Share-Based Payments (Narrative) (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 23, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of incentive awards (in years)	3 years
Contractual lives of options granted under long-term incentive compensation plans	10 years
Number of Common Share Equivalents Authorized Under Long-term Incentive Plans				60,000,000
Number of Remaining Common Share Equivalents Available for Grant Under Long-term Incentive Plans	33,000,000
Aggregate intrinsic value of exercised options	$ 8,000,000	$ 8,000,000	$ 10,000,000
Cash received from options exercised	5,000,000	5,000,000	11,000,000
Pre Tax Amount Of Non Vested Stock Options And Restricted Stock Awards And Units Not Yet Recognized	43,000,000
Total fair value of shares vested during the period	35,000,000	89,000,000	112,000,000
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	$ 1,000,000	$ 2,000,000	$ 4,000,000

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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-Name Accounting Standards Codification
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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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