EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended								12 Months Ended
	Apr. 09, 2012	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share Basic And Diluted [Line Items]
Net Income Attributable to Controlling Interests		$ 174,700	$ 207,600	$ 44,300	$ 99,300	$ 113,200	$ 90,000	$ 77,300	$ 114,200	$ 525,945	$ 394,693	$ 387,949
Basic										277,209,819	177,410,167	176,636,086
Weighted Average Number Diluted Shares Outstanding Adjustment										783,812	394,401	249,301
Diluted										277,993,631	177,804,568	176,885,387
Earnings Per Share Basic And Diluted		$ 0.55	$ 0.66	$ 0.15	$ 0.56	$ 0.64	$ 0.51	$ 0.44	$ 0.64
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount										4,266	4,314	1,578
Basic Earnings Per Common Share										$ 1.90	$ 2.22	$ 2.20
Diluted Earnings Per Common Share										$ 1.89	$ 2.22	$ 2.19
Common Stock Issuance Merger With Nstar [Abstract]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	136,049,000