401(k) Plan	12 Months Ended
Dec. 31, 2018
Postemployment Benefits [Abstract]
401(k) PLAN	401(k) PLAN Under our 401(k) plan, participants may direct the investment of contributions to their accounts among certain investments. Effective July 1, 2018, we matched 100% of individual employee 401(k) plan contributions, up to 4% of cash compensation per the calendar year, and made a one-time contribution to certain employees. Prior to July 1, 2018 and in the years ended December 31, 2017 and 2016, we matched individual employee 401(k) plan contributions at the rate of $0.50 for every dollar contributed by employees subject to a cap. We recorded matching contributions to the 401(k) plan of $11 million, $6 million, and $5 million during the years ended December 31, 2018, 2017, and 2016, respectively, which are reflected in various operating expense lines within the accompanying consolidated statements of income and comprehensive income. We also maintain multiple employer defined contribution plans, which cover WSEs for client companies electing to participate in the plan and for their internal staff employees. We contribute, on behalf of each participating client, varying amounts based on the clients’ policies and serviced employee elections.

401(k) Plan

12 Months Ended

Dec. 31, 2018

Under our 401(k) plan, participants may direct the investment of contributions to their accounts among certain investments. Effective July 1, 2018, we matched 100% of individual employee 401(k) plan contributions, up to 4% of cash compensation per the calendar year, and made a one-time contribution to certain employees. Prior to July 1, 2018 and in the years ended December 31, 2017 and 2016, we matched individual employee 401(k) plan contributions at the rate of $0.50 for every dollar contributed by employees subject to a cap. We recorded matching contributions to the 401(k) plan of $11 million, $6 million, and $5 million during the years ended December 31, 2018, 2017, and 2016, respectively, which are reflected in various operating expense lines within the accompanying consolidated statements of income and comprehensive income.

We also maintain multiple employer defined contribution plans, which cover WSEs for client companies electing to participate in the plan and for their internal staff employees. We contribute, on behalf of each participating client, varying amounts based on the clients’ policies and serviced employee elections.