Stock-Based Compensation - Stock-Based Compensation Expense and Stock Option Fair Value Assumptions (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock-Based Compensation
Stock option expense	$ 14	$ 21	$ 13
Restricted stock and unit awards expense	64	79	83
Total stock-based compensation expense	78	100	96
Tax benefit	$ 29	$ 38	$ 37
Assumptions Used In Valuing Options Granted [Line Items]
Dividend yield	1.40%
Expected life (years)	6 years 3 months 18 days
Weighted-average grant-date fair value per option	$ 27.57	$ 23.41	$ 14.46
Minimum Range [Member]
Assumptions Used In Valuing Options Granted [Line Items]
Risk-free average interest rate	0.20%	0.10%	0.10%
Dividend yield		1.40%	2.07%
Volatility	21.00%	18.00%	29.00%
Expected life (years)		6 years 2 months 16 days	6 years 1 month 6 days
Maximum Range [Member]
Assumptions Used In Valuing Options Granted [Line Items]
Risk-free average interest rate	1.90%	2.90%	2.90%
Dividend yield		1.80%	2.09%
Volatility	39.00%	41.00%	45.00%
Expected life (years)		6 years 3 months	6 years 2 months 12 days

Assumptions Used In Valuing Options Granted.

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- Definition

Represents the expense 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 14.F)
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-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14
-Section F

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- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The noncash expense that represents the cost of restricted stock or unit distributed to employees as compensation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 2
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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

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-Publisher FASB
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- Definition

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

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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-Publisher FASB
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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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- Definition

The noncash expense that accounts for the value of stock or unit options distributed to employees as compensation.

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