Retirement Plans	9 Months Ended
Sep. 30, 2018
Retirement Benefits [Abstract]
Retirement Plans	Retirement Plans Defined Contribution Savings Plan We sponsor a 401(k) Plan for U.S. employees. Employees are immediately eligible to make contributions to the plan and are also eligible for an employer contribution match at an amount equal to 100.0% of the first 6.0% of eligible employee contributions. Savings plan expense included in compensation and benefits expense in the Condensed Consolidated Statements of Income was $3 million for both the three months ended September 30, 2018 and 2017 and $10 million for both the nine months ended September 30, 2018 and 2017. Pension and Supplemental Executive Retirement Plans We maintain non-contributory, defined-benefit pension plans, non-qualified SERPs for certain senior executives and other post-retirement benefit plans for eligible employees in the U.S., collectively referred to as the Nasdaq Benefit Plans. Our pension plans and SERPs are frozen. Future service and salary for all participants do not count toward an accrual of benefits under the pension plans and SERPs. Most employees outside the U.S. are covered by local retirement plans or by applicable social laws. Benefits under social laws are generally expensed in the periods in which the costs are incurred. The total expense for these plans is included in compensation and benefits expense in the Condensed Consolidated Statements of Income and was $4 million for the three months September 30, 2018, $5 million for the three months ended September 30, 2017, $15 million for the nine months September 30, 2018, and $13 million for the nine months ended September 30, 2017. During the third quarter of 2018, we contributed $22 million to our U.S. defined-benefit pension plans. This contribution increased our funded status to approximately 100.0%. We will continue to monitor the plan's funded status.

Retirement Plans

Defined Contribution Savings Plan

We sponsor a 401(k) Plan for U.S. employees. Employees are immediately eligible to make contributions to the plan and are also eligible for an employer contribution match at an amount equal to 100.0% of the first 6.0% of eligible employee contributions. Savings plan expense included in compensation and benefits expense in the Condensed Consolidated Statements of Income was $3 million for both the three months ended September 30, 2018 and 2017 and $10 million for both the nine months ended September 30, 2018 and 2017.

Pension and Supplemental Executive Retirement Plans

We maintain non-contributory, defined-benefit pension plans, non-qualified SERPs for certain senior executives and other post-retirement benefit plans for eligible employees in the U.S., collectively referred to as the Nasdaq Benefit Plans. Our pension plans and SERPs are frozen. Future service and salary for all participants do not count toward an accrual of benefits under the pension plans and SERPs. Most employees outside the U.S. are covered by local retirement plans or by applicable social laws. Benefits under social laws are generally expensed in the periods in which the costs are incurred. The total expense for these plans is included in compensation and benefits expense in the Condensed Consolidated Statements of Income and was $4 million for the three months September 30, 2018, $5 million for the three months ended September 30, 2017, $15 million for the nine months September 30, 2018, and $13 million for the nine months ended September 30, 2017. During the third quarter of 2018, we contributed $22 million to our U.S. defined-benefit pension plans. This contribution increased our funded status to approximately 100.0%. We will continue to monitor the plan's funded status.