CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in unamortized net pension and other postretirement benefit gain (loss), tax expense (benefit)	$ (2)	$ (151)	$ 131
Changes in unamortized prior service cost, tax expense (benefit)	$ (2)	$ 0	$ (1)