Installment Receivables Installment Receivables On Gross Basis by Credit Category (Details) (Successor [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	$ 1,494	$ 740
Prime [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	1,065	487
Subprime [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	429	253
Billed Revenues [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	1,387	708
Billed Revenues [Member] | Prime [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	1,003	466
Billed Revenues [Member] | Subprime [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	384	242
Billed receivables, current [Member] | Billed Revenues [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	67	25
Billed receivables, current [Member] | Billed Revenues [Member] | Prime [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	45	16
Billed receivables, current [Member] | Billed Revenues [Member] | Subprime [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	22	9
Billed receivables, past due [Member] [Member] | Billed Revenues [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	40	7
Billed receivables, past due [Member] [Member] | Billed Revenues [Member] | Prime [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	17	5
Billed receivables, past due [Member] [Member] | Billed Revenues [Member] | Subprime [Member]
Financing Receivable, Recorded Investment [Line Items]
Installment receivables, gross	$ 23	$ 2