest expense Compensation and benefits expense 122 — 163 — 285 Insurance losses and loss adjustment expenses — — 88 — 88 Other operating expenses 288 — 494 (377 ) 405 Total noninterest expense 410 — 745 (377 ) 778 (Loss) income from continuing operations before income tax (benefit) expense and undistributed income of subsidiaries (541 ) — 909 (42 ) 326 Income tax (benefit) expense from continuing operations (134 ) — 247 — 113 Net (loss) income from continuing operations (407 ) — 662 (42 ) 213 Income (loss) from discontinued operations, net of tax 2 — (1 ) — 1 Undistributed income of subsidiaries Bank subsidiary 389 389 — (778 ) — Nonbank subsidiaries 230 — — (230 ) — Net income 214 389 661 (1,050 ) 214 Other comprehensive income, net of tax 20 5 19 (24 ) 20 Comprehensive income $ 234 $ 394 $ 680 $ (1,074 ) $ 234
Condensed Balance Sheet [Table Text Block]	Condensed Consolidating Balance Sheet March 31, 2018 ($ in millions) Parent (a) Guarantors Nonguarantors (a) Consolidating adjustments Ally consolidated Assets Cash and cash equivalents Noninterest-bearing $ 56 $ — $ 712 $ — $ 768 Interest-bearing 5 — 2,948 — 2,953 Interest-bearing — intercompany 735 — 577 (1,312 ) — Total cash and cash equivalents 796 — 4,237 (1,312 ) 3,721 Equity securities — — 680 — 680 Available-for-sale securities — — 22,726 — 22,726 Held-to-maturity securities — — 2,033 (66 ) 1,967 Loans held-for-sale, net — — 126 — 126 Finance receivables and loans, net Finance receivables and loans, net 6,443 — 118,884 — 125,327 Intercompany loans to Nonbank subsidiaries 1,311 — 415 (1,726 ) — Allowance for loan losses (145 ) — (1,133 ) — (1,278 ) Total finance receivables and loans, net 7,609 — 118,166 (1,726 ) 124,049 Investment in operating leases, net 14 — 8,516 — 8,530 Intercompany receivables from Bank subsidiary 86 — — (86 ) — Nonbank subsidiaries 41 — 61 (102 ) — Investment in subsidiaries Bank subsidiary 16,163 16,163 — (32,326 ) — Nonbank subsidiaries 7,520 — — (7,520 ) — Premiums receivable and other insurance assets — — 2,197 — 2,197 Other assets 2,221 — 5,072 (1,268 ) 6,025 Total assets $ 34,450 $ 16,163 $ 163,814 $ (44,406 ) $ 170,021 Liabilities Deposit liabilities Noninterest-bearing $ — $ — $ 122 $ — $ 122 Interest-bearing 6 — 97,318 — 97,324 Interest-bearing — intercompany — — 735 (735 ) — Total deposit liabilities 6 — 98,175 (735 ) 97,446 Short-term borrowings 2,957 — 6,607 — 9,564 Long-term debt 16,808 — 28,268 — 45,076 Intercompany debt to Bank subsidiary 65 — — (65 ) — Nonbank subsidiaries 992 — 1,311 (2,303 ) — Intercompany payables to Nonbank subsidiaries 115 — 106 (221 ) — Interest payable 209 — 285 — 494 Unearned insurance premiums and service revenue — — 2,904 — 2,904 Accrued expenses and other liabilities 216 — 2,473 (1,234 ) 1,455 Total liabilities 21,368 — 140,129 (4,558 ) 156,939 Total equity 13,082 16,163 23,685 (39,848 ) 13,082 Total liabilities and equity $ 34,450 $ 16,163 $ 163,814 $ (44,406 ) $ 170,021 (a) Amounts presented are based upon the legal transfer of the underlying assets to VIEs in order to reflect legal ownership. 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 Equity securities — — 518 — 518 Available-for-sale securities — — 22,303 — 22,303 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.
Parent Guarantor Consolidating Statement of Cash Flows [Table Text Block]	Condensed Consolidating Statement of Cash Flows Three months ended March 31, 2018 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash provided by operating activities $ 456 $ 1,000 $ 1,812 $ (2,171 ) $ 1,097 Investing activities Purchases of equity securities — — (374 ) — (374 ) Proceeds from sales of equity securities — — 220 — 220 Purchases of available-for-sale securities — — (2,360 ) — (2,360 ) Proceeds from sales of available-for-sale securities — — 328 — 328 Proceeds from repayments of available-for-sale securities — — 795 — 795 Purchases of held-to-maturity securities — — (155 ) — (155 ) Proceeds from repayments of held-to-maturity securities — — 35 — 35 Net change in investment securities — intercompany — — 9 (9 ) — Purchases of finance receivables and loans held-for-investment — — (2,317 ) 820 (1,497 ) Proceeds from sales of finance receivables and loans initially held-for-investment 820 — — (820 ) — Originations and repayments of finance receivables and loans held-for-investment and other, net 432 — (1,732 ) — (1,300 ) Net change in loans — intercompany (423 ) — 1 422 — Purchases of operating lease assets — — (969 ) — (969 ) Disposals of operating lease assets 4 — 972 — 976 Capital contributions to subsidiaries (49 ) (6 ) — 55 — Returns of contributed capital 38 — — (38 ) — Net change in nonmarketable equity investments — — (19 ) — (19 ) Other, net (3 ) — (80 ) 1 (82 ) Net cash provided by (used in) investing activities 819 (6 ) (5,646 ) 431 (4,402 ) Financing activities Net change in short-term borrowings — third party (214 ) — (1,634 ) — (1,848 ) Net (decrease) increase in deposits (6 ) — 3,776 403 4,173 Proceeds from issuance of long-term debt — third party 15 — 6,650 — 6,665 Repayments of long-term debt — third party (1,152 ) — (4,619 ) — (5,771 ) Net change in debt — intercompany (127 ) — 422 (295 ) — Repurchase of common stock (185 ) — — — (185 ) Dividends paid — third party (58 ) — — — (58 ) Dividends paid and returns of contributed capital — intercompany — (1,000 ) (1,208 ) 2,208 — Capital contributions from parent — 6 49 (55 ) — Net cash (used in) provided by financing activities (1,727 ) (994 ) 3,436 2,261 2,976 Effect of exchange-rate changes on cash and cash equivalents — — (2 ) — (2 ) Net decrease in cash and cash equivalents and restricted cash (452 ) — (400 ) 521 (331 ) Cash and cash equivalents and restricted cash at beginning of year 1,395 — 5,707 (1,833 ) 5,269 Cash and cash equivalents and restricted cash at March 31, $ 943 $ — $ 5,307 $ (1,312 ) $ 4,938 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. March 31, 2018 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Cash and cash equivalents as disclosed on the Condensed Consolidated Balance Sheet $ 796 $ — $ 4,237 $ (1,312 ) $ 3,721 Restricted cash included in other assets on the Condensed Consolidated Balance Sheet (a) 147 — 1,070 — 1,217 Total cash and cash equivalents and restricted cash as disclosed in the Condensed Consolidated Statement of Cash Flows $ 943 $ — $ 5,307 $ (1,312 ) $ 4,938 (a) Restricted cash balances relate primarily to Ally securitization arrangements. Refer to Note 11 for additional details describing the nature of restricted cash balances. Three months ended March 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Operating activities Net cash (used in) provided by operating activities $ (149 ) $ — $ 1,284 $ 40 $ 1,175 Investing activities Purchases of equity securities — — (137 ) — (137 ) Proceeds from sales of equity securities — — 314 — 314 Purchases of available-for-sale securities — — (2,696 ) — (2,696 ) Proceeds from sales of available-for-sale securities — — 731 — 731 Proceeds from repayments of available-for-sale securities — — 589 — 589 Purchases of held-to-maturity securities — — (215 ) — (215 ) Proceeds from repayments of held-to-maturity securities — — 5 — 5 Net change in investment securities — intercompany 1 — 261 (262 ) — Purchases of finance receivables and loans held-for-investment (15 ) — (390 ) — (405 ) Proceeds from sales of finance receivables and loans initially held-for-investment — — 1,164 — 1,164 Originations and repayments of finance receivables and loans held-for-investment and other, net 931 — (1,145 ) (960 ) (1,174 ) Net change in loans — intercompany 1,146 — 170 (1,316 ) — Purchases of operating lease assets — — (893 ) — (893 ) Disposals of operating lease assets 1 — 1,544 — 1,545 Capital contributions to subsidiaries (83 ) — — 83 — Returns of contributed capital 645 — — (645 ) — Net change in nonmarketable equity investments — — 213 — 213 Other, net (26 ) — 64 (94 ) (56 ) Net cash provided by (used in) investing activities 2,600 — (421 ) (3,194 ) (1,015 ) Financing activities Net change in short-term borrowings — third party 1,278 — (5,581 ) — (4,303 ) Net (decrease) increase in deposits (82 ) — 5,533 — 5,451 Proceeds from issuance of long-term debt — third party 330 — 3,196 962 4,488 Repayments of long-term debt — third party (2,870 ) — (4,703 ) — (7,573 ) Net change in debt — intercompany (203 ) — (1,146 ) 1,349 — Repurchase of common stock (169 ) — — — (169 ) Dividends paid — third party (38 ) — — — (38 ) Dividends paid and returns of contributed capital — intercompany — — (686 ) 686 — Capital contributions from parent — — 83 (83 ) — Net cash used in financing activities (1,754 ) — (3,304 ) 2,914 (2,144 ) Effect of exchange-rate changes on cash and cash equivalents — — — — — Net increase (decrease) in cash and cash equivalents and restricted cash 697 — (2,441 ) (240 ) (1,984 ) 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 March 31, $ 1,686 $ — $ 4,852 $ (641 ) $ 5,897 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. March 31, 2017 ($ in millions) Parent Guarantors Nonguarantors Consolidating adjustments Ally consolidated Cash and cash equivalents as disclosed on the Condensed Consolidated Balance Sheet $ 1,490 $ — $ 3,453 $ (641 ) $ 4,302 Restricted cash included in other assets on the Condensed Consolidated Balance Sheet (a) 196 — 1,399 — 1,595 Total cash and cash equivalents and restricted cash as disclosed in the Condensed Consolidated Statement of Cash Flows $ 1,686 $ — $ 4,852 $ (641 ) $ 5,897 (a) Restricted cash balances relate primarily to Ally securitization arrangements. Refer to Note 11 for additional details describing the nature of restricted cash balances.

Description of Business, Basi55

Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 126	$ 126
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	20	(7)
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (42)	$ 0

Revenue from Contracts with C56

Revenue from Contracts with Customers (Contract with Customer, Asset and Liability) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Premiums receivable and other insurance assets	$ 2,197		$ 2,047
Other Assets	6,025		5,663
Assets	170,021		167,148	$ 162,101
Unearned Premiums	2,904		2,604
Liabilities	156,939		153,654
Retained Earnings (Accumulated Deficit)	(6,318)		(6,406)
Stockholders' Equity Attributable to Parent	13,082	$ 13,375	13,494	$ 13,365	$ 13,317
Liabilities and Equity	$ 170,021		$ 167,148
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Premiums receivable and other insurance assets		122
Other Assets		41
Assets		163
Unearned Premiums		289
Liabilities		289
Retained Earnings (Accumulated Deficit)		(126)
Stockholders' Equity Attributable to Parent		(126)
Liabilities and Equity		163
Day One Balance [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Premiums receivable and other insurance assets		2,169
Other Assets		5,704
Assets		167,311
Unearned Premiums		2,893
Liabilities		153,943
Retained Earnings (Accumulated Deficit)		(6,532)
Stockholders' Equity Attributable to Parent		13,368
Liabilities and Equity		$ 167,311

Revenue from Contracts with C57

Revenue from Contracts with Customers (Impact of ASU 2014-09 on Balance Sheet and Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Insurance Services Revenue	$ 256	$ 241
Nonoperating Income (Expense)	354	396
Revenues	1,403	1,375
Labor and Related Expense	306	285
Other Noninterest Expense	445	405
Noninterest Expense	814	778
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	328	326
Income Tax Expense (Benefit)	76	113
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	252	213
Net Income (Loss) Attributable to Parent	250	214
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(78)	234
Premiums receivable and other insurance assets	2,197			$ 2,047
Other Assets	6,025			5,663
Assets	170,021	162,101		167,148
Unearned Premiums	2,904			2,604
Liabilities	156,939			153,654
Retained Earnings (Accumulated Deficit)	(6,318)			(6,406)
Stockholders' Equity Attributable to Parent	13,082	13,365	$ 13,375	13,494	$ 13,317
Liabilities and Equity	170,021			167,148
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Insurance Services Revenue	(6)
Nonoperating Income (Expense)	(6)
Revenues	(6)
Labor and Related Expense	(1)
Other Noninterest Expense	(2)
Noninterest Expense	(3)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(3)
Income Tax Expense (Benefit)	(1)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(2)
Net Income (Loss) Attributable to Parent	(2)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(2)
Premiums receivable and other insurance assets	125
Other Assets	42
Assets	167
Unearned Premiums	295
Liabilities	295
Retained Earnings (Accumulated Deficit)	(128)
Stockholders' Equity Attributable to Parent	(128)
Liabilities and Equity	167
Retained Earnings [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income (Loss) Attributable to Parent	250	214
Stockholders' Equity Attributable to Parent	$ (6,318)	$ (6,975)	$ (6,510)	$ (6,406)	$ (7,151)

