PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Pension Trusts' Net Investments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 4,456	$ 4,181	$ 3,979
Hedge funds \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,771	2,436	2,284
Private equity and related funds \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,594	1,649	1,575
Real estate and related funds \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	91	96	120
Qualified and Registered Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,008	4,699
Qualified and Registered Pension Plans \| Fixed income instruments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	569	541
Qualified and Registered Pension Plans \| Fixed income instruments \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	476	470
Qualified and Registered Pension Plans \| Fixed income instruments \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	93	71
Qualified and Registered Pension Plans \| Fixed income instruments \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Qualified and Registered Pension Plans \| Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,771	2,436
Qualified and Registered Pension Plans \| Hedge funds \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Qualified and Registered Pension Plans \| Hedge funds \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Qualified and Registered Pension Plans \| Hedge funds \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,771	2,436
Qualified and Registered Pension Plans \| Private equity and related funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,592	1,651
Qualified and Registered Pension Plans \| Private equity and related funds \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Qualified and Registered Pension Plans \| Private equity and related funds \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(2)	2
Qualified and Registered Pension Plans \| Private equity and related funds \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,594	1,649
Qualified and Registered Pension Plans \| Real estate and related funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	91	96
Qualified and Registered Pension Plans \| Real estate and related funds \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Qualified and Registered Pension Plans \| Real estate and related funds \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Qualified and Registered Pension Plans \| Real estate and related funds \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	91	96
Qualified and Registered Pension Plans \| Common and preferred stock and equity index instruments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	2
Qualified and Registered Pension Plans \| Common and preferred stock and equity index instruments \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1
Qualified and Registered Pension Plans \| Common and preferred stock and equity index instruments \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	1
Qualified and Registered Pension Plans \| Common and preferred stock and equity index instruments \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Qualified and Registered Pension Plans \| Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,027	4,726
Qualified and Registered Pension Plans \| Investments \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	476	471
Qualified and Registered Pension Plans \| Investments \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	95	74
Qualified and Registered Pension Plans \| Investments \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,456	4,181
Qualified and Registered Pension Plans \| Accrued liabilities, net
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(19)	(27)
Non Registered Canadian Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	15
Non Registered Canadian Pension Plans \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	15
Non Registered Canadian Pension Plans \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Non Registered Canadian Pension Plans \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Non Registered Canadian Pension Plans \| Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	12
Non Registered Canadian Pension Plans \| Cash \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	12
Non Registered Canadian Pension Plans \| Cash \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Non Registered Canadian Pension Plans \| Cash \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Non Registered Canadian Pension Plans \| Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	3
Non Registered Canadian Pension Plans \| Investments \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	3
Non Registered Canadian Pension Plans \| Investments \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Non Registered Canadian Pension Plans \| Investments \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,022	4,714	4,773
Pension \| Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 4,500

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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