PENSION AND OTHER POST-EMPLOYMENT BENEFIT PLANS - Net Pension Plan Assets, by Fair Value Hierarchy (Details) - Pension - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Cash and short-term investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 412	$ 117
Cash and short-term investments | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	5
Fixed Income Investments, Corporate | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,380	985
Fixed Income Investments, Government | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	721	1,021
Fixed Income Investments, Repurchase Agreements | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(43)	(90)
Hedge funds and related investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	4
Private equity and related investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	104	68
Derivative instruments, net | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	8
Total pension trust investments measured at fair value | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,589	2,113
Public equity investments | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	5
Total Canadian Nonregistered Plan Assets Measured At Fair Value | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	10
Pension plans defined benefit excluding hedge fund and private equity investments and accrued liabilities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,600	2,123
Fair Value, Inputs, Level 1 | Cash and short-term investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	412	117
Fair Value, Inputs, Level 1 | Cash and short-term investments | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	5
Fair Value, Inputs, Level 1 | Fixed Income Investments, Corporate | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 1 | Fixed Income Investments, Government | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 1 | Fixed Income Investments, Repurchase Agreements | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 1 | Hedge funds and related investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 1 | Private equity and related investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 1 | Derivative instruments, net | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 1 | Total pension trust investments measured at fair value | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	412	117
Fair Value, Inputs, Level 1 | Public equity investments | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	5
Fair Value, Inputs, Level 1 | Total Canadian Nonregistered Plan Assets Measured At Fair Value | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	10
Fair Value, Inputs, Level 1 | Pension plans defined benefit excluding hedge fund and private equity investments and accrued liabilities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Cash and short-term investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Cash and short-term investments | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Fixed Income Investments, Corporate | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,380	985
Fair Value, Inputs, Level 2 | Fixed Income Investments, Government | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	721	1,021
Fair Value, Inputs, Level 2 | Fixed Income Investments, Repurchase Agreements | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(43)	(90)
Fair Value, Inputs, Level 2 | Hedge funds and related investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Private equity and related investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Derivative instruments, net | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	8
Fair Value, Inputs, Level 2 | Total pension trust investments measured at fair value | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,063	1,924
Fair Value, Inputs, Level 2 | Public equity investments | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Total Canadian Nonregistered Plan Assets Measured At Fair Value | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Pension plans defined benefit excluding hedge fund and private equity investments and accrued liabilities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Cash and short-term investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Cash and short-term investments | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Fixed Income Investments, Corporate | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Fixed Income Investments, Government | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Fixed Income Investments, Repurchase Agreements | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Hedge funds and related investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	4
Fair Value, Inputs, Level 3 | Private equity and related investments | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	104	68
Fair Value, Inputs, Level 3 | Derivative instruments, net | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Total pension trust investments measured at fair value | Qualified and Registered Plans | U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	114	72
Fair Value, Inputs, Level 3 | Public equity investments | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Total Canadian Nonregistered Plan Assets Measured At Fair Value | Non Registered Plans | Canada
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Pension plans defined benefit excluding hedge fund and private equity investments and accrued liabilities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0