Goodwill and Other Intangible Assets: - Intangible Asset Amortization Methodology and Useful Lives (Details)	12 Months Ended
	Dec. 31, 2019
Franchise rights
Finite-Lived Intangible Assets [Line Items]
Amortization Methodology	straight-line
Estimated useful life (in years)	30 years
Customer lists
Finite-Lived Intangible Assets [Line Items]
Amortization Methodology	sum of years digits
Cable franchise rights
Finite-Lived Intangible Assets [Line Items]
Amortization Methodology	straight-line
Estimated useful life (in years)	15 years
Trade names
Finite-Lived Intangible Assets [Line Items]
Amortization Methodology	straight-line
Developed technology and software
Finite-Lived Intangible Assets [Line Items]
Amortization Methodology	straight-line
Patents
Finite-Lived Intangible Assets [Line Items]
Amortization Methodology	straight-line
Estimated useful life (in years)	3 years
Minimum | Customer lists
Finite-Lived Intangible Assets [Line Items]
Estimated useful life (in years)	5 years 6 months
Minimum | Trade names
Finite-Lived Intangible Assets [Line Items]
Estimated useful life (in years)	1 year
Minimum | Developed technology and software
Finite-Lived Intangible Assets [Line Items]
Estimated useful life (in years)	3 years
Maximum | Customer lists
Finite-Lived Intangible Assets [Line Items]
Estimated useful life (in years)	15 years
Maximum | Trade names
Finite-Lived Intangible Assets [Line Items]
Estimated useful life (in years)	10 years
Maximum | Developed technology and software
Finite-Lived Intangible Assets [Line Items]
Estimated useful life (in years)	5 years