Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified		6 Months Ended	3 Months Ended
Sep. 30, 2012 item	Sep. 30, 2011 Selling, general and administrative expenses	Mar. 31, 2011 Predecessor Selling, general and administrative expenses
Basis of Presentation
Number of states in which service is provided	14
Basis of Presentation
Reclassification of expenses, increase (reduction)		$ 229	$ 116

The amount of a reclassification adjustment made to prior period financial statement amounts.

No definition available.

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