Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Leases	Leases Effective January 1, 2019, the Corporation adopted the provisions of Accounting Standards Update (ASU) No. 2016-02, “Leases (Topic 842),” (ASU 2016-02), for all open leases with a term greater than one year as of the adoption date, using the modified retrospective approach. Prior comparable periods are presented in accordance with previous guidance under Accounting Standards Codification (ASC) 840, “Leases.” Topic 842 requires the recognition of a lease liability, measured as the present value of unpaid lease payments for operating leases where the Corporation is the lessee, and a corresponding right-of-use (ROU) asset for the right to use the leased properties. The Corporation elected not to reassess whether contracts are or contain leases, lease classification or initial direct costs for existing leases, a set of practical expedients for transition provided by ASU 2016-12. Further, the Corporation elected the practical expedient to use hindsight in determining the lease term and assessing impairment. The election of the hindsight practical expedient resulted in longer lease terms for a limited number of strategic locations based on relevant factors as of the adoption date. The impact at adoption was increases of $329 million and $343 million to total assets and liabilities, respectively, and a $14 million reduction to retained earnings. The increase in total assets was due to the recognition of ROU assets recorded in accrued income and other assets, and the increase in total liabilities was due to corresponding recognition of lease payment liabilities recorded in accrued expenses and other liabilities. Operating lease liabilities reflect the Corporation’s obligation to make future lease payments, primarily for real estate locations. Lease terms typically comprise contractual terms but may include extension options reasonably certain of being exercised at lease inception for certain strategic locations such as regional headquarters. Payments are discounted using the rate the Corporation would pay to borrow amounts equal to the lease payments over the lease term (the Corporation’s incremental borrowing rate). The Corporation does not separate lease and non-lease components for contracts in which it is the lessee. ROU assets are measured based on lease liabilities adjusted for incentives as well as accrued and prepaid rent. Operating lease expense is recognized on a straight-line basis over the lease term, while variable lease payments are recognized as incurred. Common area maintenance and other executory costs are the main components of variable lease payments. Operating and variable lease expenses are recorded in net occupancy expense in the Consolidated Statements of Income. The Corporation is the lessor in sales-type, direct finance and leveraged lease arrangements. Leases are recorded at the principal balance outstanding, net of unearned income and charge-offs. Interest income is recognized using the interest method. The impact of adopting Topic 842 for lessor accounting was not significant.
Pending Accounting Pronouncements	Pending Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments," (ASU 2016-13), which addresses concerns regarding the perceived delay in recognition of credit losses under the existing incurred loss model. The amendment introduces a new, single model for recognizing credit losses on all financial instruments presented on a cost basis. Under the new model, entities must estimate current expected credit losses by considering all available relevant information, including historical and current conditions, as well as reasonable and supportable forecasts of future events. ASU 2016-13 also requires additional qualitative and quantitative disclosure to allow users to better understand the credit risk within the portfolio and the methodologies for determining the allowance for credit losses. ASU 2016-13 is effective for the Corporation on January 1, 2020 and must generally be applied using the modified retrospective approach with a cumulative effect adjustment to retained earnings. In prior periods, the Corporation developed and completed internal validations of new credit estimation models. The Corporation has implemented new processes and controls for the execution of the new model and is in the process of testing them. The implementation team continues to challenge current model assumptions and outputs, refine the qualitative framework and finalize policies and disclosures. Additionally, parallel runs will continue in fourth quarter 2019 as more end-to-end processes, controls and policies are fina lized. Incorporating reasonable and supportable forecasts of economic conditions into the estimate of expected credit losses will require significant judgment, such as selecting economic variables and forecast scenarios as well as determining the appropriate length of the forecast horizon. Management will select economic variables it believes to be most relevant based on the composition of the loan portfolio and customer base, likely to include forecasted levels of employment, gross domestic product, corporate bond and treasury spreads, industrial production levels, consumer and commercial real estate price indices as well as housing statistics. Different economic forecasts ranging from more benign to more severe will be evaluated each reporting period to forecast losses over the contractual life of the loan portfolio. The Corporation anticipates using a two-year forecast horizon, which encompasses most of the remaining contractual life of its portfolio of commercial loans, reverting to its longer-term historical loss experience to estimate expected losses over any remaining contractual life. The ultimate impact of ASU 2016-13 will depend on the composition of the portfolio as well as economic conditions and forecasts at the time of adoption. Based on current factors, the Corporation estimates overall allowance for credit losses to remain within 5 percent of current levels. The commercial portfolio, comprising the majority of the Corporation’s portfolio, consists of loans and lending arrangements with short contractual maturities that are expected to result in a reduction of up to 5 percent in the allowance for credit losses. The allowance for credit losses is expected to increase between 60 to 80 percent for the consumer portfolio given its longer contractual maturities. ASU 2016-13 also requires expected credit losses on available-for-sale securities (AFS) debt securities be recorded as an allowance for credit losses. For certain types of debt securities, such as U.S. Treasuries and other securities with government guarantees, entities may expect zero credit losses. The Corporation believes the zero-loss expectation currently applies to all of its AFS securities. ASU 2016-13 will be adopted in first quarter 2020.