Equipment Installment Plan Receivables (Gross Receivables by Credit Category) (Details) (Equipment Installment Plan Receivable [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, gross	$ 4,403	$ 2,882
Unbilled [Member]
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, current	4,164	2,752
Billed [Member]
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, current	172	90
Equipment installment plan receivables, past due	67	40
Prime [Member]
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, gross	2,353	1,542
Prime [Member] | Unbilled [Member]
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, current	2,239	1,482
Prime [Member] | Billed [Member]
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, current	88	45
Equipment installment plan receivables, past due	26	15
Subprime [Member]
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, gross	2,050	1,340
Subprime [Member] | Unbilled [Member]
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, current	1,925	1,270
Subprime [Member] | Billed [Member]
Equipment Installment Plan Receivables [Line Items]
Equipment installment plan receivables, current	84	45
Equipment installment plan receivables, past due	$ 41	$ 25