Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified		3 Months Ended
	Jun. 30, 2012 item	Jun. 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)		$ 122	$ 116