SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Summary of Significant Accounting Policies - Inventory (Details) MMbtu in Millions, $ in Millions		Dec. 31, 2015 USD ($) MMbtu	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) MMbtu	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)
Natural Gas Volumes | MMbtu		43.2				34.3
Natural Gas Inventory	[1]	$ 98				$ 105
Inventory, Raw Materials and Supplies		15				14
Inventories		113	$ 99	$ 106	$ 83	119	$ 115	$ 147	$ 160
Energy Related Inventory		$ 113				$ 119

[1] Natural gas volumes held for operations at December 31, 2015 and 2014 were 43.2 TBtu and 34.3 TBtu, respectively.