Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 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 assured 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 and timing differences between operating lease expense and payments, recognized on a straight-line basis over the lease term. 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. The update 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 be applied using the modified retrospective approach with limited exceptions. The Corporation’s cross-functional implementation team, led by the Chief Financial Officer and Chief Credit Officer, continued to make progress in accordance with the detailed implementation plan for adoption. In prior periods, the Corporation developed new credit estimation models and, in the first quarter 2019, completed internal validation of the models. The Corporation is currently finalizing and documenting new processes and controls, challenging current model assumptions and outputs, refining the qualitative framework as well as drafting policies and disclosures. Additionally, limited parallel runs, which began in the fourth quarter 2018, will be enhanced throughout 2019 as the end-to-end processes, controls and policies are finalized. 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 overall allowance for credit losses is not expected to materially change due to the portfolio’s relatively short average contractual life. The commercial portfolio, which comprises most of the Corporation’s portfolio, consists of loans and lending arrangements with short contractual maturities which are expected to result in a slight reduction to the allowance for credit losses. The allowance for credit losses is expected to increase for the consumer portfolio given its longer contractual maturities. The standard will be adopted in first quarter 2020.