Revenue From Contracts with C58

Revenue From Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Insurance Commissions	$ 110	$ 99
Revenue from Contract with Customer, Excluding Assessed Tax	172
Revenue Outside of Scope of the Amendments to the Revenue Recognition Principles	182
Nonoperating Income (Expense)	354	396
Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability	289
Deferred Revenue, Revenue Recognized	22
Revenue, Remaining Performance Obligation	2,500
Deferred Sales Commission	1,400
Insurance Commissions	103
Revenue from Contract with Customer, Excluding Assessed Tax	123
Remarketing Activities [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	23
Brokerage Commissions and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	16
Brokered/Agent Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4
Deposits and Banking [Member]
Disaggregation of Revenue [Line Items]
Fees and Commissions, Debit Cards	3
Expense, Debt Cards	3
Revenue from Contract with Customer, Excluding Assessed Tax	3
Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3
Automotive Finance Operations [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	25
Revenue Outside of Scope of the Amendments to the Revenue Recognition Principles	41
Nonoperating Income (Expense)	66	101
Automotive Finance Operations [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Automotive Finance Operations [Member] | Remarketing Activities [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	23
Automotive Finance Operations [Member] | Brokerage Commissions and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Automotive Finance Operations [Member] | Brokered/Agent Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Automotive Finance Operations [Member] | Deposits and Banking [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Automotive Finance Operations [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2
Automotive Finance Operations [Member] | Sale of Off-lease Vehicles [Member]
Disaggregation of Revenue [Line Items]
Gain (Loss) on Off-Lease Vehicles	18
Insurance Operations [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	128
Revenue Outside of Scope of the Amendments to the Revenue Recognition Principles	118
Nonoperating Income (Expense)	246
Insurance Operations [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	123
Insurance Operations [Member] | Remarketing Activities [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Insurance Operations [Member] | Brokerage Commissions and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Insurance Operations [Member] | Brokered/Agent Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4
Insurance Operations [Member] | Deposits and Banking [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Insurance Operations [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1
Mortgage Finance [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Revenue Outside of Scope of the Amendments to the Revenue Recognition Principles	1
Nonoperating Income (Expense)	1
Mortgage Finance [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Mortgage Finance [Member] | Remarketing Activities [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Mortgage Finance [Member] | Brokerage Commissions and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Mortgage Finance [Member] | Brokered/Agent Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Mortgage Finance [Member] | Deposits and Banking [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Mortgage Finance [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate Finance Operations [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Revenue Outside of Scope of the Amendments to the Revenue Recognition Principles	8
Nonoperating Income (Expense)	8	18
Corporate Finance Operations [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate Finance Operations [Member] | Remarketing Activities [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate Finance Operations [Member] | Brokerage Commissions and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate Finance Operations [Member] | Brokered/Agent Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate Finance Operations [Member] | Deposits and Banking [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate Finance Operations [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	19
Revenue Outside of Scope of the Amendments to the Revenue Recognition Principles	14
Nonoperating Income (Expense)	33	$ 13
Corporate and Other [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate and Other [Member] | Remarketing Activities [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate and Other [Member] | Brokerage Commissions and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	16
Corporate and Other [Member] | Brokered/Agent Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Corporate and Other [Member] | Deposits and Banking [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3
Corporate and Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Remainder of 2018 [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue, Remaining Performance Obligation	568
2019 [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue, Remaining Performance Obligation	643
2020 [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue, Remaining Performance Obligation	528
2021 [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue, Remaining Performance Obligation	378
2022 and Thereafter [Member] | Noninsurance Contracts [Member]
Disaggregation of Revenue [Line Items]
Revenue, Remaining Performance Obligation	$ 389

Other Income, Net of Losses (Sc

Other Income, Net of Losses (Schedule of Other Income, Net of Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Nonoperating Income (Expense) [Abstract]
Fees and Commissions, Other	$ 29	$ 27
Remarketing Fees	23	29
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	8	16
Income (Loss) from Equity Method Investments	6	0
Other Income	43	42
Noninterest Income, Other Operating Income	$ 109	$ 114

Reserves for Insurance Losses60

Reserves for Insurance Losses and Loss Adjustment Expenses Reserves for Insurance Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reserves for Insurance Losses and Loss Adjustment Expense [Abstract]
Liability for Claims and Claims Adjustment Expense	$ 140	$ 149
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments	108	108
Liability for Unpaid Claims and Claims Adjustment Expense, Net	32	41
Current Year Claims and Claims Adjustment Expense	60	89
Prior Year Claims and Claims Adjustment Expense	3	(1)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	63	88
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	31	45
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	19	23
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	50	68
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss)	0	2
Liability for Unpaid Claims and Claims Adjustment Expense, Net	45	63
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments	112	112
Liability for Claims and Claims Adjustment Expense	$ 157	$ 175

Other Operating Expenses (Sched

Other Operating Expenses (Schedule Of Other Operating Expenses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Expenses [Abstract]
Insurance Commissions	$ 110	$ 99
Communications and Information Technology	71	69
Lease And Loan Administration	42	36
Marketing and Advertising Expense	39	30
Vehicle remarketing and repossession	32	28
Professional Fees	32	26
Federal Deposit Insurance Corporation Premium Expense	30	27
Depreciation, Nonproduction	20	22
Occupancy, Net	11	12
Taxes, Miscellaneous	8	8
Amortization of Intangible Assets	3	3
Other Cost and Expense, Operating	47	45
Other Noninterest Expense	$ 445	$ 405

Investment Securities (Investme

Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Investments [Line Items]
Held-to-maturity securities	$ 1,967		$ 1,899
Held-to-maturity Securities, Fair Value	1,895		1,865
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	839		1,000
US Treasury and Government [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,855		1,831
Available-for-sale Debt Securities Gross Unrealized Gain	0	$ 0
Available-for-sale Debt Securities, Gross Unrealized Loss	(86)	(54)
Available-for-sale Securities, Debt Securities	1,769		1,777
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	845		850
Available-for-sale Debt Securities Gross Unrealized Gain	5	11
Available-for-sale Debt Securities, Gross Unrealized Loss	(19)	(7)
Available-for-sale Securities, Debt Securities	831		854
Foreign Government Debt Securities [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	150		153
Available-for-sale Debt Securities Gross Unrealized Gain	1	2
Available-for-sale Debt Securities, Gross Unrealized Loss	(2)	(1)
Available-for-sale Securities, Debt Securities	149		154
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	15,316		14,412
Available-for-sale Debt Securities Gross Unrealized Gain	4	35
Available-for-sale Debt Securities, Gross Unrealized Loss	(437)	(156)
Available-for-sale Securities, Debt Securities	14,883		14,291
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	1,936		1,863
Held-to-maturity Securities, Unrecognized Holding Gain	0	3
Held-to-maturity Securities, Unrecognized Holding Loss	(72)	(37)
Held-to-maturity Securities, Fair Value	1,864		1,829
Residential Mortgage Backed Securities [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,456		2,517
Available-for-sale Debt Securities Gross Unrealized Gain	3	11
Available-for-sale Debt Securities, Gross Unrealized Loss	(75)	(34)
Available-for-sale Securities, Debt Securities	2,384		2,494
Commercial Mortgage Backed Securities [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	582		541
Available-for-sale Debt Securities Gross Unrealized Gain	1	1
Available-for-sale Debt Securities, Gross Unrealized Loss	(3)	(1)
Available-for-sale Securities, Debt Securities	580		541
Asset-backed Securities [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	901		933
Available-for-sale Debt Securities Gross Unrealized Gain	2	4
Available-for-sale Debt Securities, Gross Unrealized Loss	(3)	(1)
Available-for-sale Securities, Debt Securities	900		936
Asset-backed Securities [Member] | Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	31		36
Held-to-maturity Securities, Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	31		36
Corporate Debt Securities [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,263		1,262
Available-for-sale Debt Securities Gross Unrealized Gain	1	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(34)	(11)
Available-for-sale Securities, Debt Securities	1,230		1,256
Debt Securities [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	23,368		22,499
Available-for-sale Debt Securities Gross Unrealized Gain	17	69
Available-for-sale Debt Securities, Gross Unrealized Loss	(659)	(265)
Available-for-sale Securities, Debt Securities	22,726		22,303
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	1,967		1,899
Held-to-maturity Securities, Unrecognized Holding Gain	0	3
Held-to-maturity Securities, Unrecognized Holding Loss	(72)	$ (37)
Held-to-maturity Securities, Fair Value	1,895		1,865
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	8,000		7,800
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] | Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	993		664
Insurance Operations [Member]
Schedule of Investments [Line Items]
Deposit Assets	$ 12		$ 12

Investment Securities (Invest63

Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Cash Equivalents, at Carrying Value	$ 18	$ 10
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 1,967	$ 1,899
Held-to-Maturity Debt Securities, Yield	3.10%	3.10%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 30	$ 35
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	1.70%	1.70%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 1	$ 1
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	3.00%	3.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 1,936	$ 1,863
Held-to-Maturity Securities, Due After Ten Years, Yield	3.10%	3.10%
Available-for-sale Securities [Member] | US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 1,769	$ 1,777
Available-for-sale debt securities, Yield	1.80%	1.70%
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	$ 481	$ 487
Available-for-sale debt securities, Due after one year through five years, Yield	1.70%	1.70%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 1,288	$ 1,290
Available-for-sale debt securities, Due after five years through ten years, Yield	1.80%	1.80%
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	$ 1,855	$ 1,831
Available-for-sale Securities [Member] | US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 831	$ 854
Available-for-sale debt securities, Yield	3.00%	2.90%
Available-for-sale debt securities, Due in one year or less, Amount	$ 70	$ 76
Available-for-sale debt securities, Due in one year or less, Yield	2.30%	1.80%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 42	$ 36
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	$ 219	$ 203
Available-for-sale debt securities, Due after five years through ten years, Yield	2.60%	2.50%
Available-for-sale debt securities, Due after ten years, Amount	$ 500	$ 539
Available-for-sale debt securities, Due after ten years, Yield	3.30%	3.30%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 845	$ 850
Available-for-sale Securities [Member] | Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 149	$ 154
Available-for-sale debt securities, Yield	2.50%	2.50%
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	$ 77	$ 80
Available-for-sale debt securities, Due after one year through five years, Yield	2.60%	2.50%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 72	$ 74
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	$ 150	$ 153
Available-for-sale Securities [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 14,883	$ 14,291
Available-for-sale debt securities, Yield	3.20%	3.10%
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	$ 3
Available-for-sale debt securities, Due after five years through ten years, Yield	2.60%	2.90%
Available-for-sale debt securities, Due after ten years, Amount	$ 14,880	$ 14,288
Available-for-sale debt securities, Due after ten years, Yield	3.20%	3.10%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 15,316	$ 14,412
Available-for-sale Securities [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 2,384	$ 2,494
Available-for-sale debt securities, Yield	3.10%	3.10%
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	$ 2,384	$ 2,494
Available-for-sale debt securities, Due after ten years, Yield	3.10%	3.10%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 2,456	$ 2,517
Available-for-sale Securities [Member] | Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 580	$ 541
Available-for-sale debt securities, Yield	3.40%	3.20%
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	$ 30
Available-for-sale debt securities, Due after one year through five years, Yield	0.00%	3.10%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 31	$ 31
Available-for-sale debt securities, Due after five years through ten years, Yield	3.30%	3.10%
Available-for-sale debt securities, Due after ten years, Amount	$ 549	$ 480
Available-for-sale debt securities, Due after ten years, Yield	3.40%	3.20%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 582	$ 541
Available-for-sale Securities [Member] | Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 900	$ 936
Available-for-sale debt securities, Yield	3.20%	3.10%
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	$ 655	$ 698
Available-for-sale debt securities, Due after one year through five years, Yield	3.20%	3.10%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 121	$ 106
Available-for-sale debt securities, Due after five years through ten years, Yield	3.30%	3.10%
Available-for-sale debt securities, Due after ten years, Amount	$ 124	$ 132
Available-for-sale debt securities, Due after ten years, Yield	2.90%	2.80%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 901	$ 933
Available-for-sale Securities [Member] | Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 1,230	$ 1,256
Available-for-sale debt securities, Yield	3.00%	2.90%
Available-for-sale debt securities, Due in one year or less, Amount	$ 123	$ 140
Available-for-sale debt securities, Due in one year or less, Yield	2.80%	2.60%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 496	$ 513
Available-for-sale debt securities, Due after one year through five years, Yield	2.70%	2.60%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 573	$ 564
Available-for-sale debt securities, Due after five years through ten years, Yield	3.30%	3.20%
Available-for-sale debt securities, Due after ten years, Amount	$ 38	$ 39
Available-for-sale debt securities, Due after ten years, Yield	4.80%	4.70%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,263	$ 1,262
Available-for-sale Securities [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 22,726	$ 22,303
Available-for-sale debt securities, Yield	3.00%	3.00%
Available-for-sale debt securities, Due in one year or less, Amount	$ 193	$ 216
Available-for-sale debt securities, Due in one year or less, Yield	2.60%	2.30%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 1,751	$ 1,844
Available-for-sale debt securities, Due after one year through five years, Yield	2.60%	2.50%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 2,307	$ 2,271
Available-for-sale debt securities, Due after five years through ten years, Yield	2.30%	2.30%
Available-for-sale debt securities, Due after ten years, Amount	$ 18,475	$ 17,972
Available-for-sale debt securities, Due after ten years, Yield	3.20%	3.10%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 23,368	$ 22,499
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	194	217
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	1,776	1,852
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	2,403	2,314
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	18,995	18,116
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	$ 1,936	$ 1,863
Held-to-Maturity Debt Securities, Yield	3.10%	3.10%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 0	$ 0
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 0	$ 0
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 1,936	$ 1,863
Held-to-Maturity Securities, Due After Ten Years, Yield	3.10%	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	$ 31	$ 36
Held-to-Maturity Debt Securities, Yield	1.70%	1.70%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 30	$ 35
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	1.70%	1.70%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 1	$ 1
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	3.00%	3.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 0	$ 0
Held-to-Maturity Securities, Due After Ten Years, Yield	0.00%	0.00%

