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Recently Adopted and Recently Issued Accounting Guidance (Details) - USD ($) $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Jan. 01, 2019 | Dec. 31, 2018 | Sep. 30, 2019
Summary Of Significant Accounting Policies [Line Items] |  |  |
Right-of-use assets classified in Other noncurrent assets |  |  | $ 256
Operating lease liability |  |  | $ 268
Adoption of accounting standards (B) | $ 73 |  |
Accounting Standards Update 2016-02 |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Right-of-use assets classified in Other noncurrent assets | 320 |  |
Operating lease liability | 320 |  |
Accounting Standards Update 2017-12 |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Adoption of accounting standards (B) | 2 |  |
Other Noncurrent Liabilities and Deferred Credits | Accounting Standards Update 2016-02 |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Effect on retained earnings |  | 119 |
Property, Plant and Equipment | Accounting Standards Update 2016-02 |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Effect on retained earnings |  | (24) |
Other Noncurrent Assets | Accounting Standards Update 2016-02 |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Effect on retained earnings | $ (22) | $ (22) |

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