Employee benefit plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Defined benefit plans [Member]
Employee Benefit Plans [Abstract]
Expected contribution	$ 29.1
Other postretirement benefits [Member]
Employee Benefit Plans [Abstract]
Expected contribution	$ 1.7

The employer's best estimate, as soon as it can be reasonably determined, of contributions expected to be paid to the plan in the current remaining fiscal period. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions.

No definition available.

Name:	us-gaap_DefinedBenefitPlanEstimatedFutureEmployerContributionsInCurrentFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant