| Consolidated Statement of Partners' Equity - 6 months ended Jun. 30, 2018 - USD ($) shares in Millions, $ in Millions | Total | Common Units [Member] | Subordinated Units [Member] | General Partner [Member] | 
|---|---|---|---|---|
| Units, Outstanding, beginning of period at Dec. 31, 2017 | 348.6 | 135.4 | ||
| Partners' equity, beginning of period at Dec. 31, 2017 | $ 639 | $ 1,670 | $ (1,043) | $ 12 | 
| General partner units, Outstanding, beginning of period at Dec. 31, 2017 | 9.9 | 9.9 | ||
| Increase (Decrease) in Partners' Capital [Roll Forward] | ||||
| Net income | $ 616 | 435 | 169 | $ 12 | 
| Distributions | (527) | $ (366) | $ (142) | (19) | 
| Units, Outstanding, end of period at Jun. 30, 2018 | 348.6 | 135.4 | ||
| Partners' equity, end of period at Jun. 30, 2018 | $ 728 | $ 1,739 | $ (1,016) | $ 5 | 
| General partner units, Outstanding, end of period at Jun. 30, 2018 | 9.9 | 9.9 | 
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- Definition The number of general partner units outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available. 
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- Definition The number of limited partner units outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The amount of ownership interest of different classes of partners in limited partnership. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Total distributions to each class of partners (i.e., general, limited and preferred partners). Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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