Discontinued operations - Narrative (Details) $ in Millions			3 Months Ended		5 Months Ended	12 Months Ended
	Jul. 31, 2017 USD ($) seat	May 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 29, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Conversion ratio for every share of Tegna common stock owned by stockholders		0.3333
Pro rata distribution to stockholders (as a percent)									98.50%
Shares held by Tegna after distribution (as a percent)									1.50%
Non-cash goodwill impairment charge				$ 332.9			$ 15.2	$ 8.0
Career Builder
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total sale price	$ 198.3
Dividend issued prior to sale	$ 25.8		$ 25.8
Ownership interest (as a percent)	53.00%
Loss on disposition of business						$ (342.9)
Non-cash goodwill impairment charge				332.9		332.9
Business exit costs						10.9
Revolving Credit Facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of lines of credit		$ 609.9		609.9
Revolving Credit Facility | Cars.com
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments of distributions to affiliates		$ 650.0		$ 650.0
Career Builder
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity method investment retained after disposal (as a percent)	17.00%
Equity method investment retained after disposal, ownership Interest after disposal, diluted (as a percent)	12.00%
Number seats retained on Board of Directors | seat	2
Number of members on Board of Directors | seat	10
Income (Loss) from ongoing equity method investment in discontinued operation after disposal					$ 2.7
Parent Company | Career Builder
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on disposition of business						$ (271.7)