Investment Securities (Invest64

Investment Securities (Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Taxable interest	$ 154	$ 119
Taxable dividends	3	2
Interest and dividends exempt from U.S. federal income tax	6	5
Interest and Dividend Income, Securities, Operating, Available-for-sale	176	134
Excludes Other Earning Assets [Member]
Interest and Dividend Income, Securities, Operating, Available-for-sale	$ 163	$ 126

Investment Securities (Schedule

Investment Securities (Schedule Of Realized Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Available-for-sale Securities [Abstract]
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	$ 0	$ 0
Available-for-sale Securities, Gross Realized Gains	6	27
Available-for-sale Securities, Gross Realized Losses	0	0
Available-for-sale Securities, Gross Realized Gain (Loss)	6	27
Net realized gain (loss) on equity securities	22
Available-for-sale Equity Securities, Gross Unrealized Gain	40
Gain (Loss) on Investments	$ (12)	$ 27

Investment Securities (Schedu66

Investment Securities (Schedule of Unrealized Loss on Investments) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Fair Value, Less than 12 months	$ 1,178	$ 808
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	26	5
Held-to-maturity Securities, Fair value Less 12 months or longer	672	687
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	46	32
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	488	471
Available-for-sale Securities, Unrealized Loss Less than 12 months	(16)	(8)
Available-for-sale Securities, Fair value 12 months or longer	1,282	1,305
Available-for-sale Securities, Unrealized Loss 12 months or longer	(70)	(46)
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	436	242
Available-for-sale Securities, Unrealized Loss Less than 12 months	(9)	(2)
Available-for-sale Securities, Fair value 12 months or longer	176	183
Available-for-sale Securities, Unrealized Loss 12 months or longer	(10)	(5)
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	82	80
Available-for-sale Securities, Unrealized Loss Less than 12 months	(2)	(1)
Available-for-sale Securities, Fair value 12 months or longer	4	4
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	8,951	4,066
Available-for-sale Securities, Unrealized Loss Less than 12 months	(183)	(19)
Available-for-sale Securities, Fair value 12 months or longer	5,395	5,671
Available-for-sale Securities, Unrealized Loss 12 months or longer	(254)	(137)
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	1,439	857
Available-for-sale Securities, Unrealized Loss Less than 12 months	(29)	(2)
Available-for-sale Securities, Fair value 12 months or longer	734	773
Available-for-sale Securities, Unrealized Loss 12 months or longer	(46)	(32)
Held-to-maturity Securities, Fair Value, Less than 12 months	1,147	773
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	26	5
Held-to-maturity Securities, Fair value Less 12 months or longer	672	687
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	46	32
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	71	76
Available-for-sale Securities, Unrealized Loss Less than 12 months	(2)	(1)
Available-for-sale Securities, Fair value 12 months or longer	21	21
Available-for-sale Securities, Unrealized Loss 12 months or longer	(1)	0
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	426	220
Available-for-sale Securities, Unrealized Loss Less than 12 months	(2)	(1)
Available-for-sale Securities, Fair value 12 months or longer	76	91
Available-for-sale Securities, Unrealized Loss 12 months or longer	(1)	0
Held-to-maturity Securities, Fair Value, Less than 12 months	31	35
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	0
Held-to-maturity Securities, Fair value Less 12 months or longer	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	0
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	932	529
Available-for-sale Securities, Unrealized Loss Less than 12 months	(20)	(4)
Available-for-sale Securities, Fair value 12 months or longer	191	194
Available-for-sale Securities, Unrealized Loss 12 months or longer	(14)	(7)
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value Less than 12 months	12,825	6,541
Available-for-sale Securities, Unrealized Loss Less than 12 months	(263)	(38)
Available-for-sale Securities, Fair value 12 months or longer	7,879	8,242
Available-for-sale Securities, Unrealized Loss 12 months or longer	$ (396)	$ (227)

Finance Receivables and Loans67

Finance Receivables and Loans, Net (Schedule of Accounts, Notes, Loans and Financing Receivables) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 125,327	$ 122,893	$ 119,002
Loans and Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	586	551
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	84,001	81,821
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	69,318	68,071	65,663
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	14,683	13,750	10,937
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	12,733	11,657
Held For Investment Mortgage Finance Receivables Interest Only Mortgage Loans	$ 19	20
Consumer Portfolio Segment [Member] | Mortgage Finance [Member] | 2019 or sooner [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	34.00%
Consumer Portfolio Segment [Member] | Mortgage Finance [Member] | 2020, or sooner [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	46.00%
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 1,950	2,093
Held For Investment Mortgage Finance Receivables Interest Only Mortgage Loans	$ 459	496
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member] | Nine months, or less [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest-only mortgage loan portfolio principal amortization	2.00%
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 41,326	41,072	$ 42,402
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	32,781	33,025
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	4,184	3,887
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 4,361	$ 4,160

Finance Receivables and Loans68

Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses	$ 1,276	$ 1,144
Allowance for Loan and Lease Losses, Write-offs	(377)	(350)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	118	97
Allowance for Loan and Lease Losses Write-offs, Net	(259)	(253)
Provision for Loan Losses Expensed	261	271
Allowance for Loan and Lease Losses, Adjustments, Other		7
Financing Receivable, Allowance for Credit Losses	1,278	1,155
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	88	89
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,190	1,066
Loans and Leases Receivable, Gross	125,327	119,002	$ 122,893
Financing Receivable, Individually Evaluated for Impairment	840	757
Financing Receivable, Collectively Evaluated for Impairment	124,487	118,245
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses	1,066	932
Allowance for Loan and Lease Losses, Write-offs	(365)	(341)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	112	90
Allowance for Loan and Lease Losses Write-offs, Net	(253)	(251)
Provision for Loan Losses Expensed	253	267
Allowance for Loan and Lease Losses, Adjustments, Other		7
Financing Receivable, Allowance for Credit Losses	1,066	941
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	40	32
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,026	909
Loans and Leases Receivable, Gross	69,318	65,663	68,071
Financing Receivable, Individually Evaluated for Impairment	463	388
Financing Receivable, Collectively Evaluated for Impairment	68,855	65,275
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses	79	91
Allowance for Loan and Lease Losses, Write-offs	(12)	(9)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	6	7
Allowance for Loan and Lease Losses Write-offs, Net	(6)	(2)
Provision for Loan Losses Expensed	1	(3)
Allowance for Loan and Lease Losses, Adjustments, Other		0
Financing Receivable, Allowance for Credit Losses	74	86
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	27	33
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	47	53
Loans and Leases Receivable, Gross	14,683	10,937	13,750
Financing Receivable, Individually Evaluated for Impairment	230	249
Financing Receivable, Collectively Evaluated for Impairment	14,453	10,688
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses	131	121
Allowance for Loan and Lease Losses, Write-offs	0	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts	0	0
Allowance for Loan and Lease Losses Write-offs, Net	0	0
Provision for Loan Losses Expensed	7	7
Allowance for Loan and Lease Losses, Adjustments, Other		0
Financing Receivable, Allowance for Credit Losses	138	128
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	21	24
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	117	104
Loans and Leases Receivable, Gross	41,326	42,402	$ 41,072
Financing Receivable, Individually Evaluated for Impairment	147	120
Financing Receivable, Collectively Evaluated for Impairment	$ 41,179	$ 42,282

Finance Receivables and Loans69

Finance Receivables and Loans, Net (Schedule of Sales of Financing Receivables and Loans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Sales and Transfers	$ 1	$ 1,216
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Sales and Transfers	0	1,213
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Sales and Transfers	$ 1	$ 3

Finance Receivables and Loans70

Finance Receivables and Loans, Net (Schedule of Purchases of Financing Receivables and Loans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Purchases	$ 1,463	$ 395
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Purchases	168	68
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Significant Purchases	$ 1,295	$ 327

Finance Receivables and Loans71

Finance Receivables and Loans, Net (Past Due Financing Receivables and Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 2,496	$ 2,967
Financing Receivable, Recorded Investment, Current	122,831	119,926
Loans and Leases Receivable, Gross	125,327	122,893	$ 119,002
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,429	2,959
Financing Receivable, Recorded Investment, Current	81,572	78,862
Loans and Leases Receivable, Gross	84,001	81,821
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,186	2,740
Financing Receivable, Recorded Investment, Current	67,132	65,331
Loans and Leases Receivable, Gross	69,318	68,071	65,663
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	243	219
Financing Receivable, Recorded Investment, Current	14,440	13,531
Loans and Leases Receivable, Gross	14,683	13,750	10,937
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	123	89
Financing Receivable, Recorded Investment, Current	12,610	11,568
Loans and Leases Receivable, Gross	12,733	11,657
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	120	130
Financing Receivable, Recorded Investment, Current	1,830	1,963
Loans and Leases Receivable, Gross	1,950	2,093
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	67	8
Financing Receivable, Recorded Investment, Current	41,259	41,064
Loans and Leases Receivable, Gross	41,326	41,072	$ 42,402
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	33	8
Financing Receivable, Recorded Investment, Current	32,748	33,017
Loans and Leases Receivable, Gross	32,781	33,025
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	30	0
Financing Receivable, Recorded Investment, Current	4,154	3,887
Loans and Leases Receivable, Gross	4,184	3,887
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	4	0
Financing Receivable, Recorded Investment, Current	4,357	4,160
Loans and Leases Receivable, Gross	4,361	4,160
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,738	2,102
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	1,711	2,097
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	1,574	1,994
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	137	103
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	97	60
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	40	43
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	27	5
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	23	5
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	4	0
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	422	514
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	386	514
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	359	478
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	27	36
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	8	11
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	19	25
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	36	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	6	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	30	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	336	351
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	332	348
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	253	268
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	79	80
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	18
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	61	62
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	4	3
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	4	3
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 Loans72

Finance Receivables and Loans, Net (Schedule of Financing Receivables, Non Accrual Status) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 863	$ 792
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	716	720
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	601	603
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	115	117
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	28	25
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	87	92
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	147	72
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	68	27
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	74	44
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 5	$ 1

Finance Receivables and Loans73

Finance Receivables and Loans, Net (Financing Receivable Credit Quality Indicators) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 125,327	$ 122,893	$ 119,002
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	84,001	81,821
Consumer Portfolio Segment [Member] | Consumer Loan [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	83,285	81,101
Consumer Portfolio Segment [Member] | Consumer Loan [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	716	720
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	69,318	68,071	65,663
Consumer Portfolio Segment [Member] | Automobile Loan [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	68,717	67,468
Consumer Portfolio Segment [Member] | Automobile Loan [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	601	603
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	14,683	13,750	$ 10,937
Consumer Portfolio Segment [Member] | Residential Mortgage [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	14,568	13,633
Consumer Portfolio Segment [Member] | Residential Mortgage [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	115	117
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	12,733	11,657
Consumer Portfolio Segment [Member] | Mortgage Finance [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	12,705	11,632
Consumer Portfolio Segment [Member] | Mortgage Finance [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	28	25
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,950	2,093
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,863	2,001
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 87	$ 92

