Revenue Recognition and Related Costs	3 Months Ended
Revenue Recognition and Related Costs	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue Recognition and Related Costs	Revenue Recognition and Related Costs Policies Our revenue recognition and certain other accounting polices, as revised to reflect the impacts of our adoption of ASU 2014-09, are set forth below. Service Revenue — Cable Networks. We recognize revenue from the provision of video, broadband internet and fixed-line telephony services over our cable network to customers in the periods the related services are provided, with the exception of revenue recognized pursuant to certain contracts that contain promotional discounts, as described below. Installation fees related to services provided over our cable network are generally deferred and recognized as revenue over the contractual period, or longer if the upfront fee results in a material renewal right. Sale of Multiple Products and Services. We sell video, broadband internet, fixed-line telephony and, in most of our markets, mobile services to our customers in bundled packages at a rate lower than if the customer purchased each product on a standalone basis. Revenue from bundled packages generally is allocated proportionally to the individual products or services based on the relative standalone selling price for each respective product or service. Mobile Revenue — General. Consideration from mobile contracts is allocated to the airtime service component and the handset component based on the relative standalone selling prices of each component. In markets where we offer handsets and airtime services in separate contracts entered into at the same time, we account for these contracts as a single contract. Mobile Revenue — Airtime Services. We recognize revenue from mobile services in the periods in which the related services are provided. Revenue from pre-pay customers is deferred prior to the commencement of services and recognized as the services are rendered or usage rights expire. Mobile Revenue — Handset Revenue. Revenue from the sale of handsets is recognized at the point in which the goods have been transferred to the customer. Some of our mobile handset contracts that permit the customer to take control of the handset upfront and pay for the handset in installments over a contractual period may contain a significant financing component. For contracts with terms of one year or more, we recognize any significant financing component as revenue over the contractual period using the effective interest method. We do not record the effect of a significant financing component if the contractual period is less than one year. B2B Revenue. We defer upfront installation and certain nonrecurring fees received on B2B contracts where we maintain ownership of the installed equipment. The deferred fees are amortized into revenue on a straight-line basis, generally over the longer of the term of the arrangement or the expected period of performance. Contract Costs. Incremental costs to obtain a contract with a customer, such as incremental sales commissions, are generally recognized as assets and amortized to SG&A expenses over the applicable period benefited, which generally is the contract life. If, however, the amortization period is less than one year, we expense such costs in the period incurred. Contract fulfillment costs, such as porting costs, are recognized as assets and amortized to other operating costs over the applicable period benefited, which is generally the substantive contract term for the related service contract. Promotional Discounts. For subscriber promotions, such as discounted or free services during an introductory period, revenue is recognized uniformly over the contractual period if the contract has substantive termination penalties. If a contract does not have substantive termination penalties, revenue is recognized only to the extent of the discounted monthly fees charged to the subscriber, if any. Subscriber Advance Payments. Payments received in advance for the services we provide are deferred and recognized as revenue when the associated services are provided. Sales, Use and Other Value-Added Taxes. Revenue is recorded net of applicable sales, use and other value-added taxes. For a disaggregation of our revenue by major category and by reportable and geographic segment, see note 16. Contract Balances The timing of revenue recognition may differ from the timing of invoicing our customers. We record a trade receivable when we have transferred goods or services to a customer but have not yet received payment. Our trade receivables are reported net of an allowance for doubtful accounts. Such allowance aggregated $107.4 million and $108.0 million at March 31, 2018 and January 1, 2018, respectively. If we transfer goods or services to a customer but do not have an unconditional right to payment, we record a contract asset. Contract assets typically arise from the uniform recognition of introductory promotional discounts over the contract period. Our contract assets were $46.8 million and $42.0 million as of March 31, 2018 and January 1, 2018, respectively. The current- and long-term portions of our contract asset balance at March 31, 2018 are included within other current assets and other assets, net, respectively, in our condensed consolidated balance sheet. We record deferred revenue when we receive payment prior to transferring goods or services to a customer. We primarily defer revenue for (i) installation and other upfront services and (ii) other services that are invoiced prior to when services are provided. Our deferred revenue balances were $1,306.3 million and $1,160.6 million as of March 31, 2018 and January 1, 2018, respectively. The increase in deferred revenue for the three months ended March 31, 2018 is primarily due to increased advanced billings in certain markets, partially offset by $719.3 million of revenue recognized that was included in our deferred revenue balance at January 1, 2018. The current- and long-term portions of our deferred revenue balance at March 31, 2018 are included within deferred revenue and other long-term liabilities, respectively, in our condensed consolidated balance sheet. Contract Costs Our aggregate assets associated with incremental costs to obtain a contract and contract fulfillment costs were $186.1 million and $182.1 million at March 31, 2018 and January 1, 2018, respectively. The current and long-term portions of our assets related to contract costs at March 31, 2018 are included within other current assets and other assets, net, respectively, in our condensed consolidated balance sheet. We recorded amortization of $54.1 million during the three months ended March 31, 2018 related to these assets. Unsatisfied Performance Obligations A large portion of our revenue is derived from customers who are not subject to contracts. Revenue from customers who are subject to contracts is generally recognized over the term of such contracts, which is typically 12 to 24 months for our residential service and mobile contracts and one to five years for our B2B contracts.