Aggregate number of common shares reserved for future issuance.

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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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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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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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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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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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Employee Incentive, Retirement, Deferred Compensation, and Career Achievement Plans (Employee Incentive Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock authorized to be granted under the existing stock incentive plan (in shares)	44,000,000
Total unrecognized compensation cost, net of forfeitures, related to outstanding stock options, restricted stock awards, and restricted stock units	$ 268
Stock option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted-average period for unrecognized compensation cost, net of forfeitures, related to outstanding stock options, restricted stock awards, and restricted stock units	1 year 10 months 24 days
Restricted stock unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted-average period for unrecognized compensation cost, net of forfeitures, related to outstanding stock options, restricted stock awards, and restricted stock units	2 years 4 months 24 days
Total fair value of restricted stock awards vested	$ 127	$ 105	$ 126
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted-average period for unrecognized compensation cost, net of forfeitures, related to outstanding stock options, restricted stock awards, and restricted stock units	3 months 18 days
Employee stock purchase plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance under the ESPP (in shares)	37,000,000
Minimum [Member] \| Restricted stock unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Minimum [Member] \| Stock option plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Maximum [Member] \| Restricted stock unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years
Maximum [Member] \| Stock option plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period from the date of grant in which stock options expire	10 years
Award vesting period	4 years