Interim Financial Statements - Fair Value, Assets Held For Sale, Discontinued Operations (Details) $ in Millions	6 Months Ended
Jun. 30, 2020 USD ($) entity item	Jun. 30, 2019 entity	Dec. 31, 2019 USD ($)
Fair Value of Financial Instruments
Debt instrument, Carrying Value	$ 2,137.4		$ 2,360.3
Assets Held for Sale and Discontinued Operations
Number of entities newly classified as held for sale \| entity	0	0
3.75% senior subordinated notes due 2020
Fair Value of Financial Instruments
Interest rate (as a percent)	3.75%		3.75%
Debt instrument, Carrying Value	$ 299.9		$ 299.2
Debt instrument, Fair Value	$ 299.8		$ 302.6
5.75% senior subordinated notes due 2022
Fair Value of Financial Instruments
Interest rate (as a percent)	5.75%		5.75%
Debt instrument, Carrying Value	$ 548.1		$ 547.6
Debt instrument, Fair Value	$ 549.2		$ 556.7
5.375% senior subordinated notes due 2024
Fair Value of Financial Instruments
Interest rate (as a percent)	5.375%		5.375%
Debt instrument, Carrying Value	$ 298.3		$ 298.0
Debt instrument, Fair Value	$ 299.8		$ 306.7
5.50% senior subordinated notes due 2026
Fair Value of Financial Instruments
Interest rate (as a percent)	5.50%		5.50%
Debt instrument, Carrying Value	$ 496.1		$ 495.7
Debt instrument, Fair Value	496.3		521.7
Mortgage facilities
Fair Value of Financial Instruments
Debt instrument, Carrying Value	417.0		423.2
Debt instrument, Fair Value	$ 438.9		$ 430.9
Retail Automotive Franchise
Disposals
Number of franchises disposed \| item	4

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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