Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Narrative) (Details) $ in Millions		12 Months Ended
		Dec. 31, 2019 USD ($) markets	Jan. 01, 2020 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Number of Primary Geographic Markets | markets		3
Commitments to fund additional investments in nonmarketable equity securities		$ 1
Federal Home Loan Bank Stock		163			$ 163
Federal Reserve Bank Stock		85			85
Net Deferred Income on Originated Loans		103			115
Allowance for Credit Losses, Threshold for Individual Evaluation, Nonaccrual Loans		2
Allowance for Credit losses, Threshold for Individual Evaluation, TDR		$ 1
Delinquency Status, Period of Unpaid Scheduled Monthly Payment		30 days
Right of use assets		$ 329
Operating lease liabilities		$ 367
Number of Reporting Units		3
Notional Amount	[1]	$ 30,134			21,557
Defined Benefit Plan Investment Gain Loss Amortization Adjustment, Allowable Percentage		10.00%
Defined Benefit Plan Actuarial Gain Loss Amortization Adjustment, Allowable Percentage		10.00%
Defined Benefit Plan Market-related Value Plan Assets, Amortization Period		5 years
Overall allowance for credit losses		$ 668
Business loans percent of portfolio		91.00%
Premises the Corporation owns | Minimum
Premises and Equipment, Useful Life		3 years
Premises the Corporation owns | Maximum
Premises and Equipment, Useful Life		33 years
Furniture and equipment | Minimum
Premises and Equipment, Useful Life		3 years
Furniture and equipment | Maximum
Premises and Equipment, Useful Life		8 years
Leasehold improvements | Maximum
Premises and Equipment, Useful Life		10 years
Software
Premises and Equipment, Useful Life		5 years
Carrying Amount
Nonmarketable equity securities	[2]	$ 5			$ 6
Retail loans | Real estate mortgage
Past Due Period Residential Mortgage And Home Equity Loans Placed On Nonaccrual Status		90 days
Past Due Threshold For Charge-Off		180 days
Commercial borrower | Business loans
Past Due Period Business Loans Placed On Nonaccrual Status		90 days
Consumer borrower | Retail loans | Home equity
Maximum Past Due Status Junior Lien Home Equity Placed On Nonaccrual Status		90 days
Consumer borrower | Retail loans | Other consumer
Past Due Threshold For Charge-Off		120 days
Threshold, Days Past Due, Other Consumer Placed On Nonaccrual Status		90 days
Accounting Standards Update 2016-02 [Member]
Right of use assets				$ 329
Operating lease liabilities				343
Accounting Standards Update 2016-13 [Member]
Day-one decrease in the overall allowance for credit losses			$ 17
Reduction to deferred tax asset			$ 4
Increase in CET1			0.02%
Reduction in business loans allowance for credit losses			$ 42
Increase in retail loans allowance for credit losses			25
Retained Earnings | Accounting Standards Update 2016-02 [Member]
Cumulative effect of change in accounting principle				$ 14
Retained Earnings | Accounting Standards Update 2016-13 [Member]
Cumulative effect of change in accounting principle			$ 13
Fair Value Hedging | Short-Cut Method | Designated as Hedging Instrument | Interest rate swap
Notional Amount		$ 2,100

[1] Notional or contractual amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected on the Consolidated Balance Sheets.

[2] Certain investments that are measured at fair value using the net asset value have not been classified in the fair value hierarchy. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the Consolidated Balance Sheets.