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Accounting Principles and Practices (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2017 | Jun. 30, 2017 | Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Adoption of new accounting guidance |  |  | $ 49
Deferred tax assets | $ 575 | $ 575 | 325
Excess tax benefit amount | 19 | 48 |
Accounting Standards Update 2016-09, Excess Tax Benefit Component |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Deferred tax assets | $ 49 | $ 49 |
Income (loss) from extraordinary items, tax effect, (in dollars per share) | $ 0.07 | $ 0.18 |
Retained Earnings |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Adoption of new accounting guidance |  |  | 49
Retained Earnings | Accounting Standards Update 2016-09, Excess Tax Benefit Component |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Adoption of new accounting guidance |  |  | $ 49

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