Basis of Presentation and Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified		9 Months Ended	3 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011 Selling, general and administrative expenses	Mar. 31, 2011 Predecessor Selling, general and administrative expenses
Basis of Presentation and Summary of Significant Accounting Policies
Number of states in which service is provided	14
Basis of presentation
Reclassification of expenses, increase (reduction)		$ 338	$ 116