Finance Receivables and Loans74

Finance Receivables and Loans, Net (Schedule of Pass And Criticized Credit Quality Indicators of Finance Receivables) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 125,327	$ 122,893	$ 119,002
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	41,326	41,072	$ 42,402
Commercial Portfolio Segment [Member] | Commercial Loan [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	37,868	37,991
Commercial Portfolio Segment [Member] | Commercial Loan [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	3,458	3,081
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	32,781	33,025
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	30,433	30,982
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,348	2,043
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,184	3,887
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	3,284	2,986
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	900	901
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,361	4,160
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,151	4,023
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 210	$ 137

Finance Receivables and Loans75

Finance Receivables and Loans, Net (Impaired Financing Receivables) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 866	$ 756
Impaired Financing Receivable, Recorded Investment	840	733
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	232	172
Impaired Financing Receivable, with Related Allowance, Recorded Investment	608	561
Impaired Financing Receivable, Related Allowance	88	77
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	708	674
Impaired Financing Receivable, Recorded Investment	693	661
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	172	153
Impaired Financing Receivable, with Related Allowance, Recorded Investment	521	508
Impaired Financing Receivable, Related Allowance	67	63
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	473	438
Impaired Financing Receivable, Recorded Investment	463	430
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	107	91
Impaired Financing Receivable, with Related Allowance, Recorded Investment	356	339
Impaired Financing Receivable, Related Allowance	40	36
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	235	236
Impaired Financing Receivable, Recorded Investment	230	231
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	65	62
Impaired Financing Receivable, with Related Allowance, Recorded Investment	165	169
Impaired Financing Receivable, Related Allowance	27	27
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	9	8
Impaired Financing Receivable, Recorded Investment	9	8
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4	4
Impaired Financing Receivable, with Related Allowance, Recorded Investment	5	4
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	226	228
Impaired Financing Receivable, Recorded Investment	221	223
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	61	58
Impaired Financing Receivable, with Related Allowance, Recorded Investment	160	165
Impaired Financing Receivable, Related Allowance	27	27
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	158	82
Impaired Financing Receivable, Recorded Investment	147	72
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	60	19
Impaired Financing Receivable, with Related Allowance, Recorded Investment	87	53
Impaired Financing Receivable, Related Allowance	21	14
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	68	27
Impaired Financing Receivable, Recorded Investment	68	27
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	15	9
Impaired Financing Receivable, with Related Allowance, Recorded Investment	53	18
Impaired Financing Receivable, Related Allowance	9	3
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	85	54
Impaired Financing Receivable, Recorded Investment	74	44
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	41	10
Impaired Financing Receivable, with Related Allowance, Recorded Investment	33	34
Impaired Financing Receivable, Related Allowance	11	11
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	5	1
Impaired Financing Receivable, Recorded Investment	5	1
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1	1
Impaired Financing Receivable, Related Allowance	$ 1	$ 0

Finance Receivables and Loans76

Finance Receivables and Loans, Net (Schedule of Average Balance and Interest Income of Impaired Finance Receivables) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 776	$ 749
Impaired Financing Receivable, Interest Income, Accrual Method	10	7
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	674	628
Impaired Financing Receivable, Interest Income, Accrual Method	9	7
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	444	379
Impaired Financing Receivable, Interest Income, Accrual Method	7	5
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	230	249
Impaired Financing Receivable, Interest Income, Accrual Method	2	2
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	9	8
Impaired Financing Receivable, Interest Income, Accrual Method	0	0
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	221	241
Impaired Financing Receivable, Interest Income, Accrual Method	2	2
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	102	121
Impaired Financing Receivable, Interest Income, Accrual Method	1	0
Commercial Portfolio Segment [Member] | Commercial And Industrial Automobile [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	47	33
Impaired Financing Receivable, Interest Income, Accrual Method	1	0
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	52	83
Impaired Financing Receivable, Interest Income, Accrual Method	0	0
Commercial Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	3	5
Impaired Financing Receivable, Interest Income, Accrual Method	$ 0	$ 0

Finance Receivables and Loans77

Finance Receivables and Loans, Net (Troubled Debt Restructurings) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 742		$ 712
Loans and Leases Receivable, Impaired, Commitment to Lend	$ 6		$ 6
Financing Receivable, Modifications, Number of Contracts	7,105	6,502
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 139	$ 150
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 120	$ 134
Consumer Portfolio Segment [Member] | Consumer Loan [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	7,105	6,501
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 139	$ 127
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 120	$ 111
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	7,042	6,447
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 128	$ 115
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 110	$ 99
Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	63	54
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 11	$ 12
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 10	$ 12
Consumer Portfolio Segment [Member] | Mortgage Finance [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	1	1
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 1	$ 0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 1	$ 0
Consumer Portfolio Segment [Member] | Mortgage - Legacy [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	62	53
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 10	$ 12
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 9	$ 12
Commercial Portfolio Segment [Member] | Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	0	1
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 0	$ 23
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 23
Commercial Portfolio Segment [Member] | Commercial And Industrial Other [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts	0	1
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 0	$ 23
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 23

Finance Receivables and Loans78

Finance Receivables and Loans, Net (Finance receivables and loans redefaulted during the period) (Details) - Consumer Portfolio Segment [Member] $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	2,326	1,990
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 28	$ 25
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	$ 18	$ 16
Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	2,326	1,989
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 28	$ 24
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	$ 18	$ 16
Mortgage Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 1
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	$ 0	$ 0

Investment in Operating Lease79

Investment in Operating Leases, Net (Investments In Operating Leases) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Leases, Operating [Abstract]
Property Subject to or Available for Operating Lease, Gross	$ 10,206	$ 10,556
Property Subject to or Available for Operating Lease, Accumulated Depreciation	(1,676)	(1,815)
Property Subject to or Available for Operating Lease, Net	$ 8,530	$ 8,741

Investment in Operating Lease80

Investment in Operating Leases, Net (Schedule Of Depreciation Expense On Operating Lease Assets) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Leases, Operating [Abstract]
Depreciation Expense On Operating Lease Assets	$ 291	$ 386
Gross Remarketing (Gains) Losses	(18)	3
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	$ 273	$ 389

Securitizations and Variable 81

Securitizations and Variable Interest Entities (Schedule of Variable Interest Entities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Variable Interest Entity [Line Items]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale, Gain (Loss) on Sale	$ 0	$ 2
Assets of nonconsolidated variable interest entities	1,658		$ 1,964
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	2,573		2,791
Carrying value of assets for VIEs for which we have continuing involvement	29,155		30,776
Carrying value of liabilities for VIEs for which we have continuing involvement	12,084		10,483
Commercial Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	702		592
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	331		248
Assets of nonconsolidated variable interest entities	0		0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	882		790
Automobile Loan [Member] | Consumer Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	17,993		17,597
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	8,232		7,677
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	32		37
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0		0
Assets of nonconsolidated variable interest entities	1,658		1,964
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	1,691		2,001
Automobile Loan [Member] | Consumer Portfolio Segment [Member] | Held-to-maturity Securities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	31		36
Automobile Loan [Member] | Consumer Portfolio Segment [Member] | Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	1		1
Automobile Loan [Member] | Commercial Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	10,428		12,550
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	3,521		2,558
Unencumbered [Member] | Automobile Loan [Member] | Consumer Portfolio Segment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	8,400		8,500
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 31		$ 29

Securitizations and Variable 82

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	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flow Received and Paid to Nonconsolidated Securitization Entities [Line Items]
Cash Flows Between Transferor and Transferee, Purchases of Previously Transferred Financial Assets	$ 1
Cash Flows Between Transferor and Transferee, Servicing Fees	5	$ 9
Cash Flows Between Transferor and Transferee, Beneficial Interest	$ 5
Cash Flows Between Transferor and Transferee, Proceeds from New Transfers		1,138
Cash Flows Between Transferor and Transferee, Receipts on Transferor's Interest in Transferred Financial Assets, Other		$ 2

Securitizations and Variable 83

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	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
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	$ 2,825		$ 3,363
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	15		20
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	4	$ 4
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	1,658		1,964
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	12		16
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	3	3
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	1,658		1,964
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	12		16
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	3	3
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	1,167		1,399
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	3		$ 4
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	$ 1	$ 1

Servicing Activities (Schedule

Servicing Activities (Schedule of Total Serviced Automobile Loans Outstanding) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Automobile Serviced Assets [Line Items]
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	$ 8	$ 16
Total Primary Serviced Assets	117,134		$ 116,878
Consumer Loan [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	68,738		67,631
Commercial Loan [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	36,935		37,058
Operating Leases [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	8,489		8,682
Other Assets [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	131		121
Asset-backed Securities, Securitized Loans and Receivables [Member] | Off-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	1,666		1,977
Whole-Loan Transactions [Member] | Off-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	$ 1,175		$ 1,409

Other Assets (Schedule of Other

Other Assets (Schedule of Other Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Other Assets [Abstract]
Property, Plant and Equipment, Gross	$ 1,107	$ 1,064
Accumulated Depreciation, Depletion and Amortization, Property Plant and Equipment	(627)	(608)
Property, Plant and Equipment, Net	480	456
Nonmarketable equity securities	1,250	1,233
Restricted cash collections for securitization trusts	986	812
Interest Receivable	533	550
Deferred Tax Assets, Net	530	461
Goodwill	240	240
Accounts and Other Receivables, Net, Current	142	116
Restricted Cash and Cash Equivalents	119	94
Cash reserve deposits held for securitization trusts	112	111
Derivative Asset, Fair Value, Gross Asset	56	39
Cash and securities collateral placed with counterparties	33	29
Other Assets, Miscellaneous	1,544	1,522
Other Assets	6,025	5,663
Federal Home Loan Bank Stock	764	745
Federal Reserve Bank Stock	446	445
Equity Securities, Fair Value	40
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
Goodwill [Line Items]
Goodwill	193	193
Automotive Finance Operations [Member]
Other Assets [Abstract]
Goodwill	20	20
Goodwill [Line Items]
Goodwill	$ 20	$ 20

Deposit Liabilities (Schedule o

Deposit Liabilities (Schedule of Deposit Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Deposits [Abstract]
Noninterest-bearing deposit liabilities	$ 122	$ 108
Interest-bearing Deposit Liabilities, by Component [Abstract]
Deposits, Savings Deposits	50,293	49,267
Time Deposits	47,025	43,869
Dealer deposits	6	12
Deposits	97,446	93,256
Time Deposits, $100,000 or More	20,600	18,900
Time Deposits, at or Above FDIC Insurance Limit	$ 5,400	$ 5,300

Debt (Schedule of Short-term De

Debt (Schedule of Short-term Debt) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Demand Notes	$ 2,957	$ 3,171
Federal Home Loan Bank, Advances, Maturities Summary, Due in Next Twelve Months	5,900	7,350
Securities Sold under Agreements to Repurchase, Gross	707	892
Short-term Debt	9,564	11,413
Non-derivative Cash Collateral Placed with Counterparties Associated with the Repurchase Agreements	5	10
Non-derivative Cash Collateral received from counterparties associated with Repurchase Agreements	1	1
Unsecured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	2,957	3,171
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	2,957	3,171
Secured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	0	0
Federal Home Loan Bank, Advances, Maturities Summary, Due in Next Twelve Months	5,900	7,350
Securities Sold under Agreements to Repurchase, Gross	707	892
Short-term Debt	6,607	$ 8,242
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	707
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	432
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	$ 275

Debt (Long-term Debt) (Details)

Debt (Long-term Debt) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	$ 11,320	$ 10,981
Long-term Debt, Excluding Current Maturities	33,629	33,037
Derivative, Amount of Hedged Item	127	208
Long-term Debt	45,076	44,226
Trust preferred securities	2,600	2,600
Secured Debt	36,659	36,837
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	3,681	3,482
Long-term Debt, Excluding Current Maturities	11,153	11,909
Derivative, Amount of Hedged Item	190	240
Long-term Debt	15,024	15,631
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	7,639	7,499
Long-term Debt, Excluding Current Maturities	22,476	21,128
Derivative, Amount of Hedged Item	(63)	(32)
Long-term Debt	30,052	28,595
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Secured Debt	$ 12,700	$ 10,300

Debt (Scheduled Remaining Matur

Debt (Scheduled Remaining Maturity of Long-term Debt) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 7,835
Long-term Debt, Maturities, Repayments of Principal in Year Two	9,108
Long-term Debt, Maturities, Repayments of Principal in Year Three	9,057
Long-term Debt, Maturities, Repayments of Principal in Year Four	6,324
Long-term Debt, Maturities, Repayments of Principal in Year Five	5,113
Long-term Debt, Maturities, Repayments of Principal after Year Five	7,512
Derivative, Amount of Hedged Item	127	$ 208
Long-term debt	45,076	44,226
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	2,911
Long-term Debt, Maturities, Repayments of Principal in Year Two	1,641
Long-term Debt, Maturities, Repayments of Principal in Year Three	2,212
Long-term Debt, Maturities, Repayments of Principal in Year Four	607
Long-term Debt, Maturities, Repayments of Principal in Year Five	1,019
Long-term Debt, Maturities, Repayments of Principal after Year Five	6,444
Derivative, Amount of Hedged Item	190	240
Long-term debt	15,024	15,631
Secured Debt [Member]
Debt Instrument [Line Items]
Derivative, Amount of Hedged Item	(63)	(32)
Long-term debt	30,052	$ 28,595
Long-term Debt [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	2,987
Long-term Debt, Maturities, Repayments of Principal in Year Two	1,680
Long-term Debt, Maturities, Repayments of Principal in Year Three	2,251
Long-term Debt, Maturities, Repayments of Principal in Year Four	650
Long-term Debt, Maturities, Repayments of Principal in Year Five	1,066
Long-term Debt, Maturities, Repayments of Principal after Year Five	7,411
Derivative, Amount of Hedged Item	190
Long-term debt	16,235
Long-term Debt [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	4,924
Long-term Debt, Maturities, Repayments of Principal in Year Two	7,467
Long-term Debt, Maturities, Repayments of Principal in Year Three	6,845
Long-term Debt, Maturities, Repayments of Principal in Year Four	5,717
Long-term Debt, Maturities, Repayments of Principal in Year Five	4,094
Long-term Debt, Maturities, Repayments of Principal after Year Five	1,068
Derivative, Amount of Hedged Item	(63)
Long-term debt	30,052
original issue discount [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Derivative, Amount of Hedged Item	0
Debt Instrument, Unamortized Discount, Current	(76)
Debt Instrument, Unamortized Discount	(1,211)
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	(39)
original issue discount [Member] | Unsecured Debt [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount, Noncurrent	(43)
original issue discount [Member] | Unsecured Debt [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount, Noncurrent	(47)
original issue discount [Member] | Unsecured Debt [Member] | Debt Instrument, Redemption, Period Six [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	Mar. 31, 2018	Dec. 31, 2017
Pledged Assets related to secured borrowings [Line Items]
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	$ 8,891	$ 8,371
Pledged Assets, Mortgage assets held for investment	14,501	13,579
Pledged Assets, Investment in operating leases	350	457
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	55,832	58,761
Secured Debt	36,659	36,837
Short-term Debt	9,564	11,413
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	8,443	7,443
Pledged Assets, Mortgage assets held for investment	14,501	13,579
Pledged Assets, Investment in operating leases	0	0
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	44,141	43,694
Secured Debt	25,874	23,278
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	27,000	25,200
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	2,300
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	17,472	19,787
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	6,639	6,200
Commercial Portfolio Segment [Member] | Automobile Loan [Member]
Pledged Assets related to secured borrowings [Line Items]
Pledged Assets, Not Separately Reported, Finance Receivables	14,618	16,567
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	$ 14,558	$ 16,472

Debt (Narrative - Trust Preferr

Debt (Narrative - Trust Preferred Securities) (Details) $ / shares in Units, $ in Billions	Mar. 31, 2018USD ($)$ / shares	Dec. 31, 2017USD ($)
Narrative - Trust Preferred Securities [Line Items]
Trust preferred securities	$ 2.6	$ 2.6
Debt Instrument, Interest Rate, Stated Percentage	8.125%
Preferred Stock, Liquidation Preference Per Share | $ / shares	$ 25
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%
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 at anytime on or before February 15, 2040.	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	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Outstanding Revolving Funding Facilities	$ 8,700
Line of Credit Facility, Maximum Borrowing Capacity	8,725	$ 11,925
Long-term Line of Credit	5,755	8,115
Line of Credit Facility, Remaining Borrowing Capacity	2,970	3,810
Ally Bank [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,500	2,675
Long-term Line of Credit	1,500	1,785
Line of Credit Facility, Remaining Borrowing Capacity	0	890
Revolving secured funding facilities 1 year or greater [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	6,600
Nonbank Funding [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	7,225	9,250
Long-term Line of Credit	4,255	6,330
Line of Credit Facility, Remaining Borrowing Capacity	$ 2,970	$ 2,920

Accrued Expenses and Other Li93

Accrued Expenses and Other Liabilities (Schedule of Accrued Expenses and Other Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounts Payable and Accrued Liabilities [Abstract]
Accounts Payable	$ 390	$ 746
Accrued Employee Benefits	161	248
Liability for Claims and Claims Adjustment Expense	157	140	$ 175	$ 149
Derivative Liability, Fair Value, Gross Liability	56	41
Deferred Revenue	34	32
Cash collateral received from counterparties	31	17
Other Accrued Liabilities	626	556
Accounts Payable and Accrued Liabilities	$ 1,455	$ 1,780

Accumulated Other Comprehensi94

Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	$ (524)	$ (252)	$ (186)	$ (173)	$ (273)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(338)	21
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	19	14	20	16	14
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(1)	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	25	8	11	11	8
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	14	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	98	91	95	89	90
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	3	1
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax	578	321	250	$ 235	$ 341
Other Comprehensive Income (Loss), Net of Tax	$ (328)	$ 20
Accounting Standards Update 2016-01 [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax			27
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax			0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax			0
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax			0
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax			(27)
Accounting Standards Update 2018-02 [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax			(40)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax			4
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax			0
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax			6
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax			$ 42

Accumulated Other Comprehensi95

Accumulated Other Comprehensive Loss (Before and After Tax) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
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	$ (436)	$ 51
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	6	27
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax	(442)	24
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	103	(5)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(1)	(2)
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax	104	(3)
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	(333)	46
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	5	25
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(338)	21
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	(5)	2
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	1	(1)
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, Net of Tax	(4)	1
Other Comprehensive Income (Loss), Net investment hedges, before Tax [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period, Before Tax	4	(2)
Other Comprehensive Income (Loss), Net investment hedges, Tax [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period, Tax	(1)	1
Other Comprehensive Income (Loss), Net investment hedges, Net of Tax [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period Net of Tax	3	(1)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During the Period, Before Tax	18
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Effect [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During the Period, Tax	(4)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	14	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Tax [Abstract]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax	(3)	(1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Tax [Abstract]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	0	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax	3	1
Other Comprehensive Income (Loss), before Tax [Abstract]
Other Comprehensive Income (Loss), before Tax	(428)	23
Other Comprehensive Income (Loss), Tax [Abstract]
Other Comprehensive Income (Loss), Tax	100	(3)
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive Income (Loss), Net of Tax	$ (328)	$ 20

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
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic	$ 252	$ 213
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Basic	(2)	1
Net Income (Loss) Available to Common Stockholders, Basic	$ 250	$ 214
Weighted Average Number of Shares Outstanding, Basic	436,213	465,961
Weighted Average Number of Shares Outstanding, Diluted	438,931	466,829
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Diluted	$ 252	$ 213
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Diluted	(2)	1
Net Income (Loss) Available to Common Stockholders, Diluted	$ 250	$ 214
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.58	$ 0.46
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	(0.01)	0
Earnings Per Share, Basic	0.57	0.46
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.57	0.46
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	(0.01)	0
Earnings Per Share, Diluted	$ 0.57	$ 0.46

Regulatory Capital and Other 97

Regulatory Capital and Other Regulatory Matters (Schedule of Regulatory Capital Amount and Ratios) (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 10, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Aug. 22, 2017	Jun. 30, 2017	Jun. 28, 2017	Apr. 14, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 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%
BHC Stress Test Threshold		$ 50,000
Federal Reserve Bank Stock		$ 446	$ 445
Minimum Capital Conservation Buffer		1.875%	1.25%
Increase in Minimum Capital Conservation Buffer		2.50%
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
Dividends Payable, Amount Per Share		$ 0.13	$ 0.12	$ 0.12		$ 0.08		$ 0.08	$ 0.08	$ 0.08	$ 0.08
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		$ 13,079	$ 13,237
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets		9.26%	9.53%
Tier One Risk Based Capital		$ 15,512	$ 15,628
Tier One Risk Based Capital to Risk Weighted Assets		10.98%	11.25%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets		6.00%
Capital		$ 17,760	$ 17,974
Capital to Risk Weighted Assets		12.57%	12.94%
Capital Required to be Well Capitalized to Risk Weighted Assets		10.00%
Tier One Leverage Capital		$ 15,512	$ 15,628
Tier One Leverage Capital to Average Assets		9.26%	9.53%
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		$ 16,535	$ 17,059
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets		13.93%	15.04%
Common Equity Tier 1 Capital Required to be Well Capitalized to Risk-weighted Assets		6.50%
Tier One Risk Based Capital		$ 16,535	$ 17,059
Tier One Risk Based Capital to Risk Weighted Assets		13.93%	15.04%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets		8.00%
Capital		$ 17,480	$ 17,886
Capital to Risk Weighted Assets		14.72%	15.77%
Capital Required to be Well Capitalized to Risk Weighted Assets		10.00%
Tier One Leverage Capital		$ 16,535	$ 17,059
Tier One Leverage Capital to Average Assets		11.94%	12.87%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets		5.00%
Subsequent Event [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends Payable, Amount Per Share	$ 0.13

Regulatory Capital and Other 98

Regulatory Capital and Other Regulatory Matters (Common Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Apr. 14, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016
Accelerated Share Repurchases [Line Items]
Treasury Stock, Common, Value	$ 185	$ 190	$ 190	$ 204		$ 169	$ 167	$ 159
Treasury Stock, Common, Shares	6,473,000	7,033,000	8,507,000	10,485,000		8,097,000	8,745,000	8,298,000
Common Stock, Shares, Outstanding		437,053,936
Dividends Payable, Amount Per Share	$ 0.13	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08
Beginning of Period [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding		437,054,000	443,796,000	452,292,000		462,193,000	467,000,000	475,470,000	483,753,000
End of Period [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	432,690,882	437,054,000	443,796,000	452,292,000		462,193,000	467,000,000	475,470,000

Derivative Instruments and He99

Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash Collateral Placed with Counterparties Excluding Cash Collateral Associated with Repurchase Agreements	$ 28	$ 20
Securities Collateral Placed with Counterparties	100	97
Cash Collateral Received from Counterparties, Excluding Collateral Associated with Repurchase Agreements	30	17
Non-cash collateral received	$ 2	$ 2

Derivative Instruments and H100

Derivative Instruments and Hedging Activities (Fair Value Amounts of Derivative Instruments Reported on our Condensed Consolidated Balance Sheet) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 56	$ 39
Derivative Liability, Fair Value, Gross Liability	56	41
Derivative, Notional Amount	32,917	23,762
Designated as Hedging Instrument [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	20,395	7,051
Not Designated as Hedging Instrument [Member] | Other Trading [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	56	39
Derivative Liability, Fair Value, Gross Liability	56	40
Derivative, Notional Amount	12,522	16,711
Interest Rate Swap [Member] | Designated as Hedging Instrument [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	20,250	6,915
Foreign Exchange Forward [Member] | Designated as Hedging Instrument [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	145	136
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	56	39
Derivative Liability, Fair Value, Gross Liability	55	39
Derivative, Notional Amount	12,225	16,587
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	5	23
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	1
Derivative Liability, Fair Value, Gross Liability	55	39
Derivative, Notional Amount	6,139	8,327
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Purchased Options [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	55	38
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative, Notional Amount	6,081	8,237
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [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	297	124
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	0
Derivative Liability, Fair Value, Gross Liability	0	1
Derivative, Notional Amount	297	124
Equity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	1	0
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	1	0
Derivative, Notional Amount	$ 0	$ 0

Derivative Instruments and H101

Derivative Instruments and Hedging Activities (Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Long-term Debt	$ 45,076	$ 44,226
Last of Layer in the Hedge Relationship	9,700
Basis Adjustment - Last-of-Layer	45
Carrying Amount [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Available-for-sale Securities, Debt Securities	985	173
Financing Receivable, Net	22,121	2,305
Long-term Debt	14,958	14,640
Fair Value Hedging [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Available-for-sale Securities, Debt Securities	0	2
Financing Receivable, Net	(31)	18
Long-term Debt	127	208
Discontinued Hedge [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Available-for-sale Securities, Debt Securities	2	2
Financing Receivable, Net	14	19
Long-term Debt	$ 163	$ 235

