CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in unamortized net pension and other postretirement benefit gain (loss), tax expense (benefit)	$ 131	$ (323)	$ 480
Changes in unamortized prior service credit (loss), tax expense (benefit)	$ (1)	$ (64)	$ 23