MERGERS AND OTHER TRANSACTIONS Mergers and other transactions - discontinued operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended		1 Months Ended
	Mar. 25, 2012	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2013
Predecessor
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business	$ 0
Disposal Group, Including Discontinued Operation, Revenue	190
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	27
Successor
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business		0	0	1,008
Disposal Group, Including Discontinued Operation, Revenue		324		415
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax		43		65
Missouri Gas Energy
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business				975
New England Gas Company [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business					40
Noncash or Part Noncash Divestiture, Amount of Consideration Received					$ 20