Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 50

-Section 40

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6850294&loc=d3e12317-112629

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 50

-Section 40

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6850294&loc=d3e12355-112629

Name:	us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Debt - 2014 and 2015 Notes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Gain (Loss) on Repurchase of Debt Instrument	$ (17.2)	$ (17.2)	$ (0.2)
Debt Instruments Senior Notes Retired			11.8
2014 and 2015 Notes [Member]
Debt Instrument [Line Items]
Gain (Loss) on Repurchase of Debt Instrument		(17.2)
2015 Notes [Member]
Debt Instrument [Line Items]
Gain (Loss) on Repurchase of Debt Instrument			(0.2)
Principal Amount Of Debt Instrument Repurchased			7.5
Debt Instruments Senior Notes Retired			$ 7.7