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Income Taxes - Additional Disclosures (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Oct. 31, 2014 | Jun. 30, 2016 | Sep. 30, 2016 | Sep. 30, 2015
Deferred tax assets: |  |  |  |
Compensation and benefit accruals not currently deductible |  |  | $ 150.5 | $ 166.7
Net operating loss carryforwards |  |  | 378.0 | 195.9
Self insurance reserves |  |  | 24.7 | 46.8
Research and experimentation and other tax credits |  |  | 125.3 | 43.0
Pension liability |  |  | 180.9 | 165.6
Accrued liabilities |  |  | 221.0 | 267.3
Other |  |  | 4.3 | 11.4
Total deferred tax assets |  |  | 1,084.7 | 896.7
Deferred tax liabilities: |  |  |  |
Unearned revenue |  |  | (212.6) | (101.9)
Depreciation and amortization |  |  | (113.0) | (76.5)
Acquired intangible assets |  |  | (155.5) | (219.2)
Investment in subsidiaries |  |  | (261.4) | (239.2)
Total deferred tax liabilities |  |  | (742.5) | (636.8)
Valuation allowance |  |  | (183.8) | (239.4)
Net deferred tax assets |  |  | 158.4 | 20.5
Potential increase to equity for deferred tax assets related to equity compensation |  |  | 3.8 |
Income Taxes, additional disclosures |  |  |  |
Net deferred tax asset likely to be realized and for which no additional valuation allowance has been provided |  |  | 900.9 |
Change in valuation allowance |  |  | (55.6) |
Foreign net operating loss carryforwards |  |  | 10.7 |
Tax-deductible goodwill |  |  | 210.8 | 261.2
Gross book-tax differences from non-U.S. subsidiaries |  |  | 1,600.0 |
Deferred tax liability of foreign subsidiaries |  |  | 113.2 |
Liability for unrecognized tax benefits, including potential interest and penalties, net of related tax benefit |  |  | 96.8 | 107.6
Unrecognized tax benefits that would be included in the effective tax rate if recognized |  |  |  | 71.6
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits |  |  |  |
Balance at the beginning of the year | $ 47.5 |  | 95.2 | 47.5
Gross increase due to acquisitions |  |  |  | 49.4
Gross increase in current period's tax positions |  |  | 7.6 | 6.0
Gross increase in prior years' tax positions |  |  | 5.2 | 6.4
Gross decrease in prior years' tax positions |  |  | (16.6) | (0.2)
Decrease due to settlement with tax authorities |  |  | (3.2) | (2.0)
Decrease due to lapse of statute of limitations |  |  | (1.8) | (4.6)
Gross change due to foreign exchange fluctuations |  |  | 1.5 | (7.3)
Balance at the end of the year |  |  | 87.9 | 95.2
Accrued interest, excluding any related income tax benefits |  |  | 12.5 | 13.9
Accrued penalties, excluding any related income tax benefits |  |  | 2.6 | $ 3.5
United Kingdom and Australia |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Change in valuation allowance |  |  | (36.2) |
United Kingdom |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Change in valuation allowance |  |  | (23.3) |
Decrease in valuation allowance due to change in tax rate |  |  | (27.2) |
Australia |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Change in valuation allowance |  | $ (12.9) |  |
URS Corporation | United Kingdom |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Change in valuation allowance | 92.8 |  |  |
URS Corporation | Australia |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Change in valuation allowance | 2.9 |  |  |
URS Corporation | Canada |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Change in valuation allowance | 22.5 |  |  |
URS Corporation | United States |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Change in valuation allowance | $ 9.3 |  |  |
California Franchise Tax Board | Enterprise Zone Tax Credits |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Unused federal and state tax credits |  |  | 6.2 |
Federal |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Net operating loss carryforwards |  |  | 503.8 |
Federal | Research and development |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Unused federal and state tax credits |  |  | 67.4 |
State |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Net operating loss carryforwards |  |  | 960.1 |
State | Research and development |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Unused federal and state tax credits |  |  | 19.2 |
Foreign |  |  |  |
Income Taxes, additional disclosures |  |  |  |
Net operating loss carryforwards |  |  | $ 789.6 |

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