Employee Benefits (Fair Value) (Details) - USD ($) $ in Millions | 12 Months Ended | | |
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | $ 878.7 | $ 867.1 | $ 998.3 | $ 878.7 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 878.7 | 867.1 | | |
Fair value of plan assets at year end | 998.3 | 878.7 | | |
Fair Value, Measurements, Recurring [Member] | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investments measured at net asset value | | | 562.6 | 496.3 |
Fair value of plan assets | 878.7 | 878.7 | 998.3 | 878.7 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 878.7 | | | |
Fair value of plan assets at year end | 998.3 | 878.7 | | |
Fair Value, Measurements, Recurring [Member] | Level 1 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 164.3 | 164.3 | 170.3 | 164.3 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 164.3 | | | |
Fair value of plan assets at year end | 170.3 | 164.3 | | |
Fair Value, Measurements, Recurring [Member] | Level 2 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 176.3 | 176.3 | 212.8 | 176.3 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 176.3 | | | |
Fair value of plan assets at year end | 212.8 | 176.3 | | |
Fair Value, Measurements, Recurring [Member] | Level 3 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 41.8 | 44.2 | 52.6 | 41.8 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 41.8 | 44.2 | | |
Purchases | 3.9 | 6.7 | | |
Sales | (1.1) | (0.6) | | |
Unrealized gain (loss) | 8 | (8.5) | | |
Fair value of plan assets at year end | 52.6 | 41.8 | | |
Fair Value, Measurements, Recurring [Member] | Equities | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 87.9 | 87.9 | 104.1 | 87.9 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 87.9 | | | |
Fair value of plan assets at year end | 104.1 | 87.9 | | |
Fair Value, Measurements, Recurring [Member] | Equities | Level 1 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 87.9 | 87.9 | 101.5 | 87.9 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 87.9 | | | |
Fair value of plan assets at year end | 101.5 | 87.9 | | |
Fair Value, Measurements, Recurring [Member] | Equities | Level 2 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 0 | 0 | 2.6 | 0 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 0 | | | |
Fair value of plan assets at year end | 2.6 | 0 | | |
Fair Value, Measurements, Recurring [Member] | Equities | Level 3 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 0 | 0 | 0 | 0 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 0 | | | |
Fair value of plan assets at year end | 0 | 0 | | |
Fair Value, Measurements, Recurring [Member] | Private equities | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investments measured at net asset value | | | 143.9 | 94.6 |
Unfunded Commitments | | | 8.2 | 11 |
Fair value of plan assets | 38.3 | 38.3 | 46.6 | 38.3 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 38.3 | | | |
Fair value of plan assets at year end | 46.6 | 38.3 | | |
Fair Value, Measurements, Recurring [Member] | Private equities | Level 1 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 0 | 0 | 0 | 0 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 0 | | | |
Fair value of plan assets at year end | 0 | 0 | | |
Fair Value, Measurements, Recurring [Member] | Private equities | Level 2 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 0 | 0 | 0 | 0 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 0 | | | |
Fair value of plan assets at year end | 0 | 0 | | |
Fair Value, Measurements, Recurring [Member] | Private equities | Level 3 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 38.3 | 40 | 46.6 | 38.3 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 38.3 | 40 | | |
Purchases | 1.9 | 4 | | |
Sales | (1.1) | (0.6) | | |
Unrealized gain (loss) | 7.5 | (5.1) | | |
Fair value of plan assets at year end | 46.6 | 38.3 | | |
Fair Value, Measurements, Recurring [Member] | Corporate | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 24.8 | 24.8 | 34.2 | 24.8 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 24.8 | | | |
Fair value of plan assets at year end | 34.2 | 24.8 | | |
Fair Value, Measurements, Recurring [Member] | Corporate | Level 1 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 5.4 | 5.4 | 9.6 | 5.4 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 5.4 | | | |
Fair value of plan assets at year end | 9.6 | 5.4 | | |
Fair Value, Measurements, Recurring [Member] | Corporate | Level 2 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 15.9 | 15.9 | 18.6 | 15.9 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 15.9 | | | |
Fair value of plan assets at year end | 18.6 | 15.9 | | |
Fair Value, Measurements, Recurring [Member] | Corporate | Level 3 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 3.5 | 3.5 | 6 | 3.5 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 3.5 | | | |
Fair value of plan assets at year end | 6 | 3.5 | | |
Fair Value, Measurements, Recurring [Member] | Government | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 184.1 | 184.1 | 210.3 | 184.1 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 184.1 | | | |
Fair value of plan assets at year end | 210.3 | 184.1 | | |
Fair Value, Measurements, Recurring [Member] | Government | Level 1 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 52.4 | 52.4 | 54.2 | 52.4 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 52.4 | | | |
Fair value of plan assets at year end | 54.2 | 52.4 | | |
Fair Value, Measurements, Recurring [Member] | Government | Level 2 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 131.7 | 131.7 | 156.1 | 131.7 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 131.7 | | | |
Fair value of plan assets at year end | 156.1 | 131.7 | | |
Fair Value, Measurements, Recurring [Member] | Government | Level 3 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 0 | 0 | 0 | 0 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 0 | | | |
Fair value of plan assets at year end | 0 | 0 | | |
Fair Value, Measurements, Recurring [Member] | Interest bearing | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 47.3 | 47.3 | 40.5 | 47.3 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 47.3 | | | |
Fair value of plan assets at year end | 40.5 | 47.3 | | |
Fair Value, Measurements, Recurring [Member] | Interest bearing | Level 1 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 18.6 | 18.6 | 5 | 18.6 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 18.6 | | | |
Fair value of plan assets at year end | 5 | 18.6 | | |
Fair Value, Measurements, Recurring [Member] | Interest bearing | Level 2 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 28.7 | 28.7 | 35.5 | 28.7 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 28.7 | | | |
Fair value of plan assets at year end | 35.5 | 28.7 | | |
Fair Value, Measurements, Recurring [Member] | Interest bearing | Level 3 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 0 | 0 | 0 | 0 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 0 | | | |
Fair value of plan assets at year end | 0 | 0 | | |
Fair Value, Measurements, Recurring [Member] | Fixed income | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investments measured at net asset value | | | 181 | 186.2 |
Unfunded Commitments | | | 0.5 | 6.2 |
Fair Value, Measurements, Recurring [Member] | Fixed income | Level 3 | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Fair value of plan assets | 3.5 | 4.2 | 6 | 3.5 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] | | | | |
Fair value of plan assets beginning of year | 3.5 | 4.2 | | |
Purchases | 2 | 2.7 | | |
Sales | 0 | 0 | | |
Unrealized gain (loss) | 0.5 | (3.4) | | |
Fair value of plan assets at year end | $ 6 | $ 3.5 | | |
Fair Value, Measurements, Recurring [Member] | Equity Funds [Member] | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investments measured at net asset value | | | 112.7 | 91.7 |
Fair Value, Measurements, Recurring [Member] | Absolute Return | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investments measured at net asset value | | | $ 125 | $ 123.8 |
Minimum | Fair Value, Measurements, Recurring [Member] | Equity Funds [Member] | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investment redemption, notice period | 3 days | 3 days | | |
Minimum | Fair Value, Measurements, Recurring [Member] | Absolute Return | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investment redemption, notice period | 2 days | 2 days | | |
Maximum | Fair Value, Measurements, Recurring [Member] | Equity Funds [Member] | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investment redemption, notice period | 30 days | 30 days | | |
Maximum | Fair Value, Measurements, Recurring [Member] | Absolute Return | | | | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | | | | |
Investment redemption, notice period | 45 days | 45 days | | |