Long-Term Debt and Credit Facilities - Covenants and Guarantees (Details) $ in Millions	Dec. 31, 2020 USD ($)
Letter of Credit | Uncommitted Revolving Letter of Credit Facility | Letter of Credit
Long-term Debt and Credit Facilities
Maximum borrowing capacity	$ 225
Minimum
Long-term Debt and Credit Facilities
Coverage ratio	2.00
Qwest Corporation | Maximum
Long-term Debt and Credit Facilities
EBITDA ratio	2.85
Embarq Corporation
Long-term Debt and Credit Facilities
Maximum indebtedness, as a percent of tangible assets	15.00%
Debt Covenant, Period Two | Maximum
Long-term Debt and Credit Facilities
Leverage ratio	4.75