XML 164 R70.htm IDEA: XBRL DOCUMENT v3.10.0.1
summary of significant accounting policies - Useful lives intangible assets (Details)
 12 Months Ended
Dec. 31, 2018
Wireline subscriber base  
Useful Lives of Intangible Assets Other Than Goodwill  
Estimated useful lives of purchased intangible assets other than goodwill 25 years
Customer contracts and related customer relationships | Minimum  
Useful Lives of Intangible Assets Other Than Goodwill  
Estimated useful lives of purchased intangible assets other than goodwill 4 years
Customer contracts and related customer relationships | Maximum  
Useful Lives of Intangible Assets Other Than Goodwill  
Estimated useful lives of purchased intangible assets other than goodwill 10 years
Software | Minimum  
Useful Lives of Intangible Assets Other Than Goodwill  
Estimated useful lives of purchased intangible assets other than goodwill 2 years
Software | Maximum  
Useful Lives of Intangible Assets Other Than Goodwill  
Estimated useful lives of purchased intangible assets other than goodwill 10 years
Access to rights-of-way and other | Minimum  
Useful Lives of Intangible Assets Other Than Goodwill  
Estimated useful lives of purchased intangible assets other than goodwill 5 years
Access to rights-of-way and other | Maximum  
Useful Lives of Intangible Assets Other Than Goodwill  
Estimated useful lives of purchased intangible assets other than goodwill 30 years