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Pension and Other Postretirement Benefit Plans (Tables) | 9 Months Ended
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Sep. 30, 2015
Pension and Other Postretirement Benefit Plans [Abstract] |
Components of Net Periodic Benefit Expense (Income) [Table Text Block] |
| Pension |  | Other Postretirement
Components of Net Periodic Benefit Expense (Income) | 2015 |  | 2014 |  | 2015 |  | 2014
Millions |  |  |  |  |  |  |
Quarter Ended September 30, |  |  |  |  |  |  |
Service Cost | $2.6 |  |  |  | $2.0 |  |  | $1.0 |  |  |  | $0.9 |
Interest Cost | 7.5 |  |  | 7.5 |  |  | 1.8 |  |  | 1.8 |
Expected Return on Plan Assets | (10.2 | ) |  | (9.6 | ) |  | (2.7 | ) |  | (2.5 | )
Amortization of Prior Service Costs (Credits) | — |  |  | 0.1 |  |  | (0.7 | ) |  | (0.7 | )
Amortization of Net Loss | 4.4 |  |  | 3.6 |  |  | 0.1 |  |  | 0.1 |
Net Periodic Benefit Expense (Income) |  | $4.3 |  |  |  | $3.6 |  |  | $(0.5) |  | $(0.4)
Nine Months Ended September 30, |  |  |  |  |  |  |
Service Cost | $7.6 |  |  |  | $6.2 |  |  | $3.2 |  |  |  | $2.6 |
Interest Cost | 22.4 |  |  | 22.4 |  |  | 5.4 |  |  | 5.5 |
Expected Return on Plan Assets | (30.5 | ) |  | (28.7 | ) |  | (8.2 | ) |  | (7.7 | )
Amortization of Prior Service Costs (Credits) | 0.1 |  |  | 0.2 |  |  | (2.2 | ) |  | (1.9 | )
Amortization of Net Loss | 13.4 |  |  | 10.7 |  |  | 0.3 |  |  | 0.3 |
Net Periodic Benefit Expense (Income) |  | $13.0 |  |  |  | $10.8 |  |  | $(1.5) |  | $(1.2)

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- Definition Pension and Other Postretirement Benefit Plans [Abstract] + References No definition available. + Details
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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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