Derivative Instruments and H102

Derivative Instruments and Hedging Activities (Statement of Gains and Losses on Derivative Instruments Reported in Statement of Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ 2	$ (3)
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	(2)
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	(1)
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	2	(2)
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	0	(1)
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	$ 0	$ 1

Derivative Instruments and H103

Derivative Instruments and Hedging Activities (Derivative Instruments Designated as Fair Value Hedges, Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases	$ 1,543	$ 1,368
Interest and Dividend Income, Securities, Operating, Available-for-sale	176	134
Interest Expense, Long-term Debt	411	424
Designated as Hedging Instrument [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0	(2)
Designated as Hedging Instrument [Member] | Interest and Dividends Income [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0	0
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	1	1
Designated as Hedging Instrument [Member] | Unsecured Debt [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0	0
Designated as Hedging Instrument [Member] | Unsecured Debt [Member] | Interest and Dividends Income [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0	0
Designated as Hedging Instrument [Member] | Unsecured Debt [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	36	(2)
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	(35)	3
Designated as Hedging Instrument [Member] | Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0	0
Designated as Hedging Instrument [Member] | Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] | Interest and Dividends Income [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0	0
Designated as Hedging Instrument [Member] | Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	33	(1)
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	(33)	1
Designated as Hedging Instrument [Member] | Available-for-sale Securities [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0	0
Designated as Hedging Instrument [Member] | Available-for-sale Securities [Member] | Interest and Dividends Income [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	(3)	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	3	0
Designated as Hedging Instrument [Member] | Available-for-sale Securities [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0	0
Designated as Hedging Instrument [Member] | Fixed-rate Automotive Loans [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	(45)	(4)
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	45	2
Designated as Hedging Instrument [Member] | Fixed-rate Automotive Loans [Member] | Interest and Dividends Income [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0	0
Designated as Hedging Instrument [Member] | Fixed-rate Automotive Loans [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	$ 0	$ 0

Derivative Instruments and H104

Derivative Instruments and Hedging Activities (Interest and Amortization on Derivative Instruments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases	$ 1,543	$ 1,368
Interest and Dividend Income, Securities, Operating, Available-for-sale	176	134
Interest Expense, Long-term Debt	411	424
Earnings on cash flow hedges to be recognized within twelve months	13
Designated as Hedging Instrument [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0	(2)
Designated as Hedging Instrument [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(11)	(6)
Designated as Hedging Instrument [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Amortization and Interest [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest for Qualifying Hedge	0	0
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	0	0
Designated as Hedging Instrument [Member] | Interest and Dividends Income [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0	0
Designated as Hedging Instrument [Member] | Interest and Dividends Income [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(1)	0
Designated as Hedging Instrument [Member] | Interest and Dividends Income [Member] | Amortization and Interest [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest for Qualifying Hedge	0	0
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	0	0
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	1	1
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	19	24
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Amortization and Interest [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest for Qualifying Hedge	1	0
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	1	0
Designated as Hedging Instrument [Member] | Unsecured Debt [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	0	0
Gain (Loss) on Interest for Qualifying Hedge	0	0
Designated as Hedging Instrument [Member] | Unsecured Debt [Member] | Interest and Dividends Income [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	0	0
Gain (Loss) on Interest for Qualifying Hedge	0	0
Designated as Hedging Instrument [Member] | Unsecured Debt [Member] | Interest Expense [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	15	20
Gain (Loss) on Interest for Qualifying Hedge	3	5
Designated as Hedging Instrument [Member] | Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	0	0
Gain (Loss) on Interest for Qualifying Hedge	0	0
Designated as Hedging Instrument [Member] | Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] | Interest and Dividends Income [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	0	0
Gain (Loss) on Interest for Qualifying Hedge	0	0
Designated as Hedging Instrument [Member] | Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] | Interest Expense [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	(1)	(1)
Gain (Loss) on Interest for Qualifying Hedge	2	0
Designated as Hedging Instrument [Member] | Available-for-sale Securities [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest for Qualifying Hedge	0	0
Designated as Hedging Instrument [Member] | Available-for-sale Securities [Member] | Interest and Dividends Income [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest for Qualifying Hedge	(1)	0
Designated as Hedging Instrument [Member] | Available-for-sale Securities [Member] | Interest Expense [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest for Qualifying Hedge	0	0
Designated as Hedging Instrument [Member] | Fixed-rate Automotive Loans [Member] | Interest and Fees on Finance Receivables and Loans [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	(4)	(5)
Gain (Loss) on Interest for Qualifying Hedge	(7)	(1)
Designated as Hedging Instrument [Member] | Fixed-rate Automotive Loans [Member] | Interest and Dividends Income [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	0	0
Gain (Loss) on Interest for Qualifying Hedge	0	0
Designated as Hedging Instrument [Member] | Fixed-rate Automotive Loans [Member] | Interest Expense [Member] | Amortization and Interest [Member] | Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Amortization of Deferred Basis Adjustments	0	0
Gain (Loss) on Interest for Qualifying Hedge	$ 0	$ 0

Derivative Instruments and H105

Derivative Instruments and Hedging Activities (Derivative Instruments Used in Net Investment Hedge Accounting Relationships) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
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	$ 18	$ 0
Foreign Exchange Contract [Member] | Net Investment Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 4	$ (2)

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
Income Tax Disclosure [Abstract]
Income Tax Expense (Benefit)	$ 76	$ 113
Accounting Standards Update 2018-02 [Member]
Tax Act Impacts [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 42		$ 0

Fair Value (Fair Value Measurem

Fair Value (Fair Value Measurements - Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities	$ 680	$ 518
Available-for-sale securities	$ 22,726	$ 22,303
Available-for-sale, Equity Investment in Any One Industry Did Not Exceed Percentage	13.00%	14.00%
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 22,726	$ 22,303
Derivative Assets	56	39
Assets, Fair Value Disclosure	23,474	22,878
Derivative Liability	(56)	(41)
Financial and Nonfinancial Liabilities, Fair Value Disclosure	56	41
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	(55)	(39)
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] | 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] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities	680	518
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	1,769	1,777
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	831	854
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	149	154
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	14,883	14,291
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	2,384	2,494
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	580	541
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	900	936
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	1,230	1,256
Fair Value, Measurements, Recurring [Member] | Loans Held-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	7	13
Fair Value, Measurements, Recurring [Member] | Retained Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained Interest, Fair Value Disclosure	5	5
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	56	39
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	1,776	1,785
Derivative Assets	0	0
Assets, Fair Value Disclosure	2,444	2,303
Derivative Liability	(1)	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	1	0
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] | 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] | 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] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities	668	518
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	1,769	1,777
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	7	8
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] | Loans Held-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Retained Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained Interest, Fair Value Disclosure	0	0
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 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	20,950	20,518
Derivative Assets	55	38
Assets, Fair Value Disclosure	21,005	20,556
Derivative Liability	(55)	(41)
Financial and Nonfinancial Liabilities, Fair Value Disclosure	55	41
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	(55)	(39)
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] | 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] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities	0	0
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	831	854
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	142	146
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	14,883	14,291
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	2,384	2,494
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	580	541
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	900	936
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	1,230	1,256
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Loans Held-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Retained Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained Interest, Fair Value Disclosure	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	55	38
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
Derivative Assets	1	1
Assets, Fair Value Disclosure	25	19
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] | 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] | 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] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities	12	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] | Loans Held-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	7	13
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Retained Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained Interest, Fair Value Disclosure	5	5
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	$ 1

Fair Value (Fair Value Measu108

Fair Value (Fair Value Measurements - Reconciliation of Level 3 Assets And Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
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	$ 38	$ 29
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(3)	0
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	59	3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(66)	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(3)	(2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Assets, Ending balance	25	32
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(5)	0
Equity Securities [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	19
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(4)
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	(3)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Assets, Ending balance	12
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(5)
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	13	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	1	0
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	59	3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(66)	(2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Assets, Ending balance	7	1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	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	5	29
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	0
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	0	4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	(2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Assets, Ending balance	5	31
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	1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0
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
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 0

Fair Value (Fair Value Measu109

Fair Value (Fair Value Measurements - Nonrecurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	$ 126	$ 108
Fair Value, Measurements, Nonrecurring [Member] | Loans Held-for-Sale [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	119	77
Lower of cost or fair value or valuation reserve allowance	0	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	51	20
Lower of cost or fair value or valuation reserve allowance	(10)	(3)
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	22
Lower of cost or fair value or valuation reserve allowance	(11)	(12)
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	73	42
Lower of cost or fair value or valuation reserve allowance	(21)	(15)
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	13	14
Lower of cost or fair value or valuation reserve allowance	(1)	(1)
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
Lower of cost or fair value or valuation reserve allowance		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	205	136
Lower of cost or fair value or valuation reserve allowance	(22)	(16)
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Loans Held-for-Sale [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	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
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 [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	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
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 [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	119	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	51	20
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	22
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	73	42
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	13	14
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
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	$ 205	$ 136

Fair Value (Fair Value of Finan

Fair Value (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 1,967	$ 1,899
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	126	108
Loans and Leases Receivable, Net Amount	124,049	121,617
Nonmarketable equity securities	1,250	1,233
Deposits	97,446	93,256
Short-term Debt	9,564	11,413
Long-term Debt	45,076	44,226
Carrying Value of Deposit Liabilities with no Defined Contractual Maturities		47,400
Fair Value of Deposit Liabilities With No Defined Contractual Maturities		45,200
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,967	1,899
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	119	95
Loans and Leases Receivable, Net Amount	124,049	121,617
Nonmarketable equity securities	1,210	1,233
Deposits	49,025	45,869
Short-term Debt	9,564	11,413
Long-term Debt	45,076	44,226
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,895	1,865
Loans and Leases Receivable, Net Amount	125,530	123,302
Nonmarketable equity securities	1,210	1,239
Short-term Debt	9,567	11,417
Long-term Debt	46,973	46,624
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 and Leases Receivable, Net Amount	0	0
Nonmarketable equity securities	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	1,895	1,865
Loans and Leases Receivable, Net Amount	0	0
Nonmarketable equity securities	1,210	1,190
Short-term Debt	0	0
Long-term Debt	28,384	27,807
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 and Leases Receivable, Net Amount	125,530	123,302
Nonmarketable equity securities	0	49
Short-term Debt	9,567	11,417
Long-term Debt	18,589	18,817
Portion at Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	119	95
Deposits	48,845	45,827
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0	0
Deposits	0	0
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0	0
Deposits	0	0
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	119	95
Deposits	$ 48,845	$ 45,827

Offsetting Assets and Liabil111

Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 56	$ 39
Derivative Liability, Fair Value, Gross Liability	56	41
Customer Securities for which Entity has Right to Sell or Repledge, Fair Value	2	2
Derivative assets in net asset position [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	55	38
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	55	38
Derivative Asset, Not Subject to Master Netting Arrangement	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset	55	38
Derivative assets with no offsetting arrangements [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	1	1
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1	1
Derivative Asset, Not Subject to Master Netting Arrangement	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset	1	1
Total Derivative Assets [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	56	39
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	56	39
Derivative Asset, Not Subject to Master Netting Arrangement	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset	56	39
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	56	41
Derivative Liability, Fair Value, Amount Offset Against Collateral	56	41
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Derivative, Collateral, Right to Reclaim Cash	(1)	(1)
Derivative Liability	55	40
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	707	892
Derivative Liability, Fair Value, Amount Offset Against Collateral	707	892
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Derivative, Collateral, Right to Reclaim Cash	(707)	(892)
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	763	933
Derivative Liability, Fair Value, Amount Offset Against Collateral	763	933
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Derivative, Collateral, Right to Reclaim Cash	(708)	(893)
Derivative Liability	$ 55	$ 40

Segment Information (Financial

Segment Information (Financial Information Operating Segments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net Financing Revenue	$ 1,049	$ 979
Nonoperating Income (Expense)	354	396
Revenue, Net	1,403	1,375
Provision for Loan Losses Expensed	261	271
Noninterest Expense	814	778
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	328	326
Assets	170,021	162,101	$ 167,148
Interest Income (Expense), after Provision for Loan Loss	788	708
Automotive Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue	909	892
Nonoperating Income (Expense)	66	101
Revenue, Net	975	993
Provision for Loan Losses Expensed	259	268
Noninterest Expense	448	437
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	268	288
Assets	114,934	115,154
Insurance Operations Member
Segment Reporting Information [Line Items]
Net Financing Revenue	12	15
Nonoperating Income (Expense)	246	264
Revenue, Net	258	279
Provision for Loan Losses Expensed	0	0
Noninterest Expense	231	239
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	27	40
Assets	7,557	7,230
Mortgage Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue	43	34
Nonoperating Income (Expense)	1	0
Revenue, Net	44	34
Provision for Loan Losses Expensed	2	1
Noninterest Expense	34	24
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	8	9
Assets	12,780	8,362
Corporate Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue	46	34
Nonoperating Income (Expense)	8	18
Revenue, Net	54	52
Provision for Loan Losses Expensed	0	6
Noninterest Expense	25	21
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	29	25
Assets	4,375	3,438
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue	39	4
Nonoperating Income (Expense)	33	13
Revenue, Net	72	17
Provision for Loan Losses Expensed	0	(4)
Noninterest Expense	76	57
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(4)	(36)
Assets	$ 30,375	$ 27,917

Parent and Guarantor Condens113

Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	$ 1,543	$ 1,368
Interest and Dividend Income, Securities, Operating	176	134
Interest Income, Deposits with Financial Institutions	15	5
Operating Leases, Income Statement, Lease Revenue	382	543
Total financing revenue and other interest income	2,116	2,050
Interest Expense, Deposits	351	231
Interest Expense, Short-term Borrowings	32	27
Interest Expense, Long-term Debt	411	424
Interest Expense, Related Party	0	0
Interest Expense	794	682
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	273	389
Net Financing Revenue	1,049	979
Dividends from Bank Subsidiary	0
Dividends From Non Bank Subsidiary	0	0
Insurance Services Revenue	256	241
Gain (Loss) on Sales of Loans, Net	1	14
Gain (Loss) on Investments	(12)	27
Noninterest Income, Other Operating Income	109	114
Nonoperating Income (Expense)	354	396
Revenues	1,403	1,375
Provision for Loan Losses Expensed	261	271
Labor and Related Expense	306	285
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	63	88
Other Noninterest Expense	445	405
Noninterest Expense	814	778
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	328	326
Income Tax Expense (Benefit)	76	113
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	252	213
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(2)	1
Undistributed income of bank subsidiaries	0	0
Undistributed income of nonbank subsidiaries	0	0
Net Income (Loss) Attributable to Parent	250	214
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(328)	20
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(78)	234
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	11	(35)
Interest and Dividend Income, Securities, Operating	0	0
Interest Income, Deposits with Financial Institutions	2	2
Operating Leases, Income Statement, Lease Revenue	2	3
Total financing revenue and other interest income	19	(26)
Interest Expense, Deposits	0	1
Interest Expense, Short-term Borrowings	10	17
Interest Expense, Long-term Debt	258	281
Interest Expense, Related Party	3	4
Interest Expense	271	303
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	4	2
Net Financing Revenue	(256)	(331)
Dividends from Bank Subsidiary	1,000
Dividends From Non Bank Subsidiary	169	41
Insurance Services Revenue	0	0
Gain (Loss) on Sales of Loans, Net	28	(2)
Gain (Loss) on Investments	0	0
Noninterest Income, Other Operating Income	96	268
Nonoperating Income (Expense)	124	266
Revenues	1,037	(24)
Provision for Loan Losses Expensed	81	107
Labor and Related Expense	23	122
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	0	0
Other Noninterest Expense	182	288
Noninterest Expense	205	410
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	751	(541)
Income Tax Expense (Benefit)	(56)	(134)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	807	(407)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(1)	2
Undistributed income of bank subsidiaries	(597)	389
Undistributed income of nonbank subsidiaries	41	230
Net Income (Loss) Attributable to Parent	250	214
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(328)	20
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(78)	234
Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	0	0
Interest and Dividend Income, Securities, Operating	0	0
Interest Income, Deposits with Financial Institutions	0	0
Operating Leases, Income Statement, Lease Revenue	0	0
Total financing revenue and other interest income	0	0
Interest Expense, Deposits	0	0
Interest Expense, Short-term Borrowings	0	0
Interest Expense, Long-term Debt	0	0
Interest Expense, Related Party	0	0
Interest Expense	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	0	0
Net Financing Revenue	0	0
Dividends from Bank Subsidiary	1,000
Dividends From Non Bank Subsidiary	0	0
Insurance Services Revenue	0	0
Gain (Loss) on Sales of Loans, Net	0	0
Gain (Loss) on Investments	0	0
Noninterest Income, Other Operating Income	0	0
Nonoperating Income (Expense)	0	0
Revenues	1,000	0
Provision for Loan Losses Expensed	0	0
Labor and Related Expense	0	0
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	0	0
Other Noninterest Expense	0	0
Noninterest Expense	0	0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	1,000	0
Income Tax Expense (Benefit)	0	0
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	1,000	0
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	0	0
Undistributed income of bank subsidiaries	(597)	389
Undistributed income of nonbank subsidiaries	0	0
Net Income (Loss) Attributable to Parent	403	389
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(276)	5
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	127	394
Non-Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	1,532	1,403
Interest and Dividend Income, Securities, Operating	176	135
Interest Income, Deposits with Financial Institutions	14	3
Operating Leases, Income Statement, Lease Revenue	380	540
Total financing revenue and other interest income	2,105	2,085
Interest Expense, Deposits	354	230
Interest Expense, Short-term Borrowings	22	10
Interest Expense, Long-term Debt	153	143
Interest Expense, Related Party	2	4
Interest Expense	531	387
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	269	387
Net Financing Revenue	1,305	1,311
Dividends from Bank Subsidiary	0
Dividends From Non Bank Subsidiary	0	0
Insurance Services Revenue	256	241
Gain (Loss) on Sales of Loans, Net	1	16
Gain (Loss) on Investments	(12)	27
Noninterest Income, Other Operating Income	221	223
Nonoperating Income (Expense)	466	507
Revenues	1,771	1,818
Provision for Loan Losses Expensed	208	164
Labor and Related Expense	283	163
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	63	88
Other Noninterest Expense	471	494
Noninterest Expense	817	745
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	746	909
Income Tax Expense (Benefit)	132	247
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	614	662
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(1)	(1)
Undistributed income of bank subsidiaries	0	0
Undistributed income of nonbank subsidiaries	0	0
Net Income (Loss) Attributable to Parent	613	661
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(339)	19
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	274	680
Affiliated Entity [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	0	0
Interest Income, Deposits with Financial Institutions	0	0
Gain (Loss) on Sales of Loans, Net	0	0
Affiliated Entity [Member] | Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	2	4
Interest Income, Deposits with Financial Institutions	2	0
Gain (Loss) on Sales of Loans, Net	(423)	1,146
Affiliated Entity [Member] | Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	0	0
Interest Income, Deposits with Financial Institutions	0	0
Gain (Loss) on Sales of Loans, Net	0	0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	1	3
Interest Income, Deposits with Financial Institutions	2	1
Gain (Loss) on Sales of Loans, Net	1	170
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	0	0
Interest and Dividend Income, Securities, Operating	0	(1)
Interest Income, Deposits with Financial Institutions	(1)	0
Operating Leases, Income Statement, Lease Revenue	0	0
Total financing revenue and other interest income	(8)	(9)
Interest Expense, Deposits	(3)	0
Interest Expense, Short-term Borrowings	0	0
Interest Expense, Long-term Debt	0	0
Interest Expense, Related Party	(5)	(8)
Interest Expense	(8)	(8)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	0	0
Net Financing Revenue	0	(1)
Dividends from Bank Subsidiary	(2,000)
Dividends From Non Bank Subsidiary	(169)	(41)
Insurance Services Revenue	0	0
Gain (Loss) on Sales of Loans, Net	(28)	0
Gain (Loss) on Investments	0	0
Noninterest Income, Other Operating Income	(208)	(377)
Nonoperating Income (Expense)	(236)	(377)
Revenues	(2,405)	(419)
Provision for Loan Losses Expensed	(28)	0
Labor and Related Expense	0	0
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	0	0
Other Noninterest Expense	(208)	(377)
Noninterest Expense	(208)	(377)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(2,169)	(42)
Income Tax Expense (Benefit)	0	0
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(2,169)	(42)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	0	0
Undistributed income of bank subsidiaries	1,194	(778)
Undistributed income of nonbank subsidiaries	(41)	(230)
Net Income (Loss) Attributable to Parent	(1,016)	(1,050)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	615	(24)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(401)	(1,074)
Consolidation, Eliminations [Member] | Affiliated Entity [Member]
Condensed Income Statements, Captions [Line Items]
Interest and Fee Income, Loans and Leases	(3)	(7)
Interest Income, Deposits with Financial Institutions	(4)	(1)
Gain (Loss) on Sales of Loans, Net	$ 422	$ (1,316)

Parent and Guarantor Condens114

Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	$ 768		$ 844
Interest-bearing Deposits in Banks and Other Financial Institutions	2,953		3,408
Cash and Cash Equivalents, at Carrying Value	3,721		4,252	$ 4,302
Equity Securities	680		518
Available-for-sale securities	22,726		22,303
Held-to-maturity securities	1,967		1,899
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	126		108
Loans and Leases Receivable, Gross	125,327		122,893	119,002
Loans to nonbank subsidiary	0		0
Financing Receivable, Allowance for Credit Losses	1,278		1,276	1,155	$ 1,144
Loans and Leases Receivable, Net Amount	124,049		121,617
Property Subject to or Available for Operating Lease, Net	8,530		8,741
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	2,197		2,047
Other Assets	6,025		5,663
Assets	170,021		167,148	162,101
Noninterest-bearing deposit liabilities	122		108
Interest-bearing Deposit Liabilities	97,324		93,148
Deposits	97,446		93,256
Short-term Debt	9,564		11,413
Long-term Debt	45,076		44,226
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	494		375
Unearned Premiums	2,904		2,604
Accounts Payable and Accrued Liabilities	1,455		1,780
Liabilities	156,939		153,654
Stockholders' Equity Attributable to Parent	13,082	$ 13,375	13,494	13,365	$ 13,317
Liabilities and Equity	170,021		167,148
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	56		74
Interest-bearing Deposits in Banks and Other Financial Institutions	5		5
Cash and Cash Equivalents, at Carrying Value	796		1,217	1,490
Equity Securities	0		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		0
Loans and Leases Receivable, Gross	6,443		7,434
Loans to nonbank subsidiary	1,311		879
Financing Receivable, Allowance for Credit Losses	145		185
Loans and Leases Receivable, Net Amount	7,609		8,128
Property Subject to or Available for Operating Lease, Net	14		19
Receivables from bank subsidiary	86		80
Receivables from nonbank subsidiary	41		71
Investment in bank subsidiaries	16,163		16,962
Investment in nonbank subsidiaries	7,520		8,111
Premiums receivable and other insurance assets	0		0
Other Assets	2,221		2,207
Assets	34,450		36,795
Noninterest-bearing deposit liabilities	0		0
Interest-bearing Deposit Liabilities	6		12
Deposits	6		12
Short-term Debt	2,957		3,171
Long-term Debt	16,808		17,966
Debt Payable To Bank Subsidiaries	65		74
Debt Payable To Nonbank Subsidiaries	992		1,103
Payables to Bank Subsidiaries			4
Payables to Nonbank Subsidiaries	115		132
Interest payable	209		200
Unearned Premiums	0		0
Accounts Payable and Accrued Liabilities	216		639
Liabilities	21,368		23,301
Stockholders' Equity Attributable to Parent	13,082		13,494
Liabilities and Equity	34,450		36,795
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	0
Equity Securities	0		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		0
Loans and Leases Receivable, Gross	0		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	16,163		16,962
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	0		0
Other Assets	0		0
Assets	16,163		16,962
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	16,163		16,962
Liabilities and Equity	16,163		16,962
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	712		770
Interest-bearing Deposits in Banks and Other Financial Institutions	2,948		3,403
Cash and Cash Equivalents, at Carrying Value	4,237		4,868	3,453
Equity Securities	680		518
Available-for-sale securities	22,726		22,303
Held-to-maturity securities	2,033		1,973
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	126		108
Loans and Leases Receivable, Gross	118,884		115,459
Loans to nonbank subsidiary	415		408
Financing Receivable, Allowance for Credit Losses	1,133		1,091
Loans and Leases Receivable, Net Amount	118,166		114,776
Property Subject to or Available for Operating Lease, Net	8,516		8,722
Receivables from bank subsidiary	0		0
Receivables from nonbank subsidiary	61		77
Investment in bank subsidiaries	0		0
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	2,197		2,082
Other Assets	5,072		5,105
Assets	163,814		160,532
Noninterest-bearing deposit liabilities	122		108
Interest-bearing Deposit Liabilities	97,318		93,136
Deposits	98,175		94,383
Short-term Debt	6,607		8,242
Long-term Debt	28,268		26,260
Debt Payable To Bank Subsidiaries	0		0
Debt Payable To Nonbank Subsidiaries	1,311		879
Payables to Bank Subsidiaries			0
Payables to Nonbank Subsidiaries	106		127
Interest payable	285		175
Unearned Premiums	2,904		2,604
Accounts Payable and Accrued Liabilities	2,473		2,790
Liabilities	140,129		135,460
Stockholders' Equity Attributable to Parent	23,685		25,072
Liabilities and Equity	163,814		160,532
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		0
Affiliated Entity [Member] | Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	735		1,138
Interest-bearing Deposit Liabilities	0		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		0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	577		695
Interest-bearing Deposit Liabilities	735		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	(1,312)		(1,833)	$ (641)
Equity Securities	0		0
Available-for-sale securities	0		0
Held-to-maturity securities	(66)		(74)
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0		0
Loans and Leases Receivable, Gross	0		0
Loans to nonbank subsidiary	(1,726)		(1,287)
Financing Receivable, Allowance for Credit Losses	0		0
Loans and Leases Receivable, Net Amount	(1,726)		(1,287)
Property Subject to or Available for Operating Lease, Net	0		0
Receivables from bank subsidiary	(86)		(80)
Receivables from nonbank subsidiary	(102)		(148)
Investment in bank subsidiaries	(32,326)		(33,924)
Investment in nonbank subsidiaries	(7,520)		(8,111)
Premiums receivable and other insurance assets	0		(35)
Other Assets	(1,268)		(1,649)
Assets	(44,406)		(47,141)
Noninterest-bearing deposit liabilities	0		0
Interest-bearing Deposit Liabilities	0		0
Deposits	(735)		(1,139)
Short-term Debt	0		0
Long-term Debt	0		0
Debt Payable To Bank Subsidiaries	(65)		(74)
Debt Payable To Nonbank Subsidiaries	(2,303)		(1,982)
Payables to Bank Subsidiaries			(4)
Payables to Nonbank Subsidiaries	(221)		(259)
Interest payable	0		0
Unearned Premiums	0		0
Accounts Payable and Accrued Liabilities	(1,234)		(1,649)
Liabilities	(4,558)		(5,107)
Stockholders' Equity Attributable to Parent	(39,848)		(42,034)
Liabilities and Equity	(44,406)		(47,141)
Consolidation, Eliminations [Member] | Affiliated Entity [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	(1,312)		(1,833)
Interest-bearing Deposit Liabilities	$ (735)		$ (1,139)

