Deferred Method of Accounting for Major Overhaul (Details) (Engine and transmission overhaul, USD $) In Millions, unless otherwise specified	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Engine and transmission overhaul
Capitalized and amortized:
Property, plant and equipment, useful life	3 years 0 months 0 days	3 years 0 months 0 days	3 years 0 months 0 days
Net amount of (gains) losses netted against depreciation expense	$ 22.5	$ 20.9	$ 23.1

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration