Share-Based Associate Compensation Plans (Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) Peers compensation_plans shares	Dec. 31, 2016 USD ($) Peers shares	Dec. 31, 2015 USD ($) Peers shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of peers in peer group \| Peers	9	9	10
Number of equity compensation plans \| compensation_plans	4
Share based compensation	$ 17	$ 15	$ 14
Tax benefit from compensation expense	9	8	6
Options exercised, intrinsic value	19	25	15
Options vested, intrinsic value	8	11	7
Unrecognized compensation costs related to non-vested awards	$ 28
Expected weighted-average period to recognize the unrecognized compensation costs related to non-vested awards	1 year 8 months 18 days
Maximum number of shares awarded to each full-time employee for their service \| shares	10
Proceeds from stock options exercised	$ 13	21	24
Shares of common stock granted in period (in shares) \| shares	706,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards exercise peirod	10 years
Awards vesting period	3 years
Proceeds from stock options exercised	$ 13	$ 21	$ 24
Shares repurchased \| shares	96,030	186,097	292,414
Shares repurchased, value	$ 7	$ 13	$ 16
Weighted average remaining contractual term	8 years 8 months 8 days
Shares authorized to be granted under the shareholder-approved plans \| shares	17,300,000
Shares available for future issuance under the plans \| shares	11,300,000
Stock Options \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock granted in period (in shares) \| shares	15,040
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	2.83%		3.52%
Weighted-average expected term	2 years 10 months 21 days		2 years 10 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	1.44%		0.99%
Performance Shares [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards vesting period	3 years
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Intrinsic Value Aggregate	$ 7	$ 6	$ 6
Performance Shares [Member] \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		2.58%
Weighted-average expected term		2 years 5 months 9 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate		0.77%

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Number of equity compensation plans

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Number of peers in peer group

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Amount of difference between fair value of the underlying shares vested during the period.

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Share Based Compensation Arrangement by Share Based Payment Award, Options, Vested in Period, Total Intrinsic Value

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The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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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Net number of share options (or share units) granted during the period.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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