EMPLOYEE RETIREMENT PLANS - Qualified Defined-benefit Pension Plan Assets at Fair Value by Level within the Fair Value Hierarchy (Details) - Qualified - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value
Private equity funds	$ 695	$ 717	$ 658
Total asset at net asset value	259	185
UNITED STATES \| Common and Preferred Stocks
Fair Value
Private equity funds	191	260
Total asset at net asset value	47	118
UNITED STATES \| Private Equity and Hedge Funds
Fair Value
Private equity funds	36	37
Total asset at net asset value		0
UNITED STATES \| Corporate Debt Securities
Fair Value
Private equity funds	57	57
Total asset at net asset value	0	2
UNITED STATES \| US Treasury and Government
Fair Value
Private equity funds	53	50
Total asset at net asset value	31
UNITED STATES \| Common Collective Trust Fund
Fair Value
Private equity funds	6	4
UNITED STATES \| Short-Term and other Investments
Fair Value
Private equity funds	2	2
International \| Common and Preferred Stocks
Fair Value
Private equity funds	191	90
Total asset at net asset value	125	16
International \| Private Equity and Hedge Funds
Fair Value
Private equity funds	59	56
Total asset at net asset value	35	32
International \| Corporate Debt Securities
Fair Value
Private equity funds	28	43
Total asset at net asset value	21	17
International \| Government and Other Debt Securities
Fair Value
Private equity funds	59	80
International \| Buy-in Annuity
Fair Value
Private equity funds	12
International \| Short-Term and other Investments
Fair Value
Private equity funds	1	38
Level 1
Fair Value
Private equity funds	289	323
Level 1 \| UNITED STATES \| Common and Preferred Stocks
Fair Value
Private equity funds	144	142
Level 1 \| UNITED STATES \| Corporate Debt Securities
Fair Value
Private equity funds	31	27
Level 1 \| UNITED STATES \| US Treasury and Government
Fair Value
Private equity funds	15	46
Level 1 \| UNITED STATES \| Short-Term and other Investments
Fair Value
Private equity funds	2	2
Level 1 \| International \| Common and Preferred Stocks
Fair Value
Private equity funds	66	74
Level 1 \| International \| Government and Other Debt Securities
Fair Value
Private equity funds	31	27
Level 1 \| International \| Short-Term and other Investments
Fair Value
Private equity funds		5
Level 2
Fair Value
Private equity funds	87	130
Level 2 \| UNITED STATES \| Common and Preferred Stocks
Fair Value
Private equity funds		0
Level 2 \| UNITED STATES \| Corporate Debt Securities
Fair Value
Private equity funds	26	28
Level 2 \| UNITED STATES \| US Treasury and Government
Fair Value
Private equity funds	7	4
Level 2 \| UNITED STATES \| Common Collective Trust Fund
Fair Value
Private equity funds	6	4
Level 2 \| International \| Common and Preferred Stocks
Fair Value
Private equity funds		0
Level 2 \| International \| Corporate Debt Securities
Fair Value
Private equity funds	7	26
Level 2 \| International \| Government and Other Debt Securities
Fair Value
Private equity funds	28	53
Level 2 \| International \| Buy-in Annuity
Fair Value
Private equity funds	12
Level 2 \| International \| Short-Term and other Investments
Fair Value
Private equity funds	1	15
Level 3
Fair Value
Private equity funds	60	79
Level 3 \| UNITED STATES \| Private Equity and Hedge Funds
Fair Value
Private equity funds	36	37
Level 3 \| International \| Private Equity and Hedge Funds
Fair Value
Private equity funds	$ 24	24
Level 3 \| International \| Short-Term and other Investments
Fair Value
Private equity funds		$ 18