Share-Based Compensation Share-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Options exercised policy	10 years
Number of shares originally available for grant	6,100,000
Shares available for grant	4,000,000.0
Closing stock price per share	$ 55.86
Total intrinsic value of stock options exercised	$ 6	$ 20	$ 81
Shares in treasury	88,997,430	86,069,234
Restricted Stock
Total fair value of restricted stock awards that fully vested	$ 17	$ 31	32
Restricted Stock \| Minimum
Share-based compensation vesting period	3 years
Restricted Stock \| Maximum
Share-based compensation vesting period	5 years
Restricted Stock Units (RSUs)
Total fair value of restricted stock awards that fully vested	$ 12	$ 37	$ 24
Restricted Stock Units (RSUs) \| Minimum
Share-based compensation vesting period	3 years
Restricted Stock Units (RSUs) \| Maximum
Share-based compensation vesting period	5 years
Stock Options \| Minimum
Share-based compensation vesting period	1 year
Stock Options \| Maximum
Share-based compensation vesting period	4 years

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

Price of a single share of a number of saleable stocks of a company.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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