EMPLOYEE BENEFITS - Fair Value Estimated Using Net Asset Value per Share (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value	[1]	$ 1,024	$ 918
Unfunded commitments		0
Mutual funds | Liquid Cash Fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value		11	9
Unfunded commitments		0
Mutual funds | Equity Mutual Fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value	[2]	0	40
Unfunded commitments	[2]	$ 0
Redemption notice period	[2]	7 days
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		$ 472	386
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]
Investments measured at net asset value		$ 214	193
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]
Investments measured at net asset value		$ 150	133
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]
Investments measured at net asset value	[3]	$ 35	30
Unfunded commitments	[3]	$ 0
Redemption notice period	[3]	1 day
Limited partnerships | International equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value		$ 142	117
Unfunded commitments		$ 0
Redemption notice period		3 days
Limited partnerships | Offshore feeder fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments measured at net asset value		$ 0	$ 10
Unfunded commitments		$ 0
Redemption notice period		14 days

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

[2] The equity mutual fund seeks to offer participants capital appreciation by primarily investing in common stocks via investments in several underlying funds of the same fund family. The principal investment objective is to generate positive total return.

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