CREDIT FACILITIES AND LONG-TERM DEBT (Details) (USD $) In Millions, unless otherwise specified					12 Months Ended								1 Months Ended							0 Months Ended	1 Months Ended	2 Months Ended	0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Senior Credit Facility due 2017	Dec. 31, 2011 Senior Credit Facility due 2017	Dec. 31, 2012 Senior Credit Facility due 2017 Maximum	Dec. 31, 2012 Senior Credit Facility due 2017 LIBOR-based borrowings	Dec. 31, 2011 Senior Credit Facility due 2017 LIBOR-based borrowings	Dec. 31, 2012 Senior Credit Facility due 2017 Base rate	Dec. 31, 2012 Senior revolving credit facility	Dec. 31, 2011 Senior revolving credit facility	Jul. 13, 2011 Senior Revolving Credit Facility due December 2011	Jul. 13, 2011 Senior Revolving Credit Facility due July 2016	Jun. 30, 2011 4.65% Senior Notes due 2021	Dec. 31, 2012 4.65% Senior Notes due 2021	Dec. 31, 2011 4.65% Senior Notes due 2021	Dec. 31, 2012 6.89% Series C Senior Notes due 2012	Dec. 31, 2011 6.89% Series C Senior Notes due 2012	Dec. 31, 2012 3.82% Series D Senior Notes due 2017	Dec. 31, 2011 3.82% Series D Senior Notes due 2017	Jun. 17, 2011 Bridge loan facility	May 31, 2011 Bridge loan facility	Jun. 30, 2011 Bridge loan facility	May 03, 2011 GTN and Bison Senior Revolving Credit Facility due December 2011	May 03, 2011 GTN and Bison Bridge loan facility
Credit facility and long-term debt
Stated interest rate (as a percent)														4.65%	4.65%	6.89%	6.89%	3.82%	3.82%
Long-term debt	$ 688	$ 742	$ 312	$ 363										$ 349	$ 349		$ 3	$ 27	$ 27
Less: current portion of long-term debt	3	3
Noncurrent portion of long-term debt	685	739
Maximum borrowing capacity									500		250	500											250	400
Option to increase borrowings on the credit facility					250
Amount outstanding under credit facility									312	363
Remaining borrowing capacity									188
Line of credit facility, base rate						LIBOR	LIBOR	Lender base rate
Debt average interest rate (as a percent)						1.61%	0.86%															1.70%
Debt average interest rate, after hedging activity (as a percent)							4.07%
Debt interest rate, at period end, prior to hedging activities (as a percent)						1.47%	1.65%
Public debt offering													350.0
Debt offering term													10 years
Line of credit facility, term																					364 days
Amount drawn																							125	61
Line of credit facility, repaid and cancelled																				$ 61