SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF REGISTRANT Condensed Statements of Cash Flows (Parent Company) (Details) - USD ($) $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2015		Sep. 30, 2015	[1],[2]	Jun. 30, 2015	[1],[2]	Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014	[2],[3]	Jun. 30, 2014	[2],[3]	Mar. 31, 2014		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
CASH FLOWS FROM OPERATING ACTIVITIES
NET INCOME		$ 37,365	[1],[2]	$ 65,573		$ 72,336		$ 67,132	[1],[2]	$ 46,738	[2],[3]	$ 73,873		$ 54,336		$ 69,136	[2],[3]	$ 242,406	[1],[2]	$ 244,083	[2],[3]	$ 233,506
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on extinguishment of debt																		0		29,205		0
Share-based compensation expense																		17,609		14,652		15,666
Other																		22,031		17,697		17,864
Changes in assets and liabilities, exclusive of changes shown separately:
Prepaid and other current assets																		(3,214)		5,089		16,891
Accounts payable																		(7,263)		(19,061)		17,638
Accrued payroll																		463		525		1,619
Accrued interest																		2,039		(2,511)		8,341
Accrued taxes																		14,783		19,756		6,113
Tax benefit on the excess tax deduction of share-based compensation																		(11,707)		(7,767)		(4,302)
Other current liabilities																		5,587		(2,314)		1,630
Other non-current assets and liabilities, net																		25,355		(13,697)		7,669
Net cash provided by operating activities																		555,745		501,501		449,196
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of marketable securities																		673		495		20,844
Purchases of marketable securities																		(10,422)		(6,091)		(22,250)
Other																		(5,456)		4,040		(3,294)
Net cash used in investing activities																		(699,345)		(734,701)		(826,288)
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of long-term debt																		225,000		798,664		933,025
Borrowings under revolving credit agreement																		2,832,100		1,660,000		1,090,100
Borrowings under term loan credit agreements																		200,000		110,000		675,000
Net issuance of commercial paper, net of discount																		94,630		0		0
Retirement of long-term debt — including extinguishment of debt costs																		(175,000)		(298,625)		(452,000)
Repayments of revolving credit agreement																		(2,825,000)		(1,618,400)		(1,146,700)
Repayments of term loan credit agreements																		0		(189,000)		(635,000)
Issuance of common stock																		13,635		20,713		10,042
Dividends on common and restricted stock																		(108,275)		(95,595)		(84,129)
Repurchase and retirement of common stock																		(137,081)		(134,284)		(4,885)
Tax benefit on the excess tax deduction of share-based compensation																		11,707		7,767		4,302
Advance for forward contract of accelerated share repurchase program																		0		(20,000)		0
Return of unused advance for forward contract of accelerated share repurchase program																		0		20,000		0
Other																		(2,929)		(11,724)		1,380
Net cash (used in) provided by financing activities																		129,718		226,666		385,180
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS																		(13,882)		(6,534)		8,088
CASH AND CASH EQUIVALENTS — Beginning of period								27,741								34,275		27,741		34,275		26,187
CASH AND CASH EQUIVALENTS — End of period		13,859								27,741								13,859		27,741		34,275
Supplementary cash flows information:
Interest paid (net of interest capitalized)																		191,041		185,288		155,112
Income taxes paid — net																		55,722		44,524		20,092
ITC Holdings Corp.
CASH FLOWS FROM OPERATING ACTIVITIES
NET INCOME																		242,406		244,083		233,506
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in subsidiaries' earnings																		(307,889)		(329,799)		(318,197)
Dividends from subsidiaries	[4]																	185,303		224,167		169,973
Deferred and other income taxes																		(116,243)		(122,413)		(117,956)
Loss on extinguishment of debt																		0		29,205		0
Intercompany tax payments from subsidiaries																		120,863		124,315		112,008
Share-based compensation expense																		17,674		14,652		15,667
Other																		3,108		2,852		(226)
