Accumulated Other Comprehensive Loss (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassifications out of accumulated other comprehensive income loss by component
Net of tax	$ 38	$ 30	$ 103	$ 88
Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	51	44	154	131
Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	3	3	9	9
Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	54	47	163	140
Income tax benefit	(16)	(17)	(60)	(52)
Net of tax	$ 38	$ 30	$ 103	$ 88