Share-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise of Stock Options and the Vesting of Restricted Stock and RSUs	$ 5	$ 8
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income			$ 9
Share-Based Compensation Expense, Change	$ 1	$ 1	$ 1
Restricted Stock	50,457
Restricted Stock Units expected to vest	813,705
Share Based Compensation Restricted Stock Value	$ 3
Share Based Compensation Restricted Stock Units Aggregate Intrinsic Value	$ 42
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price	$ 51.28
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term	5 years 6 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value	$ 1
Restricted Stock Units Outstanding	1,294,070	1,400,699	1,709,813	2,047,158
Weighted Average Grant Price of Restricted Stock Forfeited	$ 44.69	$ 35.95	$ 28.12
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 34.77	$ 29.85	$ 27.06	$ 26.44
Stock Options without a fixed expiration date	19,496
Total shares authorized under stock option and incentive plan	9,000,000
Number of shares available for future grants of stock options or restricted stock	3,667,621
Compensation expense not yet recognized for nonvested share-based awards	$ 26
Nonvested share-based awards, expected weighted average period to be recognized, years	2 years 6 months
Total intrinsic value of stock options exercised	$ 13	$ 20	$ 17
Cash received from the exercise of stock options	13	18	$ 23
Aggregate intrinsic value of outstanding stock options	29	25
Aggregate intrinsic value of exercisable options	$ 29	$ 21
Outstanding stock options, Weighted average remaining contractual life (years)	3 years 2 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	432,266
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	1,676,778	2,004,598	2,560,571	3,437,910
Total fair value of restricted stock vesting	$ 21	$ 21	$ 22
Weighted average issue price	$ 42.83	$ 42.90	$ 44.55
Total fair value granted	$ 21	$ 21	$ 22
Stock Issued During Period, Shares, Restricted Stock Award, Gross	24,994	21,634	314
Restricted Stock Units Granted	536,489	461,305	587,396
Weighted Average Grant Price of Restricted Stock Units Granted	$ 47.85	$ 53.17	$ 41.78
Restricted Stock Units Vested	614,968	699,920	803,492
Weighted Average Grant Price of Restricted Stock Units Vested	$ 33.74	$ 29.56	$ 26.19
Equity Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding stock options, Weighted average remaining contractual life (years)	2 years 4 months 24 days	2 years 8 months 12 days
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Units Granted	19,116	14,796	20,711

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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