EMPLOYEE BENEFITS - Fair Value Estimated Using Net Asset Value per Share (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments		$ 0
Mutual funds | Liquid Cash Fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments		0
Common and collective funds | Global equities funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments		$ 0
Redemption notice period		3 days
Common and collective funds | Balanced funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments		$ 0
Redemption notice period		2 days
Common and collective funds | Fixed income fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments		$ 0
Redemption notice period		3 days
Managed portfolio, fixed income mutual fund | Managed Portfolio, Fixed Income Mutual Fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments	[1]	$ 0
Redemption notice period		1 day
Limited partnerships | Global equity fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments		$ 0
Redemption notice period		3 days
Investments Measured at Net Asset Value
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value	[2]	$ 931	$ 1,024
Investments Measured at Net Asset Value | Mutual funds | Liquid Cash Fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value		0	11
Investments Measured at Net Asset Value | Common and collective funds | Global equities funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value		399	472
Investments Measured at Net Asset Value | Common and collective funds | Balanced funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value		221	214
Investments Measured at Net Asset Value | Common and collective funds | Fixed income fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value		139	150
Investments Measured at Net Asset Value | Managed portfolio, fixed income mutual fund | Managed Portfolio, Fixed Income Mutual Fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value	[1]	32	35
Investments Measured at Net Asset Value | Limited partnerships | Global equity fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value		$ 140	$ 142

[1] The managed portfolio fixed income mutual fund seeks to outperform the Barclay’s U.S. Long Credit Index or similar benchmark.

[2] Certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy.