SHAREHOLDERS' INTEREST - Changes in amounts included in our cumulative other comprehensive income (loss) by component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Beginning balance	$ (1,459)	$ (1,212)
Other comprehensive income (loss) before reclassifications	(306)	(559)
Income taxes	72	207
Net other comprehensive income (loss) before reclassifications	(234)	(352)
Amounts reclassified from cumulative other comprehensive income (loss)(1)	199	162
Income taxes	(68)	(57)
Net amounts reclassified from cumulative other comprehensive income (loss)	131	105
Total other comprehensive income (loss)	(103)	(247)
Ending balance	(1,562)	(1,459)
Foreign currency translation adjustments
Beginning balance	232	207
Other comprehensive income (loss) before reclassifications	32	25
Income taxes	0	0
Net other comprehensive income (loss) before reclassifications	32	25
Amounts reclassified from cumulative other comprehensive income (loss)(1)	0	0
Income taxes	0	0
Net amounts reclassified from cumulative other comprehensive income (loss)	0	0
Total other comprehensive income (loss)	32	25
Ending balance	264	232
Unrealized gains on available-for-sale securities
Beginning balance	7	6
Other comprehensive income (loss) before reclassifications	2	1
Income taxes	0	0
Net other comprehensive income (loss) before reclassifications	2	1
Amounts reclassified from cumulative other comprehensive income (loss)(1)	0	0
Income taxes	0	0
Net amounts reclassified from cumulative other comprehensive income (loss)	0	0
Total other comprehensive income (loss)	2	1
Ending balance	9	7
Pension | Actuarial losses
Beginning balance	(1,651)	(1,372)
Other comprehensive income (loss) before reclassifications	(356)	(590)
Income taxes	76	208
Net other comprehensive income (loss) before reclassifications	(280)	(382)
Amounts reclassified from cumulative other comprehensive income (loss)(1)	195	156
Income taxes	(66)	(53)
Net amounts reclassified from cumulative other comprehensive income (loss)	129	103
Total other comprehensive income (loss)	(151)	(279)
Ending balance	(1,802)	(1,651)
Pension | Prior service credits (costs)
Beginning balance	(9)	(11)
Other comprehensive income (loss) before reclassifications	(3)	0
Income taxes	1	0
Net other comprehensive income (loss) before reclassifications	(2)	0
Amounts reclassified from cumulative other comprehensive income (loss)(1)	4	4
Income taxes	(1)	(2)
Net amounts reclassified from cumulative other comprehensive income (loss)	3	2
Total other comprehensive income (loss)	1	2
Ending balance	(8)	(9)
Other Postretirement Benefits | Actuarial losses
Beginning balance	(67)	(77)
Other comprehensive income (loss) before reclassifications	19	5
Income taxes	(5)	(1)
Net other comprehensive income (loss) before reclassifications	14	4
Amounts reclassified from cumulative other comprehensive income (loss)(1)	8	9
Income taxes	(3)	(3)
Net amounts reclassified from cumulative other comprehensive income (loss)	5	6
Total other comprehensive income (loss)	19	10
Ending balance	(48)	(67)
Other Postretirement Benefits | Prior service credits (costs)
Beginning balance	29	35
Other comprehensive income (loss) before reclassifications	0	0
Income taxes	0	0
Net other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from cumulative other comprehensive income (loss)(1)	(8)	(7)
Income taxes	2	1
Net amounts reclassified from cumulative other comprehensive income (loss)	(6)	(6)
Total other comprehensive income (loss)	(6)	(6)
Ending balance	$ 23	$ 29