Represents the number of years after which granted options expire.

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The percentage of share-based awards that vest on the second anniversary of the grant date of the awards.

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The percentage of share-based awards that vest on the third and fourth anniversaries of the grant date of the awards.

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The period of time over 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, for awards granted prior to 2010.

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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.

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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 tax benefit from exercise of stock options granted under share-based compensation arrangement.

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

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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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No definition available.

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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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Equity Incentive Plans - Narrative (Details) - USD ($) shares in Millions, $ in Millions		12 Months Ended
	Feb. 17, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Incentive Plans
Compensation expense		$ 125	$ 106	$ 80
Share-based compensation arrangement by share-based payment award, recognized tax benefits		22	22	28
Cash received from the exercise of options		92	178	187
Tax benefit realized on options exercised and stock unrestricted		28	$ 96	$ 61
Unrecognized compensation cost related to nonvested awards		$ 89
Common stock authorized for stock-based awards (in shares)		98.0
Common stock reserved for further issuance (in shares)		15.0
Nonqualified stock options
Equity Incentive Plans
Unrecognized compensation cost related to nonvested awards		$ 29
Expected period of recognition of unrecognized compensation cost		1 year 8 months 16 days
Restricted stock units
Equity Incentive Plans
Unrecognized compensation cost related to nonvested awards		$ 23
Expected period of recognition of unrecognized compensation cost		1 year 8 months 9 days
Portion of awards vesting and unrestricting on second anniversary of grant date (as a percent)		50.00%
Portion of awards vesting and unrestricting on third and fourth anniversaries of grant date (as a percent)		25.00%
Performance stock awards
Equity Incentive Plans
Unrecognized compensation cost related to nonvested awards		$ 37
Expected period of recognition of unrecognized compensation cost		1 year 7 months 2 days
Stock options
Equity Incentive Plans
Vesting period of options granted		3 years
Portion of awards vesting and unrestricting on second anniversary of grant date (as a percent)	50.00%
Portion of awards vesting and unrestricting on third and fourth anniversaries of grant date (as a percent)	25.00%
Expiration term for options		10 years