Pension and Other Postretirement Benefit Plans - Contributions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Employer Stock Contributions	$ 19.5	$ 0	$ 0
Defined Contribution Plan, Employer Contributions	9.1	8.4	7.7
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Employer Stock Contributions	19.5
Defined Benefit Plans, Employer Cash Contributions	0	0	7.3
Defined Benefit Plans, Estimated Employer Contributions	0
VEBA [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Employer Cash Contributions	0	10.8	1.5
Defined Benefit Plans, Estimated Employer Contributions	0
Irrevocable Grantor Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Employer Cash Contributions	$ 0	$ 2.0	$ 0

Amount employer contributed during the period, to match employee contributions, to a defined contribution plan. Includes, but not limited to, contributions made through Employee Stock Ownership Plans (ESOP).

No definition available.

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- Definition

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

+ 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 (g)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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- Definition

The amount of cash or cash equivalents contributed during the reporting period by the entity to fund its pension plans and its non-pension postretirement benefit plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

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- Definition

Value of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

+ References

No definition available.

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