Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans (Details)

v3.8.0.1
Employee Benefit Plans (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Employee Benefit Plans      
Defined Benefit Plan, Contributions by Employer $ 17 $ 13 $ 15