ACCOUNTING PRONOUNCEMENTS - Statement of Cash Flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
ACCOUNTING PRONOUNCEMENTS
Cumulative distributions in excess of equity earnings	$ 3
Distributions from equity investments	$ 106	$ 125	[1]
Adjustment | ASU 2016-15, Statement of Cash Flows
ACCOUNTING PRONOUNCEMENTS
Cumulative distributions in excess of equity earnings		(50)
Distributions from equity investments		$ 50

[1] Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).