SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Summary of Significant Accounting Policies - Inventory (Details) MMbtu in Millions, $ in Millions		Dec. 31, 2016 USD ($) MMbtu	Dec. 31, 2015 USD ($) MMbtu
Natural Gas Volumes | MMbtu		45.6	43.2
Natural Gas Inventory	[1]	$ 163	$ 98
Inventory, Raw Materials and Supplies		16	15
Inventories		179	113
Energy Related Inventory		$ 179	$ 113

[1] Natural gas volumes held for operations at December 31, 2016 and 2015 were 45.6 TBtu and 43.2 TBtu, respectively.