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Fair Value Measurements (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Dec. 31, 2015
Financial Instruments |  |  |  |
Cash and cash equivalents | $ 498 | $ 586 | $ 674 | $ 715
Short-term investments | $ 50 | $ 0 |  |
Institutional and Other | Minimum |  |  |  |
Financial Instruments |  |  |  |
Fair value assumption, interest rate | 3.90% | 3.78% |  |
Institutional and Other | Maximum |  |  |  |
Financial Instruments |  |  |  |
Fair value assumption, interest rate | 6.21% | 6.93% |  |
Fair Value | Level 1 |  |  |  |
Financial Instruments |  |  |  |
Cash and cash equivalents | $ 498 | $ 586 |  |
Short-term investments | 50 | 0 |  |
Fair Value | Level 2 | Retail |  |  |  |
Financial Instruments |  |  |  |
Long-term debt | 970 | 929 |  |
Fair Value | Level 2 | Institutional |  |  |  |
Financial Instruments |  |  |  |
Long-term debt | 572 | 532 |  |
Fair Value | Level 2 | Other |  |  |  |
Financial Instruments |  |  |  |
Long-term debt | 194 | 203 |  |
Book Value |  |  |  |
Financial Instruments |  |  |  |
Cash and cash equivalents | 498 | 586 |  |
Short-term investments | 50 | 0 |  |
Book Value | Retail |  |  |  |
Financial Instruments |  |  |  |
Long-term debt | 917 | 917 |  |
Book Value | Institutional |  |  |  |
Financial Instruments |  |  |  |
Long-term debt | 534 | 533 |  |
Book Value | Other |  |  |  |
Financial Instruments |  |  |  |
Long-term debt | $ 194 | $ 203 |  |

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- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3044-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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