Changes in assets and liabilities, exclusive of changes shown separately:
Accounts receivable from subsidiaries																		3,158		1,304		(979)
Prepaid and other current assets																		92		4,154		16,948
Accounts payable																		990		(3,869)		(2,294)
Accrued payroll																		621		1,572		1,190
Accrued interest																		21		(2,671)		6,501
Accrued taxes																		8,996		11,147		(179)
Tax benefit on the excess tax deduction of share-based compensation																		(11,707)		(7,767)		(4,302)
Other current liabilities																		2,416		(2,425)		2,278
Other non-current assets and liabilities, net																		6,006		3,078		12,465
Net cash provided by operating activities																		155,815		191,585		126,403
CASH FLOWS FROM INVESTING ACTIVITIES
Equity contributions to subsidiaries																		(263,150)		(348,661)		(339,770)
Return of capital from subsidiaries	[4]																	161,075		126,900		96,120
Proceeds from sale of marketable securities																		673		495		20,844
Purchases of marketable securities																		(10,422)		(6,091)		(22,250)
Other																		(750)		(984)		0
Net cash used in investing activities																		(112,574)		(228,341)		(245,056)
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of long-term debt																		0		398,664		548,484
Borrowings under revolving credit agreement																		838,900		533,900		222,800
Borrowings under term loan credit agreements																		0		60,000		390,000
Net issuance of commercial paper, net of discount																		94,630		0		0
Retirement of long-term debt — including extinguishment of debt costs																		0		(248,625)		(267,000)
Repayments of revolving credit agreement																		(754,700)		(480,400)		(252,400)
Repayments of term loan credit agreements																		0		(39,000)		(450,000)
Issuance of common stock																		13,635		20,713		10,042
Dividends on common and restricted stock																		(108,275)		(95,595)		(84,129)
Repurchase and retirement of common stock																		(137,081)		(134,284)		(4,885)
Tax benefit on the excess tax deduction of share-based compensation																		11,707		7,767		4,302
Advance for forward contract of accelerated share repurchase program																		0		(20,000)		0
Return of unused advance for forward contract of accelerated share repurchase program																		0		20,000		0
Other																		(177)		(6,932)		5,746
Net cash (used in) provided by financing activities																		(41,361)		16,208		122,960
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS																		1,880		(20,548)		4,307
CASH AND CASH EQUIVALENTS — Beginning of period								$ 6,305								$ 26,853		6,305		26,853		22,546
CASH AND CASH EQUIVALENTS — End of period		$ 8,185								$ 6,305								8,185		6,305		26,853
Supplementary cash flows information:
Interest paid (net of interest capitalized)																		103,915		105,817		90,224
Income taxes paid — net																		55,722		44,524		20,092
Supplementary non-cash investing and financing activities:
Equity transfers to subsidiaries																		$ 1,497		$ 6,227		$ 6,213

[1] During the third and fourth quarters of 2015, we recognized an aggregate regulatory liability for the refund relating to the formula rate template modifications filing as described in Note 4, which resulted in a reduction in operating revenues and operating income of $9.5 million and an estimated $6.2 million reduction to net income for the year ended December 31, 2015.

[2] During the year ended December 31, 2015 and the fourth quarter of 2014, we recognized an aggregate estimated regulatory liability for the potential refunds relating to the ROE complaints as described in Note 16, which resulted in a reduction in operating revenues and operating income of $115.1 million and $46.9 million and an estimated $73.2 million and $28.9 million reduction to net income for the years ended December 31, 2015 and 2014, respectively.

[3] During the second quarter of 2014, we incurred a loss on extinguishment of debt of $29.2 million related to the tender of ITC Holdings Senior Notes as described in Note 8, which resulted in an estimated reduction to net income of $18.2 million.

[4] Includes ITCTransmission, MTH, ITC Midwest and other subsidiaries.