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CAPITAL MANAGEMENT Changes in Invested Capital (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Changes in Invested capital [Roll Forward]      
Opening balance $ 6,387 $ 5,452  
Issuance of preferred units 220 186 $ 189
Issuance of limited partnership units and redeemable partnership units 992 749  
Ending balance 7,599 6,387 $ 5,452
Weighted Average Invested Capital $ 6,885 $ 5,592