CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Tax expense (benefit) of actuarial gains (losses)	$ 12	$ 15	$ 62	$ 40
Tax expense (benefit) of prior service credits (costs)	$ 0	$ 0	$ (1)	$ 0