Pension and Other Postretirement Benefits - Schedule of Expected Benefit Payments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
2014	$ 35.8
2015	37.4
2016	39.7
2017	41.7
2018	44.0
2019-2023	257.3
PBOP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
2014	2.9
2015	3.1
2016	3.3
2017	3.5
2018	3.6
2019-2023	18.3
SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
2014	2.5
2015	2.5
2016	2.5
2017	2.6
2018	2.6
2019-2023	$ 13.0

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Amount of benefits expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year from a defined benefit plan.

+ 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 (f)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

+ Details

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- Definition

Amount of benefits expected to be paid in the next fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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- Definition

Amount of benefits expected to be paid in the fifth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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- Definition

Amount of benefits expected to be paid in the fourth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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- Definition

Amount of benefits expected to be paid in the third fiscal year following the latest fiscal year from a defined benefit plan.

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Amount of benefits expected to be paid in the second fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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