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Investments (Schedule of Investments) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 01, 2021	Dec. 31, 2020
Schedule of Investments [Line Items]
Equity	$ 17,262.3		$ 3,488.7
Short-term, separately-managed accounts (SMAs)	2,511.4		1,600.2
Long-term, SMAs	431.2		365.7
Total investments	4,798.3		3,466.0
Total investments (g)	22,060.6		6,954.7
Short-term investments	2,511.4		1,600.2
Long-term investments	19,549.2		5,354.5
VMED O2 JV
Schedule of Investments [Line Items]
Equity	$ 13,962.7		0.0
Ownership percentage	50.00%	50.00%
VodafoneZiggo JV
Schedule of Investments [Line Items]
Equity	$ 2,741.1		3,052.3
Ownership percentage	50.00%
All3Media Group (All3Media)
Schedule of Investments [Line Items]
Equity	$ 152.0		157.7
Ownership percentage	50.00%
Atlas Edge JV
Schedule of Investments [Line Items]
Equity	$ 119.7		0.0
Ownership percentage	50.00%
Formula E Holdings Ltd (Formula E)
Schedule of Investments [Line Items]
Equity	$ 93.7		105.8
Ownership percentage	32.90%
Other
Schedule of Investments [Line Items]
Equity	$ 193.1		172.9
Long-term investments at fair value	334.1		268.8
ITV
Schedule of Investments [Line Items]
Long-term investments at fair value	$ 571.9		581.0
Ownership percentage	9.90%
Univision Holdings Inc. (Univision)
Schedule of Investments [Line Items]
Long-term, SMAs	$ 249.9		100.0
Ownership percentage	11.60%
Plume Design, Inc. (Plume)
Schedule of Investments [Line Items]
Long-term, SMAs	$ 188.7		54.9
Ownership percentage	12.00%
EdgeConneX Inc. (EdgeConneX)
Schedule of Investments [Line Items]
Long-term investments at fair value	$ 124.5		75.1
Ownership percentage	5.50%
Lions Gate Entertainment Corp (Lionsgate)
Schedule of Investments [Line Items]
Long-term investments at fair value	$ 90.0		72.0
Ownership percentage	2.90%
Aviatrix Systems, Inc. (Aviatrix)
Schedule of Investments [Line Items]
Long-term investments at fair value	$ 78.2		7.3
Ownership percentage	3.80%
Lacework Inc. (Lacework)
Schedule of Investments [Line Items]
Long-term investments at fair value	$ 74.0		23.3
Ownership percentage	3.70%
Skillz Inc. (Skillz)
Schedule of Investments [Line Items]
Long-term, SMAs	$ 72.9		225.4
Ownership percentage	1.80%
CANAL+ Polska S.A.
Schedule of Investments [Line Items]
Long-term investments at fair value	$ 71.5		$ 92.3
Ownership percentage	17.00%