Other Financial Information Other Financial Information (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Other Current Assets [Abstract]
Prepaid expenses	$ 260us-gaap_PrepaidExpenseCurrent	$ 266us-gaap_PrepaidExpenseCurrent
Materials, supplies and inventory	132us-gaap_MaterialsSuppliesAndOther	167us-gaap_MaterialsSuppliesAndOther
Assets held for sale	14	26
Deferred activation and installation charges	103us-gaap_DeferredCostsCurrent	94us-gaap_DeferredCostsCurrent
Other	71us-gaap_OtherAssetsMiscellaneousCurrent	44us-gaap_OtherAssetsMiscellaneousCurrent
Other Assets, Current	580us-gaap_OtherAssetsCurrent	597us-gaap_OtherAssetsCurrent
Selected Current Liabilities [Abstract]
Accounts payable	1,226us-gaap_AccountsPayableCurrent	1,111us-gaap_AccountsPayableCurrent
Other current liabilities:
Accrued rent	34us-gaap_AccruedRentCurrent	52us-gaap_AccruedRentCurrent
Legal reserves	27ctl_LegalReserveCurrent	273ctl_LegalReserveCurrent
Other	149us-gaap_OtherSundryLiabilitiesCurrent	189us-gaap_OtherSundryLiabilitiesCurrent
Total other current liabilities	210us-gaap_OtherLiabilitiesCurrent	514us-gaap_OtherLiabilitiesCurrent
Current liabilities
Book overdraft balance	80us-gaap_BankOverdrafts	88us-gaap_BankOverdrafts
Capital expenditures included in accounts payable	$ 185	$ 140

Carrying amount as of the balance sheet date of legal reserves.

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Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of obligations incurred through that date and payable for contractual rent under lease arrangements. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount classified as assets attributable to disposal group held for sale or disposed of, expected to be disposed of within one year or the normal operating cycle, if longer.

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Carrying value as of the balance sheet date of payments made in excess of existing cash balances, which will be honored by the bank but reflected as a loan to the entity. Overdrafts generally have a very short time frame for correction or repayment and are therefore more similar to short-term bank financing than trade financing.

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Future cash outflow to pay for purchases of fixed assets that have occurred.

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Sum of the carrying amounts as of the balance sheet date of deferred costs capitalized at the end of the reporting period that are expected to be charged against earnings within one year or the normal operating cycle, if longer.

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The carrying amount of capitalized costs of materials, supplies, and other assets, which are not included in inventory but used in production.

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Aggregate carrying amount, as of the balance sheet date, of current assets not separately disclosed in the balance sheet. Current assets are expected to be realized or consumed within one year (or the normal operating cycle, if longer).

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Amount of other miscellaneous assets expected to be realized or consumed within one year or operating cycle, if longer.

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Aggregate carrying amount of current liabilities (due within one year or within the normal operating cycle if longer) not separately disclosed in the balance sheet. Includes costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered and of liabilities not separately disclosed.

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Obligations not otherwise itemized or categorized in the footnotes to the financial statements that are due within one year or operating cycle, if longer, from the balance sheet date.

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Amount of asset related to consideration paid in advance for costs that provide economic benefits within a future period of one year or the normal operating cycle, if longer.

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