RETIREMENT BENEFITS - Plan Assets (Details) - USD ($)
$ in Millions

1 Months Ended

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2018

U.S. | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

100.00%

Company contributions

$ 105

$ 556

U.S. | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

100.00%

Company contributions

$ 176

$ 6

U.S. | Equity securities | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

20.00%

18.00%

U.S. | Equity securities | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

20.00%

18.00%

U.S. | Equity securities | Forecast | Minimum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

U.S. | Equity securities | Forecast | Maximum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

30.00%

U.S. | Debt securities | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

48.00%

47.00%

U.S. | Debt securities | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

48.00%

47.00%

U.S. | Debt securities | VEBA Trust

Defined Benefit Plan Disclosure

Company contributions

$ 140

U.S. | Debt securities | Forecast | Minimum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

25.00%

U.S. | Debt securities | Forecast | Maximum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

72.00%

U.S. | Real estate | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

5.00%

U.S. | Real estate | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

5.00%

U.S. | Real estate | Forecast | Minimum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

U.S. | Real estate | Forecast | Maximum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

10.00%

U.S. | Private equity | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

3.00%

4.00%

U.S. | Private equity | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

3.00%

4.00%

U.S. | Private equity | Forecast | Minimum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

U.S. | Private equity | Forecast | Maximum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

12.00%

U.S. | Other investments | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

24.00%

26.00%

U.S. | Other investments | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

24.00%

26.00%

U.S. | Other investments | Forecast | Minimum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

U.S. | Other investments | Forecast | Maximum

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

37.00%

Non-U.S. | Pension Plans

Defined Benefit Plan Disclosure

Company contributions

$ 135

$ 126

Non-U.S. | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Company contributions

$ 9

Non-U.S. | Weighted Average | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

100.00%

Non-U.S. | Weighted Average | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

100.00%

Non-U.S. | Equity securities | Minimum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Equity securities | Minimum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Equity securities | Maximum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

67.00%

69.00%

Non-U.S. | Equity securities | Maximum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

38.00%

Non-U.S. | Equity securities | Weighted Average | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

15.00%

14.00%

Non-U.S. | Equity securities | Weighted Average | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

38.00%

Non-U.S. | Equity securities | Forecast | Minimum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Equity securities | Forecast | Minimum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Equity securities | Forecast | Maximum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

63.00%

Non-U.S. | Equity securities | Forecast | Maximum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

37.00%

Non-U.S. | Debt securities | Minimum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Debt securities | Minimum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

58.00%

57.00%

Non-U.S. | Debt securities | Maximum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

99.00%

100.00%

Non-U.S. | Debt securities | Maximum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

100.00%

Non-U.S. | Debt securities | Weighted Average | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

79.00%

Non-U.S. | Debt securities | Weighted Average | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

58.00%

Non-U.S. | Debt securities | Forecast | Minimum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Debt securities | Forecast | Minimum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

58.00%

Non-U.S. | Debt securities | Forecast | Maximum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

100.00%

Non-U.S. | Debt securities | Forecast | Maximum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

100.00%

Non-U.S. | Real estate | Minimum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Real estate | Maximum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

18.00%

Non-U.S. | Real estate | Weighted Average | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

1.00%

Non-U.S. | Real estate | Forecast | Minimum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Real estate | Forecast | Maximum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

18.00%

Non-U.S. | Other investments | Minimum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Other investments | Minimum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Other investments | Maximum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

100.00%

Non-U.S. | Other investments | Maximum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

4.00%

Non-U.S. | Other investments | Weighted Average | Pension Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

5.00%

6.00%

Non-U.S. | Other investments | Weighted Average | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Weighted average allocation (as a percent)

4.00%

Non-U.S. | Other investments | Forecast | Minimum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Other investments | Forecast | Minimum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

0.00%

Non-U.S. | Other investments | Forecast | Maximum | Pension Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

100.00%

Non-U.S. | Other investments | Forecast | Maximum | Postretirement Benefit Plans

Defined Benefit Plan Disclosure

Target asset allocation (as a percent)

5.00%