COMMITMENTS AND CONTINGENCIES - COMMITMENTS (Details) CAD in Millions	12 Months Ended
	Dec. 31, 2017 CAD	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD	Jan. 09, 2018 USD ($)
Annual debt maturities
Total	CAD 62,927
Less than 1 year	2,831
2 years	6,273
3 years	6,722
4 years	2,505
5 years	8,839
Thereafter	35,757
Interest obligations
Total	42,083
Less than 1 year	2,485
2 years	2,298
3 years	2,117
4 years	1,941
5 years	1,853
Thereafter	31,389
Purchase of services, pipe and other materials, including transportation
Total	14,396
Less than 1 year	4,144
2 years	2,455
3 years	1,496
4 years	1,255
5 years	1,163
Thereafter	3,883
Operating leases
Total	746
Less than 1 year	91
2 years	86
3 years	80
4 years	74
5 years	78
Thereafter	337
Capital leases
Total	35
Less than 1 year	9
2 years	8
3 years	2
4 years	2
5 years	2
Thereafter	12
Maintenance agreements
Total	322
Less than 1 year	38
2 years	32
3 years	17
4 years	15
5 years	15
Thereafter	205
Land lease commitments
Total	405
Less than 1 year	15
2 years	16
3 years	16
4 years	16
5 years	16
Thereafter	326
Total
Total	120,914
Total Less than 1 year	9,613
Total 2 years	11,168
Total 3 years	10,450
Total 4 years	5,808
Total 5 years	11,966
Total thereafter	71,909
Operating leases, rent expense	CAD 118	CAD 85	CAD 72
Senior notes | 3.5% and 4.15% Senior Notes, Maturing Twenty 2028 and 2048 | Texas Eastern Transmission, LP | Subsequent Event
Total
Principal Amount | $				$ 800,000,000