Fair Value Measurements - Significant Unobservable Inputs for Fair Value Measurements (Details) $ in Millions	Dec. 31, 2020	Oct. 01, 2020 USD ($)	Mar. 31, 2020 USD ($)	Oct. 01, 2019 USD ($)
Gaming licenses
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, fair value		$ 568.0	$ 568.0	$ 290.0
Trademarks
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, fair value		$ 216.5	216.5	87.5
Level 3 | Gaming licenses
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, fair value			568.0	290.0
Level 3 | Trademarks
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, fair value			$ 216.5	$ 87.5
Level 3 | Discounted cash flow | Discount rate | Gaming licenses | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, measurement input		0.1325
Level 3 | Discounted cash flow | Discount rate | Gaming licenses | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, measurement input		0.1400
Level 3 | Discounted cash flow | Discount rate | Trademarks | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, measurement input		0.1325
Level 3 | Discounted cash flow | Discount rate | Trademarks | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, measurement input		0.1400
Level 3 | Discounted cash flow | Long-term revenue growth rate | Gaming licenses
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, measurement input		0.020
Level 3 | Discounted cash flow | Long-term revenue growth rate | Trademarks
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, measurement input		0.020
Level 3 | Discounted cash flow | Pretax royalty rate | Trademarks | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, measurement input		0.010
Level 3 | Discounted cash flow | Pretax royalty rate | Trademarks | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Indefinite-lived intangible assets, measurement input		0.020
Plainridge Park Casino | Level 3 | Discounted cash flow | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent purchase price, measurement input	0.0505