Stock Compensation Plans Employee Stock Compensation Plans - Allocated Compensation, Assumptions and Shares Available (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock or Unit Expense	$ 13	$ 18	$ 50	$ 57
Stock or Unit Option Plan Expense	1	0	2	0
Employee Stock Ownership Plan (ESOP), Compensation Expense	1	1	3	3
Employee stock compensation expense	15	19	55	60
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	0	(9)	(7)	(21)
Allocated Share-based Compensation Expense, Net of Tax	$ 15	$ 10	$ 48	$ 39

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section S99
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

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.

+ References

No definition available.

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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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The amount of plan compensation cost recognized during the period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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- Definition

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.

+ References

No definition available.

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- Definition

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

+ References

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