Equipment Installment Plans - Gross Receivables by Credit Category (Details) - USD ($) $ in Millions | Jun. 30, 2021 | Dec. 31, 2020 |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | $ 1,015 | $ 1,007 |
2018 | 2 | |
2019 | 154 | |
2020 | 474 | |
2021 | 385 | |
Unbilled | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 961 | 948 |
Billed | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 40 | 43 |
Billed | Past Due | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 14 | 16 |
Lowest Risk | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 878 | 863 |
2018 | 2 | |
2019 | 140 | |
2020 | 415 | |
2021 | 321 | |
Lowest Risk | Unbilled | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 836 | 819 |
Lowest Risk | Billed | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 35 | 36 |
Lowest Risk | Billed | Past Due | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 7 | 8 |
Lower Risk | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 103 | 108 |
2018 | 0 | |
2019 | 11 | |
2020 | 48 | |
2021 | 44 | |
Lower Risk | Unbilled | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 95 | 98 |
Lower Risk | Billed | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 4 | 5 |
Lower Risk | Billed | Past Due | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 4 | 5 |
Slight Risk | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 27 | 25 |
2018 | 0 | |
2019 | 2 | |
2020 | 8 | |
2021 | 17 | |
Slight Risk | Unbilled | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 24 | 22 |
Slight Risk | Billed | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 1 | 1 |
Slight Risk | Billed | Past Due | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 2 | 2 |
Higher Risk | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 7 | 11 |
2018 | 0 | |
2019 | 1 | |
2020 | 3 | |
2021 | 3 | |
Higher Risk | Unbilled | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 6 | 9 |
Higher Risk | Billed | Current | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | 0 | 1 |
Higher Risk | Billed | Past Due | | |
Financing Receivable, Credit Quality Indicator [Line Items] | | |
Equipment installment plan receivables, gross | $ 1 | $ 1 |