Parent and Guarantor Condens115

Parent and Guarantor Condensed Consolidating Financial Statements (Statement of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 1,097	$ 1,175
Purchases of Equity Securities	(374)	(137)
Proceeds from Sales of Equity Securities	220	314
Payments to Acquire Available-for-sale Securities	(2,360)	(2,696)
Proceeds from Sale of Available-for-sale Securities	328	731
Proceeds from maturities and repayment of available-for-sale securities	795	589
Payments to Acquire Held-to-maturity Securities	(155)	(215)
Proceeds from Sale and Maturity of Held-to-maturity Securities	35	5
Payments to Acquire Finance Receivables	(1,497)	(405)
Proceeds from Sale of Loans Held-for-investment	0	1,164
Originations and repayments of loans held-for-investment and other	(1,300)	(1,174)
Gain (Loss) on Sales of Loans, Net	1	14
Purchases Of Operating Lease Assets	(969)	(893)
Disposals of Operating Lease Assets	976	1,545
Proceeds from Contributions from Parent	0	0
Returns Of Contributed Capital	0	0
Increase (Decrease) in Non marketable equity securities	(19)	213
Payments for (Proceeds from) Other Investing Activities	(82)	(56)
Net Cash Provided by (Used in) Investing Activities	(4,402)	(1,015)
Proceeds from (Repayments of) Short-term Debt	(1,848)	(4,303)
Increase (Decrease) in Deposit Assets	4,173	5,451
Proceeds from Issuance of Long-term Debt	6,665	4,488
Repayments of Long-term Debt	(5,771)	(7,573)
Payments for Repurchase of Common Stock	(185)	(169)
Payments of Dividends	(58)	(38)
Capital contributions from parent	0	0
Net Cash Provided by (Used in) Financing Activities	2,976	(2,144)
Effect of Exchange Rate on Cash and Cash Equivalents	(2)	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(331)	(1,984)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	4,938	5,897	$ 5,269	$ 7,881
Cash and Cash Equivalents, at Carrying Value	3,721	4,302	4,252
Restricted Cash	1,217	1,595
Parent Company [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities	456	(149)
Purchases of Equity Securities	0	0
Proceeds from Sales of Equity Securities	0	0
Payments to Acquire Available-for-sale Securities	0	0
Proceeds from Sale of Available-for-sale Securities	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0	0
Payments to Acquire Finance Receivables	0	(15)
Proceeds from Sale of Loans Held-for-investment	820	0
Originations and repayments of loans held-for-investment and other	432	931
Gain (Loss) on Sales of Loans, Net	28	(2)
Purchases Of Operating Lease Assets	0	0
Disposals of Operating Lease Assets	4	1
Proceeds from Contributions from Parent	(49)	(83)
Returns Of Contributed Capital	38	645
Increase (Decrease) in Non marketable equity securities	0	0
Payments for (Proceeds from) Other Investing Activities	(3)	(26)
Net Cash Provided by (Used in) Investing Activities	819	2,600
Proceeds from (Repayments of) Short-term Debt	(214)	1,278
Increase (Decrease) in Deposit Assets	(6)	(82)
Proceeds from Issuance of Long-term Debt	15	330
Repayments of Long-term Debt	(1,152)	(2,870)
Payments for Repurchase of Common Stock	(185)	(169)
Payments of Dividends	(58)	(38)
Capital contributions from parent	0	0
Net Cash Provided by (Used in) Financing Activities	(1,727)	(1,754)
Effect of Exchange Rate on Cash and Cash Equivalents	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(452)	697
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	943	1,686	1,395	989
Cash and Cash Equivalents, at Carrying Value	796	1,490	1,217
Restricted Cash	147	196
Guarantor Subsidiaries [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities	1,000	0
Purchases of Equity Securities	0	0
Proceeds from Sales of Equity Securities	0	0
Payments to Acquire Available-for-sale Securities	0	0
Proceeds from Sale of Available-for-sale Securities	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0	0
Payments to Acquire Finance Receivables	0	0
Proceeds from Sale of Loans Held-for-investment	0	0
Originations and repayments of loans held-for-investment and other	0	0
Gain (Loss) on Sales of Loans, Net	0	0
Purchases Of Operating Lease Assets	0	0
Disposals of Operating Lease Assets	0	0
Proceeds from Contributions from Parent	(6)	0
Returns Of Contributed Capital	0	0
Increase (Decrease) in Non marketable equity securities	0	0
Payments for (Proceeds from) Other Investing Activities	0	0
Net Cash Provided by (Used in) Investing Activities	(6)	0
Proceeds from (Repayments of) Short-term Debt	0	0
Increase (Decrease) in Deposit Assets	0	0
Proceeds from Issuance of Long-term Debt	0	0
Repayments of Long-term Debt	0	0
Payments for Repurchase of Common Stock	0	0
Payments of Dividends	0	0
Capital contributions from parent	6	0
Net Cash Provided by (Used in) Financing Activities	(994)	0
Effect of Exchange Rate on Cash and Cash Equivalents	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0	0
Cash and Cash Equivalents, at Carrying Value	0	0	0
Restricted Cash	0	0
Non-Guarantor Subsidiaries [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities	1,812	1,284
Purchases of Equity Securities	(374)	(137)
Proceeds from Sales of Equity Securities	220	314
Payments to Acquire Available-for-sale Securities	(2,360)	(2,696)
Proceeds from Sale of Available-for-sale Securities	328	731
Proceeds from maturities and repayment of available-for-sale securities	795	589
Payments to Acquire Held-to-maturity Securities	(155)	(215)
Proceeds from Sale and Maturity of Held-to-maturity Securities	35	5
Payments to Acquire Finance Receivables	(2,317)	(390)
Proceeds from Sale of Loans Held-for-investment	0	1,164
Originations and repayments of loans held-for-investment and other	(1,732)	(1,145)
Gain (Loss) on Sales of Loans, Net	1	16
Purchases Of Operating Lease Assets	(969)	(893)
Disposals of Operating Lease Assets	972	1,544
Proceeds from Contributions from Parent	0	0
Returns Of Contributed Capital	0	0
Increase (Decrease) in Non marketable equity securities	(19)	213
Payments for (Proceeds from) Other Investing Activities	(80)	64
Net Cash Provided by (Used in) Investing Activities	(5,646)	(421)
Proceeds from (Repayments of) Short-term Debt	(1,634)	(5,581)
Increase (Decrease) in Deposit Assets	3,776	5,533
Proceeds from Issuance of Long-term Debt	6,650	3,196
Repayments of Long-term Debt	(4,619)	(4,703)
Payments for Repurchase of Common Stock	0	0
Payments of Dividends	0	0
Capital contributions from parent	49	83
Net Cash Provided by (Used in) Financing Activities	3,436	(3,304)
Effect of Exchange Rate on Cash and Cash Equivalents	(2)	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(400)	(2,441)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	5,307	4,852	5,707	7,293
Cash and Cash Equivalents, at Carrying Value	4,237	3,453	4,868
Restricted Cash	1,070	1,399
Consolidation, Eliminations [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities	(2,171)	40
Purchases of Equity Securities	0	0
Proceeds from Sales of Equity Securities	0	0
Payments to Acquire Available-for-sale Securities	0	0
Proceeds from Sale of Available-for-sale Securities	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0	0
Payments to Acquire Finance Receivables	820	0
Proceeds from Sale of Loans Held-for-investment	(820)	0
Originations and repayments of loans held-for-investment and other	0	(960)
Gain (Loss) on Sales of Loans, Net	(28)	0
Purchases Of Operating Lease Assets	0	0
Disposals of Operating Lease Assets	0	0
Proceeds from Contributions from Parent	55	83
Returns Of Contributed Capital	(38)	(645)
Increase (Decrease) in Non marketable equity securities	0	0
Payments for (Proceeds from) Other Investing Activities	1	(94)
Net Cash Provided by (Used in) Investing Activities	431	(3,194)
Proceeds from (Repayments of) Short-term Debt	0	0
Increase (Decrease) in Deposit Assets	403	0
Proceeds from Issuance of Long-term Debt	0	962
Repayments of Long-term Debt	0	0
Payments for Repurchase of Common Stock	0	0
Payments of Dividends	0	0
Capital contributions from parent	(55)	(83)
Net Cash Provided by (Used in) Financing Activities	2,261	2,914
Effect of Exchange Rate on Cash and Cash Equivalents	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	521	(240)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(1,312)	(641)	(1,833)	$ (401)
Cash and Cash Equivalents, at Carrying Value	(1,312)	(641)	$ (1,833)
Restricted Cash	0	0
Affiliated Entity [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments	0	0
Gain (Loss) on Sales of Loans, Net	0	0
Net Change in Debt, Intercompany	0	0
Dividends paid and returns of contributed capital, Intercompany	0	0
Affiliated Entity [Member] | Parent Company [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments	0	1
Gain (Loss) on Sales of Loans, Net	(423)	1,146
Net Change in Debt, Intercompany	(127)	(203)
Dividends paid and returns of contributed capital, Intercompany	0	0
Affiliated Entity [Member] | Guarantor Subsidiaries [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments	0	0
Gain (Loss) on Sales of Loans, Net	0	0
Net Change in Debt, Intercompany	0	0
Dividends paid and returns of contributed capital, Intercompany	(1,000)	0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments	9	261
Gain (Loss) on Sales of Loans, Net	1	170
Net Change in Debt, Intercompany	422	(1,146)
Dividends paid and returns of contributed capital, Intercompany	(1,208)	(686)
Affiliated Entity [Member] | Consolidation, Eliminations [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments	(9)	(262)
Gain (Loss) on Sales of Loans, Net	422	(1,316)
Net Change in Debt, Intercompany	(295)	1,349
Dividends paid and returns of contributed capital, Intercompany	$ 2,208	$ 686

Subsequent Events (Details)

Subsequent Events (Details) - $ / shares	Apr. 10, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Apr. 14, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share		$ 0.13	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share	$ 0.13

Uncategorized Items - ally-2018

Label	Element	Value
Common Stock Including Additional Paid in Capital [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 21,245,000,000
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax	(250,000,000)
Treasury Stock [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	(1,110,000,000)
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(20,000,000)
Accounting Standards Update 2016-01 [Member] | AOCI Attributable to Parent [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	27,000,000
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(126,000,000)
Accounting Standards Update 2018-02 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	42,000,000
Accounting Standards Update 2018-02 [Member] | AOCI Attributable to Parent [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (42,000,000)