Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 299	$ 174	$ 1,668	$ 379
OTHER COMPREHENSIVE INCOME (LOSS):
Pension and OPEB prior service costs	(19)	(18)	(37)	(36)
Amortized losses on derivative hedges	2	1	17	4
Change in unrealized gains on available-for-sale securities	0	(2)	(106)	14
Other comprehensive loss	(17)	(19)	(126)	(18)
Income tax benefits on other comprehensive loss	(4)	(7)	(57)	(7)
Other comprehensive loss, net of tax	(13)	(12)	(69)	(11)
COMPREHENSIVE INCOME	$ 286	$ 162	$ 1,599	$ 368