Income Taxes (Notes)	9 Months Ended
Sep. 30, 2018
Income Taxes [Abstract]
Income Tax Disclosure	Income Taxes On December 22, 2017, the U.S. federal government enacted the Tax Cuts and Jobs Act (the Tax Act), which significantly revised U.S. corporate income tax law by, among other things, reducing the U.S. federal corporate income tax rate from 35% to 21% and implementing a modified territorial tax system that includes a one-time transition tax on deemed repatriated earnings of foreign subsidiaries. Due to the complexities involved in accounting for the Tax Act, the SEC issued Staff Accounting Bulletin (SAB) 118, which requires that we include in our financial statements the reasonable estimate of the impact of the Tax Act on earnings to the extent such reasonable estimate has been determined. SAB 118 allows us to report provisional amounts within a measurement period up to one year due to the complexities inherent in adopting the changes. We consider both the recognition of the transition tax and the remeasurement of deferred taxes incomplete. We adjusted our provisional amounts during the nine months ended September 30, 2018 by $16.3 million due to the remeasurement of deferred taxes resulting from a change in estimate related to the finalization of the 2017 tax return. Additionally, new guidance from regulators, interpretation of the law, and refinement of our estimates from ongoing analysis of data and tax positions may change the provisional amounts recorded. Any changes in the provisional amount recorded will be reflected in income tax expense in the period identified. Income tax expense during interim periods is based on our estimated annual effective income tax rate plus any discrete items, which are recorded in the period in which they occur. Discrete items include, among others, such events as changes in estimates due to the finalization of tax returns, tax audit settlements, expiration of statutes of limitation, and increases or decreases in valuation allowances on deferred tax assets. Our effective tax rate was 19.8% and 15.7% for the three months ended September 30, 2018 and 2017, respectively. The increase in the effective tax rate for the three months ended September 30, 2018 was primarily the result of lower tax benefits recognized on the settlement of employee share-based awards. Our effective tax rate was an expense of 19.4% and a benefit of 12.3% for the nine months ended September 30, 2018 and 2017, respectively. The higher effective tax rate for the nine months ended September 30, 2018 was primarily due to the effects of the 2017 IRS audit settlement, partially offset by the decrease in the U.S. federal income tax rate and remeasurement of deferred taxes as a result of the change in estimate in the finalization of the 2017 tax return. Unrecognized Tax Benefits As of September 30, 2018, the total amount of our unrecognized tax benefits was $80.8 million and the year-to-date total amount of our accrued interest was $13.2 million. In March 2017, we received from the IRS Office of Appeals the fully executed Form 870-AD for the years 1999-2005, which effectively settled the issues under audit for those years. Tax years subsequent to 2005 remain open to review and adjustment by the IRS. In addition, we are under audit by various state jurisdictions for years 2009 through 2017. There are currently no federal or provincial audits in Canada. It is reasonably possible that the amount of unrecognized tax benefits could significantly decrease over the next 12 months as certain tax positions will be released as a result of statutes closing. However, since the years to which uncertain tax positions relate remain subject to review by the tax authorities, a current estimate of the range of decrease that may occur within the next 12 months cannot be made.

Income Taxes

On December 22, 2017, the U.S. federal government enacted the Tax Cuts and Jobs Act (the Tax Act), which significantly revised U.S. corporate income tax law by, among other things, reducing the U.S. federal corporate income tax rate from 35% to 21% and implementing a modified territorial tax system that includes a one-time transition tax on deemed repatriated earnings of foreign subsidiaries. Due to the complexities involved in accounting for the Tax Act, the SEC issued Staff Accounting Bulletin (SAB) 118, which requires that we include in our financial statements the reasonable estimate of the impact of the Tax Act on earnings to the extent such reasonable estimate has been determined.

SAB 118 allows us to report provisional amounts within a measurement period up to one year due to the complexities inherent in adopting the changes. We consider both the recognition of the transition tax and the remeasurement of deferred taxes incomplete. We adjusted our provisional amounts during the nine months ended September 30, 2018 by $16.3 million due to the remeasurement of deferred taxes resulting from a change in estimate related to the finalization of the 2017 tax return. Additionally, new guidance from regulators, interpretation of the law, and refinement of our estimates from ongoing analysis of data and tax positions may change the provisional amounts recorded. Any changes in the provisional amount recorded will be reflected in income tax expense in the period identified.

Income tax expense during interim periods is based on our estimated annual effective income tax rate plus any discrete items, which are recorded in the period in which they occur. Discrete items include, among others, such events as changes in estimates due to the finalization of tax returns, tax audit settlements, expiration of statutes of limitation, and increases or decreases in valuation allowances on deferred tax assets. Our effective tax rate was 19.8% and 15.7% for the three months ended September 30, 2018 and 2017, respectively. The increase in the effective tax rate for the three months ended September 30, 2018 was primarily the result of lower tax benefits recognized on the settlement of employee share-based awards. Our effective tax rate was an expense of 19.4% and a benefit of 12.3% for the nine months ended September 30, 2018 and 2017, respectively. The higher effective tax rate for the nine months ended September 30, 2018 was primarily due to the effects of the 2017 IRS audit settlement, partially offset by the decrease in the U.S. federal income tax rate and remeasurement of deferred taxes as a result of the change in estimate in the finalization of the 2017 tax return.

Unrecognized Tax Benefits

As of September 30, 2018, the total amount of our unrecognized tax benefits was $80.8 million and the year-to-date total amount of our accrued interest was $13.2 million.

In March 2017, we received from the IRS Office of Appeals the fully executed Form 870-AD for the years 1999-2005, which effectively settled the issues under audit for those years. Tax years subsequent to 2005 remain open to review and adjustment by the IRS. In addition, we are under audit by various state jurisdictions for years 2009 through 2017. There are currently no federal or provincial audits in Canada. It is reasonably possible that the amount of unrecognized tax benefits could significantly decrease over the next 12 months as certain tax positions will be released as a result of statutes closing. However, since the years to which uncertain tax positions relate remain subject to review by the tax authorities, a current estimate of the range of decrease that may occur within the next 12 months cannot be made.