Description and Basis of Presentation (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2013 segment	Sep. 30, 2012
BusinessDescriptionAndBasisOfPresentationTextBlockAbstract
Number of Reportable Segments (in segments)		2
Income benefit, measurement period adjustment	$ 15.1	$ 15.1	$ 15.1

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration