Shareholders' equity - Narrative (Detail)			3 Months Ended	12 Months Ended
	Mar. 01, 2018 shares	May 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	May 04, 2010 shares
Stockholders Equity Note [Line Items]
Common stock, authorized (in shares)				800,000,000	800,000,000
Preferred stock, authorized (in shares)				2,000,000	2,000,000
Common stock, outstanding (in shares)				217,500,000	215,800,000
Treasury stock (in shares)				106,955,082	108,660,002
Preferred stock, issued (in shares)				0	0
Preferred stock, outstanding (in shares)				0	0
Shares approved to be repurchased under share repurchase program, amount | $			$ 300,000,000.0
Share repurchase program, period in force			3 years
Shares repurchased under share repurchase program (in shares)				0	500,000	1,500,000
Cost of common shares repurchased | $				$ 0	$ 5,831,000	$ 23,480,000
Remaining authorized repurchase amount | $				$ 279,100,000
Shares granted with aggregate target awards (in shares)	600,000
Spin-off of Cars.com | $						$ 1,513,881,000
Minimum
Stockholders Equity Note [Line Items]
Number of units ultimately paid for performance share awards of target (as a percent)				0
Maximum
Stockholders Equity Note [Line Items]
Number of units ultimately paid for performance share awards of target (as a percent)				2
Stock Options | Employee
Stockholders Equity Note [Line Items]
Shares reserved for issuance (in shares)							60,000,000.0
Performance Based Awards
Stockholders Equity Note [Line Items]
Award vesting period				3 years
Restricted Stock Units (RSUs) | Employee
Stockholders Equity Note [Line Items]
Number of shares of common stock received for each RSU granted				1
Award vesting percentage				25.00%
Performance Shares
Stockholders Equity Note [Line Items]
Unrecognized compensation cost related to non-vested share-based compensation | $				$ 0
Spin-off adjustment, conversion factor				1.59		1.59
Restricted Stock and Restricted Stock Units
Stockholders Equity Note [Line Items]
Unrecognized compensation cost related to non-vested share-based compensation | $				$ 19,400,000
Unrecognized compensation cost related to non-vested share-based compensation for options, recognition period				2 years 7 months 6 days
Retained earnings
Stockholders Equity Note [Line Items]
Spin-off of Cars.com | $						$ 1,513,881,000
Retained earnings | Cars.com
Stockholders Equity Note [Line Items]
Spin-off of Cars.com | $		$ 1,500,000,000
Cars.com | Performance Shares
Stockholders Equity Note [Line Items]
Adjustment due to spin-off of Publishing (in shares)				0	0	178,775
Cars.com | Restricted Stock and Restricted Stock Units
Stockholders Equity Note [Line Items]
Adjustment due to spin-off of Publishing (in shares)				0	0	606,377