Income Taxes	6 Months Ended
Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	4. INCOME TAXES Income tax provisions for interim (quarterly) periods are based on an estimated annual effective income tax rate calculated separately from the effect of significant, infrequent or unusual items. Income tax expense was $33 million and $31 million for the three months ended June 30, 2017 and 2016, respectively. The increase in income tax expense was driven by an increase in income from continuing operations, partially offset by an increase in discrete benefits in the three months ended June 30, 2017. Income tax expense was $47 million and $44 million for the six months ended June 30, 2017 and 2016, respectively. The increase in income tax expense was driven by an increase in income from continuing operations, partially offset by an increase in discrete benefits in the six months ended June 30, 2017. The increase in discrete benefits was primarily driven by the recognition of excess tax benefits of stock-based compensation awards in the income statement as a result of the adoption of the accounting standard update related to employee share-based payments. Refer to Note 1, “Basis of Presentation and Summary of Significant Accounting Policies” for additional discussion.

4. INCOME TAXES

Income tax provisions for interim (quarterly) periods are based on an estimated annual effective income tax rate calculated separately from the effect of significant, infrequent or unusual items. Income tax expense was $33 million and $31 million for the three months ended June 30, 2017 and 2016, respectively. The increase in income tax expense was driven by an increase in income from continuing operations, partially offset by an increase in discrete benefits in the three months ended June 30, 2017. Income tax expense was $47 million and $44 million for the six months ended June 30, 2017 and 2016, respectively. The increase in income tax expense was driven by an increase in income from continuing operations, partially offset by an increase in discrete benefits in the six months ended June 30, 2017. The increase in discrete benefits was primarily driven by the recognition of excess tax benefits of stock-based compensation awards in the income statement as a result of the adoption of the accounting standard update related to employee share-based payments. Refer to Note 1, “Basis of Presentation and Summary of Significant Accounting Policies” for additional discussion.