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Pension Benefit Obligations - Level 3 (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Sep. 30, 2016 USD ($) | Sep. 30, 2015 USD ($) | Sep. 30, 2016 USD ($) plan
Pension Plan, Defined Benefit |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | $ 1,384.8 | $ 1,384.8 | $ 1,430.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 1,384.8 |  |
Fair value of plan assets at end of year | 1,430.1 | 1,384.8 |
Pension Plan, Defined Benefit | Cash and Cash Equivalents |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 44.4 | 44.4 | 70.6
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 44.4 |  |
Fair value of plan assets at end of year | 70.6 | 44.4 |
Pension Plan, Defined Benefit | Global equity securities |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 52.8 | 52.8 | 49.4
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 52.8 |  |
Fair value of plan assets at end of year | 49.4 | 52.8 |
Pension Plan, Defined Benefit | Domestic equity securities |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 60.0 | 60.0 | 57.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 60.0 |  |
Fair value of plan assets at end of year | 57.1 | 60.0 |
Pension Plan, Defined Benefit | Diversified Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 287.4 | 287.4 | 223.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 287.4 |  |
Fair value of plan assets at end of year | 223.1 | 287.4 |
Pension Plan, Defined Benefit | Equity Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 309.6 | 309.6 | 362.0
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 309.6 |  |
Fair value of plan assets at end of year | 362.0 | 309.6 |
Pension Plan, Defined Benefit | Fixed Income Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 542.5 | 542.5 | 548.5
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 542.5 |  |
Fair value of plan assets at end of year | 548.5 | 542.5 |
Pension Plan, Defined Benefit | Hedge Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 53.0 | 53.0 | 62.5
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 53.0 |  |
Fair value of plan assets at end of year | 62.5 | 53.0 |
Pension Plan, Defined Benefit | Assets Held by Insurance Company |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 35.1 | 35.1 | 32.3
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 35.1 |  |
Fair value of plan assets at end of year | 32.3 | 35.1 |
Pension Plan, Defined Benefit | Other |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 24.6 |  | 24.6
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at end of year | 24.6 |  |
Pension Plan, Defined Benefit | Level 1 |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 11.0 | 11.0 | 23.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 11.0 |  |
Fair value of plan assets at end of year | 23.1 | 11.0 |
Pension Plan, Defined Benefit | Level 1 | Cash and Cash Equivalents |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 11.0 | 11.0 | 14.3
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 11.0 |  |
Fair value of plan assets at end of year | 14.3 | 11.0 |
Pension Plan, Defined Benefit | Level 1 | Equity Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 5.1 |  | 5.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at end of year | 5.1 |  |
Pension Plan, Defined Benefit | Level 1 | Fixed Income Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 3.7 |  | 3.7
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at end of year | 3.7 |  |
Pension Plan, Defined Benefit | Level 2 |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 1,360.2 | 1,360.2 | 1,392.9
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 1,360.2 |  |
Fair value of plan assets at end of year | 1,392.9 | 1,360.2 |
Pension Plan, Defined Benefit | Level 2 | Cash and Cash Equivalents |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 33.4 | 33.4 | 56.3
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 33.4 |  |
Fair value of plan assets at end of year | 56.3 | 33.4 |
Pension Plan, Defined Benefit | Level 2 | Global equity securities |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 52.8 | 52.8 | 49.4
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 52.8 |  |
Fair value of plan assets at end of year | 49.4 | 52.8 |
Pension Plan, Defined Benefit | Level 2 | Domestic equity securities |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 60.0 | 60.0 | 57.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 60.0 |  |
Fair value of plan assets at end of year | 57.1 | 60.0 |
Pension Plan, Defined Benefit | Level 2 | Diversified Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 287.4 | 287.4 | 223.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 287.4 |  |
Fair value of plan assets at end of year | 223.1 | 287.4 |
Pension Plan, Defined Benefit | Level 2 | Equity Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 309.6 | 309.6 | 356.9
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 309.6 |  |
Fair value of plan assets at end of year | 356.9 | 309.6 |
Pension Plan, Defined Benefit | Level 2 | Fixed Income Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 542.5 | 542.5 | 544.8
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 542.5 |  |
Fair value of plan assets at end of year | 544.8 | 542.5 |
Pension Plan, Defined Benefit | Level 2 | Hedge Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 39.4 | 39.4 | 48.4
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 39.4 |  |
Fair value of plan assets at end of year | 48.4 | 39.4 |
Pension Plan, Defined Benefit | Level 2 | Assets Held by Insurance Company |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 35.1 | 35.1 | 32.3
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 35.1 |  |
Fair value of plan assets at end of year | 32.3 | 35.1 |
Pension Plan, Defined Benefit | Level 2 | Other |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 24.6 |  | 24.6
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at end of year | 24.6 |  |
Pension Plan, Defined Benefit | Level 3 |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 13.6 | 13.6 | 14.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 13.6 |  |
Fair value of plan assets at end of year | 14.1 | 13.6 |
Pension Plan, Defined Benefit | Level 3 | Hedge Funds |  |  |
Post-retirement plan |  |  |
Fair values of plan assets | 13.6 | 13.7 | $ 14.1
Changes in the fair value of Level 3 assets |  |  |
Fair value of plan assets at beginning of year | 13.6 | 13.7 |
Actual return on plan assets, relating to assets still held at reporting date | 0.5 | (0.1) |
Fair value of plan assets at end of year | 14.1 | 13.6 |
Multiemployer Pension Plans |  |  |
Multiemployer Pension Plans |  |  |
Number of minimum construction-industry pension plans participated | plan |  |  | 200
Aggregate contributions to plans | $ 49.5 | $ 54.5 |

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