Financial Instruments and Fair Value Measurements - Derivative Financial Instruments (Details) £ in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 GBP (£) derivative Rate	Dec. 31, 2020 USD ($) derivative Rate	Jun. 30, 2020 USD ($) derivative	Feb. 29, 2020 USD ($) derivative	Dec. 31, 2019 USD ($)
Derivative [Line Items]
Notional Amount				$ 1,541.4			$ 673.4
Fair Value - asset (liability)				(81.5)			(26.3)
Interest rate swap, maturity Sep 2021 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 0.0			7.0
Strike (percent)			6.03%	6.03%
Fair Value - asset (liability)				$ 0.0			(0.2)
Net loss from derivative	$ 0.2
Payment to terminate derivative	$ 0.2
Interest rate swap, maturity Jun 2020 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 0.0			250.0
Strike (percent)			1.72%	1.72%
Fair Value - asset (liability)				$ 0.0			(0.1)
Interest rate swap, maturity Mar 2024
Derivative [Line Items]
Number of derivative instruments | derivative			1	1
Interest rate swap, maturity Mar 2024 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 250.0			250.0
Strike (percent)			3.04%	3.04%
Fair Value - asset (liability)				$ (22.6)			(14.7)
Cross-currency swap, maturity May 2034 1 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				41.6			41.6
Fair Value - asset (liability)				$ (5.2)			(2.6)
Cross-currency swap, maturity May 2034 1 | Designated as hedging instrument | Cash flow hedge | GBP | Minimum
Derivative [Line Items]
Strike (percent)			4.82%	4.82%
Cross-currency swap, maturity May 2034 1 | Designated as hedging instrument | Cash flow hedge | GBP | Maximum
Derivative [Line Items]
Strike (percent)			10.96%	10.96%
Cross-currency swap, maturity May 2034 1 | Designated as hedging instrument | Cash flow hedge | USD
Derivative [Line Items]
Strike (percent)			9.80%	9.80%
Cross-currency swap, maturity May 2034 2 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 41.6			41.6
Fair Value - asset (liability)				$ (5.1)			(2.6)
Cross-currency swap, maturity May 2034 2 | Designated as hedging instrument | Cash flow hedge | GBP | Minimum
Derivative [Line Items]
Strike (percent)			4.82%	4.82%
Cross-currency swap, maturity May 2034 2 | Designated as hedging instrument | Cash flow hedge | GBP | Maximum
Derivative [Line Items]
Strike (percent)			10.96%	10.96%
Cross-currency swap, maturity May 2034 2 | Designated as hedging instrument | Cash flow hedge | USD
Derivative [Line Items]
Strike (percent)			9.803%	9.803%
Cross-currency swap, maturity May 2034 3 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 41.6			41.6
Fair Value - asset (liability)				$ (5.4)			(2.9)
Cross-currency swap, maturity May 2034 3 | Designated as hedging instrument | Cash flow hedge | GBP | Minimum
Derivative [Line Items]
Strike (percent)			4.82%	4.82%
Cross-currency swap, maturity May 2034 3 | Designated as hedging instrument | Cash flow hedge | GBP | Maximum
Derivative [Line Items]
Strike (percent)			10.96%	10.96%
Cross-currency swap, maturity May 2034 3 | Designated as hedging instrument | Cash flow hedge | USD
Derivative [Line Items]
Strike (percent)			9.745%	9.745%
Cross-currency swap, maturity May 2034 4 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 41.6			41.6
Fair Value - asset (liability)				$ (5.7)			(3.2)
Cross-currency swap, maturity May 2034 4 | Designated as hedging instrument | Cash flow hedge | GBP | Minimum
Derivative [Line Items]
Strike (percent)			4.82%	4.82%
Cross-currency swap, maturity May 2034 4 | Designated as hedging instrument | Cash flow hedge | GBP | Maximum
Derivative [Line Items]
Strike (percent)			10.96%	10.96%
Cross-currency swap, maturity May 2034 4 | Designated as hedging instrument | Cash flow hedge | USD
Derivative [Line Items]
Strike (percent)			9.755%	9.755%
Currency exchange swap | Not designated as hedging instrument
Derivative [Line Items]
Notional Amount			£ 463.1	$ 625.0			0.0
Strike (rate) | Rate			135.00%	135.00%
Fair Value - asset (liability)				$ (8.2)			0.0
Net loss from derivative		$ 14.5
Forward-starting swap, maturity Jun 2033 1 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 75.0			0.0
Strike (percent)			2.02%	2.02%
Fair Value - asset (liability)				$ (5.0)			0.0
Forward-starting swap, maturity Nov 2032 1 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 75.0			0.0
Strike (percent)			1.94%	1.94%
Fair Value - asset (liability)				$ (5.2)			0.0
Forward-starting swap, maturity Nov 2032 2 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 25.0			0.0
Strike (percent)			1.67%	1.67%
Fair Value - asset (liability)				$ (1.1)			0.0
Forward-starting swap, maturity Jun 2033 2 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 125.0			0.0
Strike (percent)			1.75%	1.75%
Fair Value - asset (liability)				$ (5.2)			0.0
Forward-starting swap, hybrid debt, maturity Nov 2032 3 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 125.0			0.0
Strike (percent)			1.88%	1.88%
Fair Value - asset (liability)				$ (7.9)			0.0
Forward-starting swap, hybrid debt, maturity Jun 2033 3 | Designated as hedging instrument | Cash flow hedge
Derivative [Line Items]
Notional Amount				$ 75.0			0.0
Strike (percent)			2.00%	2.00%
Fair Value - asset (liability)				$ (4.9)			$ 0.0
Treasury rate locks | Cash flow hedge
Derivative [Line Items]
Notional Amount						$ 500.0
Number of derivative instruments | derivative						5
Forward starting swaps | Cash flow hedge
Derivative [Line Items]
Notional Amount					$ 500.0
Number of derivative instruments | derivative			6	6	6