Annual report pursuant to Section 13 and 15(d)

Defined Contribution Plan (Details)

v3.10.0.1
Defined Contribution Plan (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]      
Contribution plan cost (less than) $ 1 $ 1 $ 1
First 4% of Employee's Contribution [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan, employer's matching contribution, percentage of match 100.00%    
Defined contribution plan, employer matching contribution, percent of employees' gross pay 4.00%    
Next 2% of Employee's Contribution [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan, employer's matching contribution, percentage of match 50.00%    
Defined contribution plan, employer matching contribution, percent of employees' gross pay 2.00%