COMMON SHAREHOLDER EQUIT AND NCI (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Shareholders' Equity, Beginning Balance	$ 9,237,050,000
Net Income	229,968,000	100,755,000
Net Income Attributable to Noncontrolling Interests	1,879,000	1,493,000
Other Comprehensive Income (Loss), Net of Tax	1,956,000	1,864,000
Shareholders' Equity, Ending Balance	9,345,231,000
Common Shareholders Equity [Member]
Shareholders' Equity, Beginning Balance	9,237,100,000	4,012,700,000
Net Income	230,000,000	100,800,000
Dividends on Common Shares	(116,400,000)	(52,600,000)
Dividends, Preferred Stock	(1,900,000)	(1,400,000)
Issuance of Common Shares	8,400,000	6,200,000
Other Transcations, Net	(14,000,000)	800,000
Net Income Attributable to Noncontrolling Interests		(100,000)
Other Comprehensive Income (Loss), Net of Tax	2,000,000	1,900,000
Shareholders' Equity, Ending Balance	9,345,200,000	4,068,300,000
Noncontrolling Interest Member
Shareholders' Equity, Beginning Balance		3,000,000
Contributions To Northern Pass Trans		300,000
Net Income Attributable to Noncontrolling Interests		100,000
Shareholders' Equity, Ending Balance		3,400,000
Total Equity [Member]
Shareholders' Equity, Beginning Balance		4,015,700,000
Net Income		100,800,000
Dividends on Common Shares		(52,600,000)
Dividends, Preferred Stock		(1,400,000)
Issuance of Common Shares		6,200,000
Contributions To Northern Pass Trans		300,000
Other Transcations, Net		800,000
Other Comprehensive Income (Loss), Net of Tax		1,900,000
Shareholders' Equity, Ending Balance		4,071,700,000
Preferred Stock Member
Shareholders' Equity, Beginning Balance	155,600,000	116,200,000
Dividends, Preferred Stock	(1,900,000)	(1,400,000)
Net Income Attributable to Noncontrolling Interests	1,900,000	1,400,000
Shareholders' Equity, Ending Balance	$ 155,600,000	$ 116,200,000