| **Income Taxes - Components of Provision for Income Tax Expense (Details) - USD ($) $ in Millions** | 3 Months Ended | 12 Months Ended |
|-----------------------------------------------------------------------------------------------------|----------------|-----------------|
||
| **Current:**                                                                                        |           |            |   |   |   |   |   |   |   |   |   |
| Federal                                                                                             |           |            |   |   |   |   |   |   | $ 16.1 | $ 2.6 | $ 2.5 |
| State and other                                                                                     |           |            |   |   |   |   |   |   | 14.9 | 12.2 | 10.8 |
| Total current expense                                                                               |           |            |   |   |   |   |   |   | 31.0 | 14.8 | 13.3 |
| **Deferred:**                                                                                       |           |            |   |   |   |   |   |   |   |   |   |
| Federal                                                                                             |           |            |   |   |   |   |   |   | 130.5 | 113.9 | 95.3 |
| State and other                                                                                     |           |            |   |   |   |   |   |   | 2.4 | 13.2 | 2.1 |
| Total deferred expense                                                                              |           |            |   |   |   |   |   |   | 132.9 | 127.1 | 97.4 |
| Total income tax expense related to continuing operations                                           | $ 39.7         | $ 42.1          | $ 42.4 | $ 39.7 | $ 43.5 | $ 35.9 | $ 32.2 | $ 30.3 | $ 163.9 | $ 141.9 | $ 110.7 |

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Amount of current federal tax expense (benefit) pertaining to income (loss) from continuing operations.
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Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.
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